Transforming growth factor beta inhibits the phosphorylation of pRB at multiple serine/threonine sites and differentially regulates the formation of pRB family-E2F complexes in human myeloid leukemia cells

Transforming growth factor beta (TGF beta)1 induced dephosphorylation of pR b at multiple serine and threonine residues including Ser249/Thr252, Thr373 , Ser780, and Ser807/811 in MV4-11 cells. Likewise, TGF beta 1 caused the d ephosphorylation of p130, while inhibiting accumulation of p107 protein. Ph osphorylated pRb was detected to bind E2F-1 and E2F-3, which appears to be a major form of pRb complexes in actively cycling cells. TGF beta 1 signifi cantly downregulated pRb-E2F-1 and pRb-E2F-3 complexes as a result of inhib ition of E2F-1 and E2F-3. In contrast, complexes of E2F-4 with pRb and with p130 were increased markedly upon TGF beta 1 treatment, whereas p107 assoc iated E2F-4 was dramatically decreased. In agreement with these results, p1 30-E2F-4 DNA binding activity was dominant in TGF beta 1 treated cells, whe reas p107-E2F-4 DNA binding activity was only found in proliferating cells. Our data strongly suggest that inhibition of E2Fs and differential regulat ion of pRb family-E2F-4 complexes are linked to TGF beta 1-induced growth i nhibition. E2F-4 is switched from p107 to p130 and pRb when cells are arres ted in G1 phase by TGF beta 1. (C) 2000 Academic Press.