57575

PCDH10

OL-PCDH|PCDH19;protocadherin 10;PCDH10;protocadherin 10

protocadherin-10

4q28.3

protein-coding

Protocadherins constitute the largest subgroup in the cadherin superfamily of cell adhesion molecules. Their major functions are poorly understood, although some are implicated in nervous system development. As tumor-specific promoter methylation is a marker for tumor suppressor genes (TSG), we searched for epigenetically inactivated TSGs using methylation-subtraction combined with pharmacologic demethylation, and identified the PCDH10 CpG island as a methylated sequence in nasopharyngeal carcinoma (NPC). PCDH10 is broadly expressed in all normal adult and fetal tissues including the epithelia, though at different levels. It resides at 4q28.3--a region with hemizygous deletion detected by array-CGH in NPC cell lines; however, PCDH10 itself is not located within the deletion. In contrast, its transcriptional silencing and promoter methylation were frequently detected in multiple carcinoma cell lines in a biallelic way, including 12/12 nasopharyngeal, 13/16 esophageal, 3/4 breast, 5/5 colorectal, 3/4 cervical, 2/5 lung and 2/8 hepatocellular carcinoma cell lines, but not in any immortalized normal epithelial cell line. Aberrant methylation was further frequently detected in multiple primary carcinomas (82% in NPC, 42-51% for other carcinomas), but not normal tissues. The transcriptional silencing of PCDH10 could be reversed by pharmacologic demethylation with 5-aza-2-deoxycytidine or genetic demethylation with double knockout of DNMT1 and DNMT3B, indicating a direct epigenetic mechanism. Ectopic expression of PCDH10 strongly suppressed tumor cell growth, migration, invasion and colony formation. Although the epigenetic and genetic disruptions of several classical cadherins as TSGs have been well documented in tumors, this is the first report that a widely expressed protocadherin can also function as a TSG that is frequently inactivated epigenetically in multiple carcinomas.

BACKGROUND & AIMS: By using methylation-sensitive representational difference analysis, we identified protocadherin 10 (PCDH10), a gene that encodes a protocadherin and is silenced in a tumor-specific manner. We analyzed its epigenetic inactivation, biological effects, and prognostic significance in gastric cancer. METHODS: Methylation status was evaluated by combined bisulfite restriction analysis and bisulfite sequencing. The effects of PCDH10 re-expression were determined in growth, apoptosis, proliferation, and invasion assays. PCDH10 target genes were identified by complementary DNA microarray analysis. RESULTS: PCDH10 was silenced or down-regulated in 94% (16 of 17) of gastric cancer cell lines; expression levels were restored by exposure to demethylating agents. Re-expression of PCDH10 in MKN45 gastric cancer cells reduced colony formation in vitro and tumor growth in mice; it also inhibited cell proliferation (P < .01), induced cell apoptosis (P < .001), and repressed cell invasion (P < .05), up-regulating the pro-apoptosis genes Fas, Caspase 8, Jun, and CDKN1A; the antiproliferation gene FGFR; and the anti-invasion gene HTATIP2. PCDH10 methylation was detected in 82% (85 of 104) of gastric tumors compared with 37% (38 of 104) of paired nontumor tissues (P < .0001). In the latter, PCDH10 methylation was higher in precancerous lesions (27 of 45; 60%) than in chronic gastritis samples (11 of 59; 19%) (P < .0001). After a median follow-up period of 16.8 months, multivariate analysis revealed that patients with PCDH10 methylation in adjacent nontumor areas had a significant decrease in overall survival. Kaplan-Meier survival curves showed that PCDH10 methylation was associated significantly with shortened survival in stage I-III gastric cancer patients. CONCLUSIONS: PCDH10 is a gastric tumor suppressor; its methylation at early stages of gastric carcinogenesis is an independent prognostic factor.