PATZ1 is a target of miR-29b that is induced by Ha-Ras oncogene in rat thyroid cells.

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.

PATZ1 acts as a tumor suppressor in thyroid cancer via targeting p53-dependent genes involved in EMT and cell migration.

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.

Embryonic defects and growth alteration in mice with homozygous disruption of the Patz1 gene.

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.

POZ-, AT-hook-, and zinc finger-containing protein (PATZ) interacts with human oncogene B cell lymphoma 6 (BCL6) and is required for its negative autoregulation.

The PATZ1 gene encoding a POZ/AT-hook/Kruppel zinc finger (PATZ) transcription factor, is considered a cancer-related gene because of its loss or misexpression in human neoplasias. As for other POZ/domain and Kruppel zinc finger (POK) family members, the transcriptional activity of PATZ is due to the POZ-mediated oligomer formation, suggesting that it might be not a typical transactivator but an architectural transcription factor, thus functioning either as activator or as repressor depending on the presence of proteins able to interact with it. Therefore, to better elucidate PATZ function, we searched for its molecular partners. By yeast two-hybrid screenings, we found a specific interaction between PATZ and BCL6, a human oncogene that plays a key role in germinal center (GC) derived neoplasias. We demonstrate that PATZ and BCL6 interact in germinal center-derived B lymphoma cells, through the POZ domain of PATZ. Moreover, we show that PATZ is able to bind the BCL6 regulatory region, where BCL6 itself acts as a negative regulator, and to contribute to negatively modulate its activity. Consistently, disruption of one or both Patz1 alleles in mice causes focal expansion of thymus B cells, in which BCL6 is up-regulated. This phenotype was almost completely rescued by crossing Patz1(+/-) with Bcl6(+/-) mice, indicating a key role for Bcl6 expression in its development. Finally, a significant number of Patz1 knock-out mice (both heterozygous and homozygous) also develop BCL6-expressing lymphomas. Therefore, the disruption of one or both Patz1 alleles may favor lymphomagenesis by activating the BCL6 pathway.

PIT1 upregulation by HMGA proteins has a role in pituitary tumorigenesis.

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 αT3, 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.

Expression of a truncated Hmga1b gene induces gigantism, lipomatosis and B-cell lymphomas in mice.

HMGA1 gene rearrangements have been frequently described in human lipomas. In vitro studies suggest that HMGA1 proteins have a negative role in the control of adipocyte cell growth, and that HMGA1 gene truncation acts in a dominant-negative fashion. Therefore, to define better the role of the HMGA1 alterations in the generation of human lipomas, we generated mice carrying an Hmga1b truncated (Hmga1b/T) gene. These mice develop a giant phenotype together with a drastic expansion of the retroperitoneal and subcutaneous white adipose tissue. We show that the activation of the E2F pathway likely accounts, at least in part, for this phenotype. Interestingly, the Hmga1b/T mice also develop B-cell lymphomas similar to that occurring in Hmga1-knockout mice, supporting a dominant-negative role of the Hmga1b/T mutant also in vivo.

Impairment of the p27kip1 function enhances thyroid carcinogenesis in TRK-T1 transgenic mice.

Impairment of the p27(kip1) function, caused by a drastic reduction of its expression or cytoplasmic mislocalization, has been frequently observed in thyroid carcinomas. To understand the role of p27(kip1) impairment in thyroid carcinogenesis, we investigated the consequences of the loss of p27(kip1) expression in the context of a mouse modeling of papillary thyroid cancer, expressing the TRK-T1 oncogene under the transcriptional control of thyroglobulin promoter. We found that double mutant mice homozygous for a p27(kip1) null allele (TRK-T1/p27(-/-)) display a higher incidence of papillary thyroid carcinomas, with a shorter latency period and increased proliferation index, compared with p27(kip1) wild-type compounds (TRK-T1/p27(+/+)). Consistently, double mutant mice heterozygous for a p27(kip1) null allele (TRK-T1/p27(+/-)) show an incidence of thyroid carcinomas that is intermediate between TRK-T1/p27(-/-) and TRK-T1/p27(+/+) mice. Therefore, our findings suggest a dose-dependent role of p27(kip1) function in papillary thyroid cancer development.