The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Feng Chen - One of the best experts on this subject based on the ideXlab platform.
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PTCH1 alterations are frequent but other genetic alterations are rare in sporadic odontogenic keratocysts.
Oral Diseases, 2019Co-Authors: Jianyun Zhang, Yingying Hong, Heyu Zhang, Jiemei Zhai, Yanjin Wang, Feng ChenAbstract:OBJECTIVE Odontogenic keratocysts (OKCs) are benign jaw lesions with high growth potential and propensity for recurrence. Our previous study revealed that PTCH1 mutations, which were frequently detected in sporadic OKCs, might be underestimated due to the masking effect of the stromal components within the tested tissues. We aimed to confirm these results in larger scale and further present the unbiased view of the genomic basis of sporadic OKCs except PTCH1. MATERIALS AND METHODS We analyzed PTCH1 mutations in additional 19 samples. Using whole-exome sequencing (WES), we further characterized the mutational landscape of five sporadic OKC samples lacking PTCH1 mutation and loss of heterozygosity (LOH). RESULTS Combined with our previously reported 19 cases, thirty of 38 (79%) cases harbored PTCH1 mutations. Through whole-exome sequencing and integrative analysis, 22 novel mutations were confirmed among five PTCH1-negative samples. No recurrent mutations were identified in the WES samples and validation cohort of 10 OKCs. CONCLUSIONS Our data further confirmed the frequent PTCH1 mutation and other rare genetic alterations in sporadic OKCs, highlighting the central role of SHH signaling pathway. In PTCH1-negative cases, other rare mutations scattered in a subset of OKCs were independent of the SHH pathway. These results suggested that an SHH inhibitor may be effective to treat the majority of OKCs.
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heterozygous PTCH1 mutations impact the bone metabolism in patients with nevoid basal cell carcinoma syndrome likely by regulating sparc expression
Journal of Bone and Mineral Research, 2016Co-Authors: Yingying Hong, Jianyun Zhang, Heyu Zhang, Jiemei Zhai, Lei Zhang, Feng ChenAbstract:Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by bone and skin abnormalities and a predisposition to various tumors. Keratocystic odontogenic tumors (KCOTs), which are common tumors of the jaw that cause extensive damage to the jawbone, are usually accompanied with NBCCS. Germline PTCH1 mutations in NBCCS tumorigenesis have been frequently studied; however, little is known regarding the pathogenesis of bone abnormalities in this disease. This study sought to investigate the mechanism underlying heterozygous PTCH1 mutation-mediated abnormal bone metabolism in patients with NBCCS. Stromal cells were isolated from the fibrous capsules of patients with NBCCS-associated or non-syndromic keratocystic odontogenic tumors and non-syndromic tumor stromal cells without PTCH1 mutations served as controls. Germline PTCH1 heterozygous mutations were confirmed in all NBCCS samples and differential protein expression was identified using tandem mass tag-labeled proteomics analysis. Our findings revealed that osteonectin/SPARC expression was significantly downregulated in syndromic stromal cells compared with non-syndromic stromal cells. SPARC expression was even lower in stromal cells carrying PTCH1 protein truncation mutations. PTCH1 siRNA transfection demonstrated that SPARC downregulation correlates with decreased PTCH1 expression. Furthermore, exogenous SPARC promoted osteogenic differentiation of syndromic stromal cells with enhanced development of calcium nodules. In addition, bone mineral density tests showed that patients with NBCCS exhibit weak bone mass compared with sex- and age-matched controls. This study indicates that germline PTCH1 heterozygous mutations play a major role in bone metabolism in patients with NBCCS, in particular in those with PTCH1 protein truncation mutations. SPARC may represent an important downstream modulator of PTCH1 mediation of bone metabolism. Thus, bone mineral density monitoring is critical for patients with NBCCS for prevention of osteoporosis. In addition, surgical procedures on syndromic-associated KCOTs should be performed with consideration of the weaker bone mass in such patients. © 2016 American Society for Bone and Mineral Research.
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Underestimated PTCH1 mutation rate in sporadic keratocystic odontogenic tumors.
