The FOS transcription factor negatively regulates MAFF to control myometrial cell contractility

Abstract Inflammatory signaling in the human myometrium drives uterine activation and labor, yet its transcriptional regulation remains incompletely understood. We previously identified MAFF as an inflammation-inducible transcription factor in human myometrial cells. Here, we investigated whether FOS regulates MAFF expression and whether MAFF contributes to myometrial cell contractility. FOS knockdown increased MAFF mRNA approximately 1.5-fold under basal conditions and 1.7-fold following IL1B stimulation, accompanied by increased MAFF protein after 1 h of IL1B exposure. ChIP-qPCR demonstrated FOS occupancy in the MAFF promoter region, supporting a negative regulatory relationship. Functionally, CRISPR/Cas9-generated MAFF-deficient cells displayed approximately 15–25% lower basal contractility than wild-type cells. Contractile responses to IL1B varied among the MAFF-deficient clones, although they generally remained less contractile than wild-type cells. MAFF overexpression increased contraction in wildtype cells (by 7%) and two of three MAFF-deficient clones (by 4–8%). Conversely, FOS overexpression reduced contraction in wild-type cell (−6.7%) but had no significant effect in the MAFF-deficient clones. Together, these findings identify FOS as a negative regulator of MAFF expression and support a role for MAFF in modulating myometrial cell contractility.