FK506-binding protein 51 (FKBP51) is an immunophilin with isomerase activity, which performs important biological functions in the cell. It has recently been involved in the apoptosis resistance of malignant melanoma. The aim of this study was to investigate the possible role of FKBP51 in the control of response to ionizing radiation (Rx) in malignant melanoma. FKBP51-silenced cells showed reduced clonogenic potential after irradiation compared with non-silenced cells. After Rx, we observed apoptosis in FKBP51-silenced cells and autophagy in non-silenced cells. The FKBP51-controlled radioresistance mechanism involves NF-jB. FKBP51 was required for the activation of Rx-induced NF-jB, which in turn inhibited apoptosis by stimulating X-linked inhibitor of apoptosis protein and promoting authophagy-mediated Bax degradation. Using a tumor-xenograft mouse model, the in vivo pretreatment of tumors with FKBP51-siRNA provoked massive apoptosis after irradiation. Immunohistochemical analysis of 10 normal skin samples and 80 malignant cutaneous melanomas showed that FKBP51 is a marker of melanocyte malignancy, correlating with vertical growth phase and lesion thickness. Finally, we provide evidence that FKBP51 targeting radiosensitizes cancer stem/initiating cells. In conclusion, our study identifies a possible molecular target for radiosensitizing therapeutic strategies against malignant melanoma.

Contrast-induced nephropathy accounts for >10% of all causes of hospital-acquired renal failure, causes a prolonged in-hospital stay and represents a powerful predictor of poor early and late outcome. Mechanisms of contrast-induced nephropathy are not completely understood. In vitro data suggests that contrast media (CM) induces a direct toxic effect on renal tubular cells through the activation of the intrinsic apoptotic pathway. It is unclear whether this effect has a role in the clinical setting. In this work, we evaluated the effects of CM both in vivo and in vitro. By analyzing urine samples obtained from patients who experienced contrast-induced acute kidney injury (CI-AKI), we verified, by western blot and immunohistochemistry, that CM induces tubular renal cells apoptosis. Furthermore, in cultured cells, CM caused a dose–response increase in reactive oxygen species (ROS) production, which triggered Jun N-terminal kinases (JNK1/2) and p38 stress kinases marked activation and thus apoptosis. Inhibition of JNK1/2 and p38 by different approaches (i.e. pharmacological antagonists and transfection of kinase-death mutants of the upstream p38 and JNK kinases) prevented CM-induced apoptosis. Interestingly, N-acetylcysteine inhibited ROS production, and thus stress kinases and apoptosis activation. Therefore, we conclude that CM-induced tubular renal cells apoptosis represents a key mechanism of CI-AKI.

TNF receptor-associated protein 1 (TRAP1), the main mitochondrial member of the heat shock protein (HSP) 90 family, is induced in most tumor types and is involved in the regulation of proteostasis in the mitochondria of tumor cells through the control of folding and stability of selective proteins, such as Cyclophilin D and Sorcin. Notably, we have recently demonstrated that TRAP1 also interacts with the regulatory protein particle TBP7 in the endoplasmic reticulum (ER), where it is involved in a further extra-mitochondrial quality control of nuclear-encoded mitochondrial proteins through the regulation of their ubiquitination/degradation. Here we show that TRAP1 is involved in the translational control of cancer cells through an attenuation of global protein synthesis, as evidenced by an inverse correlation between TRAP1 expression and ubiquitination/degradation of nascent stress-protective client proteins. This study demonstrates for the first time that TRAP1 is associated with ribosomes and with several translation factors in colon carcinoma cells and, remarkably, is found co-upregulated with some components of the translational apparatus (eIF4A, eIF4E, eEF1A and eEF1G) in human colorectal cancers, with potential new opportunities for therapeutic intervention in humans. Moreover, TRAP1 regulates the rate of protein synthesis through the eIF2α pathway either under basal conditions or under stress, favoring the activation of GCN2 and PERK kinases, with consequent phosphorylation of eIF2α and attenuation of cap-dependent translation. This enhances the synthesis of selective stress-responsive proteins, such as the transcription factor ATF4 and its downstream effectors BiP/Grp78, and the cystine antiporter system xCT, thereby providing protection against ER stress, oxidative damage and nutrient deprivation. Accordingly, TRAP1 silencing sensitizes cells to apoptosis induced by novel antitumoral drugs that inhibit cap-dependent translation, such as ribavirin or 4EGI-1, and reduces the ability of cells to migrate through the pores of transwell filters. These new findings target the TRAP1 network in the development of novel anti-cancer strategies.

