The retinoblastoma family member, p107, is active in non-dividing monocyte-derived dendritic cells

A member of the retinoblastoma family of cell cycle regulatory proteins, p1 07, is not normally expressed in non-cycling cells. We demonstrate here tha t p107 is expressed in monocytes as they differentiate into dendritic cells under the influence of granulocyte-macrophage colony-stimulating factor an d interleukin 4, a process shown not to involve cellular proliferation. We show that p107 is localized to the nucleus of these cells and is active, in that it binds an E2F-DNA binding site, together with E2F transcription fac tors, These findings suggest a hitherto unknown role for p107 in non-prolif erating dendritic cells that warrants further investigation.