RPSAP52 lncRNA is overexpressed in pituitary tumors and promotes cell proliferation by acting as miRNA sponge for HMGA proteins.

Long non-coding RNAs (lncRNAs) are emerging as fundamental players in cancer biology. Indeed, they are deregulated in several neoplasias and have been associated with cancer progression, tumor recurrence, and resistance to treatment, thus representing potential biomarkers for cancer diagnosis, prognosis, and therapy. In this study, we aimed to identify lncRNAs associated with pituitary tumorigenesis. We have analyzed the lncRNA expression profile of a panel of gonadotroph pituitary adenomas in comparison with normal pituitaries. Then, we focused on RPSAP52, a novel lncRNA antisense for the HMGA2 gene, whose overexpression plays a critical role in the development of pituitary adenomas. We report that RPSAP52 expression is highly upregulated in gonadotroph and prolactin-secreting pituitary adenomas, where it correlates with that of HMGA2, compared with normal pituitary tissues. Conversely, its expression showed a variable behavior in somatotroph adenomas. We also demonstrate that RPSAP52 enhances HMGA2 protein expression in a ceRNA-dependent way acting as sponge for miR-15a, miR-15b, and miR-16, which have been already described to be able to target HMGA2. Interestingly, RPSAP52 also positively modulates HMGA1, the other member of the High-Mobility Group A family. Moreover, functional studies indicate that RPSAP52 promotes cell growth by enhancing the G1-S transition of the cell cycle. The results reported here reveal a novel mechanism, based on the overexpression of the lncRNA RPSAP52, which contributes to pituitary tumorigenesis, and propose this lncRNA as a novel player in the development of these tumors. KEY MESSAGES: RPSAP52 is overexpressed in pituitary adenomas. RPSAP52 increases HMGA protein levels. A ceRNA mechanism is proposed for the increased HMGA1/2 expression.

Critical role of HMGA proteins in cancer cell chemoresistance.

The high-mobility group A (HMGA) proteins are frequently overexpressed in human malignancies and correlate with the presence of metastases and reduced patient survival. Here, we highlight the main studies evidencing a critical role of HMGA in chemoresistance, mainly by activating Akt signaling, impairing p53 activity, and regulating the expression of microRNAs that target genes involved in the susceptibility of cancer cells to antineoplastic agents. Therefore, these studies account for the association of HMGA overexpression with patient poor outcome, indicating the impairment of HMGA as a fascinating perspective for effectively improving cancer therapy.

Downregulation of miR-410 targeting the cyclin B1 gene plays a role in pituitary gonadotroph tumors.

MicroRNAs (miRNAs) are small noncoding RNAs that act as posttranscriptional regulators of gene expression, and are frequently altered in human neoplasias. Here, we have analyzed the miRNA expression profile of human gonadotroph adenomas versus normal pituitary tissue using a miRNACHIP microarray. We demonstrate that miRNA-410 is downregulated in gonadotroph adenomas when compared with normal pituitary gland. We validate CCNB1 as target of miRNA-410 since its overexpression reduces CCNB1 at protein and mRNA levels, decreasing cell proliferation. In conclusion, our study suggess that the downregulation of miRNA-410 plays a role in the behavior of gonadotroph tumors.

MiR-199a-5p and miR-375 affect colon cancer cell sensitivity to cetuximab by targeting PHLPP1.

OBJECTIVES: We aimed to analyze the differentially-expressed miRNAs in colon cancer cells in order to identify novel potential biomarkers involved in cancer cell resistance. DESIGN AND METHODS: We investigated the miRNA expression profile of GEO human colon carcinoma cells, sensitive to the EGFR inhibitor Cetuximab (CTX) and their CTX-resistant counterpart (GEO CR) by using a miRNA chip. RESULTS: We found 27 upregulated and 10 downregulated miRNAs in GEO CR compared with GEO cells with a fold change ≥ 2. Among the upregulated miRNAs, we focused on miR-199a-5p and miR-375. We report that their enforced expression promotes CTX resistance, whereas their silencing sensitizes to the same drug. The ability of miR-199a-5p and miR-375 to target PHLPP1 (PH domain and leucine-rich repeat protein phosphatase 1), a tumor suppressor that negatively regulates the AKT pathway, accounts, at least in part, for their drug-resistance activity. Indeed, restoration of PHLPP1 increases sensitivity of the GEO cells to CTX and reverts the resistance-promoting effect of miR-199a-5p and miR-375. CONCLUSION: 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.

HMGA1-pseudogene expression is induced in human pituitary tumors.

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.

High mobility group A1 protein expression reduces the sensitivity of colon and thyroid cancer cells to antineoplastic drugs.

