Bcl-2
Bcl-2, encoded in humans by the BCL2 gene, is the founding member of the Bcl-2 family of regulator proteins. BCL2 blocks programmed cell death (apoptosis) [5] while BCL2 family member can either inhibit or induce it.[6][7] It was the first apoptosis regulator identified in any organism.[8]
Bcl-2 derives its name from B-cell lymphoma 2, as it is the second member of a range of proteins initially described in chromosomal translocations involving chromosomes 14 and 18 in follicular lymphomas. Orthologs[9] (such as Bcl2 in mice) have been identified in numerous mammals for which complete genome data are available.
Like BCL3, BCL5, BCL6, BCL7A, BCL9, and BCL10, it has clinical significance in lymphoma.
Isoforms[edit]
The two isoforms of Bcl-2, Isoform 1, and Isoform 2, exhibit a similar fold. However, results in the ability of these isoforms to bind to the BAD and BAK proteins, as well as in the structural topology and electrostatic potential of the binding groove, suggest differences in antiapoptotic activity for the two isoforms.[10]
Function[edit]
BCL-2 is localized to the outer membrane of mitochondria, where it plays an important role in promoting cellular survival and inhibiting the actions of pro-apoptotic proteins. The pro-apoptotic proteins in the BCL-2 family, including Bax and Bak, normally act on the mitochondrial membrane to promote permeabilization and release of cytochrome c and ROS, that are important signals in the apoptosis cascade. These pro-apoptotic proteins are in turn activated by BH3-only proteins, and are inhibited by the function of BCL-2 and its relative BCL-Xl.[11]
There are additional non-canonical roles of BCL-2 that are being explored. BCL-2 is known to regulate mitochondrial dynamics, and is involved in the regulation of mitochondrial fusion and fission. Additionally, in pancreatic beta-cells, BCL-2 and BCL-Xl are known to be involved in controlling metabolic activity and insulin secretion, with inhibition of BCL-2/Xl showing increasing metabolic activity,[12] but also additional ROS production; this suggests it has a protective metabolic effect in conditions of high demand.[13]
Diagnostic use[edit]
Antibodies to Bcl-2 can be used with immunohistochemistry to identify cells containing the antigen. In healthy tissue, these antibodies react with B-cells in the mantle zone, as well as some T-cells. However, positive cells increase considerably in follicular lymphoma, as well as many other forms of cancer. In some cases, the presence or absence of Bcl-2 staining in biopsies may be significant for the patient's prognosis or likelihood of relapse.[20]