T cells lacking immunoproteasome subunits MECL-1 and LMP7 hyperproliferate in response to polyclonal mitogens.
Immunoproteasomes comprise a specialized subset of proteasomes that is defined by the presence of three catalytic immunosubunits: LMP2, MECL-1 (LMP10), and LMP7. Proteasomes in general serve many cellular functions through protein degradation, whereas the specific function of immunoproteasomes has been thought to be largely, if not exclusively, optimization of MHC class I Ag processing. In this report, we demonstrate that T cells from double knockout mice lacking two of the immunosubunits, MECL-1 and LMP7, hyperproliferate in vitro in response to various polyclonal mitogens. We observe hyperproliferation of both CD4(+) and CD8(+) T cell subsets and demonstrate accelerated cell cycling. We do not observe hyperproliferation of T cells lacking only one of these subunits, and thus hyperproliferation is independent of either reduced MHC class I expression in LMP7(-/-) mice or reduced CD8(+) T cell numbers in MECL-1(-/-) mice. We observe both of these latter two phenotypes in MECL-1/LMP7(-/-) mice, which indicates that they also are independent of each other. Finally, we provide evidence of in vivo T cell dysfunction by demonstrating increased numbers of central memory phenotype CD8(+) T cells in MECL-1/LMP7(-/-) mice. In summary, this novel phenotype of hyperproliferation of T cells lacking both MECL-1 and LMP7 implicates a specific role for immunoproteasomes in T cell proliferation that is not obviously connected to MHC class I Ag processing.
William S. Rowe Division of Rheumatology, Cincinnati Children's Hospital Medical Center and University of Cincinnati College of Medicine, OH 45229, USA.
Christy M
CM
Caudill
Krupakar
K
Jayarapu
Laura
L
Elenich
John J
JJ
Monaco
Robert A
RA
Colbert
Thomas A
TA
Griffin
D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D007113:Immunity, Innate; D007156:Immunologic Memory; D008213:Lymphocyte Activation; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D018345:Mice, Knockout; D008934:Mitogens / Q000276:immunology* / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000276:immunology* / Q000378:metabolism*; D021122:Protein Subunits / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D013154:Spleen / Q000276:immunology / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism
D015395:Histocompatibility Antigens Class I; D008934:Mitogens; D009097:Multienzyme Complexes; D021122:Protein Subunits; D003546:Cysteine Endopeptidases; C077436:LMP7 protein; D046988:Proteasome Endopeptidase Complex; C490920:Psmb10 protein, mouse