title: A novel Bcl-x splice product, Bcl-xAK, triggers apoptosis in human melanoma cells without BH3 domain.
abstract: Pro- and antiapoptotic proteins of the large Bcl-2 family are critical regulators of apoptosis via the mitochondrial pathway. Whereas antiapoptotic proteins of the family share all four Bcl-2 homology domains (BH1-BH4), proapoptotic members may lack some of these domains, but all so far described proapoptotic Bcl-2 proteins enclose BH3. The bcl-x gene gives rise to several alternative splice products resulting in proteins with distinct functions as the antiapoptotic Bcl-xL and proapoptotic Bcl-xS. Here, we describe a novel Bcl-x splice product of 138 amino acids termed Bcl-xAK (Atypical Killer), which encloses the Bcl-2 homology domains BH2 and BH4 as well as the transmembrane domain, but lacks BH1 and BH3. Weak endogenous expression of Bcl-xAK was seen in melanoma and other tumor cells. Interestingly, its overexpression by applying a tetracycline-inducible expression system resulted in significant induction of apoptosis in melanoma cells, which occurred in synergism with drug-induced apoptosis. After exogenous overexpression, Bcl-xAK was localized both in mitochondrial and in cytosolic cell fractions. By these findings, a completely new class of Bcl-2-related proteins is introduced, which promotes apoptosis independently from the BH3 domain and implies additional, new mechanisms for apoptosis regulation in melanoma cells.
authors.affiliation: Department of Dermatology and Allergy, Skin cancer center, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin 12203, Germany.
authors.forename: A M
authors.initials: AM
authors.lastname: Hossini
authors.forename: C C
authors.initials: CC
authors.lastname: Geilen
authors.forename: L F
authors.initials: LF
authors.lastname: Fecker
authors.forename: P T
authors.initials: PT
authors.lastname: Daniel
authors.forename: J
authors.initials: J
authors.lastname: Eberle
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D004318:Doxycycline / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008545:Melanoma / Q000473:pathology*; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012878:Skin Neoplasms / Q000473:pathology*; D013347:Subcellular Fractions; D051020:bcl-X Protein / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D012333:RNA, Messenger; D051020:bcl-X Protein; D004318:Doxycycline