Pathologies in activin A-responsive cells and a reduction in nuclear localization of Smad-2 with activin-Coverexpressionin vivoindicates antagonism of activin signaling also occursin vivo. hypertrophy and epithelial cell hyperplasia. Additionally, there was decreased evidence of nuclear Smad-2 localization in the testis, liver, and prostate, indicating that overexpression of activin-Cantagonized Smad signalingin vivo. Underlying the significance of these findings, human being testis, liver, and prostate cancers expressed improved activin-C immunoreactivity. This study provides evidence that activin-Cis (??)-BI-D an antagonist of activin A and supplies an impetus to examine its role in development and disease. During development, activin A is usually a mesoderm-inducing factor,1and different concentrations of activin are involved in (??)-BI-D establishing the body planin vivo.2In the adult, activin A is a potent regulator of cell division, differentiation, or death as exemplified in the testis, liver, and prostate.3,4,5,6,7Exposure of a cell to activin has profound consequences, and, as such, the synthesis and biological action of activin A must be tightly controlledin vivo.8,9 Activin bioactivity, or bioavailability, can be regulated in several ways including assembly of intracellular heterodimers (??)-BI-D such as inhibin A (A) that once secreted block activin binding to its receptors.10Follistatin-315 can bind to, and inactivate, activin A in the circulation, whereas cell surface-bound follistatin-288 diverts activin A to a lysosomal pathway for degradation.11 It is generally thought that the activin-Csubunit is not a significant regulator of activin bioactivity. This is because of limited expression of (??)-BI-D activin-CmRNA and a lack of abnormalities in activin-C-null mice.12However, in the context of the null mouse, there may be functional redundancy with other transforming growth factor- family members. If true, overexpression rather than underexpression is usually more likely to have physiological consequences. We propose that activin C is an antagonist of activin A bioactivity. To test our hypothesis, we produced recombinant activin C and several lines of mice overexpressing the human activin-Csubunit. Because activin A has tissue-specific patterns of expression and biological action, we examined tissues known to be responsive to activin A: testis, liver, and prostate.13,14,15In the testis, activin A is a paracrine regulator of Sertoli cell proliferation and spermatogonial maturation.5In the liver, activin A inhibits hepatocyte DNA synthesis7and induces apoptosis.6In the prostate, activin A is a negative growth regulator and involved in branching morphogenesis during development.3 Our results demonstrated activin C antagonized the effects of activin Ain vitro, and testis, liver, and prostate phenotypes consistent with our hypothesis were observedin vivo. Additionally, we show an increase in activin-Cimmunoreactivity in human malignancy tissue microarrays, thus demonstrating an analogous situation might occur in human pathology. == Materials and Methods == == Transgenic (TG) Mice == Human activin-C(under the control of a CMV promoter)-overexpressing mice were produced at Mouseworks, Department of Physiology, Monash University, by standard methods. Three impartial lines were established and crossed with wild-type (WT) C57BL/6 mice and heterozygous littermates to obtain single-heterozygous (SH) haploid, and double-heterozygous (DH) diploid, Rabbit polyclonal to ADAMTSL3 transgenes. Southern blot and semiquantitative polymerase chain reaction (PCR) were used to determine transgene copy number. SH1 had 2 to 5 copies of the transgene, SH2, 5 to 10 copies, and, SH3, 20 to 30 copies (data not shown). A competitive genomic PCR screening strategy with primers specific for the incorporated human activin-Cand endogenous mouse activin-Cwas used to identify SH- or DH-positive progeny and results were confirmed by breeding studies. == Tissue Collection == All animal handling and procedures were performed in accordance with (??)-BI-D National Health and Medical Research Council guidelines for the Care and Use of Laboratory Animal Act and according to the Animal Experimentation and Ethics Committee at Monash.