Cyclin D1 (Ccnd1) is a proto-oncogen amplified in many different cancers and nuclear accumulation of Ccnd1 is a characteristic of tumor cells. Ccnd1 activates the transcription of a large set of genes involved in cell cycle progress and proliferation. However, Ccnd1 also targets cytoplasmic proteins involved in the regulation of cell migration and invasion. In this work, we have analyzed by immunohistochemistry the localization of Ccnd1 in endometrial, breast, prostate and colon carcinomas with different types of invasion. The number of cells displaying membranous or cytoplasmic Ccnd1 was significantly higher in peripheral cells than in inner cells in both collective and pushing invasion patterns of endometrial carcinoma, and in collective invasion pattern of colon carcinoma. Also, the cytoplasmic localization of Ccnd1 was higher when tumors infiltrated as single cells, budding or small clusters of cells. To evaluate cytoplasmic function of cyclin D1, we have built a variant (Ccnd1-CAAX) that remains attached to the cell membrane therefore sequestering this cyclin in the cytoplasm. Tumor cells harboring Ccnd1-CAAX showed high levels of invasiveness and metastatic potential compared to those containing the wild type allele of Ccnd1. However, Ccnd1-CAAX expression did not alter proliferative rates of tumor cells. We hypothesize that the role of Ccnd1 in the cytoplasm is mainly associated with the invasive capability of tumor cells. Moreover, we propose that subcellular localization of Ccnd1 is an interesting guideline to measure cancer outcome.

The TGF-β/Smad and the PI3K/AKT signaling pathways are important regulators of proliferation and apoptosis, and their alterations lead to cancer development. TGF-β acts as a tumor suppressor in premalignant cells, but it is a tumor promoter for cancerous cells. Such dichotomous actions are dictated by different cellular contexts. Here, we have unveiled a PTEN-Smad3 regulatory loop that provides a new insight in the complex cross talk between TGF-β/Smad and PI3K/AKT signaling pathways. We demonstrate that TGF-β triggers apoptosis of wild-type polarized endometrial epithelial cells by a Smad3-dependent activation of PTEN transcription, which results in the inhibition of PI3K/AKT signaling pathway. We show that specific Smad3 knockdown or knockout reduces basal and TGF-β-induced PTEN expression in endometrial cells, resulting in a blockade of TGF-β-induced apoptosis and an enhancement of cell proliferation. Likewise Smad3 deletion, PTEN knockout prevents TGF-β-induced apoptosis and increases cell proliferation by increasing PI3K/AKT/mTOR signaling. In summary, our results demonstrate that Smad3-PTEN signaling axis determine cellular responses to TGF-β.

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Melanoma is a malignant neoplasia that is highly resistant to chemotherapy and radiotherapy and is associated with poor prognosis in advanced stage. Targeting melanoma that harbors the common BRAF V600E mutation with kinase inhibitors, such as vemurafenib, reduces tumor burden, but these tumors frequently acquire resistance to these drugs. We previously proposed that T-type calcium channel (TTCC) expression may serve as a biomarker for melanoma progression and prognosis, and we showed that TTCC blockers reduce migration and invasion rates because of autophagy blockade only in BRAF V600E -mutant melanoma cells. Here, we demonstrated that high expression of the TTCC Cav3.1 isoform is related to autophagic status in vemurafenib-resistant BRAF V600E -mutant melanoma cells and human biopsies, and in silico analysis revealed an enrichment of Cav3.1 expression in post-treatment melanomas. We also demonstrated that the TTCC blocker mibefradil induces apoptosis and impairs migration and invasion via inhibition of autophagy in resistant melanoma cells and mouse xenograft models. Moreover, we identified an association between PTEN status and Cav3.1 expression in these cells as a marker of sensitivity to combination therapy in resistant cells. Together, our results suggest that TTCC blockers offer a potential targeted therapy in resistant BRAF V600E -mutant melanoma and a therapeutic strategy to reduce progression toward BRAF inhibitor resistance.