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The activity of NF-jB/Rel transcription factors can downmodulate apoptosis in normal and neoplastic cells of the hematologic and other compartments, contributing in maintaining neoplastic clone survival and impairing response to therapy. Alterations in nfjb or ijB genes are documented in some hematologic neoplasias, while in others dysfunction in NF-jB/Rel-activating signaling pathways can be recognized. The prosurvival properties of NF-jB/Rel appear to rely on the induced expression of molecules (caspase inhibitors, Bcl2 protein family members, etc.), which interfere with the apoptosis pathway. Constitutive NF-jB/Rel activity in some hematologic malignancies could be advantageous for neoplastic clone expansion by counteracting stress stimuli (consumption of growth factors and metabolites) and immune system-triggered apoptosis; it is furthermore likely to play a central role in determining resistance to therapy. Based on this evidence, NFjB/Rel-blocking approaches have been introduced in antineoplastic strategies. The identification of NF-jB/Rel target genes relevant for survival in specific neoplasias is required in order to address tailored therapies and avoid possible detrimental effects due to widespread NF-jB/Rel inhibition. Moreover, comparative analyses of normal hematopoietic progenitors and neoplastic cell sensitivities to inhibitors of NF-jB/Rel and their target genes will allow to evaluate the impact of these tools on normal bone marrow. Regulation of apoptosis by NF-jB/Rel factors NF-kB/Rel transcription factors are dimers of proteins (p50/p105 or NF-kB1, p52/p100 or NF-kB2, p65 or RelA, c-Rel and RelB) containing an approximately 300 amino-acid REL homology domain (RHD), which mediates protein dimerization and binding to DNA. 1 The RHD is also involved in interacting with the ankyrin repeats of IkB, a family of proteins coevolved with NF-kB/Rel. 1,2 NF-kB/Rel dimers are retained in the cytoplasm of several cell types by inhibitors of the IkB family. Growth factors, cytokines, hormones or other agents can induce, through the IKK (IkB-kinase) cascade or other kinases, 1,2 the phosphorylation and ubiquitin-mediated degradation of the IkB proteins, allowing the NF-kB/Rel dimers to reach the nucleus. 3 NF-kB/Rel activation is also induced by stress stimuli that provoke increases in the intracellular concentration of reactive oxygen species (ROS), imbalance in calcium ions fluxes and/or accumulation of unfolded proteins in the endoplasmic reticulum (RE). Such events trigger the activation of stress kinases and other modulators, which ultimately lead to IkB degradation. [1][2][3]

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Gastrokine 1 (GKN1) is involved in the replenishment of the surface lumen epithelial cell layer, in maintaining the mucosal integrity, and could play a role in cell proliferation and differentiation. In fact, after injury of the gastric mucosa, restoration may occur very rapidly in the presence of GKN1. In contrast, if the protein is downregulated, the repair process may be hampered; however, application of GKN1 to gastrointestinal cells promoted epithelial restoration. Because GKN1 possesses some mitogenic effects on intestinal epithelial cells (IEC-6) whereas this protein was also capable of inhibiting proliferation in gastric cancer cells (MKN28), we decided to study its involvement in apoptosis to understand the role of GKN1 in the modulation of inflammatory damage or tumorigenesis in gastric mucosa. We found by cytofluorimetry, Western blot and RT-PCR that the overexpression of GKN1 in gastric cancer cell lines (AGS and MKN28) stimulated the expression of Fas receptor. Moreover, compared to control cells, a significant increase of apoptosis, evaluated by TUNEL, was observed when GKN1 transfected cells were treated with a monoclonal antibody (IgM) anti-Fas. The activation of Fas expression was also observed by the overexpression of GKN1 in other cancer cell lines. Moreover, in GKN1-overexpressing gastric cancer cells exposed to FasL, the activation of caspase-3 was also observed by Western blot and fluorescence assays. Our data represent the first report for GKN1 as modulator of apoptotic signals and suggest that GKN1 might play an important role for tissue repair during the early stages of neoplastic transformation.