Cell Cycle-Dependent Regulation of Phosphorylation of the Human Retinoblastoma Gene Product

Abstract

The human retinoblastoma gene (RB1) encodes a protein (Rb) of 105 kilodaltons that can be phosphorylated. Analysis of Rb metabolism has shown that the protein has a half-life of more than 10 hours and is synthesized at all phases of the cell cycle. Newly synthesized Rb is not extensively phosphorylated (it is "underphosphorylated") in cells in the G0 and G1 phases but is phosphorylated at multiple sites at the G1/S boundary and in S phase. HL-60 cells that were induced to terminally differentiate by various chemicals lost their ability to phosphorylate newly synthesized Rb at multiple sites when cell growth was arrested. These findings suggest that underphosphorylated Rb may restrict cell proliferation.

Anomalous retinoblastoma protein expression in Sternberg-Reed cells in Hodgkin's disease: a comparative study with p53 and Ki67 expression

“…We found that, after PHA stimulation, the amount of (Buchkovich et al, 1989;Chen et al, 1989;Mihara et al, 1989) and other studies showing variation in Rb protein levels in B and T lymphocytes, when cells entered the S-phase in response to mitogens (Martinez et al, 1993;Tereda et al, 1991). This increase in Rb protein along the cell cycle has also been detected in other cell types (Xu et al, 1991b), and is also found in this study in reactive tonsils, which show a similar pattern of staining for Rb and Ki67.…”

“…Retinoblastoma susceptibility gene (Rb) is a tumoursuppressor gene that codes for a nuclear phosphoprotein which plays a key role in cell cycle regulation (Buchkovich et al, 1989;Mihara et al, 1989;Chen et al, 1989). Although Rb protein is expressed in all the human organs examined, this expression is at heterogeneous levels which seem to be related to the growth and differentiation status of each cell type (Cordon-Cardo and Richon, 1994).…”

Regulation of tumor suppressor proteins, p53 and retinoblastoma, by estrogen and antiestrogens in breast cancer cells

“…A decrease in the levels of p53 was observed after 48 h of E 2 treatment and also an apparent reversal of ppRB to pRB although ppRB was still detectable (Figure 3). This observation may be related to cells reentering the G 1 phase of the cycle in which pRB is dephosphorylated (Mihara et al, 1989;DeCaprio et al, 1992). These results show that E 2 treatment of T47D cells cultured in stripped serum is su cient to induce hyperphosphorylation of pRB and that E 2 is capable of stimulating this event which is highly correlated with G 1 to S phase transition of the cell cycle.…”

“…As cells progress through G 1 , the suppressor function of pRB is inactivated by sequential phosphorylation at cyclin dependent kinase (cdk) consensus target sites (Mihara et al, 1989;DeCaprio et al, 1992;Mittnatch et al, 1994;Knudsen and Wang, 1996) which can be detected as an upshift during SDS ± PAGE (Mihara et al, 1989;DeCaprio et al, 1992). In the E 2 -responsive breast cancer cell line MCF-7, E 2 treatment has been shown to be su cient to induce slower mobility hyperphosphorylated form(s) of pRB (ppRB) during SDS ± PAGE (Foster and Wimalasena, 1996).…”

Early G1 growth arrest of hybridoma B cells by DMSO involves cyclin D2 inhibition and p21[CIP1] induction

“…cyclin D (Sherr, 1994) and the cyclins responsible for DNA replication and mitosis (cyclins E, A and B). Thus, in contrast to other cell types like ®broblats, where pRb phosphorylation occurs throughout the cell cycle (Buchkovich et al, 1989;Chen et al, 1989;DeCaprio et al, 1989DeCaprio et al, , 1992Mihara et al, 1989) it appears that in 7TD1 cells pRb is phosphorylated predominantly by cyclin D2/CDK4. Indeed, 4 h after the addition of fresh medium, pRb became phosphorylated ( Figure 2b) concomitantly with the increase of cyclin D2 levels (Figure 3b) and the augmentation of cyclin D2/CDK4-associated kinase activity (Figure 3a).…”