Abstract 297: Nkx2–5 Transcriptionally Activates C-kit-ligand And Regulates Cardiac Progenitor Cell Populations

Abstract

C-kit-ligand, also known as stem cell factor, is expressed broadly and has a functional role during hematopoesis, gametogenesis, melanogenesis, mast cell growth and differentiation. Although the receptor for c-kit-ligand, c-kit, has been utilized as a marker to identify cardiac stem cell and progenitor cell populations, the transcriptional regulation and biological function of c-kit-ligand during cardiogenesis has not been defined. Here we demonstrate that c-kit-ligand is a novel downstream target of Nkx2–5. The homeodomain transcription factor, Nkx2–5, is one of the earliest markers of the cardiac lineage and mice lacking this transcription factor are nonviable. To identify potential Nkx2–5 downstream target genes, we utilized ES/EBs that were engineered to overexpress Nkx2–5 and undertook transcriptome analysis of embyroid bodies with and without Nkx2–5 induction. We observed a significant increase in c-kit-ligand expression following Nkx2–5 induction suggesting a role for Nkx2–5 in the activation of c-kit-ligand. Furthermore, analysis of the c-kit-ligand promoter revealed three evolutionarily conserved Nkx2–5 response elements, supporting the notion that Nkx2–5 is a transcriptional regulator of gene expression. We undertook transcriptional assays and transfected the c-kit-ligand promoter-luciferase reporter in the absence and presence of increasing amounts of Nkx2–5. We observed that Nkx2–5, in a dose dependent fashion, was a potent transcriptional activator of c-kit-ligand. These studies enhance our understanding of Nkx2–5 mediated transcriptional networks and further emphasize that Nkx2–5 is an important transcriptional regulator of cardiac progenitor cell populations.