David Llobet-Navas

Endometrial cancer progression driven by PTEN-deficiency requires miR-424(322)~503

Abstract Endometrial cancer is the most frequent type of cancer in the female reproductive tract. Loss-of-function alterations in PTEN, leading to enhanced PI3K/AKT activation, are among the most frequent molecular alterations in endometrial cancer. Increased PI3K/AKT signaling resulting from PTEN loss promotes cellular proliferation and confers resistance to TGFβ-mediated apoptosis, a key regulator of endometrial homeostasis. In this study, we have analyzed the role of miRNAs in driving these altered cellular responses. A comprehensive transcriptomic analysis of miRNA expression revealed the upregulation of several miRNAs caused by PTEN deficiency and/or TGFβ stimulation. The miR-424(322)~503 cluster drew our attention due to its involvement in regulating apoptosis and proliferation. However, miR-424(322)~503 cluster has a paradoxical role in cancer, exhibiting either oncogenic and tumor suppressive functions depending on cell type or context. To ascertain the function of miR-424(322)~503 in endometrial carcinogenesis caused by PTEN deficiency, we generated a double Pten/miR-424(322)~503 knock-out mice. We demonstrate that loss of miR-424(322)~503 impairs proliferation of both wild type or Pten deficient endometrial organoids by interfering with growth factor and PI3K/AKT signaling. Furthermore, the absence of miR-424(322)~503 restores TGFβ-induced apoptosis, which is otherwise compromised by PTEN deficiency. In vivo, Pten/miR-424(322)~503 knock-out mice exhibit reduced endometrial cancer progression compared to Pten deficient mice through a cell-autonomous mechanism.

ARID1A ‐deficient cells require HDAC6 for progression of endometrial carcinoma

AT‐rich interactive domain‐containing protein 1A (ARID1A) loss‐of‐function mutation accompanied by a loss of ARID1A protein expression is frequently observed in endometrial carcinomas. However, the molecular mechanisms linking these genetic changes to the altered pathways regulating tumour initiation, maintenance and/or progression remain poorly understood. Thus, the main aim of this study was to analyse the role of ARID1A loss of function in endometrial tumorigenesis. Here, using different endometrial in vitro and in vivo models, such as tumoral cell lines, 3D primary cultures and metastatic or genetically modified mouse models, we show that altered expression of ARID1A is not enough to initiate endometrial tumorigenesis. However, in an established endometrial cancer context, ARID1A loss of function accelerates tumoral progression and metastasis through the disruption of the G2/M cell cycle checkpoint and ATM/ATR‐mediated DNA damage checkpoints, increases epithelial cell proliferation rates and induces epithelial mesenchymal transition through the activation of histone deacetylase 6 (HDAC6). Next, we demonstrated that the inhibition of HDAC6 function, using the HDAC6‐specific inhibitor ACY1215 or by transfection with HDAC6 short hairpin RNA (shRNA), can reverse the migratory and invasive phenotype of ARID1A‐ knockdown cells. Further, we also show that inhibition of HDAC6 activity causes an apoptotic vulnerability to etoposide treatments in ARID1A‐ deficient cells. In summary, the findings exposed in this work indicate that the inhibition of HDAC6 activity is a potential therapeutic strategy for patients suffering from ARID1A‐mutant endometrial cancer diagnosed in advanced stages.