Id Helix-Loop-Helix Proteins Antagonize Pax Transcription Factor Activity by Inhibiting DNA Binding

Abstract

The Id subfamily of helix-loop-helix (HLH) proteins plays a fundamental role in the regulation of cellular proliferation and differentiation. The major mechanism by which Id proteins are thought to inhibit differentiation is through interaction with other HLH proteins and inhibition of their DNA-binding activity. However, Id proteins have also been shown to interact with other proteins involved in regulating cellular proliferation and differentiation, suggesting a more widespread regulatory function. In this study we demonstrate functional interactions between Id proteins and members of the Pax-2/-5/-8 subfamily of paired-domain transcription factors. Members of the Pax transcription factor family have key functions in regulating several developmental processes exemplified by B lymphopoiesis, in which Pax-5 plays an essential role. Id proteins bind to Pax proteins in vitro and in vivo. Binding occurs through the paired DNA-binding domain of the Pax proteins and results in the disruption of DNA-bound complexes containing Pax-2, Pax-5, and Pax-8. In vivo, Id proteins modulate the transcriptional activity mediated by Pax-5 complexes on the B-cell-specific mb-1 promoter. Our results therefore demonstrate a novel facet of Id function in regulating cellular differentiation by functionally antagonizing the action of members of the Pax transcription factor family.

ACKNOWLEDGMENTS

We thank Margaret Bell, Linda Shore, Kelly Warrington, and Luke Peterson for excellent technical assistance and Katherine Stewart for secretarial assistance. We also thank Bob Liddell for DNA sequencing and Ben Adams, Peter Gruss, Neil Perkins, and Richard Treisman for reagents. We are grateful to Julie Stinson and Shen-Hsi Yang for comments on the manuscript and members of our laboratory for helpful discussions.

This work was supported by the Wellcome Trust, the UK Cancer Research Campaign (CRC), and an MRC studentship to E.C.R. A.D.S. is a Research Fellow of the Lister Institute of Preventative Medicine.