PTEN is one of the most frequently mutated genes in human cancers. The frequency of PTEN alterations is particularly high in endometrial carcinomas. Loss of PTEN leads to dysregulation of cell division, and promotes the accumulation of cell cycle complexes such as cyclin D1-CDK4/6, which is an important feature of the tumour phenotype. Cell cycle proteins have been presented as key targets in the treatment of the pathogenesis of cancer, and several CDK inhibitors have been developed as a strategy to generate new anticancer drugs. Palbociclib (PD-332991) specifically inhibits CDK4/6, and it has been approved for use in metastatic breast cancer in combination with letrazole. Here, we used a tamoxifen-inducible Pten knockout mouse model to assess the antitumour effects of cyclin D1 knockout and CDK4/6 inhibition by palbociclib on endometrial tumours. Interestingly, both cyclin D1 deficiency and palbociclib treatment triggered shrinkage of endometrial neoplasias. In addition, palbociclib treatment significantly increased the survival of Pten-deficient mice, and, as expected, had a general effect in reducing tumour cell proliferation. To further analyse the effects of palbociclib on endometrial carcinoma, we established subcutaneous tumours with human endometrial cancer cell lines and primary endometrial cancer xenografts, which allowed us to provide more translational and predictive data. To date, this is the first preclinical study evaluating the response to CDK4/6 inhibition in endometrial malignancies driven by PTEN deficiency, and it reveals an important role of cyclin D-CDK4/6 activity in their development. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Glioblastoma (GBM) is a highly invasive brain neoplasia with an elevated recurrence rate after surgical resection. The cyclin D1 (Ccnd1)/Cdk4-retinoblastoma 1 (RB1) axis is frequently altered in GBM, leading to overproliferation by RB1 deletion or by Ccnd1-Cdk4 overactivation. High levels of Ccnd1-Cdk4 also promote GBM cell invasion by mechanisms that are not so well understood. The purpose of this work is to elucidate the in vivo role of cytoplasmic Ccnd1-Cdk4 activity in the dissemination of GBM. We show that Ccnd1 activates the invasion of primary human GBM cells through cytoplasmic RB1-independent mechanisms. By using GBM mouse models, we observed that evaded GBM cells showed cytoplasmic Ccnd1 colocalizing with regulators of cell invasion such as RalA and paxillin. Our genetic data strongly suggest that, in GBM cells, the Ccnd1-Cdk4 complex is acting upstream of those regulators. Accordingly, expression of Ccnd1 induces focal adhesion kinase, RalA and Rac1 activities. Finally, in vivo experiments demonstrated increased GBM dissemination after expression of membrane-targeted Ccnd1. We conclude that Ccnd1-Cdk4 activity promotes GBM dissemination through cytoplasmic and RB1-independent mechanisms. Therefore, inhibition of Ccnd1-Cdk4 activity may be useful to hinder the dissemination of recurrent GBM.

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Many human cancers present Phosphatase and tensin homolog (PTEN) deficiency and between 20 and 30% of colorectal tumors show PTEN loss. The transcription factor, E2 promoter binding factor 1 (E2F-1), exhibits tumor promoter or suppressive functions depending on cellular type and tissue context, but its role in the progression and development of colorectal carcinogenesis was largely unknown. Here, using a tamoxifen-inducible PTEN knockout mouse model, we have demonstrated that loss of PTEN leads to the development of colorectal tumorigenesis through the serrated pathway. Next, we studied PTEN loss-driven colorectal lesions in the context of E2F-1 deficiency in vivo. Our results revealed that monoallelic and biallelic absence of E2F-1 led to an increased incidence and progression of serrated tumorigenesis induced by PTEN loss. Finally, we investigated the mechanisms by which double PTEN/E2F-1 deficiency leads to enhanced tumorigenesis. We found that colorectal tumors from PTEN/E2F-1 double knockout mice and the human colorectal carcinoma cell line HT29 with shRNA-mediated downregulation of PTEN and E2F-1 exhibit hyperactivation of the RAS-MAPK pathway, accumulation of DNA damage and resistance to apoptosis. To date, this is the first preclinical study evaluating the effect of genetic deletion of E2F-1 in colorectal malignancies driven by PTEN deficiency. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.