SQLE encodes squalene epoxidase, a key enzyme in cholesterol synthesis. SQLE has sporadically been reported among copy-number driven transcripts in multi-omics cancer projects. Yet, its functional relevance has never been subjected to systematic analyses. Here, we assessed the correlation of SQLE copy number (CN) and gene expression (GE) across multiple cancer types, focusing on the clinico-pathological associations in breast cancer (BC). We then investigated whether any biological effect of SQLE inhibition could be observed in BC cell line models. Breast, ovarian, and colorectal cancers showed the highest CN driven GE among 8,783 cases from 22 cancer types, with BC presenting the strongest one. SQLE overexpression was more prevalent in aggressive BC, and was an independent prognostic factor of unfavorable outcome. Through SQLE pharmacological inhibition and silencing in a panel of BC cell lines portraying the diversity of SQLE CN and GE, we demonstrated that SQLE inhibition resulted in a copy-dosage correlated decrease in cell viability, and in a noticeable increase in replication time, only in lines with detectable SQLE transcript. Altogether, our results pinpoint SQLE as a bona fide metabolic oncogene by amplification, and as a therapeutic target in BC. These findings could have implications in other cancer types.

Proteasome inhibitors possess potent antitumor activity against a broad spectrum of human malignancies. However, the effects of these compounds on the immune system still have to be clearly determined. In the present study, we have investigated the effects of proteasome inhibitors on dendritic cells (DC), antigen‐presenting cells playing a key role in the initiation of immune responses. Exposure to the proteasome inhibitors bortezomib, MG132 or epoxomicin was found to promote apoptosis of human monocyte‐derived DC and to reduce the yield of viable DC when given to monocytes early during differentiation to DC. DC apoptosis via proteasome inhibition was accompanied by mitochondria disruption and subsequent activation of the caspase cascade. Up‐regulation and intracellular redistribution of Bcl‐2‐associated X protein (Bax), a pro‐apoptotic Bcl‐2 family protein, were observed in DC treated with these compounds and represent a suitable mechanism leading to activation of the intrinsic apoptotic pathway. Finally, active protein synthesis was found to represent an upstream prerequisite for DC apoptosis induced by proteasome inhibitors, since the translation inhibitor cycloheximide blocked all of the steps of the observed apoptotic response. In conclusion, induction of apoptosis in DC may represent a novel mechanism by which proteasome inhibitors affect the immune response at the antigen‐presenting cell level.

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Mutations of the presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer disease (FAD). PS1 mutations alter the activity of the ␥-secretase on the ␤-amyloid precursor protein (APP), leading to selective overproduction of ␤-amyloid (A␤) 42 peptides, the species that forms oligomers that may exert toxic effects on neurons. Here we show that PS1 mutations, expressed both transiently and stably, in non-neuronal and neuronal cell lines increase the expression and the activity of the ␤-secretase (BACE1), the rate-limiting step of A␤ production. Also, BACE1 expression and activity are elevated in brains of PS1 mutant knock-in mice compared with wild type littermates as well as in cerebral cortex of FAD cases bearing various PS1 mutations compared with in sporadic AD cases and controls. The up-regulation of BACE1 by PS1 mutations requires the ␥-secretase cleavage of APP and is proportional to the amount of secreted A␤42. A␤42, and not AICD (APP intracellular domain), is indeed the APP derivative that mediates the overexpression of BACE1. The effect of PS1 mutations on BACE1 may contribute to determine the wide clinical and pathological phenotype of early onset FAD.The ␤-amyloid peptide (A␤) 2 that accumulates in vulnerable brain regions in Alzheimer disease (AD) is released from the ␤-amyloid precursor protein (APP) by sequential cleavages by ␤-secretase and ␥-secretase. A single protein called BACE1 is responsible for ␤-secretase activity, whereas ␥-secretase involves at least four proteins including a catalytic subunit called presenilin-1 (PS1) (1, 2). Mutations of PS1 are the most common cause of early onset familial AD (FAD). The known effect of PS1 mutations on APP processing is the increased production of A␤ species ending at residue 42, which aggregates faster than the A␤40 isoform and accumulates in the brain in the state of soluble low molecular weight oligomers (3, 4). Small, soluble, and diffusible aggregates composed of a mixture of full-length and N-terminal-truncated A␤42 species appear early in the cerebral cortex of subjects at risk of Alzheimer disease pathology (5). The rate of accumulation as well as the properties of aggregation and toxicity of cerebral soluble A␤ depend on the ratio of the three major A␤ species, 1-42, pyroglutamate 3-42, and pyroglutamate 11-42 (6). We have shown that, in the cerebral cortex of FAD cases with mutations of PS1, the relative percentage of the two N-terminal-truncated A␤ species is significantly increased in comparison to sporadic AD cases (7). A relative increase of N-terminal-truncated A␤ peptides also occurs in the brain of transgenic mice bearing a double PS1 mutation (8). When overexpressed in cell lines, BACE1 increases the production of A␤ 11-x (9) and A␤ 3-x peptides (10) in vitro. BACE1 has been found to be transcriptionally regulated by several different mechanisms involving various transcription factors and pathways (11)(12)(13)(14)(15), and given the complexity and richness in transcription factor recognition sites of its gene p...