Oral Oncology, 2015Co-Authors: Yingying Hong, Lisha Sun, Jianyun Zhang, Yan-yan Guo, Heyu Zhang, Rui-rui Shi, Feng ChenAbstract:Summary Objectives Keratocystic odontogenic tumors (KCOTs) are benign cystic lesions of the jaws that occur sporadically in isolation or in association with nevoid basal cell carcinoma syndrome (NBCCS). The protein patched homolog 1 gene (PTCH1) is associated with NBCCS development and tumor genesis associated with this syndrome. However, previous studies have revealed that more than 85% of syndromic KCOTs and less than 30% of sporadic KCOTs harbor PTCH1 mutations. The significantly lower PTCH1 mutation rates observed in sporadic KCOTs suggest that they serve a minor role in pathogenesis. We aimed to discern the importance of PTCH1 mutations in sporadic KCOTs. Materials and methods PTCH1 mutational analysis was performed with 19 new sporadic KCOT cases by direct sequencing of epithelial lining samples separated from fibrous capsules. Using this approach, we further reexamined 9 sporadic KCOTs that were previously reported to lack PTCH1 mutations by our group. Results Nineteen PTCH1 mutations were detected in patient samples from 16/19 new cases (84%) all these mutations were absent in fibrous tissues and peripheral blood specimens from the same patients. We also identified four PTCH1 mutations in 3/9 patients (33%) that were previously undetected. Discussion These data indicated that PTCH1 mutations occur in sporadic KCOTs at a higher rate than previously suspected, owing to the masking effects of the attached stromal tissues in the test samples. These results suggest that the PTCH1 gene plays a significant role in the pathogenesis of sporadic KCOTs, which is comparable to that observed in NBCCS patients.
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The large intracellular loop of PTCH1 mediates the non-canonical Hedgehog pathway through cyclin B1 in nevoid basal cell carcinoma syndrome
International Journal of Molecular Medicine, 2014Co-Authors: Yingying Hong, Feng ChenAbstract:Mutations in the transmembrane receptor patched homolog 1 (Homo sapiens) (PTCH1) are responsible for nevoid basal cell carcinoma syndrome (NBCCS), an autosomal dominant disorder that causes developmental abnormalities and predisposes the affected individuals to cancer. Many of these mutations, including mutations in the C-terminus of the large intracellular loop (ICL) of PTCH1 (p.C727VfsX745 and p.S733IfsX736), result in the premature truncation of the protein. The PTCH1‑C727VfsX745 and PTCH1-S733IfsX736 mutations have been identified in patients with NBCCS‑associated keratocystic odontogenic tumors (KCOTs). In the present study, we found that the molecular mechanisms regulated by the non-canonical Hedgehog (Hh) signaling pathway through cyclin B1 are involved in the pathogenesis of NBCCS-associated KCOTs. In contrast to wild-type PTCH1, PTCH1-C727VfsX745 and PTCH1‑S733IfsX736 clearly exhibited reduced binding to cyclin B1. Moreover, the cells expressing these two mutations demonstrated an increase in cell cycle progression and these two mutation constructs failed to inhibit cell proliferation. In addition, the mutants enhanced the activity of glioma-associated oncogene family zinc finger 1 (GLI1), a downstream reporter of Hh signaling. Thus, our data suggest that the non-canonical Hh pathway mediated through PTCH1 and cyclin B1 is involved in the pathogenesis of NBCCS-associated KCOTs. The C-terminus of ICL in PTCH1 may also be a potential therapeutic target in the treatment of this disease.
Yingying Hong - One of the best experts on this subject based on the ideXlab platform.
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PTCH1 alterations are frequent but other genetic alterations are rare in sporadic odontogenic keratocysts.
Oral Diseases, 2019Co-Authors: Jianyun Zhang, Yingying Hong, Heyu Zhang, Jiemei Zhai, Yanjin Wang, Feng ChenAbstract:OBJECTIVE Odontogenic keratocysts (OKCs) are benign jaw lesions with high growth potential and propensity for recurrence. Our previous study revealed that PTCH1 mutations, which were frequently detected in sporadic OKCs, might be underestimated due to the masking effect of the stromal components within the tested tissues. We aimed to confirm these results in larger scale and further present the unbiased view of the genomic basis of sporadic OKCs except PTCH1. MATERIALS AND METHODS We analyzed PTCH1 mutations in additional 19 samples. Using whole-exome sequencing (WES), we further characterized the mutational landscape of five sporadic OKC samples lacking PTCH1 mutation and loss of heterozygosity (LOH). RESULTS Combined with our previously reported 19 cases, thirty of 38 (79%) cases harbored PTCH1 mutations. Through whole-exome sequencing and integrative analysis, 22 novel mutations were confirmed among five PTCH1-negative samples. No recurrent mutations were identified in the WES samples and validation cohort of 10 OKCs. CONCLUSIONS Our data further confirmed the frequent PTCH1 mutation and other rare genetic alterations in sporadic OKCs, highlighting the central role of SHH signaling pathway. In PTCH1-negative cases, other rare mutations scattered in a subset of OKCs were independent of the SHH pathway. These results suggested that an SHH inhibitor may be effective to treat the majority of OKCs.
