Silvia Alvarez-Diaz

Aberrant miR-182 expression promotes melanoma metastasis by repressing FOXO3 and microphthalmia-associated transcription factor.

The highly aggressive character of melanoma makes it an excellent model for probing the mechanisms underlying metastasis, which remains one of the most difficult challenges in treating cancer. We find that miR-182, member of a miRNA cluster in a chromosomal locus (7q31–34) frequently amplified in melanoma, is commonly up-regulated in human melanoma cell lines and tissue samples; this up-regulation correlates with gene copy number in a subset of melanoma cell lines. Moreover, miR-182 ectopic expression stimulates migration of melanoma cells in vitro and their metastatic potential in vivo, whereas miR-182 down-regulation impedes invasion and triggers apoptosis. We further show that miR-182 over-expression promotes migration and survival by directly repressing microphthalmia-associated transcription factor-M and FOXO3, whereas enhanced expression of either microphthalmia-associated transcription factor-M or FOXO3 blocks miR-182s proinvasive effects. In human tissues, expression of miR-182 increases with progression from primary to metastatic melanoma and inversely correlates with FOXO3 and microphthalmia-associated transcription factor levels. Our data provide a mechanism for invasion and survival in melanoma that could prove applicable to metastasis of other cancers and suggest that miRNA silencing may be a worthwhile therapeutic strategy.

MicroRNA-22 is induced by vitamin D and contributes to its antiproliferative, antimigratory and gene regulatory effects in colon cancer cells

Vitamin D deficiency is associated with the high risk of colon cancer and a variety of other diseases. The active vitamin D metabolite 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) regulates gene transcription via its nuclear receptor (VDR), and posttranscriptional regulatory mechanisms of gene expression have also been proposed. We have identified microRNA-22 (miR-22) and several other miRNA species as 1,25(OH)(2)D(3) targets in human colon cancer cells. Remarkably, miR-22 is induced by 1,25(OH)(2)D(3) in a time-, dose- and VDR-dependent manner. In SW480-ADH and HCT116 cells, miR-22 loss-of-function by transfection of a miR-22 inhibitor suppresses the antiproliferative effect of 1,25(OH)(2)D(3). Additionally, miR-22 inhibition increases cell migration per se and decreases the antimigratory effect of 1,25(OH)(2)D(3) in both cell types. In silico analysis shows a significant overlap between genes suppressed by 1,25(OH)(2)D(3) and miR-22 putative target genes. Consistently, miR-22 inhibition abrogates the 1,25(OH)(2)D(3)-mediated suppression of NELL2, OGN, HNRPH1, RERE and NFAT5 genes. In 39 out of 50 (78%) human colon cancer patients, miR-22 expression was found lower in the tumour than in the matched normal tissue and correlated directly with that of VDR. Our results indicate that miR-22 is induced by 1,25(OH)(2)D(3) in human colon cancer cells and it may contribute to its antitumour action against this neoplasia.

NLRP3 inflammasome activation downstream of cytoplasmic LPS recognition by both caspase‐4 and caspase‐5

Humans encode two inflammatory caspases that detect cytoplasmic LPS, caspase‐4 and caspase‐5. When activated, these trigger pyroptotic cell death and caspase‐1‐dependent IL‐1β production; however the mechanism underlying this process is not yet confirmed. We now show that a specific NLRP3 inhibitor, MCC950, prevents caspase‐4/5‐dependent IL‐1β production elicited by transfected LPS. Given that both caspase‐4 and caspase‐5 can detect cytoplasmic LPS, it is possible that these proteins exhibit some degree of redundancy. Therefore, we generated human monocytic cell lines in which caspase‐4 and caspase‐5 were genetically deleted either individually or together. We found that the deletion of caspase‐4 suppressed cell death and IL‐1β production following transfection of LPS into the cytoplasm, or in response to infection with Salmonella typhimurium. Although deletion of caspase‐5 did not confer protection against transfected LPS, cell death and IL‐1β production were reduced after infection with Salmonella. Furthermore, double deletion of caspase‐4 and caspase‐5 had a synergistic effect in the context of Salmonella infection. Our results identify the NLRP3 inflammasome as the specific platform for IL‐1β maturation, downstream of cytoplasmic LPS detection by caspase‐4/5. We also show that both caspase‐4 and caspase‐5 are functionally important for appropriate responses to intracellular Gram‐negative bacteria.

