1. Department of Neurology,
2. Department of Developmental and Molecular Biology, and
3. Comprehensive Cancer Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA

Correspondence to: Antonio Iavarone^1,2,3 Correspondence and requests for materials should be addressed to A.I. (e-mail: Email: iavarone@aecom.yu.edu). The sequence of human Id2 promoter is deposited in GenBank under accession number AF270493.

Abstract

In mammalian cells, Id proteins coordinate proliferation and differentiation. Id2 is a dominant-negative antagonist of basic helix–loop–helix transcription factors and proteins of the retinoblastoma (Rb) family. Here we show that Id2–Rb double knockout embryos survive to term with minimal or no defects in neurogenesis and haematopoiesis, but they die at birth from severe reduction of muscle tissue. In neuroblastoma, an embryonal tumour derived from the neural crest, Id2 is overexpressed in cells carrying extra copies of the N-myc gene. In these cells, Id2 is in molar excess of the active form of Rb. The overexpression of Id2 results from transcriptional activation by oncoproteins of the Myc family. Cell-cycle progression induced by Myc oncoproteins requires inactivation of Rb by Id2. Thus, a dual connection links Id2 and Rb: during normal cell-cycle, Rb prohibits the action of Id2 on its natural targets, but oncogenic activation of the Myc–Id2 transcriptional pathway overrides the tumour-suppressor function of Rb.