Overexpression of a dominant-negative signal transducer and activator of transcription 3 variant in tumor cells leads to production of soluble factors that induce apoptosis and cell cycle arrest.
Gene therapy of B16 tumors with a dominant-negative signal transducer and activator of transcription (Stat3) variant, designated Stat3beta, results in inhibition of tumor growth and tumor regression. Although only 10-15% of the tumor cells are transfected in vivo, the Stat3beta-induced antitumor effect is associated with massive apoptosis of B16 tumor cells, indicative of a potent bystander effect. Here, we provide evidence that blocking Stat3 signaling in B16 cells results in release of soluble factors that are capable of inducing apoptosis and cell cycle arrest of nontransfected B16 cells. RNase protection assays using multi-template probes specific for key physiological regulators of apoptosis reveal that overexpression of Stat3beta in B16 tumor cells induces the expression of the apoptotic effector, tumor necrosis factor-related apoptosis-inducing ligand. These in vitro results suggest that the observed in vivo bystander effect leading to tumor cell growth inhibition is mediated, at least in part, by soluble factors produced as a result of overexpression of Stat3beta in tumor cells.
Niu
G
G
Immunology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, Florida 33613, USA.
Shain
K H
KH
Huang
M
M
Ravi
R
R
Bedi
A
A
Dalton
W S
WS
Jove
R
R
Yu
H
H
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D002453:Cell Cycle / Q000502:physiology; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008546:Melanoma, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology; D012995:Solubility; D053221:TNF-Related Apoptosis-Inducing Ligand; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics
D051017:Apoptosis Regulatory Proteins; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D053221:TNF-Related Apoptosis-Inducing Ligand; C505654:Tnfsf10 protein, mouse; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha