Expression and transcriptional regulation of functionally distinct Bmf isoforms in B-chronic lymphocytic leukemia cells.
Bmf is a BH3-only Bcl-2 family member that is normally sequestered to myosin V motors by binding to the dynein light chain 2 (DLC2). Certain damage signals release Bmf, which then binds prosurvival Bcl-2 proteins and triggers apoptosis. Here, two novel isoforms of human Bmf, Bmf-II and Bmf-III, were identified and cloned from cDNA derived from B-chronic lymphocytic leukemia (B-CLL) cells. Bmf-II and Bmf-III were characterized as two splice variants, lacking the BH3 domain but retaining the DLC2 binding domain. Bmf (here called Bmf-I) expression in HeLa cells induced apoptosis and reduced colony formation in contrast to Bmf-II and Bmf-III, which had no effect on apoptosis and instead increased colony formation. While bmf-I mRNA was expressed in many cell types, expression was higher in B lymphoid cells and bmf-II and bmf-III were mainly detected in B-CLL and normal B cells. bmf-I mRNA was upregulated in normal and leukemic B cells, while bmf-III mRNA was downregulated only in B-CLL cells by serum deprivation. We show that Bmf is regulated by transcriptional activation and alternative splicing and conclude that the relative levels of Bmf isoforms may have a role in regulating growth and survival in B cells and leukemic B-CLL cells.
Morales
A A
AA
Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden.
Olsson
A
A
Celsing
F
F
Osterborg
A
A
Jondal
M
M
Osorio
L M
LM
D048868:Adaptor Proteins, Signal Transducing; D017398:Alternative Splicing; D017209:Apoptosis; D001402:B-Lymphocytes / Q000378:metabolism; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; C486655:BMF protein, human; D002352:Carrier Proteins; D016895:Culture Media, Serum-Free; D018076:DNA, Complementary; D020033:Protein Isoforms; D012333:RNA, Messenger