p120-catenin suppresses proliferation and tumor growth of oral squamous cell carcinoma via inhibiting nuclear phospholipase C-gamma1 signaling.

p120-catenin (p120) serves as a stabilizer of the calcium-dependent cadherin-catenin complex and loss of p120 expression has been observed in several types of human cancers. The p120-dependent E-cadherin-beta-catenin complex has been shown to mediate calcium-induced keratinocyte differentiation via inducing activation of plasma membrane phospholipase C-gamma1 (PLC-gamma1). On the other hand, PLC-gamma1 has been shown to interact with phosphatidylinositol 3-kinase enhancer in the nucleus and plays a critical role in epidermal growth factor-induced proliferation of oral squamous cell carcinoma (OSCC) cells. To determine whether p120 suppresses OSCC proliferation and tumor growth via inhibiting PLC-gamma1, we examined effects of p120 knockdown or p120 and PLC-gamma1 double knockdown on proliferation of cultured OSCC cells and tumor growth in xenograft OSCC in mice. The results showed that knockdown of p120 reduced levels of PLC-gamma1 in the plasma membrane and increased levels of PLC-gamma1 and its signaling in the nucleus in OSCC cells and OSCC cell proliferation as well as xenograft OSCC tumor growth. However, double knockdown of p120 and PLC-gamma1 or knockdown of PLC-gamma1 alone did not have any effect. Immunohistochemical analysis of OSCC tissue from patients showed a lower expression level of p120 and a higher expression level of PLC-gamma1 compared with that of adjacent noncancerous tissue. These data indicate that p120 suppresses OSCC cell proliferation and tumor growth by inhibiting signaling mediated by nuclear PLC-gamma1.