New Perspectives, Opportunities, and Challenges in Exploring the Human Protein Kinome.

The human protein kinome comprises 535 proteins that, with the exception of approximately 50 pseudokinases, control intracellular signaling networks by catalyzing the phosphorylation of multiple protein substrates. While a major research focus of the last 30 years has been cancer-associated Tyr and Ser/Thr kinases, over 85% of the kinome has been identified to be dysregulated in at least one disease or developmental disorder. Despite this remarkable statistic, for the majority of protein kinases and pseudokinases, there are currently no inhibitors progressing toward the clinic, and in most cases, details of their physiologic and pathologic mechanisms remain at least partially obscure. By curating and annotating data from the literature and major public databases of phosphorylation sites, kinases, and disease associations, we generate an unbiased resource that highlights areas of unmet need within the kinome. We discuss strategies and challenges associated with characterizing catalytic and noncatalytic outputs in cells, and describe successes and new frontiers that will support more comprehensive cancer-targeting and therapeutic evaluation in the future. Cancer Res; 78(1); 15-29. ©2017 AACR.

Pseudokinases: update on their functions and evaluation as new drug targets.

The pseudokinase complement of the human kinase superfamily consists of approximately 60 signaling proteins, which lacks one or more of the amino acids typically required to correctly align ATP and metal ions, and phosphorylate protein substrates. Recent studies in the pseudokinase field have begun to expose the biological relevance of pseudokinases, which are now thought to perform a diverse range of physiological roles and are connected to a multitude of human diseases, including cancer. In this review, we discuss how and why members of the 'pseudokinome' represent important new targets for drug discovery, and describe how knowledge of protein structure and function provides informative clues to help guide the rational chemical design or repurposing of inhibitors to target pseudokinases.

Human TRIB2 Oscillates during the Cell Cycle and Promotes Ubiquitination and Degradation of CDC25C.

Tribbles homolog 2 (TRIB2) is a member of the mammalian Tribbles family of serine/threonine pseudokinases (TRIB1-3). Studies of TRIB2 indicate that many of the molecular interactions between the single Drosophila Tribbles (Trbl) protein and interacting partners are evolutionary conserved. In this study, we examined the relationship between TRIB2 and cell division cycle 25 (CDC25) family of dual-specificity protein phosphatases (mammalian homologues of Drosophila String), which are key physiological cell cycle regulators. Using co-immunoprecipitation we demonstrate that TRIB2 interacts with CDC25B and CDC25C selectively. Forced overexpression of TRIB2 caused a marked decrease in total CDC25C protein levels. Following inhibition of the proteasome, CDC25C was stabilized in the nuclear compartment. This implicates TRIB2 as a regulator of nuclear CDC25C turnover. In complementary ubiquitination assays, we show that TRIB2-mediated degradation of CDC25C is associated with lysine-48-linked CDC25C polyubiquitination driven by the TRIB2 kinase-like domain. A cell cycle associated role for TRIB2 is further supported by the cell cycle regulated expression of TRIB2 protein levels. Our findings reveal mitotic CDC25C as a new target of TRIB2 that is degraded via the ubiquitin proteasome system. Inappropriate CDC25C regulation could mechanistically underlie TRIB2 mediated regulation of cellular proliferation in neoplastic cells.