Protein Kinase C Signaling Transduces Endorphin-Primed Cardiogenesis in GTR1 Embryonic Stem Cells

Carlo Ventura, Elisabetta Zinellu, Emiliana Maninchedda, Marina Fadda, Margherita Maioli
Abstract—The prodynorphin gene and its product, dynorphin B, have been found to promote cardiogenesis in embryonic
cells by inducing the expression of GATA-4 and Nkx-2.5, two transcription factor– encoding genes essential for
cardiogenesis. The molecular mechanism(s) underlying endorphin-induced cardiogenesis remain unknown. In the
present study, we found that GTR1 embryonic stem (ES) cells expressed cell surface  opioid receptors, as well as
protein kinase C (PKC)-, -1, -2, -, -, and -. Cardiac differentiation was associated with a marked increase in the
Bmax value for a selective opioid receptor ligand and complex subcellular redistribution of selected PKC isozymes.
PKC-, -1, -2, -, and - all increased in the nucleus of ES-derived cardiac myocytes, compared with nuclei from
undifferentiated cells. In both groups of cells, PKC- and - were mainly expressed at the nuclear level. The nuclear
increase of PKC-, -1, and -2 was due to a translocation from the cytosolic compartment. In contrast, the increase of
both PKC- and PKC- in the nucleus of ES-derived cardiomyocytes occurred independently of enzyme translocation,
suggesting changes in isozyme turnover and/or gene expression during cardiogenesis. No change in PKC- expression
was observed during cardiac differentiation. Opioid receptor antagonists prevented the nuclear increase of PKC-,
PKC-1, and PKC-2 and reduced cardiomyocyte yield but failed to affect the nuclear increase in PKC- and -. PKC
inhibitors prevented the expression of cardiogenic genes and dynorphin B in ES cells and abolished their development
into beating cardiomyocytes. (Circ Res. 2003;92:617-622.)
Key Words: protein kinase C  cardiac differentiation  embryonic stem cells  gene expression  endorphins