Activin A protein is involved in regulating developmental genes such as cell cycle regulators like p21, p15, paired box protein (Pax-6) and hormones like follicle-stimulating hormone (FSH). This protein also regulates its antagonist like follistatin and mothers against decapentaplegic homolog 7 (SMAD7). Activin A protein binds to the type 1 receptor activin receptor type 1B (ActR1B) and type 2 receptor activin receptor 2A and 2B (ActRIIA and ActRIIB). Activin A gene is highly expressed in esophageal carcinoma, lung adenocarcinoma, and malignant pleural mesothelioma (MPM). This gene expression is decreased during breast cancer, neuroblastoma, and hepatocellular carcinoma (HCC). Activins bind to the type II Activin receptor triggering phosphorylation of type I Activin receptor (ALK4) and activation of downstream pathways such as proliferation and apoptosis. Activin acts as a tumor suppressor by reducing cell proliferation in cancer cells.
