Semaphorin 4D Signaling Requires the Recruitment of Phospholipase Cγ into the Plexin-B1 Receptor Complex

Abstract

The semaphorin 4D (Sema4D) receptor plexin-B1 constitutively interacts with particular Rho guanine nucleotide exchange factors (RhoGEFs) and thereby mediates Sema4D-induced RhoA activation, a process which involves the tyrosine phosphorylation of plexin-B1 by ErbB-2. It is, however, unknown how plexin-B1 phosphorylation regulates RhoGEF activity. We show here that activation of plexin-B1 by Sema4D and its subsequent tyrosine phosphorylation creates docking sites for the SH2 domains of phospholipase Cγ (PLCγ). PLCγ is thereby recruited into the plexin-B1 receptor complex and via its SH3 domain activates the Rho guanine nucleotide exchange factor PDZ-RhoGEF. PLCγ-dependent RhoGEF activation is independent of its lipase activity. The recruitment of PLCγ has no effect on the R-Ras GTPase-activating protein activity of plexin-B1 but is required for Sema4D-induced axonal growth cone collapse as well as for the promigratory effects of Sema4D on cancer cells. These data demonstrate a novel nonenzymatic function of PLCγ as an important mechanism of plexin-mediated signaling which links tyrosine phosphorylation of plexin-B1 to the regulation of a RhoGEF protein and downstream cellular processes.

ACKNOWLEDGMENTS

We thank Evelyne Jones (London) for kindly providing Lec3.2.8.1 CHO cells expressing part of human Sema4D and Peter Gierschik (Ulm) for kindly providing (Myc)-PLCγ1 cDNA. We thank Martina Kurejova for support, H.-P. Gensheimer for technical assistance, and R. LeFaucheur for help with the preparation of the manuscript.

J. Swiercz and T. Worzfeld were recipients of a postdoctoral scholarship of the Medical Faculty Heidelberg.