Oncogene
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The inactive transcription factor NF-kappaB is localized in the cytoplasm and rapidly responds to a variety of extracellular factors and intracellular stress conditions to initiate multiple cellular responses. While the knowledge regarding NF-kappaB signaling pathways initiated by extracellular ligands is rapidly expanding, the mechanisms of activation by intracellular stress conditions are not well understood. We recently described a critical role for a small ubiquitin-like modifier (SUMO) modification of NF-kappaB essential modulator (NEMO), the regulatory subunit of the IkappaB kinase, in response to certain genotoxic stress conditions. ⋯ Here, we report that a variety of other stress conditions, including oxidative stress, ethanol exposure, heat shock and electric shock, also induce NEMO SUMOylation, thus demonstrating that DNA damage per se is not necessary for this NEMO modification to occur. Moreover, combinations of certain SUMO stress and ATM (ataxia telangiectasia mutated) activation conditions lead to NF-kappaB activation without inducing DNA damage. Our study helps to conceptualize how individual or a combination of different stress conditions may funnel into this previously unappreciated signal transduction mechanism to regulate the activity of the ubiquitous NF-kappaB transcription factor.
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Transgenic mice overexpressing Notch4 intracellular domain (Int3) under the control of the whey acidic protein (WAP) or mouse mammary tumor virus-long terminal repeat promoters, develop mammary tumors. Microarray analysis of these tumors revealed high levels of c-Kit expression. Gleevec is a tyrosine kinase inhibitor that targets c-Kit, platelet-derived growth factor receptors (PDGFRs) and c-Abl. ⋯ To examine the signaling mechanisms underlying Notch4/Int3 tumorigenesis, we employed small interfering RNA (siRNA) to knock down c-Kit, PDGFRs and c-Abl alone or in combination and observed the effects on soft agar growth of HC11 cells overexpressing Int3. Only siRNA constructs for c-Kit and/or PDGFR-alpha were able to inhibit HC11-Int3 colony formation in soft agar. Our data demonstrate an inhibitory effect of Gleevec on Int3-induced transformation of HC11 cells and mammary tumors and indicate an oncogenic role for c-Kit and PDGFR-alpha tyrosine kinases in the context of Int3 signaling.
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Neoplastic cells transport large amounts of glucose in order to produce anabolic precursors and energy within the inhospitable environment of a tumor. The ras signaling pathway is activated in several cancers and has been found to stimulate glycolytic flux to lactate. Glycolysis is regulated by ras via the activity of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFK2/FBPase), which modulate the intracellular concentration of the allosteric glycolytic activator, fructose-2,6-bisphosphate (F2,6BP). ⋯ This marked reduction in the intracellular concentration of F2,6BP sensitizes transformed cells to the antimetabolic effects of PFK2/FBPase inhibition. Moreover, despite co-expression of all four mRNA species (PFKFB1-4), heterozygotic genomic deletion of the inducible PFKFB3 gene in ras-transformed mouse lung fibroblasts suppresses F2,6BP production, glycolytic flux to lactate, and growth as soft agar colonies or tumors in athymic mice. These data indicate that the PFKFB3 protein product may serve as an essential downstream metabolic mediator of oncogenic ras, and we propose that pharmacologic inhibition of this enzyme should selectively suppress the high rate of glycolysis and growth by cancer cells.
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Squamous cell carcinoma (SCC) is an invasive malignancy of epidermal keratinocytes. Surgical excision is currently the main treatment; however, this can cause scarring and disfigurement. There is accordingly, an acute need for alternative strategies to treat SCC. ⋯ We further demonstrate that Dz13 inhibits c-Jun, together with matrix metalloproteinase (MMP)-2 and MMP-9 expression in the tumors, consistent with DNAzyme inhibition of MMP-2 and MMP-9 gelatinolytic activity by zymography. Dz13 also suppressed the expression of vascular endothelial growth factor and fibroblast growth factor-2 in the tumors. These findings demonstrate that c-Jun regulates SCC growth and suggest that DNAzymes targeting this transcription factor may potentially be useful as inhibitors of cutaneous carcinoma.
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The Clathrin Assembly Lymphoid Myeloid leukemia gene (CALM or PICALM) was first identified as the fusion partner of AF10 in the t(10;11)(p13;q14) translocation, which is observed in acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL) and malignant lymphoma. The CALM/AF10 fusion protein plays a crucial role in t(10;11)(p13;q14) associated leukemogenesis. Using the N-terminal half of CALM as a bait in a yeast two-hybrid screen, a novel protein named CATS (CALM interacting protein expressed in thymus and spleen) was identified. ⋯ CATS localizes to the nucleus and shows a preference for nucleoli. Expression of CATS was able to markedly increase the nuclear localization of CALM and of the leukemogenic fusion protein CALM/AF10. The possible implications of these findings for CALM/AF10-mediated leukemogenesis are discussed.