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Background: The use of targeted agents to impel dual inhibition of anti-apoptotic mechanisms and mTOR-mediated pro-survival signaling in colorectal carcinoma (CRC) cell lines with KRAS or BRAF mutation has been shown to induce apoptosis, a timely result given CRC entities harboring such mutations are in need of new therapies. Since CRC comprises heterogeneous tumors with predominant hypoxic components, we investigated effects of an inhibitor of anti-apoptotic Bcl-2 family proteins (ABT-737) in combination with an mTOR inhibitor (AZD8055)-collectively referred to as combo-Rx, in hypoxic CRC cell lines.Methods: Cell viability measures, expression of proteins implicated in apoptosis and MAPK/PI3K-AKT/mTOR pathway signaling, and profiling of composite kinase activities were undertaken in a panel of 14 cell lines.Results: In hypoxic conditions, combo-Rx suppressed viability of 13 of the cell lines, albeit ABT-737 did not significantly potentiate the inhibitory effect of single-agent AZD8055 in six of the models. Hypoxic KRAS/PIK3CA-mutant HCT-116 and HCT-15 cell lines (both with low endogenous expression of the anti-apoptotic Mcl-1 protein and showing augmented inhibition of viability following the addition of ABT-737 to AZD8055) responded to combo-Rx by induction of apoptosis but with the simultaneous strong Mcl-1 up-regulation and activation of MAPK/PI3K-conducted signaling. In contrast, in hypoxic KRAS-mutant LoVo (devoid of PIK3CA mutation), BRAF/PIK3CA-mutant RKO, and wild-type Colo320DM cell lines (all with high endogenous Mcl-1 expression and being resistant to the additional effect of ABT-737 to AZD8055), combo-Rx did not elicit apoptotic or pro-survival responses.Conclusions: The concurrent inhibition of anti-apoptotic proteins and mTOR-mediated signaling in hypoxic KRAS/PIK3CA-mutant CRC cell lines resulted in pro-survival responses in parallel with the intended anti-proliferative effects, a finding that should be of note if considering combinatory targeting of multiple pathways in this CRC entity. [ABSTRACT FROM AUTHOR]

Abstract: Protein kinase C (PKC) δ plays an important role in cellular proliferation and apoptosis. The catalytic fragment of PKCδ generated by caspase-dependent cleavage is essential for the initiation of etoposide-induced apoptosis. In this study, we identified a novel mouse PKCδ isoform named PKCδIX (Genebank Accession No. HQ840432). PKCδIX is generated by alternative splicing and is ubiquitously expressed, as seen in its full-length PKCδ. PKCδIX lacks the C1 domain, the caspase 3 cleavage site, and the ATP binding site but preserves an almost intact c-terminal catalytic domain and a nuclear localization signal (NLS). The structural characteristics of PKCδIX provided a possibility that this PKCδ isozyme functions as a novel dominant-negative form for PKCδ due to its lack of the ATP-binding domain that is required for the kinase activity of PKCδ. Indeed, overexpression of PKCδIX significantly inhibited etoposide-induced apoptosis in NIH3T3 cells. In addition, an in vitro kinase assay showed that recombinant PKCδIX protein could competitively inhibit the kinase activity of PKCδ. We conclude that PKCδIX can function as a natural dominant-negative inhibitor of PKCδin vivo. [Copyright &y& Elsevier]

Fas-associated protein with death domain (FADD) was originally reported as a proapoptotic adaptor molecule that mediates receptor-induced apoptosis. Recent studies have revealed a potential role of FADD in NF-κB activation, embryogenesis, and cell cycle regulation and proliferation. Overexpression of FADD and its phosphorylation have been associated with the transformed phenotype in many cancers and is therefore a potential target for therapeutic intervention. In an effort to delineate signaling events that lead to FADD phosphorylation and to identify novel compounds that impinge on this pathway, the authors developed a cell-based reporter for FADD kinase activity. The reporter assay, optimized for a high-throughput screen (HTS), measures bioluminescence in response to modulation of FADD kinase activity in live cells. In addition, the potential use of the reporter cell line in the rapid evaluation of pharmacologic properties of HTS hits in mouse models has been demonstrated. (Journal of Biomolecular Screening 2010:1063-1070) [ABSTRACT FROM PUBLISHER]

The serine/threonine kinase, PIM1, is involved in promoting cell survival in part by phosphorylation and inhibition of proapoptotic proteins. Apoptosis signaling kinase 1 (ASK1), a mitogen-activated protein kinase kinase kinase, is involved in the so-called stress-activated pathways that contribute to apoptotic cell death. Here we show that PIM1 phosphorylates ASK1 specifically on serine residue 83 (Ser83) both in vitro and in vivo and that PIM1 binds to ASK1 in cells by co-immunoprecipitation. Using H1299 cells, our results further demonstrate that PIM1 phosphorylation of ASK1 decreases its kinase activity induced by oxidative stress. PIM1 phosphorylation of ASK1 on Ser83 inhibited ASK1-mediated c-Jun N-terminal kinase phosphorylation as well as p38 kinase phosphorylation. Under H2O2-induced stress conditions that normally lead to apoptosis, these phosphorylation events were associated with inhibition of caspase-3 activation and resulted in reduced cell death. Moreover, knockdown of PIM1 in H1299 cells decreased phosphorylation of endogenous Ser83 of ASK1 and was associated with a decrease in cell viability after H2O2 treatment. Taken together, these data reveal a novel mechanism by which PIM1 promotes cell survival that involves negative regulation of the stress-activated kinase, ASK1. [ABSTRACT FROM AUTHOR]

