Proteomic screening identifies calreticulin as a miR-27a direct target repressing MHC class I cell surface exposure in colorectal cancer.

Impairment of the immune response and aberrant expression of microRNAs are emerging hallmarks of tumour initiation/progression, in addition to driver gene mutations and epigenetic modifications. We performed a preliminary survey of independent adenoma and colorectal cancer (CRC) miRnoma data sets and, among the most dysregulated miRNAs, we selected miR-27a and disclosed that it is already upregulated in adenoma and further increases during the evolution to adenocarcinoma. To identify novel genes and pathways regulated by this miRNA, we employed a differential 2DE-DIGE proteome analysis. We showed that miR-27a modulates a group of proteins involved in MHC class I cell surface exposure and, mechanistically, demonstrated that calreticulin is a miR-27a direct target responsible for most downstream effects in epistasis experiments. In vitro miR-27a affected cell proliferation and angiogenesis; mouse xenografts of human CRC cell lines expressing different miR-27a levels confirmed the protein variations and recapitulated the cell growth and apoptosis effects. In vivo miR-27a inversely correlated with MHC class I molecules and calreticulin expression, CD8(+) T cells infiltration and cytotoxic activity (LAMP-1 exposure and perforin release). Tumours with high miR-27a, low calreticulin and CD8(+) T cells' infiltration were associated with distant metastasis and poor prognosis. Our data demonstrate that miR-27a acts as an oncomiRNA, represses MHC class I expression through calreticulin downregulation and affects tumour progression. These results may pave the way for better diagnosis, patient stratification and novel therapeutic approaches.

Panobinostat synergizes with zoledronic acid in prostate cancer and multiple myeloma models by increasing ROS and modulating mevalonate and p38-MAPK pathways.

Patients with advanced prostate cancer (PCa) and multiple myeloma (MM) have limited long-term responses to available therapies. The histone deacetylase inhibitor panobinostat has shown significant preclinical and clinical anticancer activity in both hematological and solid malignancies and is currently in phase III trials for relapsed MM. Bisphosphonates (BPs), such as zoledronic acid (ZOL), inhibit osteoclast-mediated bone resorption and are indicated for the treatment of bone metastasis. BPs, including ZOL, have also shown anticancer activity in several preclinical and clinical studies. In the present report, we found a potent synergistic antiproliferative effect of panobinostat/ZOL treatment in three PCa and three MM cell lines as well as in a PCa ZOL-resistant subline, independently of p53/KRAS status, androgen dependency, or the schedule of administration. The synergistic effect was also observed in an anchorage-independent agar assay in both ZOL-sensitive and ZOL-resistant cells and was confirmed in vivo in a PCa xenograft model. The co-administration of the antioxidant N-acetyl-L-cysteine blocked the increased reactive oxygen species generation and apoptosis observed in the combination setting compared with control or single-agent treatments, suggesting that oxidative injury plays a functional role in the synergism. Proapoptotic synergy was also partially antagonized by the addition of geranyl-geraniol, which bypasses the inhibition of farnesylpyrophosphate synthase by ZOL in the mevalonate pathway, supporting the involvement of this pathway in the synergy. Finally, at the molecular level, the inhibition of basal and ZOL-induced activation of p38-MAPK by panobinostat in sensitive and ZOL-resistant cells and in tumor xenografts could explain, at least in part, the observed synergism.

Acquired resistance to zoledronic acid and the parallel acquisition of an aggressive phenotype are mediated by p38-MAP kinase activation in prostate cancer cells.

The nitrogen-containing bisphosphonates (N-BP) zoledronic acid (ZOL) inhibits osteoclast-mediated bone resorption, and it is used to prevent skeletal complications from bone metastases. ZOL has also demonstrated anticancer activities in preclinical models and, recently, in cancer patients, highlighting the interest in determining eventual mechanisms of resistance against this agent. In our study, we selected and characterised a resistant subline of prostate cancer (PCa) cells to better understand the mechanisms, by which tumour cells can escape the antitumour effect of ZOL. DU145R80-resistant cells were selected in about 5 months using stepwise increasing concentrations of ZOL from DU145 parental cells. DU145R80 cells showed a resistance index value of 5.5 and cross-resistance to another N-BP, pamidronate, but not to the non-nitrogen containing BP clodronate. Notably, compared with DU145 parental cells, DU145R80 developed resistance to apoptosis and anoikis, as well as overexpressed the anti-apoptotic protein Bcl-2 and oncoprotein c-Myc. Moreover, DU145R80 cells underwent epithelial to mesenchymal transition (EMT) and showed increased expression of the metalloproteases MMP-2/9, as well as increased invading capability. Interestingly, compared with DU145, DU145R80 cells also increased the gene expression and protein secretion of VEGF and the cytokines Eotaxin-1 and IL-12. At the molecular level, DU145R80 cells showed strong activation of the p38-MAPK-dependent survival pathway compared with parental sensitive cells. Moreover, using the p38-inhibitor SB203580, we completely reversed the resistance to ZOL, as well as EMT marker expression and invasion. Furthermore, SB203580 treatment reduced the expression of VEGF, Eotaxin-1, IL-12, MMP-9, Bcl-2 and c-Myc. Thus, for the first time, we demonstrate that the p38-MAPK pathway can be activated under continuous extensive exposure to ZOL in PCa cells and that the p38-MAPK pathway has a critical role in the induction of resistance, as well as in the acquisition of a more aggressive and invasive phenotype.