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p16/MTS1/INK4A suppresses prostate cancer by both pRb dependent and independent pathways
1University of Tennessee Urologic Research Laboratories, Department of Urology, University of Tennessee-Memphis, Memphis, Tennessee 38163, USA.
Abstract:
Tumor suppressor gene p16 is a cyclin-dependent kinase inhibitor and an important negative cell cycle regulator. The inactivation of p16 appears to be a common event in prostate cancer. Replacement of p16 inhibits prostate tumor cell growth, but the mechanism is not known. Human prostate cancer cell lines PPC-1, which has an inactivated p16, and DU145, which has a nonfunctional retinoblastoma Rb protein (pRb), were used to determine the possible mechanism of p16 mediated growth inhibition. PPC-1 cells treated with 5-aza-2'-deoxycytidine (5-aza-dC), a demethylating agent, induced p16 expression, inhibited cell growth, and induced senescence. Similarly, PPC-1 cells transduced by an adenoviral vector containing the p16 gene (AdRSVp16) produced a p16 protein that suppressed cellular proliferation and induced senescence. Co-staining of AdRSVp16-transduced PPC-1 cells by p16 immunohistochemistry and by beta-galactosidase substrate X-gal showed that the morphologically enlarged cells expressed both p16 and senescence-associated beta-galactosidase. In contrast, AdRSVp16 did not induce senescence in DU145 cells, but did inhibit its growth. However, when wild-type pRb was introduced in DU145 cells, AdRSVp16 was able to induce senescence. Thus, the mechanism by which p16 suppressed prostate cancer was dependent on the pRb functional status of cells whereby p16 caused pRb+ cells to undergo inhibition by senescence, whereas pRb- cells were also inhibited, but not by senescence.
Insights
The tumor suppressor gene p16 inhibits prostate cancer cell growth by inducing senescence in cells with functional retinoblastoma protein (pRb). In pRb-deficient cells, p16 still inhibits growth but does not induce senescence.
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- The tumor suppressor gene p16 acts as a negative regulator of the cell cycle.
- Inactivation of p16 is frequently observed in prostate cancer.
- The precise mechanism by which p16 inhibits prostate tumor cell growth remains unclear.
Purpose of the Study:
- To elucidate the mechanism of p16-mediated growth inhibition in prostate cancer.
- To investigate the role of retinoblastoma protein (pRb) functional status in p16's mechanism of action.
Main Methods:
- Utilized human prostate cancer cell lines PPC-1 (inactivated p16) and DU145 (nonfunctional pRb).
- Administered 5-aza-2'-deoxycytidine (5-aza-dC) to induce p16 expression in PPC-1 cells.
- Transduced PPC-1 and DU145 cells with an adenoviral vector expressing p16 (AdRSVp16).
- Assessed cell growth, proliferation, senescence markers (beta-galactosidase), and p16/pRb expression via immunohistochemistry.
Main Results:
- Demethylation and AdRSVp16 transduction induced p16 expression, inhibited cell growth, and triggered senescence in PPC-1 cells.
- PPC-1 cells exhibiting senescence co-expressed p16 and senescence-associated beta-galactosidase.
- AdRSVp16 inhibited growth in DU145 cells but did not induce senescence.
- Introduction of wild-type pRb into DU145 cells enabled AdRSVp16 to induce senescence, indicating pRb dependence.
Conclusions:
- p16-mediated suppression of prostate cancer growth is dependent on the functional status of pRb.
- In pRb-positive cells, p16 induces growth inhibition through senescence.
- In pRb-negative cells, p16 inhibits growth but not via senescence, highlighting distinct cellular responses based on pRb presence.