Transcriptional Regulation of Vascular Endothelial Growth Factor Gene Expression in Ovarian Bovine Granulosa Cells

Abstract

The expression of vascular endothelial growth factor (VEGF) in cultured bovine granulosa cells has been studied. As shown by northern blot analysis, granulosa cells express the VEGF gene. Analysis of the VEGF transcripts by the polymerase chain reaction technique shows that granulosa cells express predominantly the smallest VEGF coding forms (VEGF₁₂₁, and VEGF₁₆₄). Since in the promoter region of the VEGF gene there are four potential AP-1 sites and two potential AP-2 sites we have studied if TPA and forskolin could regulate VEGF gene expression. TPA induces VEGF transcription in a time- and dose-dependent fashion. Maximal VEGF mRNA levels are detected 6 h after TPA treatment. Induction apparently requires de novo protein synthesis since it does not occur when translation is inhibited by cycloheximide. Forskolin, a naturally occurring diterpene that activates adenylylcyclase, also increases VEGF mRNA content in a time-dependent manner. Induction does not require de novo protein synthesis and, in contrast to TPA, induction is strongly potentiated by cycloheximide. Luteotrophic hormone, a known activator of adenylylcyclase, also induces VEGF transcription. These results imply that granulosa cells may be a source of VEGF which could play a role in the angiogenic process associated with ovulation and corpus luteum formation.

Key Words:

• growth factors
• angiogenesis
• TPA
• cAMP
• LH
• estrogens