BackgroundActivins are members of the TGF-β family of ligands that have multiple biological functions in embryonic stem cells as well as in differentiated tissue. Serum levels of activin A were found to be elevated in pathological conditions such as cachexia, osteoporosis and cancer. Signaling by activin A through canonical ALK4-ACVR2 receptor complexes activates the transcription factors SMAD2 and SMAD3. Activin A has a strong affinity to type 2 receptors, a feature that they share with some of the bone morphogenetic proteins (BMPs). Activin A is also elevated in myeloma patients with advanced disease and is involved in myeloma bone disease.ResultsIn this study we investigated effects of activin A binding to receptors that are shared with BMPs using myeloma cell lines with well-characterized BMP-receptor expression and responses. Activin A antagonized BMP-6 and BMP-9, but not BMP-2 and BMP-4. Activin A was able to counteract BMPs that signal through the type 2 receptors ACVR2A and ACVR2B in combination with ALK2, but not BMPs that signal through BMPR2 in combination with ALK3 and ALK6.ConclusionsWe propose that one important way that activin A regulates cell behavior is by antagonizing BMP-ACVR2A/ACVR2B/ALK2 signaling.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-015-0104-z) contains supplementary material, which is available to authorized users.

Cancer patients are often encouraged to receive seasonal influenza vaccination. The monoclonal antibody rituximab is widely used in treatment of non-Hodgkin lymphoma. This results in a prolonged depletion of normal B cells, which might impair humoral responses. The aim of the present study was to investigate whether lymphoma patients undergoing rituximab-containing treatment regimens or having received such regimens within the past 6 months were able to mount protective antibody responses to the influenza A(H1N1) 2009 virus vaccine Pandemrix during the 2009 “swine flu” pandemic. Contrary to the control group, where 82% responded adequately to the vaccine, none of the 67 patients achieved protective antibody titers, suggesting that lymphoma patients receiving rituximab-containing regimens might not benefit from this vaccine. It is important that doctors who care for such patients are aware that they may fail to respond not only to the influenza vaccine, but also to other common vaccines.

Janssen and Celgene.

Multiple myeloma is a malignancy of plasma cells predominantly located in the bone marrow. A number of bone morphogenetic proteins (BMPs) induce apoptosis in myeloma cells in vitro, and with this study we add BMP-9 to the list. BMP-9 has been found in human serum at concentrations that inhibit cancer cell growth in vitro. We here show that the level of BMP-9 in serum was elevated in myeloma patients (median 176 pg/ml, range 8–809) compared with healthy controls (median 110 pg/ml, range 8–359). BMP-9 was also present in the bone marrow and was able to induce apoptosis in 4 out of 11 primary myeloma cell samples by signaling through ALK2. BMP-9-induced apoptosis in myeloma cells was associated with c-MYC downregulation. The effects of BMP-9 were counteracted by membrane-bound (CD105) or soluble endoglin present in the bone marrow microenvironment, suggesting a mechanism for how myeloma cells can evade the tumor suppressing activity of BMP-9 in multiple myeloma.