THE RETINOBLASTOMA GENE-PRODUCT (RB) INDUCES BINDING OF A CONFORMATIONALLY INACTIVE NUCLEAR FACTOR-KAPPA-B

Nuclear factor-kappa B (NF-KB) regulates expression of several viral a nd cellular genes including the human immunodeficiency virus long term inal repeat, major histocompatibility complex class I, and interleukin 2R alpha cytokine genes. Here we report that the retinoblastoma gene product (Rb) stimulates binding of the NF-kappa B p50 homodimer. The a ddition of Rb protein to an in vitro gel shift binding assay stimulate d p50 binding greater than 10-fold. Interestingly, by analyzing NF-kap pa B-dependent transcription activity in vitro, we demonstrate that Rb suppresses transcriptional activity of p50. Chymotrypsin analysis sug gests that Rb induces a conformational change in the NF-kappa B-DNA co mplex, resulting in binding of a transcriptionally inactive complex, F inally, we demonstrate by coimmunoprecipitation analysis that the Rb-p 50 complex is present in Jurkat cell extracts. Our results suggest tha t Rb may play an important role in regulation of NF-kappa B transcript ional activity.