These information indicate that PI3K activity contributes to CXCL12-promoted melanoma cell CXC Chemokines Proteins Species invasion across basement membranes independently of enhancement in MT1-MMP expression.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author VEGF & VEGFR Proteins Biological Activity ManuscriptDiscussionInvasion of melanoma cells across basement membranes in response to CXCL12 needs functional interplay between GTPases Rac and Rho and MT1-MMP activities (47). Activation of Rho GTPases is dependent on their interaction with GEFs, which catalyze the exchange of bound GDP by GTP on the GTPases (35). Hence, characterization of GEFs that activate Rac and Rho in the course of CXCL12-promoted melanoma cell invasion, also as identification of upstream and downstream molecules participating within this signaling pathway, is of important significance to identify mechanisms controlling invasion. In the present study, we show that melanoma cells express the GEFs Vav1 and Vav2 and that Vav activation by CXCL12 is needed for subsequent Rac and Rho activation and for invasion across Matrigel basement membranes. Importantly, we deliver evidence that up-regulation by CXCL12 of MT1-MMP expression requires activation of Vav-Rho GTPase signaling pathway. Lastly, we show that MT1-MMP plays a vital function on CXCL12-promoted melanoma cell invasion by activating pro-MMP-2 processing to mature MMP-2, which in turn is actually a most important MMP facilitating the invasion across basement membranes and sort I collagen in response to this chemokine. Expression of Vav1 and Vav2 was found on melanoma cells isolated from lymph node metastases too as on many melanoma cell lines, such as hugely metastatic BLM cells. The levels of Vav proteins identified on melanoma cells had been regularly low as detected by immunoprecipitation, immunofluorescence confocal microscopy, and immunohistochemistry. Remarkably, Vav proteins have been localized at submembrane places each in BLM cells and in metastatic melanoma tissue sections. Vav-containing bleb-like protrusions surrounded by 1 integrins that were located close to the leading lamellae on BLM cells might be associated with similar structures defined on melanoma tumor cells invading three-dimensional Matrigel (59). Though a lot of reported function on Vav proteins issues cells on the hematopoietic lineage, quite small is identified on Vav expression on strong tumor cells, and to our knowledge, this can be the first description of Vav expression and function on melanoma cells. Several previous functions also reported Vav expression on neuroblastoma and pancreatic tumor cells (45,46). Phosphorylation of Vav proteins is actually a essential step for the stimulation of their GEF activity on Rho GTPases (42,43). We found that CXCL12 efficiently phosphorylated both Vav1 and Vav2 on BLM melanoma cells. As soon as phosphorylated, Vav1 predominantly interacted with Rac and, to a lesser extent, with RhoA in BLM cells, similarly to what has been reported in Vav1-Rho GTPase interactions on immune cells (391). Rather, phosphorylated Vav2 showed related tendency to bind both Rac and RhoA. Preliminary confocal microscopy experiments revealed that if there was a Vav preferential localization at plasma membrane on cell stimulation with five CXCL12 this was also subtle to be detected utilizing this technique . Importantly, transfection of dominant-negative Vav types or knocking down Vav1 and Vav2 expression by transfection of their siRNA resulted within a exceptional impairment in CXCL12promoted Rac and Rho activation at the same time as invasion of melanoma cells toward CXCL12,5I. Molin.