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heterozygous PTCH1 mutations impact the bone metabolism in patients with nevoid basal cell carcinoma syndrome likely by regulating sparc expression
Journal of Bone and Mineral Research, 2016Co-Authors: Yingying Hong, Jianyun Zhang, Heyu Zhang, Jiemei Zhai, Lei Zhang, Feng ChenAbstract:Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by bone and skin abnormalities and a predisposition to various tumors. Keratocystic odontogenic tumors (KCOTs), which are common tumors of the jaw that cause extensive damage to the jawbone, are usually accompanied with NBCCS. Germline PTCH1 mutations in NBCCS tumorigenesis have been frequently studied; however, little is known regarding the pathogenesis of bone abnormalities in this disease. This study sought to investigate the mechanism underlying heterozygous PTCH1 mutation-mediated abnormal bone metabolism in patients with NBCCS. Stromal cells were isolated from the fibrous capsules of patients with NBCCS-associated or non-syndromic keratocystic odontogenic tumors and non-syndromic tumor stromal cells without PTCH1 mutations served as controls. Germline PTCH1 heterozygous mutations were confirmed in all NBCCS samples and differential protein expression was identified using tandem mass tag-labeled proteomics analysis. Our findings revealed that osteonectin/SPARC expression was significantly downregulated in syndromic stromal cells compared with non-syndromic stromal cells. SPARC expression was even lower in stromal cells carrying PTCH1 protein truncation mutations. PTCH1 siRNA transfection demonstrated that SPARC downregulation correlates with decreased PTCH1 expression. Furthermore, exogenous SPARC promoted osteogenic differentiation of syndromic stromal cells with enhanced development of calcium nodules. In addition, bone mineral density tests showed that patients with NBCCS exhibit weak bone mass compared with sex- and age-matched controls. This study indicates that germline PTCH1 heterozygous mutations play a major role in bone metabolism in patients with NBCCS, in particular in those with PTCH1 protein truncation mutations. SPARC may represent an important downstream modulator of PTCH1 mediation of bone metabolism. Thus, bone mineral density monitoring is critical for patients with NBCCS for prevention of osteoporosis. In addition, surgical procedures on syndromic-associated KCOTs should be performed with consideration of the weaker bone mass in such patients. © 2016 American Society for Bone and Mineral Research.
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Underestimated PTCH1 mutation rate in sporadic keratocystic odontogenic tumors.
Oral Oncology, 2015Co-Authors: Yingying Hong, Lisha Sun, Jianyun Zhang, Yan-yan Guo, Heyu Zhang, Rui-rui Shi, Feng ChenAbstract:Summary Objectives Keratocystic odontogenic tumors (KCOTs) are benign cystic lesions of the jaws that occur sporadically in isolation or in association with nevoid basal cell carcinoma syndrome (NBCCS). The protein patched homolog 1 gene (PTCH1) is associated with NBCCS development and tumor genesis associated with this syndrome. However, previous studies have revealed that more than 85% of syndromic KCOTs and less than 30% of sporadic KCOTs harbor PTCH1 mutations. The significantly lower PTCH1 mutation rates observed in sporadic KCOTs suggest that they serve a minor role in pathogenesis. We aimed to discern the importance of PTCH1 mutations in sporadic KCOTs. Materials and methods PTCH1 mutational analysis was performed with 19 new sporadic KCOT cases by direct sequencing of epithelial lining samples separated from fibrous capsules. Using this approach, we further reexamined 9 sporadic KCOTs that were previously reported to lack PTCH1 mutations by our group. Results Nineteen PTCH1 mutations were detected in patient samples from 16/19 new cases (84%) all these mutations were absent in fibrous tissues and peripheral blood specimens from the same patients. We also identified four PTCH1 mutations in 3/9 patients (33%) that were previously undetected. Discussion These data indicated that PTCH1 mutations occur in sporadic KCOTs at a higher rate than previously suspected, owing to the masking effects of the attached stromal tissues in the test samples. These results suggest that the PTCH1 gene plays a significant role in the pathogenesis of sporadic KCOTs, which is comparable to that observed in NBCCS patients.
