Atypical mechanism of regulation of the Wrch-1 Rho family small GTPase.
Rho family GTPases are GDP/GTP-regulated molecular switches that regulate signaling pathways controlling diverse cellular processes. Wrch-1 was identified as a Wnt-1 regulated Cdc42 homolog, upregulated by Wnt1 signaling in Wnt1-transformed mouse mammary cells, and was able to promote formation of filopodia and activate the PAK serine/threonine kinase. Wrch-1 shares significant sequence and functional similarity with the Cdc42 small GTPase. However, Wrch-1 possesses a unique N-terminal 46 amino acid sequence extension that contains putative Src homology 3 (SH3) domain-interacting motifs. We determined the contribution of the N terminus to Wrch-1 regulation and activity. We observed that Wrch-1 possesses properties that distinguish it from Cdc42 and other Rho family GTPases. Unlike Cdc42, Wrch-1 possesses an extremely rapid, intrinsic guanine nucleotide exchange activity. Although the N terminus did not influence GTPase or GDP/GTP cycling activity in vitro, N-terminal truncation of Wrch-1 enhanced its ability to interact with and activate PAK and to cause growth transformation. The N terminus associated with the Grb2 SH3 domain-containing adaptor protein, and this association increased the levels of active Wrch-1 in cells. We propose that Grb2 overcomes N-terminal negative regulation to promote Wrch-1 effector interaction. Thus, Wrch-1 exhibits an atypical model of regulation not seen in other Rho family GTPases.
Shutes
Adam
A
Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Berzat
Anastacia C
AC
Cox
Adrienne D
AD
Der
Channing J
CJ
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D017931:DNA Primers; D005454:Fluorescence Polarization; D051380:GRB2 Adaptor Protein; D005786:Gene Expression Regulation; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D041681:NIH 3T3 Cells; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011554:Pseudopodia / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D018909:src Homology Domains / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; D017346:Protein Serine-Threonine Kinases; C432668:RHOU protein, human; D020741:rho GTP-Binding Proteins