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Recombinant human retinoblastoma protein inhibits cancer cell growth
L C Pagliaro1, D Antelman, D E Johnson
1Division of Medicine, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Abstract:
Aberrant expression of the tumor suppressor gene RB1 is associated with a variety of solid tumors and hematopoietic neoplasms. Certain cancer cell lines in which the protein encoded by RB1 (p110RB) is absent have been reported to show decreased growth rate, clonogenicity, or tumorigenicity following insertion of a transcriptionally active RB1 gene. We asked whether these RB-deficient cells could be growth inhibited by direct exposure to purified p110RB. We report a decrease in uptake of tritiated thymidine by 5637 bladder carcinoma cells (RB-negative) when purified recombinant p110RB is added to culture media. Internalization of the protein by cells and translocation to the nucleus are demonstrated by immunohistochemistry, FACS, and detection of radiolabeled protein in subcellular fractions. Next, we chose a well-described leukemia cell culture model to investigate the potential effect of recombinant p110RB in clinical disease. We observed dose-related decreases in cell number of colony formation in vitro in 8 of 20 acute myelogenous leukemia samples, 7 of which did show endogenous p110RB detectable by immunohistochemistry. Histological appearance following exposure to p110RB shows cytoplasmic vacuolization and nuclear lobulation of degenerating cells. We conclude that purified p110RB added to culture media is internalized by cells, translocated to the nucleus, and exerts a growth-inhibitory effect on certain cancer cell types.
Insights
Purified tumor suppressor protein p110RB inhibits growth of RB-deficient cancer cells. Direct protein administration halts proliferation and induces cell death in certain leukemia and carcinoma cell lines.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Aberrant expression of the RB1 tumor suppressor gene is linked to various cancers.
- RB1-deficient cancer cells may regain growth control upon RB1 gene reintroduction.
Purpose of the Study:
- To investigate if purified p110RB protein can directly inhibit the growth of RB-deficient cancer cells.
- To explore the potential of recombinant p110RB as a therapeutic agent for specific cancers.
Main Methods:
- Administered purified recombinant p110RB protein to RB-negative 5637 bladder carcinoma cells.
- Utilized immunohistochemistry, FACS, and radiolabeling to confirm protein internalization and nuclear translocation.
- Tested recombinant p110RB on acute myelogenous leukemia (AML) cell cultures.
Main Results:
- Reduced tritiated thymidine uptake in 5637 bladder carcinoma cells upon p110RB addition.
- Demonstrated p110RB internalization and nuclear translocation in treated cells.
- Observed dose-related inhibition of cell proliferation and colony formation in 40% of AML samples.
Conclusions:
- Purified p110RB protein is internalized by cancer cells and translocates to the nucleus.
- Direct administration of p110RB exerts a growth-inhibitory effect on certain cancer cell types, including some AML cells.
- Recombinant p110RB shows potential for therapeutic application in specific cancers.