TGF beta 1

Transforming growth factor beta 1 or TGF-β1 is a polypeptide member of the is_associated_with::transforming growth factor beta superfamily of is_associated_with::cytokines. It is a secreted protein that performs many cellular functions, including the control of is_associated_with::cell growth, is_associated_with::cell proliferation, is_associated_with::cell differentiation and is_associated_with::apoptosis. In humans, TGF-β1 is encoded by the TGFB1 is_associated_with::gene.

Function
TGF-β is a multifunctional set of peptides that controls proliferation, differentiation, and other functions in many cell types. TGF-β acts synergistically with TGFA in inducing transformation. It also acts as a negative is_associated_with::autocrine is_associated_with::growth factor. Dysregulation of TGF-β activation and signaling may result in is_associated_with::apoptosis. Many cells synthesize TGF-β and almost all of them have specific receptors for this peptide. TGF-β1, is_associated_with::TGF-β2, and is_associated_with::TGF-β3 all function through the same receptor signaling systems.

TGF-β1 was first identified in human is_associated_with::platelets as a protein with a molecular mass of 25 is_associated_with::kilodaltons with a potential role in is_associated_with::wound healing. It was later characterized as a large is_associated_with::protein precursor (containing 390 is_associated_with::amino acids) that was proteolytically processed to produce a mature peptide of 112 amino acids.

TGF-β1 plays an important role in controlling the is_associated_with::immune system, and shows different activities on different types of cell, or cells at different developmental stages. Most immune cells (or is_associated_with::leukocytes) secrete TGF-β1.

T cells
Some is_associated_with::T cells (e.g. is_associated_with::regulatory T cells) release TGF-β1 to inhibit the actions of other T cells. is_associated_with::Interleukin 1- and is_associated_with::interleukin 2-dependent proliferation of activated T cells, and the activation of quiescent is_associated_with::helper T cells and is_associated_with::cytotoxic T cells is prevented by the activity of TGF-β1. Similarly, TGF-β1 can inhibit the secretion and activity of many other is_associated_with::cytokines including interferon-γ, is_associated_with::tumor necrosis factor-alpha (TNF-α) and various is_associated_with::interleukins. It can also decrease the expression levels of cytokine receptors, such as the is_associated_with::IL-2 receptor to down-regulate the activity of immune cells. However, TGF-β1 can also increase the expression of certain cytokines in T cells and promote their proliferation, particularly if the cells are immature.

B cells
TGF-β1 has similar effects on is_associated_with::B cells that also vary according to the differentiation state of the cell. It inhibits proliferation and stimulates is_associated_with::apoptosis of B cells, and plays a role in controlling the expression of is_associated_with::antibody, is_associated_with::transferrin and is_associated_with::MHC class II proteins on immature and mature B cells.

Myeloid cells
The effects of TGF-β1 on is_associated_with::macrophages and is_associated_with::monocytes is predominantly suppressive; this cytokine can inhibit the proliferation of these cells and prevent their production of reactive oxygen (e.g. superoxide (O2&minus;)) and nitrogen (e.g. nitric oxide (NO)) intermediates. However, as with other cell types, TGF-β1 can also have the opposite effect on cells of myeloid origin. For example, TGF-β1 acts as a is_associated_with::chemoattractant, directing an immune response to some is_associated_with::pathogens; macrophages and monocytes respond to low levels of TGF-β1 in a chemotactic manner. Furthermore, the expression of monocytic cytokines (including is_associated_with::interleukin-1(IL-1)-alpha, IL-1-beta, and TNF-α), and phagocytic killing by macrophages can be increased by the action of TGF-β1.

Interactions
TGF beta 1 has been shown to interact with:


 * is_associated_with::Decorin,
 * is_associated_with::EIF3I
 * LTBP1,
 * is_associated_with::TGF beta receptor 1,  and
 * is_associated_with::YWHAE.