title: Id3 induces an Elk-1-caspase-8-dependent apoptotic pathway in squamous carcinoma cells.
abstract: Inhibitor of differentiation/DNA-binding (Id) proteins are helix-loop-helix (HLH) transcription factors. The Id protein family (Id1-Id4) mediates tissue homeostasis by regulating cellular processes including differentiation, proliferation, and apoptosis. Ids typically function as dominant negative HLH proteins, which bind other HLH proteins and sequester them away from DNA promoter regions. Previously, we have found that Id3 induced apoptosis in immortalized human keratinocytes upon UVB exposure, consistent with its role as a tumor suppressor. To investigate the role of Id3 in malignant squamous cell carcinoma (SCC) cells (A431), a tetracycline-regulated inducible system was used to induce Id3 in cell culture and mouse xenograft models. We found that upon Id3 induction, there was a decrease in cell number under low serum conditions, as well as in soft agar. Microarray, RT-PCR, immunoblot, siRNA, and inhibitor studies revealed that Id3 induced expression of Elk-1, an E-twenty-six (ETS)-domain transcription factor, inducing procaspase-8 expression and activation. Id3 deletion mutants revealed that 80 C-terminal amino acids, including the HLH, are important for Id3-induced apoptosis. In a mouse xenograft model, Id3 induction decreased tumor size by 30%. Using immunofluorescent analysis, we determined that the tumor size decrease was also mediated through apoptosis. Furthermore, we show that Id3 synergizes with 5-FU and cisplatin therapies for nonmelanoma skin cancer cells. Our studies have shown a molecular mechanism by which Id3 induces apoptosis in SCC, and this information can potentially be used to develop new treatments for SCC patients.
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: You-Shin
authors.initials: YS
authors.lastname: Chen
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Joseph
authors.initials: J
authors.lastname: Aubee
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Kyle A
authors.initials: KA
authors.lastname: DiVito
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Hengbo
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Weiyi
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Institute of Biochemistry and Biotechnology, Chung Shan Medical University, Taichung, 402, Taiwan.
authors.forename: Fen-Pi
authors.initials: FP
authors.lastname: Chou
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Simbulan-Rosenthal
authors.affiliation: Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, 20057.|Lombardi Comprehensive Cancer Center, Georgetown University, Washington, District of Columbia, 20057.
authors.forename: Dean S
authors.initials: DS
authors.lastname: Rosenthal
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D053181:Caspase 8 / Q000378:metabolism*; D061945:Caspase Inhibitors / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D004357:Drug Synergism; D005472:Fluorouracil / Q000494:pharmacology; D064593:Heterografts; D006801:Humans; D051796:Inhibitor of Differentiation Proteins / Q000494:pharmacology / Q000502:physiology*; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000494:pharmacology / Q000502:physiology*; D009368:Neoplasm Transplantation; D015398:Signal Transduction; D047368:Tumor Burden; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D061945:Caspase Inhibitors; D051796:Inhibitor of Differentiation Proteins; D009363:Neoplasm Proteins; D050807:ets-Domain Protein Elk-1; C075640:ID3 protein, human; D053181:Caspase 8; D002945:Cisplatin; D005472:Fluorouracil
keywords: Apoptosis; Elk-1; HLH; Id3; SCC; caspase-8