LYSOPHOSPHATIDIC ACID-INDUCED NEURITE RETRACTION IN PC12 CELLS - CONTROL BY PHOSPHOINOSITIDE-CA2+ SIGNALING AND RHO

The endogenous phospholipid mediator lysophosphatidic acid (LPA) cause d growth cone collapse, neurite retraction, and cell flattening in dif ferentiated PC12 cells, Neurite retraction was blocked by cytochalasin B and ADP-ribosylation of the small-molecular-weight G protein Rho by the Clostridium botulinum C-3 toxin, LPA induced a transient rise in the level of inositol 1,4,5-trisphosphate, and retraction was blocked by inhibitors of phospholipase beta, Repeated application of LPA elici ted homologous desensitization of the Ca2+ mobilization response, The activation of the phosphoinositide (PIP)-Ca2+ second messenger system played a permissive role in the morphoregulatory response, Blockers of protein kinase C-chelerythrine, a myristoylated pseudosubstrate pepti de, staurosporine, and depletion of protein kinase C from the cells by long-term phorbol ester treatment-all diminshed neurite retraction by interfering with LPA-induced Ca2+ mobilization, which was required fo r the withdrawal of neurites, A brief 15-min treatment with 4 beta-pho rbol 12-myristate 13-acetate also blocked retraction and Ca2+ mobiliza tion, by inactivating the LPA receptor, Inhibition of protein tyrosine phosphorylation by herbimycin diminished retraction. Although activat ion of the PIP-Ca2+ second messenger system appears necessary for the Rho-mediated rearrangements of the actin cytoskeleton, bradykinin, whi ch activates similar signaling events, failed to cause retraction, ind icating that a yet unidentified novel mechanism is also involved in th e LPA-induced morphoregulatory response.