Activin and inhibin are closely related protein complexes that have almost directly opposite biological effects.
Activin is a dimer composed of two identical or very similar beta subunits.
Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle.
Activin functions include roles in cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine function.
Activin, inhibin belong to the TGF-β protein superfamily.
The activin and inhibin protein complexes both dimeric in structure.
The two monomers in a to in and inhibit are linked to one another by a single disulfide bond.
The alpha and beta subunits share approximately 25% sequence similarity, whereas the similarity between beta subunits is approximately 65%.
Activin is a dimer composed of two identical or very similar beta subunits.
Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle.
Activin functions include roles in cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine function.
Activins interact with two types of cell surface transmembrane receptors (Types I and II).
These transmembrane have intrinsic serine/threonine kinase activities in their cytoplasmic domains.
Activin binds to the Type II receptor and initiates a reactions that lead to the recruitment, phosphorylation, and activation of Type I activin receptor.
Activation of type I interacts with and then phosphorylates cytoplasmic proteins modulating as transcription factor complexes responsible for the expression of a large variety of genes.
Inhibits function may involve competing with activin for binding to activin receptors and/or binding to inhibin-specific receptors.
Activin A is at higher levels in adipose tissue of obese, compared to lean persons, and promotes the proliferation of adipocyte progenitor cells, while inhibiting their differentiation into adipocytes.
Activin A increases inflammatory cytokines in macrophages.
The gene for the activin receptor ACVR1 that undergoes mutation results in fibrodysplasia ossificans progressiva.
Fibrodysplasia ossificans progressiva is a fatal illness that causes muscle and soft tissue to gradually be replaced by bone tissue.
The mutation in ACVR1 causes
Activin A normally acts as an antagonist of the receptor and blocks osteogenesis.
A mutation in ACVR1 causes it to behave as an agonist of the receptor and to induce hyperactive bone growth.
Mutations in the ACVR1 gene have also been linked to cancers, especially diffuse intrinsic pontine glioma.
Elevated Activin B levels with normal Activin A levels provided a biomarker for myalgic encephalomyelitis/chronic fatigue syndrome.
The measurement of inhibin A is part of the prenatal quad screen that can be administered during pregnancy at a gestational age of 16–18 weeks.