Activin Receptor Type IIB antibody

Activin, a disulfide-linked homodimeric protein is secreted by Sertolicells in the testis and granulosa cells in the ovary. In early studies, this peptide was thought to be an inhibin and not recognized as a unique compound. Activins and inhibins are members of the TGF-beta superfamily due to amino acid homology with respect to the conservation of 7 of the 9 cysteine residues common to all TGF-beta forms. Activins are homodimers or heterodimers of the various beta subunit isoforms, while inhibins are heterodimers of a unique alpha subunit and one of the various beta subunits. Five beta subunits have been cloned (mammalian beta A, beta B, beta C, beta E, and Xenopus beta D). The activin/inhibin nomenclature reflects the subunit composition of the proteins: activin A (beta A-beta A), activin B (beta B-beta B), activin AB (beta B-beta A), inhibin A (alpha-beta A) abd inhibin B (alpha-beta B). Activins have a wide range of biological activities including mesoderm induction neural cell differentiation, bone remodeling, hematopoiesis, and reproductive physiology. Activins are also involved in growth and differentiation of several tissues from different species. This protein also plays a key role in the production and regulation of hormones such as FSH, LH, GnRH, and ACTH. Activin influences erythropoiesis and the potentiation of erythroid colony formation, oxytocin secretion, paracrine, and autocrine regulation. Similar to other TGF-beta family members, activins exert their biological activities through the effects of the heterodimeric complex composed of two membrane spanning serine-threonine kinases designated type I and type II receptors. Activin type I and type II receptors are distinguished by the level of sequence homology of their kinase domains and other structural and functional features. To date, seven type I and five type II activin receptors have been cloned from mammals, including activin receptor IA, activin receptor IIA, activin receptor IB, and activin receptor IIB. In addition, two splice variants of activin receptor IIA and five splice variants of activin receptor IIB have been reported. Type I activin receptors do not bind directly to activin but will associate with the type II receptor-activin complex and initiate signal transduction. Recombinant soluble activin type II receptors bind activin with high affinity and are potent activin antagonists. Activin type II receptors are highly conserved and will also bind inhibin, BMP2, and BMP7 with lower affinities. Human, mouse, and rat type II activin receptors share 98 % homology.