Lint, Johan Van

Abstract The protein kinase D (PKD) family of kinases belongs to the CAMK group and consists of three highly homologous enzymes. They play a versatile role in cancer cell signaling, primarily downstream of PKC isoforms. Classically PKDs are activated upon co-localization with PKC at DAG containing membranes, where PKC phosphorylates the PKD activation loop, generating active PKD. Besides this, PKDs are also activated in oxidative stress conditions, where PKD1 protects against cellular damage via signaling to NF-kB. While the three isoforms are highly homologous, they are not redundant in their biological function and oncogenic potential. A picture has emerged which associates PKD1 expression and activity with decreased migration and inhibition of epithelial mesenchymal transition (EMT). PKD2 and PKD3 on the other hand are upregulated in various cancers, and show oncogenic potential e.g. via enhanced ECM breakdown and potentiation of angiogenesis. While non-redundant biological roles continue to surface, the biochemical mechanisms behind these discrepant functions remain mostly elusive. Here, we identify an isoform specific regulation of PKD2 in oxidative stress conditions via the phosphorylation of a key Tyrosine residue in the substrate binding loop of the activation segment which is highly conserved in most Ser/Thr kinases. Phosphorylation of this residue selectively occurs in PKD2 (and not in PKD1). While wild-type PKD1 signals to NF-kB in oxidative stress, we could show that wild-type PKD2 signaling to NF-kB is impeded in these conditions. Substitution of the activation segment Tyr-717 in PKD2 with a non-phosphorylatable Phe restores signaling to NF-kB, indicating that Tyr-717 phosphorylation is a key determinant for the signaling outcome of PKDs in oxidative stress. Note: This abstract was not presented at the conference. Citation Format: Mathias Cobbaut, Rita Derua, Etienne Waelkens, Peter Störz, Veerle Janssens, Johan Van Lint. Differential regulation of Protein Kinase D isoforms in oxidative stress conditions via tyrosine phosphorylation in the activation segment [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B08.

Abstract Introduction and Objective: The serine/threonine kinases of the protein kinase D family (PKCmu/PKD1, PKD2, PKCnu/PKD3), a subfamily of the CAMK superfamily, have been implicated in regulation of multiple biological processes including proliferation, survival, apoptosis, angiogenesis and motility. The precise mechanisms by which the three PKDs modulate these processes are incompletely understood and require a better knowledge of their signaling context. Methodology and Results: Using the ProtoArray Human Protein Microarray v4.0 (Invitrogen), we identified Abelson interactor 1 (ABI1) as a novel PKD2 substrate. ABI1 was first identified as the downstream target of Abl tyrosine kinase and is an adaptor protein involved in actin reorganization and lamellipodia formation along with WAVE2. In the present study we illustrate that PKD2 interacts and phosphorylates ABI1 in vitro and in vivo at two potential serine residues. The sites were validated using an antibody that specifically identifies the consensus PKD substrate sequence. Furthermore, PKD2-induced phosphorylation of ABI1 destabilized the interaction between ABI1 and WAVE2 and resulted in relocation of both the proteins from plasma membrane to perinuclear region. Consequences of this destabilization and its potential impact on WAVE2 driven actin polymerization and the associated processes are in the process of investigation. Preliminary results also suggest reduced migration velocity and directedness of a tumor cell. Conclusion: In conclusion, our data demonstrate that ABI1 is a novel substrate of PKD2 that might negatively regulate tumor cell migration via terminating a constitutive interaction between ABI1 and WAVE2. *Impact of ABI1-WAVE2 subcomplex destabilization on WAVE2 induced actin polymerization and lamellipodia extension will be presented at the meeting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-513. doi:1538-7445.AM2012-LB-513