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The large intracellular loop of PTCH1 mediates the non-canonical Hedgehog pathway through cyclin B1 in nevoid basal cell carcinoma syndrome
International Journal of Molecular Medicine, 2014Co-Authors: Yingying Hong, Feng ChenAbstract:Mutations in the transmembrane receptor patched homolog 1 (Homo sapiens) (PTCH1) are responsible for nevoid basal cell carcinoma syndrome (NBCCS), an autosomal dominant disorder that causes developmental abnormalities and predisposes the affected individuals to cancer. Many of these mutations, including mutations in the C-terminus of the large intracellular loop (ICL) of PTCH1 (p.C727VfsX745 and p.S733IfsX736), result in the premature truncation of the protein. The PTCH1‑C727VfsX745 and PTCH1-S733IfsX736 mutations have been identified in patients with NBCCS‑associated keratocystic odontogenic tumors (KCOTs). In the present study, we found that the molecular mechanisms regulated by the non-canonical Hedgehog (Hh) signaling pathway through cyclin B1 are involved in the pathogenesis of NBCCS-associated KCOTs. In contrast to wild-type PTCH1, PTCH1-C727VfsX745 and PTCH1‑S733IfsX736 clearly exhibited reduced binding to cyclin B1. Moreover, the cells expressing these two mutations demonstrated an increase in cell cycle progression and these two mutation constructs failed to inhibit cell proliferation. In addition, the mutants enhanced the activity of glioma-associated oncogene family zinc finger 1 (GLI1), a downstream reporter of Hh signaling. Thus, our data suggest that the non-canonical Hh pathway mediated through PTCH1 and cyclin B1 is involved in the pathogenesis of NBCCS-associated KCOTs. The C-terminus of ICL in PTCH1 may also be a potential therapeutic target in the treatment of this disease.
Rune Toftgard - One of the best experts on this subject based on the ideXlab platform.
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distinct roles of ptch2 splice variants in hedgehog signalling
Biochemical Journal, 2004Co-Authors: Fahimeh Rahnama, Rune Toftgard, Peter G ZaphiropoulosAbstract:The human PTCH2 gene is highly similar to PTCH1 , a tumour suppressor gene frequently mutated in basal cell carcinoma and several other tumour types. PTCH1 is a transmembrane protein believed to inhibit another transmembrane protein SMO (Smoothened), which mediates HH (Hedgehog) signalling. In this study, we analysed the biological properties of several PTCH2 splice variants. An mRNA form that lacked the last exon was abundantly expressed in all tissues examined, in contrast with the one that included it. Moreover, a transcript lacking exon 9, which is a part of a conserved sterol-sensing domain, was identified in intestine, prostate and cerebellum. In ovary, spleen, testis, cerebellum and skin, an mRNA lacking both exons 9 and 10 could also be observed. The different PTCH2 isoforms localized in the cytoplasm were capable of internalizing the N-terminal fragment of Sonic HH (Shh-N). Additionally, the PTCH2 gene was found to be a target of HH signalling. PTCH2 promoter regulation assays demonstrated that only one of the PTCH2 variants could inhibit the activity of SHH-N, whereas none was capable of inhibiting the activated form of SMO (SMO-M2) and this contrasts with PTCH1. Despite the fact that the PTCH2 isoforms lacked the ability to inhibit SMO-M2 activity, all PTCH2 variants as well as PTCH1, on co-transfection with Smo, were able to change Smo localization from being largely dispersed in the cytoplasm to the juxtanuclear region. Furthermore, the PTCH2 isoforms and PTCH1 co-localized in doubly transfected cells and an interaction between them was confirmed using immunoprecipitation assays. Using PTCH1 −/− mouse cells, it was shown that the PTCH2 variants and PTCH1 differentially act to reconstitute not only the SHH but also the Desert HH-dependent transcriptional response. We conclude that in spite of their structural similarities, the PTCH2 isoforms have distinct functional properties when compared with PTCH1.
