title: E2F suppression and Sp1 overexpression are sufficient to induce the differentiation-specific marker, transglutaminase type 1, in a squamous cell carcinoma cell line.
abstract: Recently, E2F function has expanded to include the regulation of differentiation in human epidermal keratinocytes (HEKs). We extend these findings to report that in HEKs, Sp1 is a differentiation-specific activator and a downstream target of E2F-mediated suppression of the differentiation-specific marker, transglutaminase type 1 (TG-1). Deletion of elements between -0.084 to -0.034 kb of the TG-1 promoter disabled E2F1-induced suppression of promoter activity. Electrophoretic mobility shift assays (EMSAs) demonstrated that Sp1 and Sp3 bound this region. Protein expression analysis suggested that squamous differentiation was accompanied by increased Sp1/Sp3 ratio. Cotransfection of proliferating HEKs or the squamous cell carcinoma (SCC) cell line, KJD-1/SV40, with an E2F inhibitor (E2Fd/n) and Sp1 expression plasmid was sufficient to activate the TG-1 promoter. The suppression of Sp1 activity by E2F in differentiated cells appeared to be indirect since we found no evidence of an Sp1/E2F coassociation on the TG-1 promoter fragment. Moreover, E2F inhibition in the presence of a differentiation stimulus induced Sp1 protein. These data demonstrate that (i) Sp1 can act as a differentiation stimulus, (ii) E2F-mediated suppression of differentiation-specific markers is indirect via Sp1 inhibition and (iii) a combination of E2F inhibition and Sp1 activation could form the basis of a differentiation therapy for SCCs.
authors.affiliation: Epithelial Pathobiology Group, Cancer Biology Programme, Centre for Immunology and Cancer Research, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Queensland 4102, Australia.
authors.forename: Chung Fai
authors.initials: CF
authors.lastname: Wong
authors.forename: Liam M
authors.initials: LM
authors.lastname: Barnes
authors.forename: Alison L
authors.initials: AL
authors.lastname: Dahler
authors.forename: Louise
authors.initials: L
authors.lastname: Smith
authors.forename: Claudia
authors.initials: C
authors.lastname: Popa
authors.forename: Magdalena M
authors.initials: MM
authors.lastname: Serewko-Auret
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Saunders
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology*; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics*; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics*; D015536:Down-Regulation; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D024202:Electrophoretic Mobility Shift Assay; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015603:Keratinocytes; D016329:Sp1 Transcription Factor / Q000096:biosynthesis* / Q000235:genetics*; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics*; D014162:Transfection; D011503:Transglutaminases / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D011503:Transglutaminases; C105804:transglutaminase 1