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4732 Nicotinamide phosphoribosyltransferase (Nampt) inhibitors such as FK866 are potent inhibitors of NAD+ synthesis that show promise for the treatment of different forms of cancer. Based on Nampt upregulation in activated T lymphocytes and on preliminary reports of lymphopenia in FK866 treated patients, we have investigated FK866 for its capacity to interfere with T lymphocyte function and survival. Intracellular pyridine nucleotides, ATP, mitochondrial function, viability, proliferation, activation markers and cytokine secretion were assessed in resting and in activated human T lymphocytes. In addition, we used experimental autoimmune encephalomyelitis (EAE) as a model of T-cell mediated autoimmune disease to assess FK866 efficacy in vivo. We show that activated, but not resting, T lymphocytes undergo massive NAD+ depletion upon FK866 mediated Nampt inhibition. As a consequence, impaired proliferation, reduced TNF-a production, ATP shortage, and, finally, autophagic cell demise result. We demonstrate that upregulation of the of the NAD+-degrading enzyme poly-(ADP-ribose)-polymerase (PARP) by activated T cells enhances their susceptibility to NAD+ depletion. We relate defective TNF-a production in response to FK866 to impaired SIRT6 activity. Finally, in line with its capacity to interfere with T lymphocyte function and survival, we show that FK866 strikingly reduces the neurological damage and the clinical manifestations of EAE. In conclusion, Nampt inhibitors (and possibly sirtuin inhibitors) could be used to modulate T cell-mediated immune responses and thereby be beneficial in immune-mediated disorders. Disclosures: No relevant conflicts of interest to declare.

Purpose: Bcl-2 overexpression is frequently detected in lymphoid malignancies, being associated with poor prognosis and reduced response to therapy. Here, we evaluated whether Bcl-2 overexpression affects the cytotoxic activity of proteasome inhibitors taken alone or in association with conventional anticancer drugs or tumor necrosis factor–related apoptosis-inducing ligand (TRAIL). Experimental Design: Jurkat cells engineered to overexpress Bcl-2 were treated with proteasome inhibitors (MG132, epoxomicin, and bortezomib), anticancer drugs (etoposide and doxorubicin), TRAIL, or combinations of these compounds. Cell death and loss of mitochondrial transmembrane potential were detected by flow cytometry. Cytosolic relocalization of cytochrome c and SMAC/Diablo, caspase cleavage, and Bcl-2 and Mcl-1 levels were determined by immunoblotting. Nuclear factor-κB inhibition was done by retroviral transduction with a dominant-negative mutant of IκBα. Results: Bcl-2 overexpression results in significant inhibition of apoptosis in response to proteasome inhibitors, antiblastics, and TRAIL. Addition of TRAIL to proteasome inhibitors results in a synergistic cytotoxic effect in Bcl-2-overexpressing cells, whereas this result is not reproduced by the combination of proteasome inhibitors with antiblastic drugs. Importantly, proteasome inhibitors plus TRAIL induce mitochondrial dysfunction irrespective of up-regulated Bcl-2. Bcl-2 cleavage to a fragment with putative proapoptotic activity and elimination of antiapoptotic Mcl-1 may both play a role in proteasome inhibitors-TRAIL cooperation. Conversely, nuclear factor-κB inhibition by proteasome inhibitors is per se insufficient to explain the observed synergy. Conclusions: Combined proteasome inhibitors and TRAIL overcome the apoptotic threshold raised by Bcl-2 and may prove useful in the treatment of chemoresistant malignancies with up-regulated Bcl-2.