Cancer is, fundamentally, a disorder of cell growth and proliferation, which requires adequate supplies of energy and nutrients. In this study, we report that the haplo-insufficient tumor suppressor ASPP2, a p53 activator, negatively regulates the mevalonate pathway to mediate its inhibitory effect on tumor growth in hepatocellular carcinoma (HCC). Gene expression profile analysis revealed that the expression of key enzymes in the mevalonate pathway were increased when ASPP2 was downregulated. HCC cells gained higher cholesterol levels and enhanced tumor-initiating capability in response to the depletion of ASPP2. Simvastatin, a mevalonate pathway inhibitor, efficiently abrogated ASPP2 depletion-induced anchorage-independent cell proliferation, resistance to chemotherapy drugs in vitro, and tumor growth in xenografted nude mice. Mechanistically, ASPP2 interacts with SREBP-2 in the nucleus and restricts the transcriptional activity of SREBP-2 on its target genes, which include key enzymes involved in the mevalonate pathway. Moreover, clinical data revealed better prognosis in patients with high levels of ASPP2 and low levels of the mevalonate pathway enzyme HMGCR. Our findings provide functional and mechanistic insights into the critical role of ASPP2 in the regulation of the mevalonate pathway and the importance of this pathway in tumor initiation and tumor growth, which may provide a new therapeutic opportunity for HCC.

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Obesity is a major risk factor for many chronic diseases, including diabetes, fatty livers, and cancer. Expansion of the adipose mass has been shown to be related to adipogenic differentiation of adipose-derived mesenchymal stem cells (ASCs). However, the underlying mechanism of this effect has yet to be elucidated. We found that osteopontin (OPN) is downregulated in ASCs and adipose tissues of obese mice and overweight human beings because of methylation on its promoter, indicating that OPN may affect the development of obesity. Silencing of OPN in wild-type ASCs promotes adipogenic differentiation, while reexpression of OPN reduced adipogenic differentiation in OPN−/− ASCs. The role of extracellular OPN in ASC differentiation was further demonstrated by supplementation and neutralization of OPN. Additionally, OPN suppresses adipogenic differentiation in ASCs through the C/EBP pathways. Consistent with these in vitro results, by intravenous injection of OPN-expressing adenovirus to the mice, we found OPN can delay the development of obesity and improve insulin sensitivity. Therefore, our study demonstrates an important role of OPN in regulating the development of obesity, indicating OPN might be a novel target to attenuate obesity and its complications.

No abstract