The inhibition of Wnt/β-catenin signalling by 1α,25-dihydroxyvitamin D3 is abrogated by Snail1 in human colon cancer cells

The Wnt/beta-catenin signalling pathway is activated in 90% of human colon cancers by nuclear accumulation of beta-catenin protein due to its own mutation or to that of adenomatous polyposis coli. In the nucleus, beta-catenin regulates gene expression promoting cell proliferation, migration and invasiveness. 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) inhibits beta-catenin signalling by inducing its binding to vitamin D receptor (VDR) and by promoting beta-catenin nuclear export. The transcription factor Snail1 represses VDR expression and we demonstrate here that Snail1 also abolishes the nuclear export of beta-catenin induced by 1,25(OH)(2)D(3) in SW480-ADH cells. Accordingly, Snail1 relieves the inhibition exerted by 1,25(OH)(2)D(3) on genes whose expression is driven by beta-catenin, such as c-MYC, ectodermal-neural cortex-1 (ENC-1) or ephrin receptor B2 (EPHB2). In addition, Snail1 abrogates the inhibitory effect of 1,25(OH)(2)D(3) on cell proliferation and migration. In xenografted mice, Snail1 impedes the nuclear export of beta-catenin and the inhibition of ENC-1 expression induced by EB1089, a 1,25(OH)(2)D(3) analogue. The elevation of endogenous SNAIL1 protein levels reproduces the effect of an ectopic Snail1 gene. Remarkably, the expression of exogenous VDR in cells with high levels of Snail1 normalizes the transcriptional responses to 1,25(OH)(2)D(3). However, this exogenous VDR failed to fully restore the blockage of the Wnt/beta-catenin pathway by 1,25(OH)(2)D(3). This suggests that the effects of Snail1 on this pathway are not merely due to the repression of VDR gene. We conclude that Snail1 is a positive regulator of the Wnt/beta-catenin signalling pathway in part through the abrogation of the inhibitory action of 1,25(OH)(2)D(3).

Vitamin D: Proteases, protease inhibitors and cancer

The active vitamin D metabolite 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3, Calcitriol) is a major regulator of gene expression in higher organisms. Protein abundance is an endpoint of gene expression that results from the balance between induction and degradation and is essential for adequate cell function. Proteins are degraded by proteases whose activity is in turn controlled by a number of endogenous protease inhibitors. 1,25(OH)2D3 regulates several proteases and protease inhibitors in different cell types, putatively contributing to its regulatory effects of cell physiology. We have recently shown that 1,25(OH)2D3 strongly induces the expression of cystatin D, an inhibitor of several cysteine proteases of the cathepsin family. Cystatin D induction may contribute to the antitumor effect of 1,25(OH)2D3 against colon cancer by mechanisms that are both dependent and independent of cathepsin inhibition. Transcriptomic studies suggest that 1,25(OH)2D3 also modulates the function of the ubiquitin-proteasome system. Thus, proteases and protease inhibitors are candidates to mediate to a certain extent the complex action of 1,25(OH)2D3 in cancer cells.

Is SIRT2 required for necroptosis

Arising from N. Narayan et al. 492, 199–204 (2012)10.1038/nature11700Sirtuins can promote deacetylation of a wide range of substrates in diverse cellular compartments to regulate many cellular processes; recently, Narayan et al. reported that SIRT2 was required for necroptosis on the basis of their findings that SIRT2 inhibition, knockdown or knockout prevented necroptosis. We sought to confirm and explore the role of SIRT2 in necroptosis and tested four different sources of the SIRT2 inhibitor AGK2, three independent short interfering RNAs (siRNAs) against Sirt2, and cells from two independently generated Sirt2−/− mouse strains; however, we were unable to show that inhibiting or depleting SIRT2 protected cells from necroptosis. Furthermore, Sirt2−/− mice succumbed to tumour-necrosis factor (TNF)-induced systemic inflammatory response syndrome (SIRS) more rapidly than wild-type mice, whereas Ripk3−/− mice were resistant. Our results therefore question the importance of SIRT2 in the necroptosis cell death pathway.

