Lysophosphatidic Acid‐Induced Neurite Retraction in PC12 Cells: Control by Phosphoinositide‐Ca²⁺ Signaling and Rho

Abstract

The endogenous phospholipid mediator lysophosphatidic acid (LPA) caused growth cone collapse, neurite retraction, and cell flattening in differentiated 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 β. Repeated application of LPA elicited 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 peptide, staurosporine, and depletion of protein kinase C from the cells by long‐term phorbol ester treatment—all diminished neurite retraction by interfering with LPA‐induced Ca2+ mobilization, which was required for the withdrawal of neurites. A brief 15‐min treatment with 4β‐phorbol 12‐myristate 13‐acetate also blocked retraction and Ca2+ mobilization, by inactivating the LPA receptor. Inhibition of protein tyrosine phosphorylation by herbimycin diminished retraction. Although activation of the PIP‐Ca2+ second messenger system appears necessary for the Rho‐mediated rearrangements of the actin cytoskeleton, bradykinin, which activates similar signaling events, failed to cause retraction, indicating that a yet unidentified novel mechanism is also involved in the LPA‐induced morphoregulatory response.

Rho/ROCK pathway is essential to the expansion, differentiation, and morphological rearrangements of human neural stem/progenitor cells induced by lysophosphatidic acid

“…In particular, LPA is shown to induce neurite retraction and cell rounding through the Rho/ROCK pathway in rodent immortalized neuroblasts and PC12 ( 26,61 ). We observed a similar pattern of morphological changes in early human neurons, which, following exposure to LPA, underwent immediate and rapid retraction, cell rounding, and migration to form cell clusters and compaction in a Rho/ROCK-dependent manner.…”

Rho Kinase Inhibition Enhances Axonal Regeneration in the Injured CNS

“…The introduction of dominant-negative or constitutively active Rac blocks growth cone collapse in response to semaphorin 3A (Jin and Strittmatter, 1997) or myelin (Kuhn et al, 1999), and Rac participates in axonal patterning in vivo (Hakeda-Suzuki et al, 2002;. Rho activation leads to growth cone collapse and neurite inhibition in a variety of cell lines and primary neurons, and these responses can be attenuated by the inactivation of Rho with C3 transferase (Jalink and Moolenaar, 1992;Jalink et al, 1994;Tigyi et al, 1996;Jin and Strittmatter, 1997;Kozma et al, 1997;Hirose et al, 1998;Kranenburg et al, 1999;Lehmann et al, 1999).…”

Antagonistic Regulation of Neurite Morphology through Gq/G11 and G12/G13

“…1C). However, neurons lacking G␣ q and G␣ 11 showed a slightly reduced number of growth cone-positive neurites compared with wild-type or G␣ 12 /G␣ 13 -deficient neurons (Fig. 1D).…”

“…Mice-Mice with nervous system-specific G␣ q /G␣ 11 and G␣ 12 /G␣ 13 deficiency have been described (24,25).…”

“…Although there is good evidence that G 12 /G 13 -mediated RhoA activation via increased actomyosin contractility plays an important role in LPA-and thrombin-induced neurite retraction and growth cone collapse (9,11,21,22), evidence has also been provided that G q /G 11 -mediated signaling can mediate neurite retraction and growth cone collapse (21,23). However, studies analyzing the role of G-proteins in the regulation of neurite morphology via G-protein-coupled receptors have been based primarily on the use of constitutively active mutants of G-protein ␣-subunits.…”