Role for Hes1-Induced Phosphorylation in Groucho-Mediated Transcriptional Repression

Abstract

Transcriptional corepressors of the Groucho/transducin-like Enhancer of split (Gro/TLE) family regulate a number of developmental pathways in both invertebrates and vertebrates. They form transcription repression complexes with members of several DNA-binding protein families and participate in the regulation of the expression of numerous genes. Despite their pleiotropic roles, little is known about the mechanisms that regulate the functions of Gro/TLE proteins. It is shown here that Gro/TLEs become hyperphosphorylated in response to neural cell differentiation and interaction with the DNA-binding cofactor Hairy/Enhancer of split 1 (Hes1). Hyperphosphorylation of Gro/TLEs is correlated with a tight association with the nuclear compartment through interaction with chromatin, suggesting that hyperphosphorylated Gro/TLEs may mediate transcriptional repression via chromatin remodeling mechanisms. Pharmacological inhibition of protein kinase CK2 reduces the Hes1-induced hyperphosphorylation of Gro/TLEs and causes a decrease in the chromatin association of the latter. Moreover, the transcription repression activity of Gro/TLEs is reduced by protein kinase CK2 inhibition. Consistent with these observations, Gro/TLEs are phosphorylated in vitro by purified protein kinase CK2. Taken together, these results implicate protein kinase CK2 in Gro/TLE functions. They suggest further that this kinase is involved in a hyperphosphorylation mechanism activated by Hes1 that promotes the transcription repression functions of Hes1-Gro/TLE protein complexes.

We thank Elena Torban for providing neural progenitor cell extracts, Rita Lo for invaluable help during this work, K. Shigesada and M. Osato for pEF-BOS-RUNX1 plasmids, C. D. Allis for antibodies against histone H3, D. Kaplan for reagents, and Julie Nadeau for important observations.

This work was supported by grants from the Canadian Institutes of Health Research (GR-14971) (50%) and the Cancer Research Society, Inc. (50%) to S.S. S.S. is a Scholar of the Fonds de la Recherche en Santé du Québec and a Killam Scholar of the Montreal Neurological Institute.