Sphingolipid receptor signaling and function in human bladder carcinoma cells: inhibition of LPA- but enhancement of thrombin-stimulated cell motility

Sphingosine-1-phosphate (SPP) induces a variety of cellular responses, incl uding Ca2+ signaling, proliferation, and inhibition of motility, apparently by acting at specific G protein coupled receptors. Here, the expression, s ignaling, and motile responses of sphingolipid receptors were examined in h uman bladder carcinoma (J82) cells, for which lysophosphatidic acid (LPA) a nd thrombin act as potent agonists. SPP potently and rapidly mobilized Ca2, stimulated phospholipases C and D, and inhibited cAMP accumulation, witho ut affecting growth of J82 cells, which express the recently identified SPP receptors, Edg-1 and Edg-3. The effects of SPP were mimicked by sphingosyl phosphorylcholine (SPPC) and strongly attenuated by pertussis toxin (PTX). SPP and SPPC by themselves induced a small, PTX-sensitive motile response. However, stimulation of cell motility by LPA, which by itself was also PTX- sensitive, was blocked by SPP and SPPC. In contrast, motility stimulation b y thrombin, which by itself was PTX-insensitive, was strongly augmented by the sphingolipids in a PTX-sensitive manner. The bidirectional regulation o f LPA- and thrombin-stimulated motility was not due to selective alteration s in the activation of Rho GTPases which control cell motility. In fact, Rh oA activation and Rho-dependent actin stress fiber formation induced by LPA and thrombin were mimicked, but not altered by SPP and SPPC. We conclude t hat J82 cells express sphingolipid receptors, coupled via G proteins to sev eral signaling pathways. Most importantly, these sphingolipid receptors pot ently regulate thrombin- and LPA-stimulated motility, but in opposite direc tions, suggesting that migration of these human bladder carcinoma cells is controlled by a complex network of interacting extracellular ligands.