ABSTRACT
The study was designed to elucidate the influence of the protein kinase A (PKA) signal transduction pathway on transcription of the LIPE gene encoding hormone-sensitive lipase/cholesteryl esterase (HSL) in H295R cells. HSL is one of the key enzymes involved in steroid hormone synthesis, and ACTH, with mediation of the PKA pathway, increases its activity. However, the mode of regulation of LIPE gene expression by ACTH remains unknown. It was found that stimulation of the PKA pathway by the adenylyl cyclase activator, forskolin, caused a twofold increase in LIPE transcript accompanied by appreciable rise in the protein product of the gene and cortisol output. RNA polymerase II inhibitor abolished, and protein synthesis inhibitor attenuated this effect. Forskolin and PKA catalytic subunit increased transcriptional activity of LIPE promoter A in cells transfected with the luciferase reporter vector. Overexpression of steroidogenic factor-1 (SF-1) increased LIPE promoter activity, while transient silencing of SF-1 expression with specific siRNAs abolished forskolin-stimulated LIPE transcription. It is concluded that ACTH via the PKA pathway stimulates expression of SF-1, which activates transcription of LIPE presumably by interaction with putative binding sequences within promoter A. A novel mechanism contributing to the long-term effect of ACTH on adrenal steroidogenesis is proposed: ACTH stimulates transcription of SF-1, which interacts with the putative SF-1-binding sequences within the promoter and activates LIPE transcription. An increased level of HSL results in an enhanced supply of cholesterol required for steroid hormone synthesis.
