Activin signaling pathway

The **activin signaling pathway** is a cellular communication system involving dimeric protein ligands called *activins* that bind to specific cell surface serine/threonine kinase receptors—primarily the *type II* receptors (**ACVR2A**, **ACVR2B**) which then recruit and phosphorylate *type I* receptors (**ACVR1B**, also known as ALK4; **ACVR1C**, ALK7). This triggers intracellular phosphorylation cascades activating SMAD transcription factors (*SMAD 2/3*, then complexing with *SMAD 4*) that regulate gene expression involved in diverse biological processes such as cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response modulation, wound repair, endocrine function—and notably muscle mass regulation. Dysregulation of this pathway has been implicated in cancer progression/metastasis/immunosuppression; metabolic diseases including obesity; sarcopenia/muscle wasting; fibrosis; neurological disorders; and inflammatory conditions. Therapeutic targeting focuses on blocking ligand-receptor interactions using monoclonal antibodies against either the ligands (*Activins*, *GDF8/myostatin*) or their primary receptors (*ActRIIA/B*), aiming for benefits such as increased muscle mass or reduced tumor progression. However, because the activin/TGF-beta superfamily regulates many essential physiological functions across tissues—including reproductive hormone control—therapeutic intervention carries risks related to systemic side effects.

Other names

Activin signalingTGF-beta/activin pathwayActivin receptor signalingACVR signaling

Antagonism/blockade of activin receptors to inhibit downstream SMAD-mediated gene transcription and prevent muscle atrophy/promote muscle growth.\nInhibition of ligand-receptor binding for metabolic/fibrotic/cancer indications.