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Activin is a peptide that enhances FSH synthesis and secretion and participates in the regulation of the menstrual cycle. It performs the opposite function from inhibin. Many other functions have been found to be exerted by activin, including their roles in cell proliferation, differentiation, apoptosis,1 metabolism, homeostasis, immune response, wound repair,2 and endocrine function.
Like inhibin (and AMH), activin belongs to the TGF-β superfamily.
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Structure
Activins are formed by the homo- or heterodimerization of activin beta subunits. In mammals, four subunits have been described called activin beta A, activin beta B, activin beta C and activin beta E. Activin beta A and beta B are identical to the two beta subunits of inhibin. A fifth subunits, activin beta D has been described in Xenopus laevis. Two activin beta A subunits give rise to activin A, one beta A and one beta B subunit gives rise to activin AB and so on. Various, but not all theoretically possible, heterodimers have been described.34 The subunits are linked by a single covalent disulfide bond.
Function
Activin is produced in the gonads, pituitary gland, placenta and other organs:
- In the ovarian follicle, activin increases FSH binding and FSH induced aromatization. It participates in androgen synthesis enhancing LH action in the ovary and testis. In the male, activin enhances spermatogenesis.
- Activin is strongly expressed in wounded skin, and overexpression of activin in epidermis of transgenic mice improves wound healing and enhances scar formation. Its action in wound repair and skin morphogenesis is through stimulation of keratinocytes and stromal cells in a dose-dependent manner.5
- Activin also regulates the morphogenesis of branching organs such as the prostate, lung, and especially kidney. Activin A increased the expression level of type-I collagen suggesting that activtin A acts as a potent activator of fibroblasts.
Mechanism
As with other members of the superfamily, activins interact with two types of cell surface transmembrane receptors (Types I and II) which have intrinsic serine/threonine kinase activities in their cytoplasmic domains.
Activin binds to the Type II receptor and initiates a cascade reaction that leads to the recruitment, phosphorylation, and activation of Type I activin receptor. This then interacts with and then phosphorylates SMAD2 and SMAD3, two of the cytoplasmic SMAD proteins.
Smad3 then translocates to the nucleus and interacts with SMAD4 through multimerization, resulting in their modulation as transcription factor complexes responsible for the expression of a large variety of genes.
References
- ^ Chen YG, Wang Q, Lin SL, Chang CD, Chuang J, Chung J, Ying SY (May 2006). "Activin signaling and its role in regulation of cell proliferation, apoptosis, and carcinogenesis". Exp. Biol. Med. (Maywood) 231 (5): 534–44. PMID 16636301. http://www.ebmonline.org/cgi/pmidlookup?view=long&pmid=16636301.
- ^ Sulyok S, Wankell M, Alzheimer C, Werner S (October 2004). "Activin: an important regulator of wound repair, fibrosis, and neuroprotection". Mol. Cell. Endocrinol. 225 (1-2): 127–32. doi:. PMID 15451577.
- ^ Xu P, Hall AK (November 2006). "The role of activin in neuropeptide induction and pain sensation". Dev. Biol. 299 (2): 303–9. doi:. PMID 16973148.
- ^ Deli A, Kreidl E, Santifaller S, Trotter B, Seir K, Berger W, Schulte-Hermann R, Rodgarkia-Dara C, Grusch M (March 2008). "Activins and activin antagonists in hepatocellular carcinoma". World J. Gastroenterol. 14 (11): 1699–709. PMID 18350601. http://www.wjgnet.com/1007-9327/14/1699.asp.
- ^ Bamberger C, Schärer A, Antsiferova M, Tychsen B, Pankow S, Müller M, Rülicke T, Paus R, Werner S (September 2005). "Activin controls skin morphogenesis and wound repair predominantly via stromal cells and in a concentration-dependent manner via keratinocytes". Am. J. Pathol. 167 (3): 733–47. PMID 16127153. PMC: 1698729. http://ajp.amjpathol.org/cgi/pmidlookup?view=long&pmid=16127153.
External links
- Activin at eMedicine Dictionary
- MeSH Activin
- Grusch M, Kreidl E (2008-08-01). "Activin and follistatin in liver biology and hepatocellular carcinoma". SciTopics. Elsevier. http://www.scitopics.com/Activin_and_follistatin_in_liver_biology_and_hepatocellular_carcinoma.html. Retrieved on 2008-12-24.
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Wikipedia content modification information:
- This page was last modified on 24 December 2008, at 19:07.
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