Summary Hepatocyte nuclear factor 4α (HNF4α) is essential for liver development and hepatocyte function. Here, we show that transient inhibition of HNF4α initiates hepatocellular transformation through a microRNA-inflammatory feedback loop circuit consisting of miR-124, IL6R, STAT3, miR-24 and miR-629. Moreover, we show that once this circuit is activated, it maintains suppression of HNF4a and sustains oncogenesis. Systemic administration of miR-124, which modulates inflammatory signaling, prevents and suppresses hepatocellular carcinogenesis by inducing tumor-specific apoptosis without toxic side-effects. As we also show that this HNF4α circuit is perturbed in human hepatocellular carcinomas, our data raise the possibility that manipulation of this microRNA feedback-inflammatory loop has therapeutic potential for treating liver cancer.

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The PPARγ nuclear receptor pathway is involved in cancer, but it appears to have both tumor suppressor and oncogenic functions. In neuroblastoma cells, miR-27b targets the 3′UTR of PPARγ and inhibits its mRNA and protein expression. miR-27b overexpression or PPARγ inhibition blocks cell growth in vitro and tumor growth in mouse xenografts. PPARγ activates expression of the pH regulator NHE1, which is associated with tumor progression. Lastly, miR-27b through PPARγ regulates NF-κB activity and transcription of inflammatory target genes. Thus, in neuroblastoma, miR-27b functions as a tumor suppressor by inhibiting the tumor-promoting function of PPARγ, which triggers an increased inflammatory response. In contrast, in breast cancer cells, PPARγ inhibits NHE1 expression and the inflammatory response, and it functions as a tumor suppressor. We suggest that the ability of PPARγ to promote or suppress tumor formation is linked to cell-type specific differences in regulation of NHE1 and other target genes.

Long recognized to confer an extremely poor prognosis, sarcomatoid dedifferentiation of renal cell carcinoma (sRCC) is a tumor phenotype that is finally beginning to be better understood on the molecular and genetic levels. With an overall incidence that ranges from 1 to 32% depending on associated RCC subtype, the survival of sarcomatoid RCC patients rarely exceeds 2 years. The main reasons for its poor outcome include its aggressive biology, its tendency to present at an advanced or metastatic stage at the time of diagnosis, its high rate of tumor recurrence after nephrectomy, and its limited response to systemic therapies. Molecular pathology studies suggest that sarcomatoid dedifferentiation originates from a focal epithelial-mesenchymal transition (EMT) arising in the carcinomatous component of the tumor. It is hoped that the growing understanding of the molecular biology of sRCC will soon make it possible to adapt treatments based on the identification of actionable tumor alterations. The deliberate inclusion of these patients in the multicenter clinical trials of immune, targeted and combination therapies is a necessary next step in pioneering future treatment strategies.

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