Unique recognition of activin and inhibin by polyclonal antibodies to inhibin subunits

Changes in extracellular activin A:follistatin ratio during differentiation of a mesenchymal progenitor cell line, ROB-C26 into osteoblasts and adipocytes

We investigated the effects of BMP-2 and dexamethasone (Dex) on follistatin (FS) and activin A expressions in a mesenchymal progenitor cell line, ROB-C26 (C26). C26 cells stimulated to differentiate into osteoblastic cells by blocking myogenic differentiation after BMP-2 treatment and into adipocytes with Dex treatment. Alkaline phosphatase (ALP) mRNA expression and its activity in the confluent C26 cells were dose- and time-dependently stimulated by BMP-2, but inhibited by Dex. The stimulatory effect on FS and activin A mRNA expressions by BMP-2 and Dex were dose-dependent. Cycloheximide pre-treatment indicated that FS and activin A expressions appear to be the direct target of BMP-2 and Dex signaling. BMP-2 time-dependently increased FS and activin A levels. Dex also increased FS level, but induced a time-dependent biphasic effect on activin A level, a decrease (2-6 h) followed by an increase (12-72 h). The data of the ratio of activin A concentration in the culture media to that of FS (activin A:FS ratio) measured by ELISA showed that BMP-2-induced osteoblastic differentiation involved an activin-dominant microenvironment, whereas Dex-induced adipocyte differentiation involved a FS-dominant microenvironment. Excess FS suppressed the stimulatory ALP activity of BMP-2, whereas activin A prevented not only Dex-induced inhibitory ALP activity, but also adipogenesis via suppression of the adipocyte transcriptional factor cascade. These results indicate that BMP-2-induced activin-dominant microenvironment may be critical for osteoblastic differentiation by restricting the antagonistic effects of FS on BMP activity, while Dex-induced FS-dominant microenvironment may be critical for adipocyte differentiation by restricting the inhibitory action of activin A on adipocyte differentiation.

Expression of tocopherol-associated protein in mast cells

Tocopherol-associated protein (TAP) was expressed in mouse mast cells. TAP was predominantly localized in the cytoplasm, and the subcellular localization was not changed by alpha-tocopherol. The results suggest that the physiological role of TAP in mast cells is not regulation of tocopherol function but an as-yet-unidentified activity.

Follistatin: a multifunctional regulatory protein

Follistatin was first described in 1987 as a follicle-stimulating hormone inhibiting substance present in ovarian follicular fluid. We now know that this effect of follistatin is only one of its many properties in a number of reproductive and nonreproductive systems. A majority of these functions are facilitated through the affinity of follistatin for activin, where activin's effects are neutralized through its binding to follistatin. As such, the interplay between follistatin and activin represents a powerful regulatory mechanism that impinges on a variety of cellular processes within the body. In this review we focus on the biochemical characteristics of follistatin and its interaction with activin and discuss the emerging role of these proteins as potent tissue regulators in the gonad, pituitary gland, pregnancy membranes, vasculature, and liver. Consideration is also given to the larger family of proteins that contain follistatin-like modules, in particular with regard to their functional and structural implications.