1. ¹Cancer Research UK Centre for Cancer Therapeutics, The Institute of Cancer Research, Sutton, UK
2. ²Cancer Research UK Centre for Cell and Molecular Biology, The Institute of Cancer Research, London, UK

Correspondence: Dr SA Eccles, Cancer Research UK Centre for Cancer Therapeutics, The Institute of Cancer Research, McElwain Labs, 15 Cotswold Road, Sutton, Surrey SM2 5NG, UK. E-mail: Sue.Eccles@icr.ac.uk

Received 18 August 2007; Revised 19 October 2007; Accepted 24 October 2007; Published online 26 November 2007.

Abstract

Phospholipase C1 (PLC1) 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 PLC1 knockdown in PC3LN3 human prostate carcinoma cells for further evaluation of PLC1 in tumour cell biology. Using this approach, we revealed a role for PLC1 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 PLC1-knockdown cells revealed Rap GEF1 mRNA to be decreased in response to PLC1 loss. This translated into a decrease in Rap GEF1 protein levels and a significant loss of Rap1 activity in PLC1-knockdown cells. Transient knockdown of Rap GEF1 caused a reduction in PC3LN3 adhesion while overexpression of Rap GEF1 rescued the PLC1 knockdown-induced adhesion defect. These data highlight control of the Rap GEF1–Rap1 molecular switch as a specific requirement for PLC1-mediated tumour cell adhesion.