Activin betaC and betaE genes are not essential for mouse liver growth, differentiation, and regeneration

Activins and inhibins in endocrine and other tumors

Inhibin and activin are members of the TGF beta superfamily of growth and differentiation factors. They were first identified as gonadal-derived regulators of pituitary FSH and were subsequently assigned multiple actions in a wide range of tissues. More recently, the inhibin alpha subunit was considered as a tumor suppressor based on functional studies employing transgenic mouse models. This review evaluates the functional and molecular evidence that the inhibin alpha subunit is a tumor suppressor in endocrine cancers. The evaluation highlights the discrepant results from the human and mouse studies, as well as the differences between endocrine tumor types. In addition, we examine the evidence that the activin-signaling pathway is tumor suppressive and identify organ-specific differences in the actions and putative roles of this pathway in endocrine tumors. In summary, there is a considerable body of evidence to support the role of inhibins and activins in endocrine-related tumors. Future studies will define the mechanisms by which inhibins and activins contribute to the process of initiation, promotion, or progression of endocrine-related cancers.

The contribution of inhibins and activins to malignant prostate disease

The normal human prostate expresses inhibin and activin subunits. In prostate cancer, the inhibin alpha subunit gene is down regulated and this is associated with loss of heterozygosity (LOH) at the gene locus and methylation of the promoter. These data support the hypothesis that the inhibin alpha subunit is tumor suppressive in the prostate. The pluripotent effects of activins and the similarities to transforming growth factor beta (TFGbeta) suggest a role for activins in progression to malignancy, whereby, the normal growth inhibitory action of activin A observed on benign cells is lost with the acquisition of activin resistance in prostate cancer cells. The mechanisms of rendering tumor cells resistant to activin A may include: alteration in activin binding protein (follistatin) synthesis and/or dimerisation with activin beta(C) to form novel activin dimers. The contribution of the activin signalling cascade to malignancy requires further evaluation to identify the synergies and differences to other members of the TGFbeta superfamily.

Studying TGF-beta superfamily signaling by knockouts and knockins

The transforming growth factor beta (TGF-beta) superfamily has profound effects on many aspects of animal development. In the last decade, our laboratory and others have performed in vivo functional studies on multiple components of the TGF-beta superfamily signal transduction pathway, including upstream ligands, transmembrane receptors, receptor-associated proteins and downstream Smad proteins. We have taken gene knockout approaches to generate null alleles of the genes of interest, as well as a gene knockin approach to replace the mature region of one TGF-beta superfamily ligand with another. We found that activin betaB, expressed in the spatiotemporal pattern of activin betaA, can function as a hypomorphic allele of activin betaA and rescue the craniofacial defects and neonatal lethal phenotype of activin betaA-deficient mice. With the knockout approach, we have shown that the expression pattern of a component in the TGF-beta superfamily signal transduction cascade does not necessarily predict its in vivo function. Two liver-specific activins, activin betaC and activin betaE are dispensable for liver development, regeneration and function, whereas ubiquitously expressed Smad5 has specific roles in the development of multiple embryonic and extraembryonic tissues.

Enzyme immunoassays for inhibins, activins and follistatins

In this short review, the authors summarise the inhibin, activin and follistatin assays developed by the Oxford group and collaborators, and some of the main purposes for which they have been applied. Over 500 research publications have used these assays. We also discuss new assays recently developed at the request of our collaborators for particular applications, and comment on outstanding assay problems.

Divergence and convergence of TGF-beta/BMP signaling

The transforming growth factor-beta (TGF-beta) superfamily includes more than 30 members which have a broad array of biological activities. TGF-beta superfamily ligands bind to type II and type I serine/threonine kinase receptors and transduce signals via Smad proteins. Receptor-regulated Smads (R-Smads) can be classified into two subclasses, i.e. those activated by activin and TGF-beta signaling pathways (AR-Smads), and those activated by bone morphogenetic protein (BMP) pathways (BR-Smads). The numbers of type II and type I receptors and Smad proteins are limited. Thus, signaling of the TGF-beta superfamily converges at the receptor and Smad levels. In the intracellular signaling pathways, Smads interact with various partner proteins and thereby exhibit a wide variety of biological activities. Moreover, signaling by Smads is modulated by various other signaling pathways allowing TGF-beta superfamily ligands to elicit diverse effects on target cells. Perturbations of the TGF-beta/BMP signaling pathways result in various clinical disorders including cancers, vascular diseases, and bone disorders.

Genes highly expressed in the early phase of murine graft-versus-host reaction

Graft-versus-host reaction (GVHR) is a complex process initiated upon allorecognition. For detection of early molecular events in GVHR, we first assessed time courses with respect to symptoms and serum interferon (IFN)-gamma levels and then used the differential display method to compare gene transcript patterns during the early phase between acute lethal GVHR mice and syngeneic controls. In the GVHR mice, high expression levels of seven genes encoding the following molecules were detected: TGTP/Mg21 (an IFN-gamma-related signaling molecule), vitronectin, Nedd5 (a mammalian septin), manganese superoxide dismutase, activin betaC subunit, PRCC (a papillary renal cell carcinoma-associated molecule), and an uncharacterized gene corresponding to a mouse expressed sequence tag (EST). The expression levels of most genes peaked before the symptomatological onset and the peak of IFN-gamma levels. Thus, gene expression monitoring may characterize the inductive process of GVHR and aid in the development of gene-based diagnostics and therapies.