The FOS/AP-1 regulates the expression of selective genes involved in ovulation and luteinization in human granulosa cells

FOS, a subunit of the activator protein-1 (AP-1) transcription factor, has been implicated in various cellular changes. In the human ovary, the expression of FOS and its heterodimeric binding partners JUN, JUNB, and JUND increases in periovulatory follicles. However, the specific role of the FOS/AP-1 remains elusive. The present study determined the regulatory mechanisms driving the expression of FOS and its partners and functions of the FOS/AP-1 using primary human granulosa/lutein cells (hGLC). hCG induced a biphasic increase in the expression of FOS, peaking at 1-3h and 12h. The levels of JUN proteins were also increased by hCG, with varying expression patterns. Co-immunoprecipitation analyses revealed that FOS is present as heterodimers with all JUN proteins. hCG immediately activated PKA and p42/44MAPK signaling pathways, and inhibitors for these pathways abolished hCG-induced increases in the levels of FOS, JUN, and JUNB. To identify the genes regulated by FOS, high throughput RNA sequencing was performed using hGLC treated with hCG ± T-5224 (FOS inhibitor). Sequencing data analysis revealed that FOS inhibition affects the expression of numerous genes, including a cluster of genes involved in the periovulatory process such as matrix remodeling, prostaglandin synthesis, glycolysis/gluconeogenesis, and cholesterol biosynthesis. qPCR analysis verified hCG-induced, T-5224-regulated expression of a selection of these genes. Consistently, T-5224 attenuated hCG-induced increases in metabolic activities and cholesterol levels. This study unveiled potential downstream target genes of and a role for the FOS/AP-1 in granulosa cell metabolic changes and cholesterol biosynthesis in human periovulatory follicles. Cultured human granulosa-lutein cells treated with hCG and hCG+T-5224 were used to perform RNA-seq analysis.