Transcriptional Regulation Of Differentiation-associated Genes By Transcription Factor C-Jun/AP-1 In Esophageal Squamous Cell Carcinoma

Transcriptional activation of eukaryotic genes depends on the precise and ordered recruitment of activators, chromatin modifiers, and general transcription factors to the promoters of target genes. Previously, we identified differentiation-associated genes were coordinately down-regulated in human esophageal squamous cell carcinoma (ESCC) including SPRRs (small proline-rich proteins), keratins, cystatin A and involucrin, all of which contain AP-1 DNA binding sites in the promoter regions. However, the mechanisms of down-regulation of these genes were poorly understood. We investigated the endogenous expression pattern of AP-1 in paired ESCC tissue specimens. Coincident with the down-regulation of these genes, c-Jun expression was obviously decreased in cancer tissues. It suggested that the downregulation of c-Jun may be associated with the underexpression of differentiation-associated genes in ESCC.Based on the expression of c-Jun and response to TPA stimulation, we selected KYSE450 cells as a useful model system to determine whether c-Jun/AP-1 regulated the expression of these genes. 12-o-tetradecanoylophorbol-13-acetate (TPA) and pharmacological reagents were used to induce or block c-Jun expression and activation. The mRNA and protein expression of these genes increased in response to TPA-induced c-Jun/AP-1 expression. Activation of MAPK pathways was followed by acquisition of AP-1 DNA binding and transactivation capacities. Inhibitors of PKC (GF109203X) and JNK (SP600125) mainly blocked expression and phosphorylation of c-Jun, while inhibition of MEK-ERK activity with PD98059 had little effect. Expression of involucrin and keratin 4 in response to TPA was attenuated by pretreatments with GF109203X and SP600125, but not PD98059, suggesting involvement of PKC and JNK in the induction of differentiation-associated genes by c-Jun/AP-1.Chromatin immunoprecipitation (ChIP) assay indicated that c-Jun and c-Fos were mainly involved in regulation of the differentiation-associated genes in vivo. c-Jun activated the transcription of these genes by enhancing the binding of c-Jun to...