Contribution of transcription factor, SP1, to the promotion of HB- EGF expression in defense mechanism against the treatment of irinotecan in ovarian clear cell carcinoma.

Ovarian clear cell carcinoma ( OCCC) is a worst histological subtype than other ovarian malignant tumor. Heparin-binding epidermal growth factor-like growth factor ( HB- EGF) is a promising target for ovarian cancer therapy. The aims of this study were to validate the efficacy of HB- EGF-targeted therapy for OCCC and to identify the transcription factor that contributed to the induction of HB- EGF by SN38 treatment in OCCC cells. HB- EGF was highly expressed in OCCC cells, and an increase of HB- EGF was induced by SN38 which had only antitumor effect among conventional anticancer agents on OCCC. A specific inhibitor of HB- EGF, a cross-reacting material 197 ( CRM197), led to a synergistic increase in the number of apoptotic OCCC cells with the treatment of SN38. The luciferase assay with 5′-deletion promoter constructs identified a GC-rich element between −125 and −178 (the distal transcription start site was denoted +1) as a cis-regulatory region, and the treatment of SN38 induced luciferase activity in this region. An in silico and chromatin immunoprecipitation analysis estimated that SP1 bound to the cis-regulatory region of HB- EGF in OCCC cells. Real-time PCR and cell viability assays showed that the transfection of a small interfering RNA targeting SP1 suppressed the expression of HB- EGF induced by SN38, resulting in the enhanced sensitivity of SN38. Taken together, these results indicate that induction of HB- EGF expression contributed to defense mechanism against treatment of SN38 through the transcriptional activity of SP1 in OCCC cells. [ABSTRACT FROM AUTHOR]