Differential downregulation of Rbm5 and Rbm10 during skeletal and cardiac differentiation.

RBM5 and RBM10 play an important role in transformed cells. This role includes influencing the alternative splicing and/or expression of factors involved in apoptosis and cell cycle arrest. To date, all apoptosis studies relating to RBM5 and RBM10 have been performed in transformed cell lines, potentially confounding mechanistic interpretation because of the many mutations present in this population. The objective of this study was to identify a physiologically relevant non-transformed system in which to examine the expression of RBM5 and RBM10 for future mechanistic and target identification studies. Our system of choice was H9c2 myoblast differentiation. Expression of Rbm5, Rbm10, and selected splice variants was examined by end-point or real-time PCR and Western blot. We determined that all of the examined Rbm5 and Rbm10 variants were expressed in H9c2 myoblasts and throughout skeletal and cardiac myoblast differentiation. Furthermore, expression was differentially downregulated in a lineage-specific manner, suggesting lineage-specific regulation and roles. There was no correlation between mRNA and protein expression for Rbm5, Rbm10v1, and Rbm10v2, suggesting post-transcriptional and/or post-translational regulation. The differentiation expression profiles suggest the products encoded by Rbm5 and Rbm10 play a more important role in skeletal than cardiac myoblast differentiation and influence similar processes in non-tumor, differentiating cells as in transformed cells. The data also suggest that full-length Rbm5 and Rbm10 play a less important role than their alternative splice variants and/or shorter protein isoforms. This work establishes myoblast differentiation as a relevant model in which to conduct functional studies regarding Rbm5 and Rbm10.