1. ¹Cancer Research UK Centre for Cell and Molecular Biology, Chester Beatty Laboratories, The Institute of Cancer Research, Fulham Road, London SW3 6JB, UK
2. ²National Heart and Lung Institute Division, Faculty of Medicine, Imperial College London, Armstrong Road, London SW7 2AZ, UK

Correspondence: M Katan, E-mail: matilda@icr.ac.uk

Received 8 April 2004; Revised 3 August 2004; Accepted 12 August 2004; Published online 22 November 2004.

Abstract

Phospholipase C (PLC) is a novel member of phosphoinositide-specific phospholipase C enzymes with a unique regulatory link to Ras GTP-ases. In the present studies, we establish existence of two splice variants (PLC1a and PLC1b) derived from human PLC1 gene. When expressed in COS or HEK293 cells, PLC1a and PLC1b have similar potential to be stimulated by diverse signaling pathways via tyrosine kinase and G-protein coupled receptors and share the ability to function as an effector of Ras. The expression pattern shows broader mRNA expression of PLC1a in normal tissues; furthermore, in most cell lines expressing PLC, PLC1a is the only splice variant present. Analysis of normal/tumor matched pairs derived from colon and rectum demonstrates greatly reduced expression levels in tumor tissues. Further studies in a colorectal tumor cell line lacking PLC show restoration of transcription of PLC1a and PLC1b by demethylating agent 5-aza-2'-deoxycytidine, suggesting epigenetic silencing through hypermethylation. In addition, expression of exogenous PLC in this cell line demonstrates inhibitory effects of PLC on cell viability and proliferation. Taken together, our findings suggest that regulatory mechanisms controlling expression of PLC, broadened by diversity introduced by splice variants, could play important role in PLC regulation in normal and tumor cells.