Association of atypical protein kinase C isotypes with the docker protein FRS2 in fibroblast growth factor signaling

FRS2 is a docker protein that recruits signaling proteins to the plasma mem brane in fibroblast growth factor signal transduction. We report here that FRS2 was associated with PKC lambda when Swiss 3T3 cells were stimulated wi th basic fibroblast growth factor. PKC zeta, the other member of the atypic al PKC subfamily, could also bind FRS2. The association between FRS2 and PK C lambda is likely to be direct as shown by yeast two-hybrid analysis. The C-terminal fragments of FRS2 (amino acid residues 300-508) and SNT2 (amino acids 281-492), an isoform bearing 50% identity to FRS2, interacted with PK C lambda at a region (amino acids 240-562) that encompasses the catalytic d omain. In vitro kinase assays revealed neither FRS2 nor SNT2 was a substrat e of PKC lambda or zeta. Mutation of the alanine residue (Ala-120) to gluta mate in the pseudo-substrate region of PKC lambda results in a constitutive ly active kinase that exhibited more than 2-fold greater binding to FRS2 in vitro than its "closed" wildtype counterpart. Tyrosine phosphorylation of FRS2 did not affect its binding to the constitutively active PRC lambda mut ant, suggesting that the activation of PKC lambda is necessary and sufficie nt for its association with FRS2. It is likely that FRS2 serves as an ancho ring protein for targeting activated atypical PKCs to the cell plasma membr ane in signaling pathways.