BACKGROUND: Development of resistance to conventional drugs and novel biological agents often impair long-term chemotherapy. HMGA gene overexpression is often associated with antineoplastic drug resistance and reduced survival. Inhibition of HMGA expression in thyroid cancer cells reduces levels of ATM protein, the main cellular sensor of DNA damage, and enhances cellular sensitivity to DNA-damaging agents. HMGA1 overexpression promotes chemoresistance to gemcitabine in pancreatic adenocarcinoma cells through an Akt-dependent mechanism. METHODS: To elucidate the role of HMGA1 proteins in chemoresistance we analyzed resistance to conventional drugs and targeted therapies of human colon carcinoma cells (GEO) that are sensitive to the epidermal growth factor receptor inhibitor cetuximab, and express minimal levels of HMGA1 and cetuximab-resistant (GEO CR) cells expressing high HMGA1 protein levels. RESULTS: GEO CR cells were less sensitive than GEO cells to cetuximab and 5-fluorouracil. GEO CR cells silenced for HMGA1 expression were more susceptible than empty vector-transfected cells to the drugs' cytotoxicity. Similar results were obtained with anaplastic thyroid carcinoma cells expressing or not HMGA1 proteins, treated with doxorubicin or the HDAC inhibitor LBH589. Finally, HMGA1 overexpression promoted the DNA-damage response and stimulated Akt phosphorylation and prosurvival signaling. CONCLUSIONS: Our findings suggest that the blockage of HMGA1 expression is a promising approach to enhance cancer cell chemosensitivity, since it could increase the sensitivity of cancer cells to antineoplastic drugs by inhibiting the survival signal and DNA damage repair pathways.

Mir-23b and miR-130b expression is downregulated in pituitary adenomas.

MicroRNA (miRNA) deregulation plays a critical role in tumorigenesis. miR-23b and miR-130b are induced by thyrotropin in thyroid cells in a cAMP-dependent manner. The aim of our work has been to investigate the possible role of miR-23b and miR-130b in pituitary tumorigenesis. We have analyzed their expression in a panel of pituitary adenomas (PAs) including GH and NFPA adenomas. We report that miR-23b and miR-130b are drastically reduced in GH, gonadotroph and NFPA adenomas in comparison with normal pituitary gland. Interestingly, the overexpression of miR-23b and miR-130b inhibits cell proliferation arresting the cells in the G1 and G2 phase of the cell cycle, respectively. Moreover, we demonstrate that miR-23b and miR-130b target HMGA2 and cyclin A2 (CCNA2) genes, respectively. Finally, downregulation of miR-23b and miR-130b expression is associated with increased levels of their respective targets in human PAs. These findings suggest that miR-23b and miR-130b downregulation may contribute to pituitary tumorigenesis.

The High Mobility Group A proteins contribute to thyroid cell transformation by regulating miR-603 and miR-10b expression.

The overexpression of the HMGA1 proteins is a feature of human malignant neoplasias and has a causal role in cell transformation. The aim of our study has been to investigate the microRNAs (miRNAs or miRs) regulated by the HMGA1 proteins in the process of cell transformation analyzing the miRNA expression profile of v-ras-Ki oncogene-transformed thyroid cells expressing or not HMGA1 proteins. We demonstrate that, among the miRNAs regulated by cell transformation, there are miR-10b, miR-21, miR-125b, miR-221 and miR-222 that are positively and miR-34a and miR-603 that are negatively regulated by HMGA1 expression. Then, we focused our attention on the miR-10b and miR-603 whose expression was dependent on the presence of HMGA1 also in other cell systems. We found that miR-10b is able to target the PTEN gene, whereas miR-603 targets the CCND1 and CCND2 genes coding for the cyclin D1 and cyclin D2 proteins, respectively. Moreover, functional studies showed that miR-10b and miR-603 regulate positively and negatively, respectively, cell proliferation and migration suggesting a role of their dysregulation in thyroid cell transformation.

Altered microRNA expression profile in human pituitary GH adenomas: down-regulation of miRNA targeting HMGA1, HMGA2, and E2F1.

CONTEXT: MicroRNA (miRNA) are an important class of regulators of gene expression. Altered miRNA expression has been constantly found in human neoplasias and plays an important role in the process of carcinogenesis. OBJECTIVE: The aim of this study was to identify specific miRNA whose expression is altered in GH-secreting pituitary adenomas. DESIGN: Using a miRNACHIP microarray, we have analyzed the miRNA expression profile of human GH adenomas vs. normal pituitary gland. RESULTS: We report the identification of a set of miRNA, including miR-34b, miR-326, miR-432, miR-548c-3p, miR-570, and miR-603, drastically and constantly down-regulated in GH adenomas. We demonstrate that these miRNA target genes such as high-mobility group A1 (HMGA1), HMGA2, and E2F1, whose overexpression and/or activation plays a critical role in pituitary tumorigenesis. We also show that the enforced expression of the down-regulated miRNA has a negative role on the growth regulation of pituitary adenoma cells. Finally, an inverse correlation is found between the expression of these miRNA and HMGA1 and HMGA2 protein levels in GH adenomas. CONCLUSION: Our study identifies a specific subset of miRNA, whose down-regulation might contribute to pituitary tumorigenesis.