Srebf1a is a key regulator of transcriptional control for adipogenesis

Adipogenesis is regulated by a complex cascade of transcriptional factors, but little is known about the early events that regulate the adipogenic program. Here, we report the role of the srebf1a gene in the differentiation of fibroblastic 3T3-F442A cells. We found that expression of srebf1a depended on GSK3β activity and that GSK3β activity was necessary for C/EBPβ phosphorylation at Thr188. Knockdown of srebf1a inhibited the adipogenic program because it blocked the expression of genes encoding PPARγ2, C/EBPα, SREBP1c and even FABP4, demonstrating that SREBP1a activation is upstream of these three essential adipogenic transcription factors. Kinetic analysis during differentiation illustrated that the order of expression of adipogenic genes was the following: cebpb, srebf1a, pparg2, cebpa, srebp1c and fabp4. Our data suggest that srebf1a acts as an essential link between the GSK3β-C/EBPβ signaling axis and the beginning of the adipogenic transcriptional cascade

Cholesterol Homeostasis in Two Commonly Used Human Prostate Cancer Cell-Lines, LNCaP and PC-3

BACKGROUND:Recently, there has been renewed interest in the link between cholesterol and prostate cancer. It has been previously reported that in vitro, prostate cancer cells lack sterol-mediated feedback regulation of the major transcription factor in cholesterol homeostasis, sterol-regulatory element binding protein 2 (SREBP-2). This could explain the accumulation of cholesterol observed in clinical prostate cancers. Consequently, perturbed feedback regulation to increased sterol levels has become a pervasive concept in the prostate cancer setting. Here, we aimed to explore this in greater depth. METHODOLOGY/PRINCIPAL FINDINGS:After altering the cellular cholesterol status in LNCaP and PC-3 prostate cancer cells, we examined SREBP-2 processing, downstream effects on promoter activity and expression of SREBP-2 target genes, and functional activity (low-density lipoprotein uptake, cholesterol synthesis). In doing so, we observed that LNCaP and PC-3 cells were sensitive to increased sterol levels. In contrast, lowering cholesterol levels via statin treatment generated a greater response in LNCaP cells than PC-3 cells. This highlighted an important difference between these cell-lines: basal SREBP-2 activity appeared to be higher in PC-3 cells, reducing sensitivity to decreased cholesterol levels. CONCLUSION/SIGNIFICANCE:Thus, prostate cancer cells are sensitive to changing sterol levels in vitro, but the extent of this regulation differs between prostate cancer cell-lines. These results shed new light on the regulation of cholesterol metabolism in two commonly used prostate cancer cell-lines, and emphasize the importance of establishing whether or not cholesterol homeostasis is perturbed in prostate cancer in vivo