Received for publication October 1, 2004.
Revised March 23, 2005.
Accepted for publication March 23, 2005.

Differential effects of Gq, G14 and G15 on vascular smooth muscle cells survival and gene expression profiles

Abstract

Gq family members (Gq, G11, G14 and G15/16) stimulate phospholipase C (PLC) and inositol lipid signaling, but differ markedly in amino acid sequence and tissue distribution predicting unappreciated functional diversity. To examine functional differences, we compared the signaling properties of Gq, G14 and G15 and their cellular responses in vascular smooth muscle cells (VSMC). Constitutively active forms of Gq, G14 or G15 elicit markedly different responses when introduced to VSMC. Whereas each G stimulated PLC to similar extents when expressed at equal protein levels, Gq and G14, but not G15 initiated profound cell death within 48 hours. This response was due to activation of apoptotic pathways since Gq and G14, but not G15, stimulated caspase-3 activation and did not alter phospho-Akt, a regulator of cell survival pathways. Gq and G14 stimulate NFAT activation in VSMC, but G-induced cell death appears independent of PKC, InsP₃/Ca⁺⁺, and NFAT because pharmacological inhibitors of these pathways did not block cell death. Gene expression analysis indicates that Gq, G14 and G15 each elicit markedly different profiles of altered gene sets in VSMC after 24 hrs. Whereas all three G stimulated changes (2-fold) in 50 shared mRNA, Gq and G14 (but not G15) stimulated changes in 221 shared mRNA of which many are reported to be pro-apoptotic and/or involved with TNF signaling. Surprisingly, each G also stimulated changes in non-overlapping G-specific gene sets. These findings demonstrate that Gq family members activate both overlapping and distinct signaling pathways, and are more functionally diverse than previously thought.

Key words: Gq/11 family, Phospholipase C's, IP3/DAG, Calcium (G Protein Coupled Signals), Protein Kinase C, G protein regulation, NFAT, Regulation of gene expression, Cyclooxygenases