Cloning and molecular characterization of mouse bcl-x in B and T lymphocytes.
We report the cloning and initial characterization of the mouse homologues of the bcl-2-related gene, bcl-x. We compare these to the two major isoforms of human bcl-x that were previously identified, bcl-xLong (bcl-xL) which has death repressor activity similar to bcl-2, and bcl-xShort (bcl-xS), an alternative mRNA splice product that deletes a highly conserved domain shared by bcl-2 family members and promotes cell death in transfection studies. In addition to murine (m) bcl-xL and mbcl-xS, we have cloned a novel cDNA isoform that we designate mbcl-x delta TM. This cDNA deletes, by means of alternative splicing, the carboxy terminal transmembrane domain of bcl-x and is predicted to be a soluble, rather than membrane-bound, protein. We found that mbcl-x mRNA is highly inducible in splenocytes stimulated with either anti-CD3 Abs or LPS/dextran sulfate, and that the major species of mbcl-x mRNA in a variety of cell lines and tissues was the xL isoform. Transfection of mbcl-xL or mbcl-xS into Hela cells resulted in targeting primarily to mitochondria, whereas mbcl-x delta TM localized diffusely throughout the cytosol. Overexpression of the novel delta TM isoform in an IL-3-dependent cell line delayed the onset of apoptosis induced by growth factor withdrawal. Thus, a naturally-occurring form of mbcl-x present in lymphocytes that does not localize to the mitochondrial membrane is functional in preventing apoptotic cell death. Moreover, these data suggest that bcl-x provides a life signal in activated lymphocytes.
Fang
W
W
Department of Medicine/Rheumatology, University of Minnesota, Minneapolis 55455.
Rivard
J J
JJ
Mueller
D L
DL
Behrens
T W
TW
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D013154:Spleen / Q000166:cytology; D014162:Transfection; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051020:bcl-X Protein