Editors' ChoiceDevelopment

Building a Heart with Cyclin

Sci. Signal.  04 Feb 2014:
Vol. 7, Issue 311, pp. ec34
DOI: 10.1126/scisignal.2005145

The transcription factor GATA4 is required for cardiomyocyte proliferation and differentiation during development and for cardiac regeneration in adult animal models. GATA4 enhances the expression of genes encoding proteins that promote the cell cycle, such as cyclin D2 (CycD2) and its associated cyclin-dependent kinase CDK4. Among other functions, cyclins and CDKs can bind to transcription factors and alter their activity. Yamak et al. found that CycD2 binds to GATA4 to promote transcription. Overexpression of CycD2 (but not CycD1) with GATA4 enhanced luciferase activity from GATA4-dependent promoter-based reporters in National Institutes of Health (NIH) 3T3 cells and HL1 mouse atrial cardiomyocytes. Chromatin immunoprecipitation showed that CycD2 and GATA4 were enriched on the promoter of an endogenous GATA4-dependent gene, and coimmunoprecipitation, in vitro binding, and functional domain mapping experiments demonstrated that a conserved N-terminal region of GATA4 bound directly to CycD2. Mutation of GATA4 Ser160, which is mutated in patients with congenital heart defects, reduced the interaction between GATA4 and CycD2 and activation of GATA4-dependent reporters by GATA4 and CycD2. CDK4 phosphorylated GATA4, but not GATA4 S160G, in vitro; in cells, pharmacological inhibition of CDK4 reduced GATA4-mediated activation of the reporter. In contrast, CDK4 inhibition was less effective at inhibiting GATA4-mediated reporter activity stimulated by coexpression of CycD2 and GATA4. Moreover, coexpression of GATA4 with CycD2 K112A, which compromises CDK4 binding, enhanced reporter activity as compared with overexpression of GATA4 alone, suggesting that CycD2 may promote GATA4 activity independent of CDK4. Co-injection of GATA4 and CycD2 mRNAs into Xenopus embryos enhanced expression of cardiac-specific genes in ectodermal explants as compared to GATA4 injection alone or co-injection of GATA4 S160G and CycD2. Thus, during development, GATA4 increases the abundance of CycD2, which then binds to GATA4, enhancing its activity and establishing a feed-forward loop to promote cardiogenesis.

A. Yamak, B. V. Latinkić, R. Dali, R. Temsah, M. Nemer, Cyclin D2 is a GATA4 cofactor in cardiogenesis. Proc. Natl. Acad. Sci. U.S.A. 111, 1415–1420 (2014). [Abstract] [Full Text]