| Novel p62dok family members , dok 4 and dok 5 , are substrates of the c Ret receptor tyrosine kinase and mediate neuronal differentiation . ^^^ In addition to dok 1 , dok 2 , and dok 3 , we identified two new family members , dok 4 and dok 5 , that can directly associate with Y 1062 of c Ret . ^^^ Dok 4 and dok 5 constitute a subgroup of dok family members that is coexpressed with c Ret in various neuronal tissues . ^^^ Activated c Ret promotes neurite outgrowth of PC 12 cells ; for this activity , Y 1062 in c Ret is essential . c Ret / dok fusion proteins , in which Y 1062 of c Ret is deleted and replaced by the sequences of dok 4 or dok 5 , induce ligand dependent axonal outgrowth of PC 12 cells , whereas a c Ret fusion containing dok 2 sequences does not elicit this response . ^^^ Moreover , dok 4 and dok 5 enhance c Ret dependent activation of mitogen activated protein kinase . ^^^ |