The family of beta growth factor transforming cytokines (TGF-beta) consists of more than 30 structurally related polypeptides, including TGF-beta, activins and bone morphogenetic proteins (BMP). This family regulates a wide range of biological functions, including cell proliferation, differentiation, apoptosis, migration and the production of extracellular matrix. Signaling by these cytokines occurs via binding to specific receptors with serine / threonine kinase activity and the activation of specific intracellular effectors downstream (the transcription factors Smad regulated by receptors). TGF-beta is a regulator of all stages of hematopoiesis. Depending on the stage of differentiation of the target cell, the local environment and the concentration of TGF-beta, TGF-beta can be positive or negative regulators of the proliferation, apoptosis or differentiation of hematopoietic cells. TGF-beta inhibits the growth of primitive hemopoietic cells with a stem cell immunophenotype but has no effect or in some cases stimulates the growth of committed progenitors. Persistent loss of TGF-beta signaling in hemopoietic stem cells and primary hemopoietic progenitor cells may possibly be involved in the development of malignant transformation.
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