Insulin-induced serine 22 phosphorylation of retinoid X receptor alpha is dispensable for adipogenesis in brown adipocytes

• Published in: Adipocyte 2020-01, Vol.9 (1), p.142-152
• Main Authors: Ardenkjær-Larsen, Jacob, Rupar, Kaja, Sinkevičiūtė, Goda, Petersen, Patricia S. S., Villarroel, Julia, Lundh, Morten, Barrès, Romain, Rabiee, Atefeh, Emanuelli, Brice
• Format: Article
• Language: English
• Subjects: Adipocytes, Brown - cytology; Adipocytes, Brown - metabolism; Adipogenesis; adipose tissue; Animals; Cell Differentiation; insulin; Insulin - metabolism; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphorylation; Retinoid X receptor alpha; Retinoid X Receptor alpha - metabolism; Serine - metabolism; transcriptional regulation
• ISSN: 2162-3945; 2162-397X
• DOI: 10.1080/21623945.2020.1747352

Insulin action initiates a series of phosphorylation events regulating cellular differentiation, growth and metabolism. We have previously discovered, in a mass spectrometry-based phosphoproteomic study, that insulin/IGF-1 signalling induces phosphorylation of retinoid x receptor alpha (RXRα) at S22 in mouse brown pre-adipocytes. Here, we show that insulin induces the phosphorylation of RXRα at S22 in both brown precursor and mature adipocytes through a pathway involving ERK, downstream of IRS-1 and −2. We also found that RXRα S22 phosphorylation is promoted by insulin and upon re-feeding in brown adipose tissue in vivo, and that insulin-stimulated S22 phosphorylation of RXRα is dampened by diet-induced obesity. We used Rxra knockout cells re-expressing wild type (WT) or S22A non-phosphorylatable forms of RXRα to further characterize the role of S22 in brown adipocytes. Knockout of Rxra in brown pre-adipocytes resulted in decreased lipid accumulation and adipogenic gene expression during differentiation, and re-expression of RxraWT alleviated these effects. However, we observed no significant difference in cells re-expressing the RxraS22A mutant as compared with the cells re-expressing RxraWT. Furthermore, comparison of gene expression during adipogenesis in the WT and S22A re-expressing cells by RNA sequencing revealed similar transcriptomic profiles. Thus, our data propose a dispensable role for RXRα S22 phosphorylation in adipogenesis and transcription in differentiating brown pre-adipocytes.