Neuropilin-2 regulates a6b1 integrin in the formation of focal adhesions and signaling

The neuropilins (NRPs) contribute to the function of cancer cells in their capacity as VEGF receptors. Given that NRP2 is induced in breast cancer and correlates with aggressive disease, we examined the role of NRP2 in regulating the interaction of breast cancer cells with the ECM. Using epithelial cells from breast tumors, we defined NRP2 and NRP2 populations that differed in integrin expression and adhesion to laminin. Specifically, the NRP2 population adhered more avidly to laminin and expressed high levels of the a6b1 integrin than the NRP2 population. The NRP2 population formed numerous focal adhesions on laminin that were not seen in the NRP2 population. These results were substantiated using breast carcinoma cell lines that express NRP2 and a6b1 integrin. Depletion experiments revealed that adhesive strength on laminin but not collagen is dependent on NRP2, and that VEGF is needed for adhesion on laminin. A specific interaction between NRP2 and a6b1 integrin was detected by co-immunoprecipitation. NRP2 is necessary for focal adhesion formation on laminin and for the association of a6b1 integrin with the cytoskeleton. NRP2 also facilitates a6b1-integrin-mediated activation of FAK and Src. Unexpectedly, we discovered that NRP2 is located in focal adhesions on laminin. The mechanism by which NRP2 regulates the interaction of a6b1 integrin with laminin to form focal adhesions involves PKC activation. Together, our data reveal a new VEGF–NRP2 signaling pathway that activates the a6b1 integrin and enables it to form focal adhesions and signal. This pathway is important in the pathogenesis of breast cancer.