The effects of 1,25-dihydroxyvitamin D3 on colon cancer cells depend on RhoA-ROCK-p38MAPK-MSK signaling

Many studies support a protective action of vitamin D against colon cancer. 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) exerts wide gene regulatory effects in human colon cancer cells. We previously reported that 1,25(OH)2D3 increases cytosolic Ca2+ concentration and transiently activates RhoA and its effector the Rho-associated coiled-kinase (ROCK), and later p38MAPK-MSK. We found that the inhibition of ROCK signaling by Y27632 or that of MSK by Ro318220 prevent the formation of epithelioid islands of SW480-ADH cells by 1,25(OH)2D3 and disrupts the adhesive phenotype of HT29 cells. ROCK and MSK inhibition also abrogates the induction of 1,25(OH)2D3 24-hydroxylase (CYP24), E-cadherin, and vinculin and the repression of cyclin D1 by 1,25(OH)2D3. Moreover, 1,25(OH)2D3 does not promote the localization of the tight junction protein occludin at the plasma membrane in cells expressing a dominant negative RhoA (N19-RhoA). In addition, 1,25(OH)2D3 specifically increases the level of the cysteine protease-inhibitor cystatin D, whereas that of cystatin SN is unaffected. The increase of cystatin D protein caused by 1,25(OH)2D3 is abrogated in N19-RhoA cells. Thus, activation of the RhoA-ROCK-p38MAPK-MSK signaling pathway is essential for the regulation of the phenotype and of the CST5/cystatin D candidate tumor suppressor and other target genes by 1,25(OH)2D3 in colon cancer cells.

Linear ubiquitin chain assembly complex coordinates late thymic T-cell differentiation and regulatory T-cell homeostasis

The linear ubiquitin chain assembly complex (LUBAC) is essential for innate immunity in mice and humans, yet its role in adaptive immunity is unclear. Here we show that the LUBAC components HOIP, HOIL-1 and SHARPIN have essential roles in late thymocyte differentiation, FOXP3+ regulatory T (Treg)-cell development and Treg cell homeostasis. LUBAC activity is not required to prevent TNF-induced apoptosis or necroptosis but is necessary for the transcriptional programme of the penultimate stage of thymocyte differentiation. Treg cell-specific ablation of HOIP causes severe Treg cell deficiency and lethal immune pathology, revealing an ongoing requirement of LUBAC activity for Treg cell homeostasis. These data reveal stage-specific requirements for LUBAC in coordinating the signals required for T-cell differentiation.

Synthesis and Biological Evaluation of 1α,25-Dihydroxyvitamin D3 Analogues with a Long Side Chain at C12 and Short C17 Side Chains

Structure-guided optimization was used to design new analogues of 1α,25-dihydroxyvitamin D₃ bearing the main side chain at C12 and a shorter second hydroxylated chain at C17. The new compounds 5a-c were efficiently synthesized from ketone 9 (which is readily accessible from the Inhoffen-Lythgoe diol) with overall yields of 15%, 6%, and 3% for 5a, 5b, and 5c, respectively. The triene system was introduced by the Pd-catalyzed tandem cyclization-Suzuki coupling method. The new analogues were assayed against human colon and breast cancer cell lines and in mice. All new vitamin D₃ analogues bound less strongly to the VDR than 1α,25-dihydroxyvitamin D₃ but had similar antiproliferative, pro-differentiating, and transcriptional activity as the native hormone. In vivo, the three analogues had markedly low calcemic effects.

Cystatin D Locates in the Nucleus at Sites of Active Transcription and Modulates Gene and Protein Expression

Background: Cystatin D is a cysteine protease inhibitor with tumor suppressor action. Results: A proportion of cystatin D protein localizes within the cell nucleus at specific active chromatin sites and regulates gene transcription. Conclusion: Cystatin D is a multifunctional protein with protease inhibitory and gene regulatory activities. Significance: Regulation of cystatin D in colon cancer cells has phenotypic consequences beyond the inhibition of lysosomal and secreted cysteine proteases. Cystatin D is an inhibitor of lysosomal and secreted cysteine proteases. Strikingly, cystatin D has been found to inhibit proliferation, migration, and invasion of colon carcinoma cells indicating tumor suppressor activity that is unrelated to protease inhibition. Here, we demonstrate that a proportion of cystatin D locates within the cell nucleus at specific transcriptionally active chromatin sites. Consistently, transcriptomic analysis show that cystatin D alters gene expression, including that of genes encoding transcription factors such as RUNX1, RUNX2, and MEF2C in HCT116 cells. In concordance with transcriptomic data, quantitative proteomic analysis identified 292 proteins differentially expressed in cystatin D-expressing cells involved in cell adhesion, cytoskeleton, and RNA synthesis and processing. Furthermore, using cytokine arrays we found that cystatin D reduces the secretion of several protumor cytokines such as fibroblast growth factor-4, CX3CL1/fractalkine, neurotrophin 4 oncostatin-M, pulmonary and activation-regulated chemokine/CCL18, and transforming growth factor B3. These results support an unanticipated role of cystatin D in the cell nucleus, controlling the transcription of specific genes involved in crucial cellular functions, which may mediate its protective action in colon cancer.