Our study identifies a specific subset of miRNA, whose down-regulation might contribute to pituitary tumorigenesis.

Previous studies have demonstrated that high mobility group A proteins have a critical role on the onset of human pituitary adenomas. Indeed, both high mobility group A (HMGA) genes are overexpressed in pituitary adenomas, and consistently transgenic mice overexpressing either the Hmga1 or the Hmga2 gene develop mixed growth hormone/prolactin (GH-PRL)-secreting pituitary adenomas. Trisomy of chromosome 12, where HMGA2 is located, and/or amplification of the HMGA2 gene locus account for the HMGA2 overexpression in most human prolactinomas. Conversely, HMGA1 overexpression is not associated to any rearrangement or amplification of the HMGA1 locus. We have first identified micro RNAs (miRNAs) able to target both HMGA1 and HMGA2 messenger RNAs. Then, all of these miRNAs have been found downregulated in pituitary adenomas of different histotypes, compared with normal pituitary. Interestingly, their downregulation was also observed in nonfunctioning pituitary adenomas where HMGA2 overexpression is not associated to any alteration of the HMGA2 locus. Functional studies show that all these HMGA-targeting miRNAs inhibit the proliferation of the rat pituitary adenoma cell line GH3. Therefore, these results indicate that the downregulation of the miRNAs able to target the HMGA genes could contribute to increase HMGA protein levels in human pituitary adenomas, and then to pituitary tumorigenesis.

These results indicate the involvement of miR-1 in thyroid cell proliferation and migration, validating a role of miR-1 down-regulation in thyroid carcinogenesis.

The high-mobility group A (HMGA, types 1 and 2) proteins are low-molecular-weight nuclear factors that orchestrate the assembly of nucleoprotein complexes involved in gene transcription, replication, and chromatin structure. HMGAs possess oncogenic activity [1,2] and proteins of type 1 (HMGA1) have been correlated to cellular invasiveness and drug-resistance in human malignancies.[3] In particular, blockage of expression of these proteins significantly enhances the responsiveness of tumor cell lines that are otherwise resistant to cytotoxic agents. Thus, phenotypic assays based on cells with reduced levels of HMGA are a possible tool for a rational search of novel compounds against tumors whose aggressiveness and resistance reduce the success of normal screening methods.Herein, we report the elucidation of the structure of mycalol (1), a novel polyoxygenated ether lipid that showed a promising in vitro specific activity against different cell lines derived from human anaplastic thyroid carcinoma (ATC), the most aggressive human thyroid gland malignancy.[4] Mycalol was identified by a novel screening method based on the parallel use of FRO cells, which are human ATC-derived cells with high constitutive levels of HMAG1, but not HMGA2, and FRO-asHMGA1 cells, a genetically modified population of FRO cells that stably express an anti-HMGA1 antisense construct that blocks HMGA1 synthesis.[5] The effects of extracts and fractions were measured on the paired cell lines by MTS proliferation assay.Mycalol was isolated from a chloroform extract of the sponge Mycale (Oxymycale) acerata Kirkpatrick 1907 collected along the coasts of Terra Nova Bay (Antarctica) during the Austral summer of 2005. The sponge, frozen soon after collection, was extracted with MeOH and fractionated according to a modified Kupchan method.[6] The chloroform extract showed no activity against FRO cells up to 50 mg mL À1 , but gave a good response (IC 50 = 7.5 mg mL À1 ) against HMGA1-silenced FRO cells (FRO-asHMGA), thus supporting the potential of a novel screening method based on HMGA-interference. Sequential steps of silica gel radial chromatography and reverse-phase HPLC (see the Supporting information) gave alkyl glyceryl ether 1 together with a number of minor compounds that are still under study. The HR-ESI+ MS spectrum of 1 showed a MÀNa + ion at m/z 573.3959, thus accounting for the molecular formula C 29 H 58 O 9 (calcd m/z 573.3979 for C 29 H 58 O 9 Na) and requiring only one formal unsaturation. Accordingly, 1 H and 13 C 2D NMR data indicated a C 27 linear structure with nine oxygenated carbons and an acetyl group (for full assignment, see the Supporting Information, Table S1). COSY spectra identified seven of these carbons as part of a glycerol moiety (H1' This methylene group showed scalar couplings with the diastereomeric protons at d 2.40 and d 2.16 (H 2 2), both also coupled to one of the oxymethine protons (d 4.18, H3) of the two gem-diol systems. Characterization and location of these groups were unambiguously accomplished by 2D NMR...

DNA-damaging therapies represent a keystone in cancer treatment. Unfortunately, many tumors often relapse because of a group of cancer cells, which are resistant to conventional therapies. High-mobility group A (HMGA) proteins has a key role in cell transformation, and their overexpression is a common feature of human malignant neoplasias, representing a poor prognostic index often correlated to anti-cancer drug resistance. Our previous results demonstrated that HMGA1 is a substrate of ataxiatelangiectasia mutated (ATM), the main cellular sensor of genotoxic stress. Here we also report thatHMGA2, the other member of the HMGA family, is a novel substrate of ATM. Interestingly, we found that HMGA proteins positively regulate ATM gene expression. Moreover, induction of ATM kinase activity by DNA-damaging agents enhances HMGA-dependent transcriptional activation of ATM promoter, suggesting that ATM expression is modulated by a DNA-damage-and HMGA-dependent positive feedback loop. Finally, inhibition of HMGA expression in mouse embryonic fibroblasts and in cancer cells strongly reduces ATM protein levels, impairing the cellular DNA-damage response and enhancing the sensitivity to DNA-damaging agents. These findings indicate this novel HMGA-ATM pathway as a new potential target to improve the effectiveness of conventional anti-neoplastic treatments on the genotoxic-drug resistant cancer cells.

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Numerous studies have established that High Mobility Group A (HMGA) proteins play a pivotal role on the onset of human pituitary tumors. They are overexpressed in pituitary tumors, and, consistently, transgenic mice overexpressing either the Hmga1 or the Hmga2 gene develop pituitary tumors. In contrast with HMGA2, HMGA1 overexpression is not related to any rearrangement or amplification of the HMGA1 locus in these tumors. We have recently identified 2 HMGA1 pseudogenes, HMGA1P6 and HMGA1P7, acting as competitive endogenous RNA decoys for HMGA1 and other cancer related genes. Here, we show that HMGA1 pseudogene expression significantly correlates with HMGA1 mRNA levels in growth hormone and nonfunctioning pituitary adenomas likely inhibiting the repression of HMGA1 through microRNAs action. According to our functional studies, these HMGA1 pseudogenes enhance the proliferation and migration of the mouse pituitary tumor cell line, at least in part, through their upregulation. Our results point out that the overexpression of HMGA1P6 and HMGA1P7 could contribute to increase HMGA1 levels in human pituitary tumors, and then to pituitary tumorigenesis.

This study proposes miR-199a-5p and miR-375 as contributors to CTX resistance in colon cancer and suggests a novel approach based on miRNAs as tools for the therapy of this tumor.