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Expression of the PTCH1 tumor suppressor gene is regulated by alternative promoters and a single functional Gli-binding site.
Gene, 2004Co-Authors: Marie Ågren, Priit Kogerman, Marika I. Kleman, Martina Wessling, Rune ToftgardAbstract:The PTCH1 tumor suppressor gene encodes a receptor for secreted hedgehog (HH) ligands and is important for proper proliferation, differentiation and patterning in almost every tissue and organ during embryogenesis. The PTCH1 protein works as a negative regulator of the HH-signaling pathway by repressing downstream signaling by the coreceptor smoothened (SMOH). Mutations in PTCH1 lead to constitutive expression of HH target genes and a relationship between mutated PTCH1 and the most common tumor form in the Western world, Basal Cell Carcinoma (BCC) has been clearly established. We here show that PTCH1 is transcriptionally regulated by three independent promoters generating transcripts with alternative first exons. We demonstrate that only one of two putative Gli-binding sites that were identified in the promoter region of PTCH1 is functional, and that the transactivating Gli proteins, GLI1, Gli2 and GLI3, bind and enhance transcription through this site. Moreover, a strong repression of both basal and induced PTCH1 transcription was observed following expression of a truncated version of GLI3. Most interestingly, the upstream components in the HH-signaling cascade, Sonic HH (SHH) and SMOH, solely operate through the functional Gli-binding site because mutation of the Gli-binding site resulted in the disappearance of the enhanced transcription induced by the Gli proteins, as well as by SHH or SMOH. This finding suggests that transcriptional activation of the PTCH1 gene mediated via the HH-signaling pathway is dependent on the single functional Gli-binding site.
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indian hedgehog and β catenin signaling role in the sebaceous lineage of normal and neoplastic mammalian epidermis
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: C Niemann, Anne Birgitte Undén, Rune Toftgard, S Lyle, Ch C Zouboulis, Fiona M WattAbstract:In mammalian epidermis, the level of β-catenin signaling regulates lineage selection by stem cell progeny. High levels of β-catenin stimulate formation of hair follicles, whereas low levels favor differentiation into interfollicular epidermis and sebocytes. In transgenic mouse epidermis, overexpression of β-catenin leads to formation of hair follicle tumors, whereas overexpression of N-terminally truncated Lef1, which blocks β-catenin signaling, results in spontaneous sebaceous tumors. Accompanying overexpression of β-catenin is up-regulation of Sonic hedgehog (SHH) and its receptor, Patched (PTCH/Ptch). In ΔNLef1 tumors Ptch mRNA is up-regulated in the absence of SHH. We now show that PTCH is up-regulated in both human and mouse sebaceous tumors and is accompanied by overexpression of Indian hedgehog (IHH). In normal sebaceous glands IHH is expressed in differentiated sebocytes and the transcription factor GLI1 is activated in sebocyte progenitors, suggesting a paracrine signaling mechanism. PTCH1 and IHH are up-regulated during human sebocyte differentiation in vitro and inhibition of hedgehog signaling inhibits growth and stimulates differentiation. Overexpression of ΔNLef1 up-regulates IHH and stimulates proliferation of undifferentiated sebocytes. We present a model of the interactions between β-catenin and hedgehog signaling in the epidermis in which SHH promotes proliferation of progenitors of the hair lineages whereas IHH stimulates proliferation of sebocyte precursors.
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Alternative first exons of PTCH1 are differentially regulated in vivo and may confer different functions to the PTCH1 protein
Oncogene, 2002Co-Authors: Priit Kogerman, Fahimeh Rahnama, Darren Krause, Lembi Kogerman, Anne Birgitte Undén, Peter G Zaphiropoulos, Rune ToftgardAbstract:The PTCH1 gene is a human tumour suppressor gene frequently mutated in basal cell carcinoma (BCC) and several other tumour types. It encodes a receptor for soluble factors of the hedgehog family. Binding of hedgehog to the receptor relieves its inhibitory action on the transmembrane co-receptor Smoh. In this study we describe alternative first exons of the PTCH1 tumour suppressor gene and show that they are differentially regulated in normal tissues, exon 1B being expressed at very low levels and the major mRNA species containing exon 1 or 1A. Exon 1B transcripts were found to be specifically upregulated in nodular BCCs. The different PTCH1 transcripts all encode proteins that interact with Smoh in doubly transfected cells. Furthermore, functional assays demonstrated that whereas all PTCH1 isoforms can inhibit the activity of SHH, only the PTCH1B isoform is capable of fully inhibiting Smoh activity. The results indicate that in tumour cells the PTCH1B promoter is specifically activated and importantly, that the N-terminal part of PTCH1 including exon 1B is required for full inhibition of Smoh signaling but not for physical interaction with Smoh.
