Activin B is a TGF-beta superfamily cytokine that regulates cellular migration by inducing actin stress fiber formation. It signals through heterodimeric receptor complexes composed of type I (Activin RIA or RIB) and type II (Activin RIIA or RIIB) transmembrane Ser/Thr kinases. It also modulates signaling through E-Cadherin and Integrin beta 3. Activin B upregulation is associated with tumor cell adhesion, migration, and metastasis. It also promotes wound healing through increased cellular migration. Activin B additionally induces hair follicle formation and expression of Hepicin in the liver, but it inhibits lipolysis in adipocytes and glucose-stimulated calcium influx in pancreatic beta cells. Alterations of Activin B serum levels of Activin B are associated with ectopic pregnancy and chronic fatigue syndrome, and it is upregulated in alveolar epithelial cells in pulmonary fibrosis.
