Albumin expression is required for adipocyte differentiation of 3T3-L1 cells.

We have previously demonstrated that albumin is directly involved in the formation of cytoplasmic lipid droplets in pancreatic stellate cells and may act as a downstream effector of adipogenic transcription factors, PPAR-γ and C/EBP-α. Here, we investigated the role of albumin in adipocyte differentiation using 3T3-L1 cells. Albumin expression was significantly increased at later stages of adipocyte differentiation, which was accompanied with increased C/EBP-β binding to albumin promoter. Suppression of albumin expression using short-hairpin RNA (shRNA) during differentiation led to a considerable reduction in lipid droplet formation, whereas albumin overexpression was stimulatory. Furthermore, point mutation in its fatty acid-binding sites inhibited lipid droplet formation. Consistent with these in vitro finding, Nagase analbuminemic rats displayed reduced fat accumulation. Therefore, our findings suggest that albumin may play a distinct role in adipocyte differentiation by promoting lipid accumulation.