Retinoblastoma protein-initiated cellular growth arrest overcomes the ability of cotransfected wild-type p53 to induce apoptosis

Abstract

The retinoblastoma gene, RB, participates in the regulation of the G1/S-phase transition and in p53-mediated apoptosis. We have previously reported that stably transfected RB functions as a growth and tumour suppressor in HTB9 human bladder carcinoma cells, which carry a mutation of the p53 gene at codon 280 and lack RB expression. To elucidate the potential role of RB in the regulation of p53-mediated apoptosis, we transfected a wt p53 expression plasmid under the control of the human cytomegalovirus promoter into parental and RB-transfected HTB9 cells. The p53+/RB– cells were susceptible to apoptosis under various experimental conditions: 1) incubation in serum-free culture for 72 h, 2) short-term (6 h) or long-term (48 h) exposure to etoposide, and 3) culturing in soft agar. In contrast, p53+/RB+ cells were significantly resistant to apoptosis under similar conditions and exhibited efficient growth arrest, as measured by laser scanning cytometry. Tumorigenicity in nude mice of parental HTB9 cells was lost by exogenous expression of wt p53. Likewise, none of mice injected subcutaneously with either p53–/RB+ or p53+/RB+ cells developed tumours, indicating that RB allows suppression of tumorigenesis, regardless of p53 status. These results suggest that the growth-inhibitory function of RB may overcome the ability of wt p53 to induce apoptosis. © 2000 Cancer Research Campaign

Shift in Monocyte Apoptosis with Increasing Viral Load and Change in Apoptosis-Related ISG/Bcl2 Family Gene Expression in Chronically HIV-1-Infected Subjects

“…The impact of HIV-1 on Bcl2-mediated apoptosis in the CD4 compartment is also well described (reviewed in reference 39), and the effect on non-CD4 cell types, namely, CD8 T cells (71), dendritic cells (72), and now monocytes, suggests a global impact of HIV-1 viremia and immune activation on Bcl2-mediated apoptosis regulation. In addition, it has been established that Rb1 can override p53-mediated apoptosis induction in vitro (50), yet it remains to be determined whether Bax and ISG12 family expression can override antiapoptotic Rb1 expression as suggested by our data. The multiple genes measured ex vivo as contributing to apoptosis regulation makes it highly unlikely that the functional phenotype can be accounted for by any one gene.…”

“…Based on prior reports identifying key genes associated with monocyte apoptosis, such as Rb1 (18,33), and type I interferon gene expression in monocytes from highly viremic HIV-1 patients (7,8,19), we focused on testing if functional changes in monocyte apoptosis were associated with changes in p53 (33,49,50), Bcl2/cytochrome c (51-55), and ISG (56-63) family expression due to their known apoptosis regulation functions (Table 2). Quantitative reverse transcription-PCR (RT-qPCR) analysis at time of isolation showed significantly higher Rb1 expression in the total HIV ϩ group than in the HIV Ϫ group (P ϭ 0.0100) but no association with viral load, consistent with reports of Rb1 contributions to apoptosis resistance (33) in circulating monocytes during HIV infection.…”

RB Activity Alters Checkpoint Response and Chemosensitivity in Lung Cancer Lines

“…Thus, specific manipulation of RB in the genetic background of a human neoplasm can offer a system that more accurately models the clinical setting in which the effect of RB on checkpoint control is relevant. Our approach to replace RB in RB-deficient lines has been used by others [25,38,39]. Yet, it is possible that overexpressed RB after adenoviral delivery may not respond to the complex regulation to which the endogenous protein is normally subjected.…”

p53 and Retinoblastoma protein (pRb): A complex network of interactions

“…[11][12][13] Taken together, this data supports a model in which pRb plays an important role in the outcome of p53 activation. 14 These properties are emphasized by the fact that p53 can, in turn, regulate the pRb gene expression through sequence-specific transactivation. 15,16 Moreover, p53 also controls pRb activity by means of the transcriptional induction of p21 which maintain pRb active by inhibiting its phosphorylation by cyclin-cdk complexes (Figure 1).…”