We have previously found retinoid X receptor alpha (RXRα) to be phosphorylated on serine 22 upon IGF-1 stimulation using mass spectrometry-based phosphoproteomics in mouse brown pre-adipocytes. To gain more insight into the role of S22 phosphorylation in the modulation of RXRα function, we generated Rxra knockout brown pre-adipocytes using CRISPR/Cas9 and stably transfected them with EV, RxraWT, or RxraS22A. During differentiation, lipid content and levels of adipogenic markers were lower in Rxra KO cells and partially rescued when re-expressing Rxra, with no differences between reexpression of RxraWT and RxraS22A. However, an unbiased transcriptomic approach using the RxraWT and RxraS22A cell lines revealed that the cell lines have different transcriptomic profiles during the differentiation process, suggesting a role of the S22 phosphorylation in the transcriptional control during adipogenesis. Interestingly, a missense single nucleotide polymorphism (SNP) in the RXRA gene is predicted to cause a loss-of-phosphorylation at serine 22, which may play a role in metabolism. Our results suggest that RXRα phosphorylation is dispensable for adipogenesis, however, it may be involved in other cellular processes
