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.

PATZ1 is a transcriptional factor functioning either as an activator or a repressor of gene transcription depending upon the cellular context. It appears to have a dual oncogenic/anti-oncogenic activity. Indeed, it is overexpressed in colon carcinomas, and its silencing inhibits colon cancer cell proliferation or increases sensitivity to apoptotic stimuli of glioma cells, suggesting an oncogenic role. Conversely, the development of B-cell lymphomas, sarcomas, hepatocellular carcinomas and lung adenomas in Patz1-knockout (ko) mice supports its tumour suppressor function. PATZ1 role in mouse lymphomagenesis is mainly because of the involvement of PATZ1 in BCL6-negative autoregulation. However, this does not exclude that PATZ1 may be involved in tumorigenesis by other mechanisms. Here, we report that PATZ1 interacts with the tumour suppressor p53 and binds p53-dependent gene promoters, including those of BAX, CDKN1A and MDM2. Knockdown of PATZ1 in HEK293 cells reduces promoter activity of these genes and inhibits their expression, suggesting a role of PATZ in enhancing p53 transcriptional activity. Consistently, Patz1-ko mouse embryonic fibroblasts (MEFs) show decreased expression of Bax, Cdkn1a and Mdm2 compared with wild-type (wt) MEFs. Moreover, Patz1-ko MEFs show a decreased percentage of apoptotic cells, either spontaneous or induced by treatment with 5-fluorouracil (5FU), compared with wt controls, suggesting a pro-apoptotic role for PATZ1 in these cells. However, PATZ1 binds p53-target genes also independently from p53, exerting, in the absence of p53, an opposite function on their expression. Indeed, knockdown of PATZ1 in p53-null osteosarcoma cells upregulates BAX expression and decreases survival of 5FU-treated cells, then suggesting an anti-apoptotic role of PATZ1 in p53-null cancer cells. Therefore, these data support a PATZ1 tumour-suppressive function based on its ability to enhance p53-dependent transcription and apoptosis. Conversely, its opposite and anti-apoptotic role in p53-null cancer cells provides the perspective of PATZ1 silencing as a possible adjuvant in the treatment of p53-null cancer.

PATZ1, a POZ-Zinc finger protein, is emerging as an important regulator of development and cancer, but its cancer-related function as oncogene or tumor-suppressor is still debated. Here, we investigated its possible role in thyroid carcinogenesis. We demonstrated PATZ1 is down-regulated in thyroid carcinomas compared to normal thyroid tissues, with an inverse correlation to the degree of cell differentiation. In fact, PATZ1 expression was significantly further down-regulated in poorly differentiated and anaplastic thyroid cancers compared to the papillary histotype, and it resulted increasingly delocalized from the nucleus to the cytoplasm proceeding from differentiated to undifferentiated thyroid carcinomas. Restoration of PATZ1 expression in three thyroid cancer-derived cell lines, all characterized by fully dedifferentiated cells, significantly inhibited their malignant behaviors, including in vitro proliferation, anchorage-independent growth, migration and invasion, as well as in vivo tumor growth. Consistent with recent studies showing a role for PATZ1 in the p53 pathway, we showed that ectopic expression of PATZ1 in thyroid cancer cells activates p53-dependent pathways opposing epithelial-mesenchymal transition and cell migration to prevent invasiveness. These results provide insights into a potential tumor-suppressor role of PATZ1 in thyroid cancer progression, and thus may have potential clinical relevance for the prognosis and therapy of thyroid cancer.

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.

PATZ1 is an emerging cancer-related gene coding for a POZ/AT-hook/kruppel Zinc finger transcription factor, which is lost or misexpressed in human neoplasias. Here, we investigated its role in development exploring wild-type and Patz1-knockout mice during embryogenesis. We report that the Patz1 gene is ubiquitously expressed at early stages of development and becomes more restricted at later stages, with high levels of expression in actively proliferating neuroblasts belonging to the ventricular zones of the central nervous system (CNS). The analysis of embryos in which Patz1 was disrupted revealed the presence of severe defects in the CNS and in the cardiac outflow tract, which eventually lead to a pre-mature in utero death during late gestation or soon after birth. Moreover, the Patz1-null mice showed a general growth retardation, which was consistent with the slower growth rate and the increased susceptibility to senescence of Patz1(-/-) mouse embryonic fibroblasts (MEFs) compared to wild-type controls. Therefore, these results indicate a critical role of PATZ1 in the control of cell growth and embryonic development.

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We have previously demonstrated that HMGA1B and HMGA2 overexpression in mice induces the development of GH and prolactin (PRL) pituitary adenomas mainly by increasing E2F1 transcriptional activity. Interestingly, these adenomas showed very high expression levels of PIT1, a transcriptional factor that regulates the gene expression of Gh, Prl, Ghrhr and Pit1 itself, playing a key role in pituitary gland development and physiology. Therefore, the aim of our study was to identify the role of Pit1 overexpression in pituitary tumour development induced by HMGA1B and HMGA2. First, we demonstrated that HMGA1B and HMGA2 directly interact with both PIT1 and its gene promoter in vivo, and that these proteins positively regulate Pit1 promoter activity, also co-operating with PIT1 itself. Subsequently, we showed, by colony-forming assays on two different pituitary adenoma cell lines, GH3 and aT3, that Pit1 overexpression increases pituitary cell proliferation. Finally, the expression analysis of HMGA1, HMGA2 and PIT1 in human pituitary adenomas of different histological types revealed a direct correlation between PIT1 and HMGA expression levels. Taken together, our data indicate a role of Pit1 upregulation by HMGA proteins in pituitary tumours.

The regulatory transcriptional factor PATZ1 is constantly downregulated in human thyroid cancer where it acts as a tumour suppressor by targeting p53-dependent genes involved in Epithelial-Mesenchymal Transition and cell migration. The aim of the present work was to elucidate the upstream signalling mechanisms regulating PATZ1 expression in thyroid cancer cells. The bioinformatics search for microRNAs able to potentially target PATZ1 led to the identification of several miRNAs. Among them we focused on the miR-29b since it was found upregulated in rat thyroid differentiated cells transformed by the Ha-Ras oncogene towards a high proliferating and high migratory phenotype resembling that of anaplastic carcinomas. Functional assays confirmed PATZ1 as a target of miR-29b, and, consistently, an inverse correlation between miR-29b and PATZ1 protein levels was found upon induction of Ha-Ras oncogene expression in these cells. Interestingly, restoration of PATZ1 expression in rat thyroid cells stably expressing the Ha-Ras oncogene decreased cell proliferation and migration, indicating a key role of PATZ1 in Ras-driven thyroid transformation. Together, these results suggest a novel mechanism regulating PATZ1 expression based on the upregulation of miR-29b expression induced by Ras oncogene.