title: Involvement of the TNF-alpha autocrine-paracrine loop, via NF-kappaB and YY1, in the regulation of tumor cell resistance to Fas-induced apoptosis.
abstract: Many tumors are resistant to Fas ligand (FasL)-induced apoptosis. This study examined the role of tumor-derived TNF-alpha, via an autocrine/paracrine loop, in the regulation of tumor-cell resistance to FasL-induced apoptosis. We have reported that Fas expression and sensitivity to FasL is negatively regulated by the transcription repressor factor Yin Yang 1 (YY1). Thus, we hypothesized that tumor-derived TNF-alpha induces the activation of NF-kappaB and the transcription repressor YY1, both of which negatively regulate Fas expression and sensitivity to FasL-induced apoptosis. This hypothesis was tested in PC-3 prostate cancer cells which synthesize and secrete TNF-alpha and express constitutively active NF-kappaB and YY1. Treatment of PC-3 cells with TNF-alpha (10 units) resulted in increased NF-kappaB and YY1 DNA-binding activity, upregulation of YY1 expression, downregulation of surface and total Fas expression and enhanced resistance of PC-3 to apoptosis induced by the FasL agonist antibody CH-11. In contrast, blocking the binding of secreted TNF-alpha on PC-3 cells with soluble recombinant sTNF-RI resulted in significant inhibition of constitutive NF-kappaB and YY1 DNA-binding activity, downregulation of YY1 expression, upregulation of Fas expression and sensitization of tumor cells to CH-11-induced apoptosis. The regulation of YY1 expression and activity by NF-kappaB was demonstrated by the use of the NF-kappaB inhibitor Bay 11-7085 and by the use of a GFP reporter system whereby deletion of the YY1-tandem binding site in the promoter significantly enhanced GFP expression. The direct role of YY1 expression in the regulation of PC-3 resistance to CH-11-induced apoptosis was shown in cells transfected with siRNA YY1 whereby such cells exhibited upregulation of Fas expression and were sensitized to CH-11-induced apoptosis. These findings demonstrate that the TNF-alpha autocrine-paracrine loop is involved in the constitutive activation of the transcription factors NF-kappaB and YY1 in the tumor cells and this loop leads to inhibition of Fas expression and resistance to FasL-induced apoptosis. Further, these findings identify new targets such as TNF-alpha, NF-kappaB and YY1, whose inhibition can reverse tumor cell resistance to FasL-mediated apoptosis.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, University of California-Los Angeles, 10833 Le Conte Ave., Los Angeles, CA 90095-1747, USA.
authors.forename: Sara
authors.initials: S
authors.lastname: Huerta-Yepez
authors.forename: Mario
authors.initials: M
authors.lastname: Vega
authors.forename: Hermes
authors.initials: H
authors.lastname: Garban
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bonavida
mesh_terms: D000230:Adenocarcinoma / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D001483:Base Sequence; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000276:immunology; D045744:Cell Line, Tumor; D053222:Fas Ligand Protein; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000276:immunology; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000276:immunology*; D009570:Nitriles / Q000494:pharmacology; D011471:Prostatic Neoplasms / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D012334:RNA, Neoplasm / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013450:Sulfones / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology; D048069:Tumor Necrosis Factors / Q000276:immunology; D050986:YY1 Transcription Factor / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D019014:fas Receptor / Q000096:biosynthesis / Q000276:immunology*
chemical_list: C416282:BAY 11-7085; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D009570:Nitriles; D012334:RNA, Neoplasm; D013450:Sulfones; D014409:Tumor Necrosis Factor-alpha; D048069:Tumor Necrosis Factors; D050986:YY1 Transcription Factor; C494698:YY1 protein, human; D019014:fas Receptor; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases