The major isoforms of Bim contribute to distinct biological activities that govern the processes of autophagy and apoptosis in interleukin-7 dependent lymphocytes.
Bim is a BH3-only member of the Bcl-2 family that enables the death of T-cells. Partial rescue of cytokine-deprived T-cells occurs when Bim and the receptor for the T-cell growth factor, interleukin-7, are deleted, implicating Bim as a possible target of interleukin-7-mediated signaling. Alternative splicing yields three major isoforms: BimEL, BimL and BimS. To study the effect of Bim deficiency and define the function of the major isoforms, Bim-containing and Bim-deficient T-cells, dependent on interleukin-7 for growth, were used. Loss of total Bim in interleukin-7-deprived T-cells resulted in delayed apoptosis. However, loss of Bim also impeded the later degradative phase of autophagy. p62, an autophagy-adaptor protein which is normally degraded, accumulated in Bim deficient cells. To explain this, BimL was found to support acidification of lysosomes that later may associate with autophagic vesicles. Key findings showed that inhibition of lysosomal acidification accelerated death upon interleukin-7 withdrawal only in Bim-containing T-cells. intereukin-7 dependent T-cells lacking Bim were less sensitive to inhibition of lysosomal acidification. BimL co-immunoprecipitated with dynein and Lamp1-containing vesicles, indicating BimL could be an adaptor for dynein to facilitate loading of lysosomes. In Bim deficient T-cells, lysosome-tracking probes revealed vesicles of less acidic pH. Over-expression of BimL restored acidic vesicles in Bim deficient T-cells, while other isoforms, BimEL and BimS, promoted intrinsic cell death. These results reveal a novel role for BimL in lysosomal positioning that may be required for the formation of degradative autolysosomes.
Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, USA.
Shannon M
SM
Ruppert
Wenqing
W
Li
Ge
G
Zhang
Adina L
AL
Carlson
Arati
A
Limaye
Scott K
SK
Durum
Annette R
AR
Khaled
D000143:Acids / Q000378:metabolism; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000172:deficiency / Q000378:metabolism*; D001343:Autophagy / Q000187:drug effects; D000072224:Bcl-2-Like Protein 11; D049109:Cell Proliferation / Q000187:drug effects; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D019610:Cytoprotection / Q000187:drug effects; D004398:Dyneins / Q000378:metabolism; D015851:Interleukin-7 / Q000378:metabolism* / Q000494:pharmacology; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008214:Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000172:deficiency / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D020033:Protein Isoforms / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D000143:Acids; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D015851:Interleukin-7; D008565:Membrane Proteins; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D051028:bcl-2-Associated X Protein; C025946:3-methyladenine; D004398:Dyneins; D000225:Adenine