Oxidative stress leads to perturbation of a variety of cellular processes resulting in inhibition of cell proliferation. This study has determined the effect of oxidative stress on protein synthesis in human K562 cells using a hydrophilic peroxyl radical initiator, AAPH and H2O2. The results indicated that oxidative stress leads to a significant decrease in the rate of protein synthesis caused due to induced activation as well as expression of the erythroid cell-specific eIF-2α kinase, called the Heme Regulated Inhibitor (HRI). Elevated levels of HRI expression and activity were accompanied by increased lipid peroxidation and decreased cell proliferation. Further, oxidative stress also caused inactivation of p34cdc2 kinase, thereby arresting cell division leading to apoptosis. Thus, the data provides the mechanism of inhibition of protein synthesis and perturbation of a cell cycle regulatory protein leading to inhibition of cell proliferation in K562 cells during oxidative stress. [ABSTRACT FROM AUTHOR]

Glutathione S-transferase P1 (GSTP1) plays an important role in detoxification and the metabolism of xenobiotics. Here we show that GSTP1 also regulates the MEKK1-MKK7 signaling pathway. Over-expression of GSTP1 in HEK293 cells inhibited both ΔMEKK1- and etoposide-induced apoptosis, and inhibited procaspase- 3 activation and PARP cleavage. MEKK1- induced apoptosis requires both its kinase activity and proteolytic cleavage. ΔMEKK1 activity was inhibited by over-expression of GSTP1 in vivo and MEKK1 kinase activity was also inhibited by GSTP1 in vitro when assayed with bacterially-expressed MKK7(KM) protein as substrate. GSTP1 inhibition of etoposideinduced cell apoptosis was mainly due to its ability to suppress MEKK1 kinase activity. The glutathioneconjugating activity of GSTP1 was essential for the above effects. These findings provide insight into the mechanism by which GSTP1 protects cells from genotoxin-induced apoptosis. [ABSTRACT FROM AUTHOR]

Abstract: p110C, a 50-kDa isoform of the PITSLRE kinase family, was demonstrated to play an important role in cell apoptosis. However, how p110C exactly promotes apoptosis is unclear. Our previous study showed that p110C interacted with p21-activated kinase 1 (PAK1), an important kinase of the proapoptotic BCL-2 family member BAD, and evidently inhibited its kinase activity. Here, we report that overexpression of p110C leads to decreased phosphorylation of BAD and its subsequent translocation from cytosol to mitochondria, which in turn induces the release of cytochrome c and the onset of apoptosis. Knocking down endogenous BAD expression will inhibit p110C induced apoptosis. Two kinase dead forms of p110C, D149N and K36N, lose the ability to inhibit the kinase activity of PAK1 and fail to induce the translocation of BAD and the BAD and such proapoptotic ability is associated with the kinase activity of p110C. [Copyright &y& Elsevier]

• A series of flavonol derivatives of fisetin were synthesized, characterized, and evaluated as potential anti-skin-cancer agents. • Several of these compounds showed micromolar range in vitro anti-proliferative activity in melanoma (A375, SK-MEL-28) and non-melanoma (A431 and UWBCC-1) skin cancer cells. • Molecular docking and in-vitro enzymatic kinase assays identified CDK2, c-KIT, and mTOR inhibitions, with potencies as single, dual or multi-target inhibitors. • Analogs, F20 , F9 and F17 significantly induced apoptosis and inhibited clonogenicity, wound healing and downregulated cancer-related molecular targets CDK2, c-Kit and effectors including mTOR, S6K, p90RSK, Stat3, and MAPK (ERK1/2). Due to hurdles, including resistance, adverse effects, and poor bioavailability, among others linked with existing therapies, there is an urgent unmet need to devise new, safe, and more effective treatment modalities for skin cancers. Herein, a series of flavonol-based derivatives of fisetin, a plant-based flavonoid identified as an anti-tumorigenic agent targeting the mammalian targets of rapamycin (mTOR)-regulated pathways, were synthesized and fully characterized. New potential inhibitors of receptor tyrosine kinases (c-KITs), cyclin-dependent kinase-2 (CDK2), and mTOR, representing attractive therapeutic targets for melanoma and non-melanoma skin cancers (NMSCs) treatment, were identified using inverse-docking, in vitro kinase activity and various cell-based anticancer screening assays. Eleven compounds exhibited significant inhibitory activities greater than the parent molecule against four human skin cancer cell lines, including melanoma (A375 and SK-Mel-28) and NMSCs (A431 and UWBCC1), with IC 50 values ranging from 0.12 to < 15 μM. Seven compounds were identified as potentially potent single, dual or multi-kinase c-KITs, CDK2, and mTOR kinase inhibitors after inverse-docking and screening against twelve known cancer targets, followed by kinase activity profiling. Moreover, the potent compound F20 , and the multi-kinase F9 and F17 targeted compounds, markedly decreased scratch wound closure, colony formation, and heightened expression levels of key cancer-promoting pathway molecular targets c-Kit, CDK2, and mTOR. In addition, these compounds downregulated Bcl-2 levels and upregulated Bax and cleaved caspase-3/7/8 and PARP levels, thus inducing apoptosis of A375 and A431 cells in a dose-dependent manner. Overall, compounds F20, F9 and F17 , were identified as promising c-Kit, CDK2 and mTOR inhibitors, worthy of further investigation as therapeutics, or as adjuvants to standard therapies for the control of melanoma and NMSCs. [ABSTRACT FROM AUTHOR]