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ptch2 a novel human patched gene undergoing alternative splicing and up regulated in basal cell carcinomas
Cancer Research, 1999Co-Authors: Peter G Zaphiropoulos, Fahimeh Rahnama, Anne Birgitte Undén, Robert E. Hollingsworth, Rune ToftgardAbstract:By a combination of cDNA library screening, rapid amplification of cDNA ends analysis, and BAC sequencing, a novel human patched-like gene ( PTCH2 ) has been cloned and sequenced. The genomic organization is similar to PTCH1 with 22 exons and, by radiation hybrid mapping, PTCH2 has been localized to chromosome 1p33-34, a region often lost in a variety of tumors. Several alternatively spliced mRNA forms of PTCH2 were identified, including transcripts lacking segments thought to be involved in sonic hedgehog binding and mRNAs with differentially defined 3′ terminal exons. In situ hybridization revealed high expression of PTCH2 transcripts in both familial and sporadic basal cell carcinomas in similarity to what has been observed for PTCH1, suggesting a negative regulation of PTCH2 by PTCH1. This finding tightly links PTCH2 with the sonic hedgehog/PTCH signaling pathway, implying that PTCH2 has related, but yet distinct, functions than PTCH1.
Toshiyuki Miyashita - One of the best experts on this subject based on the ideXlab platform.
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Frameshift mutation in the PTCH2 gene can cause nevoid basal cell carcinoma syndrome
Familial Cancer, 2013Co-Authors: Katsunori Fujii, Hiromi Hatsuse, Tadashi Shiohama, Hideki Uchikawa, Maiko Suzuki, Hirofumi Ohashi, Toshiyuki MiyashitaAbstract:Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by developmental defects and tumorigenesis. The gene responsible for NBCCS is PTCH1 , encoding a receptor for the secreted protein, sonic hedgehog. Recently, a Chinese family with NBCCS carrying a missense mutation in PTCH2 , a close homolog of PTCH1 , was reported. However, the pathological significance of missense mutations should be discussed cautiously. Here, we report a 13-year-old girl diagnosed with NBCCS based on multiple keratocystic odontogenic tumors and rib anomalies carrying a frameshift mutation in the PTCH2 gene (c.1172_1173delCT). Considering the deleterious nature of the frameshift mutation, our study further confirmed a causative role for the PTCH2 mutation in NBCCS. The absence of typical phenotypes in this case such as palmar/plantar pits, macrocephaly, falx calcification, hypertelorism and coarse face, together with previously reported cases, suggested that individuals with NBCCS carrying a PTCH2 mutation may have a milder phenotype than those with a PTCH1 mutation.
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Selective haploinsufficiency of longer isoforms of PTCH1 protein can cause nevoid basal cell carcinoma syndrome.
Journal of Human Genetics, 2012Co-Authors: Maiko Suzuki, Hiromi Hatsuse, Yuji Kabasawa, Katsunori Fujii, Ken Omura, Kazuaki Nagao, Yoshinaga Takayama, Kohzoh Kameyama, Masayuki Yoshida, Toshiyuki MiyashitaAbstract:Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by developmental defects and tumorigenesis. The gene responsible for NBCCS is PTCH1. The PTCH1 gene has five alternatively used first exons resulting in the translation of three isoforms of the PTCH1 protein; that is, PTCHL, PTCHM and PTCHS. However, the biological significance of each isoform is unclear. Here we show an individual with NBCCS carrying a nonsense mutation in PTCH1 exon2, c.387G>A (p.W129X). As the mutation lay upstream of the ATG codon used for PTCHS translation, the mutant allele still expressed RNA isoforms that encode PTCHS. These results clearly demonstrate that a selective haploinsufficiency of longer isoforms of the PTCH1 protein, PTCHL and PTCHM, but not PTCHS is sufficient to cause NBCCS. Although mice selectively deficient in PTCHS isoforms are currently unavailable, this study sheds light on the complex in vivo roles of PTCH1 isoforms.
