Intracellular localization and binding partners of death associated protein kinase-related apoptosis-inducing protein kinase 1

Potent, Selective, and Orally Bioavailable Quinazoline-Based STK17A/B Dual Inhibitors

STK17A is a novel uncharacterized member of the death-associated protein family of serine and threonine kinases. Overexpression of STK17A is observed in many cancers. We identified a lead compound that is based on a quinazoline core. Optimizations of the lead compound led to the discovery of potent and selective STK17A/B inhibitors with drug-like properties and oral bioavailability. Compound 9 had an STK17A inhibitory IC50 of 23 nM. Based on profiling studies against two wild-type kinase panels (375 and 398 kinases, respectively), compound 9 had strong inhibition of both STK17A and STK17B but moderate off-target inhibition only for AAK1, MYLK4, and NEK3/5. In addition, compound 9 had good oral bioavailability, paving the way for in vivo studies against various cancers.

Targeting Death-Associated Protein Kinases for Treatment of Human Diseases: Recent Advances and Future Directions

The death-associated protein kinase (DAPK) family is a member of the calcium/calmodulin-regulated serine/threonine protein kinase family, and studies have shown that its role, as its name suggests, is mainly to regulate cell death. The DAPK family comprises five members, including DAPK1, DAPK2, DAPK3, DRAK1 and DRAK2, which show high homology in the common N-terminal kinase domain but differ in the extra-catalytic domain. Notably, previous research has suggested that the DAPK family plays an essential role in both the development and regulation of human diseases. However, only a few small-molecule inhibitors have been reported. In this Perspective, we mainly discuss the structure, biological function, and role of DAPKs in diseases and the currently discovered small-molecule inhibitors, providing valuable information for the development of the DAPK field.

Illuminating the Dark: Highly Selective Inhibition of Serine/Threonine Kinase 17A with Pyrazolo[1,5-a]pyrimidine-Based Macrocycles

Serine/threonine kinase 17A (death-associated protein kinase-related apoptosis-inducing protein kinase 1─DRAK1) is a part of the death-associated protein kinase (DAPK) family and belongs to the so-called dark kinome. Thus, the current state of knowledge of the cellular function of DRAK1 and its involvement in pathophysiological processes is very limited. Recently, DRAK1 has been implicated in tumorigenesis of glioblastoma multiforme (GBM) and other cancers, but no selective inhibitors of DRAK1 are available yet. To this end, we optimized a pyrazolo[1,5-a]pyrimidine-based macrocyclic scaffold. Structure-guided optimization of this macrocyclic scaffold led to the development of CK156 (34), which displayed high in vitro potency (K_D = 21 nM) and selectivity in kinomewide screens. Crystal structures demonstrated that CK156 (34) acts as a type I inhibitor. However, contrary to studies using genetic knockdown of DRAK1, we have seen the inhibition of cell growth of glioma cells in 2D and 3D culture only at low micromolar concentrations.

Identification and characterization of apoptosis-related gene serine/threonine kinase 17A (STK17A) from Japanese flounder Paralichthys olivaceus

Apoptosis plays important roles in regulation of the immune response and has a direct impact on disease resistance in teleost. Death associated protein kinase (DAPK)-related Serine/Threonine kinase 17A (STK17A) is a positive apoptosis regulator. However, the expression and function of STK17A in fish still remains uninvestigated. In this study, we identified and characterized a STK17A gene (termed PoSTK17A) from Japanese flounder Paralichthys olivaceus. We also investigated the pro-apoptotic role of PoSTK17A in fish. Real-time quantitative PCR analysis revealed that PoSTK17A is widely present in various Japanese flounder tissues, and dominantly expressed in liver. Immune challenge experiments showed that PoSTK17A expression was upregulated by inflammatory challenge, Edwardsiella tarda infection and DNA-damaging agent cisplatin treatment as well. Immunofluorescence microscopy revealed that the recombinant PoSTK17A proteins are mainly located in the nucleus of Japanese flounder FG-9307 cells, and human Hela and MCF7 cells. However, PoSTK17A was translocated from the nucleus to cytoplasm following cisplatin treatment. Overexpression of PoSTK17A significantly increased the apoptosis in human MCF7 cells through both cisplatin-dependent and independent manners. Importantly, PoSTK17A also promotes the ATP-gated P2X7 receptor-mediated apoptosis in Japanese flounder FG-9307 cells. Collectively, we characterized an inducible STK17A gene (PoSTK17A) that may play a conserved pro-apoptotic role in fish.

RNase L Induces Expression of A Novel Serine/Threonine Protein Kinase, DRAK1, to Promote Apoptosis

Apoptosis of virus-infected cells is an effective antiviral mechanism in addition to interferon induction to establish antiviral state to restrict virus spread. The interferon-inducible 2'-5' oligoadenylate synthetase/RNase L pathway results in activation of RNase L in response to double stranded RNA and cleaves diverse RNA substrates to amplify interferon induction and promote apoptosis. Here we show that RNase L induces expression of Death-associated protein kinase-Related Apoptosis-inducing protein Kinase 1 (DRAK1), a member of the death-associated protein kinase family and interferon-signaling pathway is required for induction. Overexpression of DRAK1 triggers apoptosis in the absence of RNase L activation by activating c-Jun N-terminal kinase (JNK), translocation of BCL2 Associated X (Bax) to the mitochondria accompanied by cytochrome C release and loss of mitochondrial membrane potential promoting cleavage of caspase 3 and Poly(ADP-Ribose) Polymerase 1 (PARP). Inhibitors of JNK and caspase 3 promote survival of DRAK1 overexpressing cells demonstrating an important role of JNK signaling pathway in DRAK1-mediated apoptosis. DRAK1 mutant proteins that lack kinase activity or nuclear localization fail to induce apoptosis highlighting the importance of cellular localization and kinase function in promoting cell death. Our studies identify DRAK1 as a mediator of RNase L-induced apoptosis.

Serine Threonine Kinase 17A Maintains the Epithelial State in Colorectal Cancer Cells

Serine threonine kinase 17A (STK17A) is a ubiquitously expressed kinase originally identified as a regulator of apoptosis; however, whether it functionally contributes to colorectal cancer has not been established. Here, we have analyzed STK17A in colorectal cancer and demonstrated decreased expression of STK17A in primary tumors, which is further reduced in metastatic lesions, indicating a potential role in regulating the metastatic cascade. Interestingly, changes in STK17A expression did not modify proliferation, apoptosis, or sensitivity of colorectal cancer cell lines to treatment with the chemotherapeutic 5-fluorouracil. Instead, STK17A knockdown induced a robust mesenchymal phenotype consistent with the epithelial-mesenchymal transition, including spindle-like cell morphology, decreased expression of adherens junction proteins, and increased migration and invasion. Additionally, overexpression of STK17A decreased cell size and induced widespread membrane blebbing, a phenotype often associated with activation of cell contractility. Indeed, STK17A-overexpressing cells displayed heightened phosphorylation of myosin light chain in a manner dependent on STK17A catalytic activity. Finally, patient-derived tumor organoid cultures were used to more accurately determine STK17A's effect in primary human tumor cells. Loss of STK17A induced morphologic changes, decreased E-cadherin, increased invasion, and augmented organoid attachment on 2D substrates, all together suggesting a more metastatic phenotype. Collectively, these data indicate a novel role for STK17A in the regulation of epithelial phenotypes and indicate its functional contribution to colorectal cancer invasion and metastasis. IMPLICATIONS: Loss of serine threonine kinase 17A occurs in colorectal cancer metastasis, induces mesenchymal morphologies, and contributes to tumor cell invasion and migration in colorectal cancer.