Characterization of a novel tumor-suppressor gene PLC delta 1 at 3p22 in esophageal squamous cell carcinoma.

Deletion of 3p is one of the most frequent chromosomal alterations in many solid tumors, including esophageal squamous cell carcinoma (ESCC), suggesting the existence of one or more tumor-suppressor genes at 3p. Recently, our loss of heterozygosity study revealed that 3p22 was frequently deleted in ESCC and a candidate tumor-suppressor gene (TSG), phospholipase C-delta 1 (PLC delta 1), was identified within the 3p22 region. In this study, absent expression of PLC delta 1 was detected in 26 of 50 (52%) primary ESCCs and 4 of 9 (44.4%) ESCC cell lines, which was significantly associated with DNA copy number loss and promoter hypermethylation (P < 0.05). Functional studies showed that PLC delta 1 was able to suppress both in vitro and in vivo tumorigenic ability of ESCC cells, including foci formation, colony formation in soft agar, and tumor formation in nude mice. The tumor-suppressive mechanism of PLC delta 1 was associated with its role in the cell cycle arrest at the G(1)-S checkpoint by up-regulation of p21 and down-regulation of phosphorylated Akt (Ser(473)). In addition, down-regulation of PLC delta 1 protein was significantly correlated with ESCC metastasis (P = 0.014), which was associated with its function in increasing cell adhesion and inhibiting cell mobility. Taken together, our results suggest that PLC delta 1 plays an important suppressive role in the development and progression of ESCC.