A Novel Rb- and p300-Binding Protein Inhibits Transactivation by MyoD

Abstract

The retinoblastoma protein (Rb) regulates both the cell cycle and tissue-specific transcription, by modulating the activity of factors that associate with its A-B and C pockets. In skeletal muscle, Rb has been reported to regulate irreversible cell cycle exit and muscle-specific transcription. To identify factors interacting with Rb in muscle cells, we utilized the yeast two-hybrid system, using the A-B and C pockets of Rb as bait. A novel protein we have designated E1A-like inhibitor of differentiation 1 (EID-1), was the predominant Rb-binding clone isolated. It is preferentially expressed in adult cardiac and skeletal muscle and encodes a 187-amino-acid protein, with a classic Rb-binding motif (LXCXE) in its C terminus. Overexpression of EID-1 in skeletal muscle inhibited tissue-specific transcription. Repression of skeletal muscle-restricted genes was mediated by a block to transactivation by MyoD independent of G₁ exit and, surprisingly, was potentiated by a mutation that prevents EID-1 binding to Rb. Inhibition of MyoD may be explained by EID-1's ability to bind and inhibit p300's histone acetylase activity, an essential MyoD coactivator. Thus, EID-1 binds both Rb and p300 and is a novel repressor of MyoD function.

ACKNOWLEDGMENTS

We thank T. Durfee, Y. Shi, and W. Kaelin for the indicated plasmids, Frank Graham for the CMV.βgal virus, and J. Kim and the Baylor Flow Cytometry Lab for their technical assistance. We thank Satoshi Miyake and Bill Kaelin for their discussions and for sharing data prior to publication.

This work was supported by a gift from the Laubisch Fund and by NIH grant K08 HL03671 to W.R.M. and NIH grants R01 HL47567 and R01 HL61668 to M.D.S.