Phospholipase Cγ1 regulates the Rap GEF1-Rap1 signalling axis in the control of human prostate carcinoma cell adhesion

Phospholipase Cγ1 (PLCγ1) is activated downstream of a variety of extracellular stimuli and has previously been implicated in the regulation of motility responses central to tumour cell invasion. In this study, we used a novel RNAi vector system to achieve conditional PLCγ1 knockdown in PC3LN3 human prostate carcinoma cells for further evaluation of PLCγ1 in tumour cell biology. Using this approach, we revealed a role for PLCγ1 in the regulation of PC3LN3 cell adhesion that appears to be independent of its effects on tumour cell chemotactic migration and spreading in response to extracellular matrix. Subsequent microarray analysis of PLCγ1-knockdown cells revealed Rap GEF1 mRNA to be decreased in response to PLCγ1 loss. This translated into a decrease in Rap GEF1 protein levels and a significant loss of Rap1 activity in PLCγ1-knockdown cells. Transient knockdown of Rap GEF1 caused a reduction in PC3LN3 adhesion while overexpression of Rap GEF1 rescued the PLCγ1 knockdown-induced adhesion defect. These data highlight control of the Rap GEF1–Rap1 molecular switch as a specific requirement for PLCγ1-mediated tumour cell adhesion.