Requirement of tyrosine-phosphorylated Vav for morphological differentiation of all-trans-retinoic acid-treated HL-60 cells

Our previous data demonstrated that cellular and nuclear tyrosine-phosphory lated Vav associate with phosphoinositide 3-kinase during all-trans-retinoi c acid-dependent granulocytic differentiation of HL-60 cells. In this study , aimed to analyze the mechanism by which Vav is recruited and activated, w e report that the Src homology 2 domain of Vav interacts with tyrosine-phos phorylated proteins in a differentiation-dependent manner. Two adaptor prot eins, Cbl and SLP-76, were identified, showing a discrete distribution insi de the cells, with Cbl absent from the nuclei and SLP-76 particularly abund ant in the nuclear compartment, Of note, Vav interacts with the tyrosine ki nase Syk, which is also present in the nuclear compartment and may phosphor ylate Vav in vitro when cells differentiate. Inhibition of Syk activity by piceatannol prevents both in vitro and in vivo Vav tyrosine phosphorylation , its association with the regulatory subunit of phosphoinositide 9-kinase, and the nuclear modifications typically observed during granulocytic diffe rentiation of this cell line. These findings suggest that tyrosine-phosphor ylated Vav and its association with phosphoinositide 3-kinase play a crucia l role in all-trans-retinoic acid-induced reorganization of the nucleoskele ton, which is responsible for the changes in nuclear morphology observed du ring granulocytic differentiation of HL-60 cells.