Paul A. Hamel - One of the best experts on this subject based on the ideXlab platform.
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The protein-specific activities of the transmembrane modules of PTCH1 and Ptch2 are determined by their adjacent protein domains
Journal of Biological Chemistry, 2018Co-Authors: Andrew Fleet, Paul A. HamelAbstract:Signaling through the Hedgehog (Hh) pathway is mediated by the Patched (Ptch) family of proteins. Although the vertebrate Ptch proteins PTCH1 and Ptch2 harbor two closely related transmembrane modules related to sterol-sensing domains (SSDs), the role of these closely related receptors in the Hh pathway are not equivalent. PTCH1 is essential for development and appears to be the principal receptor mediating responses to Hh ligands, whereas Ptch2 is nonessential, and its role in Hh-signaling remains ambiguous. We hypothesized that the SSDs of the Ptch proteins function as generic modules whose protein-specific activities are determined by the adjacent cytoplasmic and luminal domains. We first showed that individual N-terminal and C-terminal halves of PTCH1 associated noncovalently to mediate ligand-dependent regulation of Hh signaling. The analogous regions of Ptch2 also interacted noncovalently but did not repress the Hh pathway. However, the SSD of Ptch2 were capable of repressing Hh signaling, as determined using chimeric proteins where the SSDs of PTCH1 were replaced by those from Ptch2. Replacement of the SSDs of PTCH1 with the analogous regions from the cholesterol transporter NPC1 failed to produce a chimeric protein capable of Hh repression. Further refinement of the specific regions in PTCH1 and Ptch2 revealed that specific cytoplasmic domains of PTCH1 were necessary but not sufficient for repression of Hh signaling and that the two principal luminal domains of PTCH1 and Ptch2 were interchangeable. These data support a model where the SSDs of the Ptch family proteins exhibit generic activities and that the adjacent cytoplasmic and luminal domains determine their protein-specific activities.
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distinct effects of the mesenchymal dysplasia gene variant of murine patched 1 protein on canonical and non canonical hedgehog signaling pathways
Journal of Biological Chemistry, 2014Co-Authors: Malcolm C Harvey, Andrew Fleet, Nadia Okolowsky, Paul A. HamelAbstract:Hedgehog (Hh) signaling requires regulation of the receptor Patched-1 (PTCH1), which, in turn, regulates Smoothened activity (canonical Hh signaling) as well as other non-canonical signaling pathways. The mutant PTCH1 allele mesenchymal dysplasia (mes), which truncates the PTCH1 C terminus, produces a limited spectrum of developmental defects in mice as well as deregulation of canonical Hh signaling in some, but not all, affected tissues. Paradoxically, mes suppresses canonical Hh signaling and binds to Hh ligands with an affinity similar to wild-type mouse PTCH1 (mPTCH1). We characterized the distinct activities of the mes variant of mPTCH1 mediating Hh signaling through both canonical and non-canonical pathways. We demonstrated that mPTCH1 bound c-src in an Hh-regulated manner. Stimulation with Sonic Hedgehog (Shh) of primary mammary mesenchymal cells from wild-type and mes animals activated Erk1/2. Although Shh activated c-src in wild-type cells, c-src was constitutively activated in mes mesenchymal cells. Transient assays showed that wild-type mPTCH1, mes, or mPTCH1 lacking the C terminus repressed Hh signaling in PTCH1-deficient mouse embryo fibroblasts and that repression was reversed by Shh, revealing that the C terminus was dispensable for mPTCH1-dependent regulation of canonical Hh signaling. In contrast to these transient assays, constitutively high levels of mGli1 but not mPTCH1 were present in primary mammary mesenchymal cells from mes mice, whereas the expression of mPTCH1 was similarly induced in both mes and wild-type cells. These data define a novel signal transduction pathway involving c-src that is activated by the Hh ligands and reveals the requirement for the C terminus of Ptch in regulation of canonical and non-canonical Hh signaling pathways.