Inactivation of activin-dependent transcription by kinase-deficient activin receptors.

Activin, a member of the transforming growth factor-beta superfamily, binds to two classes of cell surface receptors. These receptors, designated type I and type II, are structurally related members of transmembrane serine kinase superfamily. Antibodies specific for either type I or type II activin receptor can coprecipitate complexes containing both affinity-labeled receptors from activin-responsive cells. Two type I receptors show cell-specific expression and associate with the ligand-binding, type II receptors. To investigate the roles of the cytoplasmic receptor domains in signaling through a heteromeric ligand receptor complex, we have made kinase-deficient activin receptors and correlated their losses in kinase activity with inhibitory effects on an activin-dependent transcriptional response in activin-responsive cell lines. Wild-type activin type II receptors phosphorylate activin type I receptors in transfected COS cells. In contrast, kinase-deficient activin type II receptors fail to phosphorylate type I receptors in transfected COS cells and act as dominant negative mutants to block activin-induced transcriptional activity in both Chinese hamster ovary and K562 (human erythroleukemia) cells. Kinase-deficient activin type IB receptors also block activin-induced transcriptional activity in both Chinese hamster ovary and K562 cells, whereas kinase-deficient activin type I receptors have no effect in either cell line. These results indicate that kinase activities of both type II and type I receptors are required for activin signaling, and that the two type I receptors, which are expressed in a tissue-specific manner, are functionally distinct.

Residues in the C-terminal region of activin A determine specificity for follistatin and type II receptor binding.

Activin is a secreted growth factor that signals by binding two related classes of single transmembrane receptors at the cell surface. The interaction of activin with its receptors is highly regulated by other cell surface receptors, antagonistic ligands, and high affinity extracellular binding proteins such as follistatin. Two activin A mutants, the deletion mutant des[85-109]-activin A and the point mutant K102E-activin A (K102E), were investigated with respect to their ability to bind cell surface receptors and the binding protein follistatin. The deletion mutant exhibits low affinity for both receptors and follistatin whereas the point mutant fails to bind cell surface receptors but binds follistatin-288 with high affinity. K102E is able to compete with wild type activin to bind to follistatin and can thus increase the concentration of activin available for receptor binding and signaling. These findings underline the importance of the C-terminal region of activin for binding interactions and show that different residues in this region are involved in cell surface receptor and follistatin interactions.

[Analysis of pregnancy course and delivery in girls below 19 years of age]. / Analiza przebiegu ciazy i sposobu ukonczenia porodu u dziewczat ponizej 19. roku zycia.

Courses of pregnancy and ways of delivery in 216 girls below 19 years of age, who delivered between 1991-1997 were analyzed. Control group consisted 216 women aged 22-28, who delivered in the same period. Among the women delivering below 19 years of age, complications of pregnancy appeared more rarely than in control group. In comparison to older patients the preterm delivery was more often in study group.

High-dose melphalan and autologous hematopoietic stem cell transplantation in primary amyloidosis: single-center results.

BACKGROUND: Systemic immunoglobulin light-chain amyloidosis (AL) is a plasma cell dyscrasia resulting in multisystem organ failure and death. Autologous hematopoietic stem-cell transplantation (ASCT) has been widely used to treat patients with AL. However, treatment-related mortality remains high and reported series are subject to selection bias. METHODS: To define the role of patient selection in stem cell transplantation, we evaluated 24 consecutive AL patients transplanted at our center. RESULTS: Complete hematologic response was achieved in all 20 patients surviving >100 days posttransplantation. The 1-year overall survival (OS) rate after ASCT was 78.5%. The 5- and 10-year progression-free and OS rates were 57% and 47%, respectively. Treatment-related deaths owing to cardiovascular problems occurred in 16% of cases. CONCLUSION: ASCT for AL amyloidosis can be safely performed in experienced transplantation centers, and increased risk is associated mainly with cardiovascular system involvement.

Betaglycan binds inhibin and can mediate functional antagonism of activin signalling.

Activins and inhibins, structurally related members of the TGF-beta superfamily of growth and differentiation factors, are mutually antagonistic regulators of reproductive and other functions. Activins bind specific type II receptor serine kinases (ActRII or IIB) to promote the recruitment and phosphorylation of the type I receptor serine kinase, ALK4 (refs 7-9), which then regulates gene expression by activating Smad proteins. Inhibins also bind type II activin receptors but do not recruit ALK4, providing a competitive model for the antagonism of activin by inhibin. Inhibins fail to antagonize activin in some tissues and cells, however, suggesting that additional components are required for inhibin action. Here we show that the type III TGF-beta receptor, betaglycan, can function as an inhibin co-receptor with ActRII. Betaglycan binds inhibin with high affinity and enhances binding in cells co-expressing ActRII and betaglycan. Inhibin also forms crosslinked complexes with both recombinant and endogenously expressed betaglycan and ActRII. Finally, betaglycan confers inhibin sensitivity to cell lines that otherwise respond poorly to this hormone. The ability of betaglycan to facilitate inhibin antagonism of activin provides a variation on the emerging roles of proteoglycans as co-receptors modulating ligand-receptor sensitivity, selectivity and function.