Vascular endothelial growth factor-induced migration of multiple myeloma cells is associated with β ₁ integrin- and phosphatidylinositol 3-kinase-dependent PKCα activation

In multiple myeloma (MM), migration is necessary for the homing of tumor cells to bone marrow (BM), for expansion within the BM microenvironment, and for egress into the peripheral blood. In the present study we characterize the role of vascular endothelial growth factor (VEGF) and β ₁ integrin (CD29) in MM cell migration. We show that protein kinase C (PKC) α is translocated to the plasma membrane and activated by adhesion of MM cells to fibronectin and VEGF. We identify β ₁ integrin modulating VEGF-triggered MM cell migration on fibronectin. We show that transient enhancement of MM cell adhesion to fibronectin triggered by VEGF is dependent on the activity of both PKC and β ₁ integrin. Moreover, we demonstrate that PKCα is constitutively associated with β ₁ integrin. These data are consistent with PKCα-dependent exocytosis of activated β ₁ integrin to the plasma membrane, where its increased surface expression mediates binding to fibronectin; conversely, catalytically active PKCα-driven internalization of β ₁ integrin results in MM cell de-adhesion. We show that the regulatory subunit of phosphatidylinositol (PI) 3-kinase (p85) is constitutively associated with FMS-like tyrosine kinase-1 (Flt-1). VEGF stimulates activation of PI 3-kinase, and both MM cell adhesion and migration are PI 3-kinase-dependent. Moreover, both VEGF-induced PI 3-kinase activation and β ₁ integrin-mediated binding to fibronectin are required for the recruitment and activation of PKCa. Time-lapse phase contrast video microscopy (TLVM) studies confirm the importance of these signaling components in VEGF-triggered MM cell migration on fibronectin.