title: Phosphorylation of the pro-apoptotic protein BIK: mapping of phosphorylation sites and effect on apoptosis.
abstract: BIK is a pro-apoptotic BCL-2 family member and is the founding member of a subfamily of pro-apoptotic proteins known as "BH3-alone" proteins. Ectopic expression of BIK induces apoptosis in variety of mammalian cells. BIK complexes with various anti-apoptotic BCL-2 family proteins such as adenovirus E1B-19K and BCL-2 via the BH3 domain. However, the heterodimerization activity of BIK alone is insufficient for its apoptotic activity. Previous studies have shown that phosphorylation regulates the functional activity of both anti-apoptotic and pro-apoptotic members of the BCL-2 family. Here, we have examined phosphorylation of BIK and its effect on the apoptotic activity of BIK. We show that BIK exists as a phosphoprotein and is phosphorylated at residues 33 (threonine) and 35 (serine). Mutation of the phosphorylation sites, in which the Thr and Ser residues were changed to alanine residues, reduced the apoptotic activity of BIK without significantly affecting its ability to heterodimerize with BCL-2. Our results suggest that phosphorylation of BIK is required for eliciting efficient apoptotic activity. Partial purification of the protein kinase from HeLa cell cytoplasmic extracts suggest that BIK may be phosphorylated by a casein kinase II-related enzyme.
authors.affiliation: Institute for Molecular Virology, St. Louis University Health Sciences Center, St. Louis, MO 63110, USA.
authors.forename: S
authors.initials: S
authors.lastname: Verma
authors.forename: L J
authors.initials: LJ
authors.lastname: Zhao
authors.forename: G
authors.initials: G
authors.lastname: Chinnadurai
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D047390:Casein Kinase II; D002460:Cell Line; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C096820:BIK protein, human; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D010750:Phosphoproteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D010769:Phosphothreonine; D010768:Phosphoserine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases