Abstract
The impact of human chorionic gonadotropin (hCG) on prostate carcinoma viability was investigated. Treatment of LNCaP and PC-3 cells with hCG modestly reduced cell viability within 96 h. Treatment of cells with hCG followed by exposure to ionizing radiation enhanced radiosensitivity. Exposure of LNCaP cells to hCG promoted activation of epidermal growth factor receptor (ERBB1) via a Gαi-, mitogen-activated protein kinase kinase (MEK)1/2-, and metalloprotease-dependent paracrine mechanism, effects that were further enhanced after radiation exposure, and that were causal in prolonged intense activation of poly(ADP-ribose) polymerase (PARP). Inhibition of ERBB1, MEK1, or PARP1 function suppressed the radiosensitizing properties of hCG. Radiosensitization was also, in part, dependent upon c-Jun NH2-terminal kinase 1/2 signaling. PARP1-dependent radiosensitization was suppressed by a pan-caspase inhibitor and by knockdown of apoptosis-inducing factor expression. Inhibition of phosphatidylinositol 3-kinase, expression of dominant-negative AKT, or treatment with the HMG CoA reductase inhibitor lovastatin suppressed AKT phosphorylation and enhanced the cytotoxic effects of hCG. The enhancing effect of lovastatin was reproduced by incubation with a geranylgeranyl transferase inhibitor and blocked by coexposure to geranylgeranyl pyrophosphate. Treatment with hCG and lovastatin decreased expression of BCL-XL and XIAP, and increased expression of IκB. The cytotoxic effects of hCG were enhanced by expression of dominant-negative IκB, and they were abolished by coexpression of activated AKT. Expression of activated AKT maintained BCL-XL levels in cells expressing dominant-negative IκB. The promotion of hCG lethality by lovastatin was abolished by overexpression of BCL-XL, and was dependent upon activation of caspase-9. Thus, hCG, in combination with radiation and lovastatin, may represent a novel approach to kill prostate cancer cells.
Footnotes
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This work was funded by Friede LLC, The Goodwin Foundation, The V Foundation, and Public Health Service Grants R01-CA88906, R01-DK52825, R01-DK057543, P01-CA72955, P01-CA104177, and R01-CA108520 (to P.D.); Department of Defense Award DAMD17-03-1-0262 and Public Health Service Grants P01-CA72955, R01-CA63753, and R01-CA77141, and Leukemia Society of America grant 6405-97 (to S.G.). A portion of funding for A.Y. is from the Department of Radiation Oncology, Virginia Commonwealth University. P.D. is the holder of the Universal Inc. Professorship in Signal Transduction Research.
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ABBREVIATIONS: hCG, human chorionic gonadotropin; LH, luteinizing hormone; PI3K, phosphatidylinositol 3-kinase; ERK, extracellular signal regulated kinase; EGF, epidermal growth factor; TGF, transforming growth factor; NF-κB, nuclear factor-κB; HRP, horseradish peroxidase; ECL, enhanced chemiluminescence; PJ-34, N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-2-(N,N-dimethylamino) acetamide, hydrochloride; JNK, c-Jun NH2-terminal kinase; JNK-IP, c-Jun NH2-terminal kinase-inhibitory peptide; MAPK, mitogen-activated protein kinase; GGPP, geranylgeranyl pyrophosphate; GGTI-286, [(2R)-1-[[4-[[(1S)-1-methoxycarbonyl-3-methyl-butyl]carbamoyl]-3-phenyl-phenyl]amino]-3-sulfanyl-propan-2-yl]azanium; AG-1478, 4-(3′-chloroanilino)-6,7-dimethoxy-quinazoline; PD184352, 2-[(2-chloro-4-iodo-phenyl)amino]-N-(cyclopropylmethoxy)-3,4-difluoro-benzamide; LY294002, 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride; GM6001, (2R)-N′-hydroxy-N-[(1S)-2-(5H-in-dol-3-yl)-1-(methylcarbamoyl)ethyl]-2-(2-methylpropyl)butanediamide; VEH, vehicle; DMSO, dimethyl sulfoxide; PBS, phosphate-buffered saline; si, small interfering RNA; PAGE, polyacrylamide gel electrophoresis; AIF, apoptosis-inducing factor; PARP, poly(ADP-ribose) polymerase; MEK, mitogen-activated protein kinase kinase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium; GPCR, G protein-coupled receptor; CMV, cytomegalovirus; dn, dominant-negative; L, lovastatin; z, N-benzyloxycarbonyl.
- Received September 23, 2006.
- Accepted October 18, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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