Mass Spectrometry and 3D Modeling Indicate the SBK2 Kinase Phosphorylates Splicing Factor SRSF7 to Regulate Cardiac Development

SH3 Domain Binding Kinase Family Member 2 (SBK2) is a critical kinase in atrial cardiomyocyte differentiation. However, its phospho-targets, its role in ventricle function, and its role in cardiac disease progression are unknown. Notably, SBK2 has been shown to be downregulated in the ventricular myocardium of several mouse models that recapitulate human desmin-related cardiomyopathies. To restore SBK2 expression, adenoviruses were constructed to promote cardiomyocyte-restricted SBK2 expression and injected at postnatal day 0. This significantly increased ejection fraction at 1 month of age relative to control hearts. However, in 3-month nontransgenic (NTG) and desmin-related cardiomyopathy hearts, the overexpression of SBK2 opposed increases in ejection fraction and left ventricular posterior wall thickness. These findings provide the first in vivo evidence that SBK2 plays a vital role in left ventricular function. To elucidate the molecular mechanism behind the physiological effects of SBK2 on the heart, we performed mass spectrometry combined with phospho-enrichment on ventricular tissue with and without SBK2 overexpression. We identified multiple phosphorylation sites on SBK2 and used AlphaFold3 to model how this phosphorylation likely affects SBK2’s role in phosphorylating the splicing factor SRSF7. We propose a novel mechanism by which SBK2 regulates splicing to promote cardiomyocyte development.