5333

PLCD1

NDNC3|PLC-III;phospholipase C, delta 1;PLCD1;phospholipase C, delta 1

1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase delta-1|1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase delta-1|PLC-delta-1|phosphoinositide phospholipase C-delta-1|phospholipase C-III

3p22-p21.3

protein-coding

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.

Located at the important tumor suppressor locus, 3p22, PLCD1 encodes an enzyme that mediates regulatory signaling of energy metabolism, calcium homeostasis and intracellular movements. We identified PLCD1 as a downregulated gene in aerodigestive carcinomas through expression profiling and epigenetic characterization. We found that PLCD1 was expressed in all normal adult tissues but low or silenced in 84% (16/19) gastric cancer cell lines, well correlated with its CpG island (CGI) methylation status. Methylation was further detected in 62% (61/98) gastric primary tumors, but none of normal gastric mucosa tissues. PLCD1 methylation was significantly correlated with tumor high stage. Detailed methylation analysis of 37 CpG sites at the PLCD1 CGI by bisulfite genomic sequencing confirmed its methylation. PLCD1 silencing could be reversed by pharmacological demethylation with 5-aza-2-deoxycytidine, indicating a direct epigenetic silencing. Ectopic expression of PLCD1 in silenced gastric tumor cells dramatically inhibited their clonogenicity and migration, possibly through downregulating MMP7 expression and hampering the reorganization of cytoskeleton through cofilin inactivation by phosphorylation. Thus, epigenetic inactivation of PLCD1 is common and tumor-specific in gastric cancer, and PLCD1 acts as a functional tumor suppressor involved in gastric carcinogenesis.

Chromosome 3p harbors multiple tumor-suppressor genes. PLCD1, located at 3p22, encodes an enzyme that mediates regulatory signaling of energy metabolism, calcium homeostasis and intracellular movement. We investigated the epigenetic alterations of PLCD1 and its tumor suppressor function in breast cancer. Frequent downregulation/silencing of PLCD1 was shown in most breast cancer cell lines by using semi-quantitative PCR. Promoter methylation of PLCD1 was detected in 78% (7/9) of cell lines and 52% (13/25) of primary tumors by Methylation-specific PCR (MSP), but not in any tumor adjacent breast tissues and normal breast tissues, which was further confirmed by bisulfite genomic sequencing (BGS). The silencing of PLCD1 could be reversed by pharmacological demethylation, indicating a methylation-mediated mechanism. Ectopic expression of PLCD1 in silenced breast cancer cells significantly inhibited their colony formation. In addition, PLCD1 inhibited tumor cell migration and induced cell cycle G(2)/M arrest. Thus, this study for the first time demonstrates the frequent inactivation of PLCD1 by promoter methylation and its tumor inhibitory function in breast cancer. Tumor-specific methylation of PLCD1 might serve as a biomarker for possible early detection and prognosis prediction of breast cancer.