DOCK180, A MAJOR CRK-BINDING PROTEIN, ALTERS CELL MORPHOLOGY UPON TRANSLOCATION TO THE CELL-MEMBRANE

CRK belongs to a family of adaptor proteins that consist mostly of SH2 and SH3 domains, Far Western blotting with CRK SH3 has demonstrated t hat it binds to 135- to 145-, 160-, and 180-kDa proteins. The 135- to 145-kDa protein is C3G, a CRK SH3-binding guanine nucleotide exchange protein, Here, we report on the molecular cloning of the 18O-kDa prote in, which is designated DOCK180 (18O-kDa protein downstream of CRK), T he isolated cDNA contains a 5,598-bp open reading frame encoding an 1, 866-amino-acid protein. The deduced amino acid sequence did not reveal any significant homology to known proteins, except that an SH3 domain was identified at its amino terminus. To examine the function of DOCK 180, a Ki-Ras farnesylation signal was fused to the carboxyl terminus of DOCK180, a strategy that has been employed successfully for activat ion of adaptor-binding proteins in vivo., Whereas wild-type DOCK180 ac cumulated diffusely in the cytoplasm and did not have any effect on ce ll morphology, farnesylated DOCK180 was localized on the cytoplasmic m embrane and changed spindle 3T3 cells to flat, polygonal cells, These results suggest that DOCK180 is a new effector molecule which transduc es signals from tyrosine kinases through the CRK adaptor protein.