Molecular mechanisms of tumorigenesis in nevoid basal cell carcinoma syndrome

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Mutations in the human homologue of Drosophfla patched (PTCH) have been identified in patients with nevoid basal cell carcinoma syndrome(NBCCS) as well as sporadic basal cell carcinoma and medulloblastomas. However, using PCR-SSCP analysis, mutations in PTCH have been found in only fraction (about one third to a half) of NBCCS patients. In this study, we determined the whole genomic organizations of the PTCH gene and developed a new set of more accurate primers for the analysis of mutations in PTCH. Using these primers, we examined 8 Japanese NBCCS patients for mutations in PTCH exons by direct sequencing of the PCR products. As a result, we identified 5 novel PTCH mutations in 6 out of 8 patients inckuding two sistersas well as 5 polymorphisms, two of them,1704G>C and 2928G>C were novel. Four of these mutations, 900delC,1247insT,1999delC and 933+5G>T, cause protein truncation due to the insertion or deletion of a single nucleotide or aberrant splicing. The remaining mutation,1514G>A w … More as a missense alteration (G509D). Interestingly, the amino acid substitution, G509V has been reported previously in an NBCCS patient, suggesting an important role of this amino acid residue in the function of PTCH protein. The difference in the detection rate of PTCH mutations among NBCCS patients between previous reports and ours is due to the difference eithr in ethnicity or in the detection methods.We reported the case of a 14-year-old Japanese girl who had both NBCCS and ulcerative colitis. She had complained of blood stools for 6 months and severe scoliosis form her infancy. Physical examination revealed multiple nevi, palmar and plantar pits, jaw cysts, and calcification of the falx cerebri, leading to the diagnosis of NBCCS. Total colonoscopy revealed an edematous and spotty bleeding mucosaextending from the anus to the transverse colon. Histological examination was also compatible with ulcerative colitis. Thus, we diagnosed her as having NBCCS with ulcerative colitis. Gene analysis revealed a mutation, 1247InsT, in the human patched gene (PTCH), resulting in the truncation of PTCH protein. Since NBCCS and ulcerative colitis are rare disorders in childhood, this association is interesting, suggesting a correlation between the hedgehog signaling and intestinal disorders.We identified seven and five isoforms of human and mouse PTCH mRNA, respectively., which are generated by the complex alternative use of five exons as the first exon (exons 1a to 1e in the 5'-to-3'order). Although expression profiles of these isoforms were highly variable among human tissues, three of them, PTCHa, PTCHb, and PTCHd, were predominantly expressed in most tissues, PTCHd being most ubiquitous. In contrast, PTCHb was always predominant and readied a maximum at E10.5 during mouse development. These three mRNA isoforms encode three PTCH proteins with distinct N-termini,PTCHL,PTCHM, and PTCHS. The expression of these three isoforms was regulated by GLI transcription factors, and at least two functional GLI-binding sequences were identified, one in exon la and other between exon 1a and exon 1b. Less