XBP1
Description
The XBP1 (X-box binding protein 1) is a protein-coding gene located on chromosome 22.
X-box binding protein 1, also known as XBP1, is a protein which in humans is encoded by the XBP1 gene. The XBP1 gene is located on chromosome 22 while a closely related pseudogene has been identified and localized to chromosome 5. The XBP1 protein is a transcription factor that regulates the expression of genes important to the proper functioning of the immune system and in the cellular stress response.
== Discovery == The X-box binding protein 1 (XBP1) is a transcription factor containing a bZIP domain. It was first identified by its ability to bind to the Xbox, a conserved transcriptional element in the promoter of the human leukocyte antigen (HLA) DR alpha.
== Function ==
=== MHC class II gene regulation === The expression of this protein is required for the transcription of a subset of class II major histocompatibility genes. Furthermore, XBP1 heterodimerizes with other bZIP transcription factors such as c-fos. XBP1 expression is controlled by the cytokine IL-4 and the antibody IGHM. XBP1 in turn controls the expression of IL-6 which promotes plasma cell growth and of immunoglobulins in B lymphocytes.
=== Plasma cell differentiation === XBP1 is also essential for differentiation of plasma cells (a type of antibody secreting immune cell). This differentiation requires not only the expression of XBP1 but the expression of the spliced isoform of XBP1s.
XBP1 acts as a transcription factor during endoplasmic reticulum (ER) stress, regulating the unfolded protein response (UPR). It is essential for cardiac and liver development during embryogenesis, as well as the development of secretory tissues like the pancreas and salivary glands. XBP1 is involved in the terminal differentiation of B lymphocytes into plasma cells, leading to immunoglobulin production. The protein modulates the cellular response to ER stress in a PIK3R-dependent manner. It binds to the X box in the promoter regions of major histocompatibility complex class II genes. XBP1 plays a role in VEGF-induced endothelial cell proliferation and retinal blood vessel formation during development, and is involved in angiogenesis in adult tissues under ischemic conditions. The protein also acts as a major regulator of the UPR in obesity-induced insulin resistance and type 2 diabetes, potentially aiding in obesity and diabetes prevention.
XBP1 is also known as TREB-5, TREB5, XBP-1, XBP2.
