View source for Activin

{{Protein
   |Name=inhibin, beta A (activin A, activin AB alpha polypeptide)
   |image=2ARV.png
   |caption=The Activin dimer, from 2ARV.pdb
   |Symbol=INHBA 
   |AltSymbols=
   |HGNCid=6066
   |Chromosome=7
   |Arm=p
   |Band=
   |LocusSupplementaryData=15-p13
   |ECnumber=
   |OMIM=147290
   |EntrezGene=3624
   |RefSeq=NM_002192
   |UniProt=P08476
   |PDB=
}}
{{Protein
   |Name=inhibin, beta B (activin B, activin AB beta polypeptide)
   |image=
   |caption=
   |Symbol=INHBB 
   |AltSymbols=
   |HGNCid=6067
   |Chromosome=2
   |Arm=
   |Band=
   |LocusSupplementaryData=cen-q13
   |ECnumber=
   |OMIM=147390
   |EntrezGene=3625
   |RefSeq=NM_002193
   |UniProt=P09529
   |PDB=
}}
{{SI}}
{{GS}}



==Overview==
'''Activin''' is a peptide that enhances [[FSH]] [[synthesis]] and [[secretion]] and participates in the regulation of the [[menstrual cycle]]. It does the opposite as [[inhibin]]. Many other functions have been found to be exerted by activin, including their roles in cell proliferation, [[differentiation]], [[apoptosis]]<ref>Chen YG, Wang Q, Lin SL, Chang CD, Chung J, and Ying SY.  Activin Signaling and its Role in Regulation of Cell Proliferation, Apoptosis and Carcinogenesis.  Exp Biol Med. 2006; 231: 534-544.  </ref>, [[metabolism]], [[homeostasis]], [[immune response]], [[wound repair]]<ref>Sulyok S, 20 M, Alzheimer C, Werner S.  Activin: an important regulator of wound repair, fibrosis, and neuroprotection.  Molecular and Cellular Endocrinology.  2005; 225: 126-132.</ref>, and [[endocrine]] function

Like inhibin (and  [[Anti-müllerian hormone|AMH]]) activin belongs to [[Transforming growth factor beta|TGF-β]] superfamily.  

==Structure==
Activin contains two beta subunit that are identical to the two beta subunits (A or B) of inhibin, allowing for the formation of three forms of activin: A, AB, and B.

They 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.<ref>Bamberger C, Schärer A, Antsiferova M, Tychsen B, Pankow S, Müller M, Rülicke T, Paus R, and Werner S.  Activin Controls Skin Morphogenesis and Wound Repair Predominantly via Stromal Cells and in a Concentration-Dependent Manner via Keratinocytes.  American Journal of Pathology.  2005; 167 (3): 733-741. </ref> 

* 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 [[fibroblast]]s.

==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==
<references/>

==External links==
* {{eMedicineDictionary|Activin}}
* {{MeshName|Activin}}

{{Template:TGF beta signaling}}
{{Glycoproteins}}
{{Hormones}}

[[Category:Reproductive system]]
[[Category:Hormones of the ovary]]
[[Category:Peptide hormones]]
[[Category:TGFβ domain]]
[[Category:Endocrinology]]

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[[ja:アクチビン]]