KLF4 functions as an activator of the androgen receptor through reciprocal feedback.

In prostate cancer, Krüppel-like factor 4 (KLF4) depletion occurs frequently, suggesting a role as suppressor tumor. KLF4 is a transcription factor associated with androgen receptor (AR) expression; however, its cellular functions and signaling regulation mechanism remain largely unknown. In this study, we demonstrated that activated AR binds to the KLF4 promoter and enhances KLF4 expression, which reciprocally targets the AR promoter, thus sustaining KLF4 activity. Ectopic KLF4 expression in androgen-independent prostate cancer cells induced AR expression and decreased cell proliferation, invasion and bone metastasis. We previously showed that increased microRNA (miR)-1 expression is associated with reduced bone metastasis of prostate cancer cells. Here we observed that KLF4 targets the primary miR-1-2 stem-loop promoter and stimulates miR-1 expression. In clinical prostate cancer specimens, KLF4 levels were positively correlated with miR-1 and AR levels. These data suggest that the loss of KLF4 expression is one mechanistic link between aggressive prostate cancer progression and low canonical AR output through miR-1 inactivation.

Transforming growth factor-ß promotes prostate bone metastasis through induction of microRNA-96 and activation of the mTOR pathway.

Transforming growth factor-ß (TGFß) is enriched in the bone matrix and serves as a key factor in promoting bone metastasis in cancer. In addition, TGFß signaling activates mammalian target of rapamycin (mTOR) functions, which is important for the malignant progression. Here, we demonstrate that TGFß regulates the level of microRNA-96 (miR-96) through Smad-dependent transcription and that miR-96 promotes the bone metastasis in prostate cancer. The enhanced effects in cellular growth and invasiveness suggest that miR-96 functions as an oncomir/and metastamir. Supporting this idea, we identified a downstream target of the TGFß-miR-96 signaling pathway to be AKT1S1 mRNA, whose translated protein is a negative regulator of mTOR kinase. Our findings provide a novel mechanism accounting for the TGFß signaling and bone metastasis.

Cell cycle regulation of the BRCA1/acetyl-CoA-carboxylase complex.

Germ-line alterations in BRCA1 are associated with an increased susceptibility to breast and ovarian cancer. The BRCA1 protein has been implicated in multiple cellular functions. We have recently demonstrated that BRCA1 reduces acetyl-CoA-carboxylase alpha (ACCA) activity through its phospho-dependent binding to ACCA, and further established that the phosphorylation of the Ser1263 of ACCA is required for this interaction. Here, to gain more insight into the cellular conditions that trigger the BRCA1/ACCA interaction, we designed an anti-pSer1263 antibody and demonstrated that the Ser1263 of ACCA is phosphorylated in vivo, in a cell cycle-dependent manner. We further showed that the interaction between BRCA1 and ACCA is regulated during cell cycle progression. Taken together, our findings reveal a novel mechanism of regulation of ACCA distinct from the previously described phosphorylation of Ser79, and provide new insights into the control of lipogenesis through the cell cycle.

Telomerase activation in a model of lung adenocarcinoma.

Ovine pulmonary adenocarcinoma (OPA) is a lung cancer strikingly similar to the pneumonic-type mixed invasive adenocarcinoma with a predominant bronchioloalveolar component in humans. Telomerase activity in OPA and the potential involvement of the kinase Akt in telomerase activation and regulation of cell proliferation were investigated. Lung tissues were collected from sheep with a histopathological diagnosis of OPA or controls. Epithelial cell cultures were derived in vitro from lung tissues. Telomerase activity was evaluated using the telomeric repeat amplification protocol method. Phosphorylation of Akt was detected by Western blotting. Telomerase activity was significantly higher in OPA lung tissues compared to control lung tissues. A high telomerase activity was detected in eight out of 12 (67%) primary cell cultures derived from tumours. A high level of expression of phosphorylated Akt was found in 10 out of 27 (37%) tumours, with abolition of Akt activation in response to epidermal growth factor stimulation demonstrated in primary cell cultures derived from tumours. Telomerase activation takes place in ovine pulmonary adenocarcinoma tumour cells and may be partly attributable to Akt activation. Telomerase may inhibit cellular senescence and contribute to the accumulation of tumour cells in mixed adenocarcinoma with a bronchioloalveolar component. Further work is necessary to identify alternative signalling pathways of telomerase activation in tumours.

[JSRV (jaagsiekte sheep retrovirus) and ovine pulmonary carcinoma]. / JSRV (jaagsiekte sheep retrovirus) et cancer du poumon associé chez le mouton.

JSRV (jaagsiekte sheep retrovirus) is a betaretrovirus, infecting small ruminants. This virus is responsible for the development of pulmonary adenocarcinoma, by the transformation of epithelial cells of the bronchioli and alveoli. This animal cancer is related to human bronchioloalveolar cancer (BAC), a specific form of human lung cancer for which a viral etiology has been proposed for several decades. In small ruminants JSRV interacts with the cells through the Hyal2 receptor. JSRV genome is simple and does not contain already known oncogene. It is now well established that the envelope protein is oncogenic by itself, via the cytoplasmic domain of the transmembrane glycoprotein and some domains of the surface glycoprotein. Activation of the PI3K/Akt and MAPK pathways participates to the envelope-induced transformation. The tumour development is associated with telomerase activation.