Background: PU box-binding protein (PU.1) is a master gene of hematopoietic lineage and an important specific transcription factor in osteoclast lineage. There is proof of its expression in adipose tissue, and it is known to significantly and negatively affect adipogenesis. However, it is unclear whether there are any other molecules involved in this process.
Methods: We wished to explore the effect of PU.1's co-activator microphthalmia-associated transcription factor (MITF) on the adipogenic differentiation of ovine primary preadipocytes. The expression vectors pcDNA-MITF and pcDNA-PU.1, and MITF siRNA and PU.1 siRNA were transfected or co-transfected into ovine tail primary preadipocytes. Real-time PCR and western blot analysis were applied to investigate the expression levels of PU.1 and MITF. The morphologic changes in the cells were observed under a microscope at a magnification of × 200 after staining with Oil Red O. The triglyceride (TG) content in cells was also determined after transfection.
Results: MITF and its co-activator PU.1 synergistically exhibited an opposite expression pattern to that of CCAAT-enhancer-binding protein-β (C/EBPβ) during adipogenic differentiation of ovine primary preadipocytes. Before induction of differentiation, overexpression of MITF or PU.1 inhibited the expression of C/EBPβ and adipogenesis in the cells; and knockdown of MITF or PU.1 promoted the expression of C/EBPβ and adipogenesis in the cells. The inhibitory or promotive effect was enhanced when MITF and PU.1 were co-overexpressed or co-silenced. However, when MITF and/or PU.1 were overexpressed after day 2 of differentiation, no changes in adipogenesis of the cells were observed.
Conclusions: MITF and its co-activator PU.1 inhibited adipogenesis of ovine primary preadipocytes by restraining C/EBPβ.
Keywords: Adipogenesis; CCAAT-enhancer-binding protein-β; Lineage-specific transcription factor; Microphthalmia-associated transcription factor; PU box-binding protein.