Selective tyrosine phosphorylation of the PKD2 activation segment: a novel regulatory mechanism to achieve isoenzyme specific signaling within the protein kinase D family.

Most protein kinase enzymes occur as families of 2 up to sometimes >10 members. A fundamental question in kinase signaling remains: how can we explain the often very different cellular roles of members within a kinase family? The protein kinase D family consists of its members PKD1, 2 and 3 and is the focus of our attention in this project. These enzymes have important and often opposite roles in cancer (PKD1 inhibiting, whereas PKD2/3 promoting cancer signaling pathways). Hence, the elucidation of such fundamentally diverse signaling functions within a kinase family deserves attention. We noticed that the 3 PKD isoenzymes are in part identically, but also in part differentially phosphorylated. More in particular, we noticed that in a number of cancer cell lines PKD2 (but not PKD1/3) is tyrosine phosphorylated on Y717 in the activation segment, an area that is well known crucial to the regulation of protein kinases. The PKD2 Y717 phosphorylation occurs in conditions that are often seen in tumours, such as oxidative stress, hypoxia and EGFR stimulation. This phosphorylation is likely to be of fundamental importance for kinases, as we found it in > 70 kinases upon inspection of publicly available database data of phosphoproteomics experiments. Here, we will study : 1) kinases that cause PKD2 Y717 phosphorylation, 2) mechanisms and consequences of PKD2 Y717 phosphorylation induced by the EGFR and hypoxia, 3) signaling pathways downstream of PKD2 Y717 phosphorylation.