Post-translational regulation of IgM expression in B lymphocytes. Selective nonlysosomal degradation of assembled secretory IgM is temperature-dependent and occurs prior to the trans-Golgi.
B cells express on their surface the membrane form of IgM (mIgM). Upon differentiation, the resulting plasma cells synthesize and secrete large amounts of the secretory form of IgM (sIgM). Surprisingly, B lymphocytes synthesize an excess of secretory mu chain over the expressed membrane mu chain. However, the sIgM is degraded intracellularly, indicating regulation of IgM expression at the post-translational level. In the present report, we show that the assembly, maturation, and degradation of IgM in 38C B lymphocytes are highly accelerated above a certain threshold temperature. Furthermore, the degradation of sIgM is delayed and takes place by the time the maturation of mIgM in the trans-Golgi is almost completed. Neither chloroquine nor monensin has any effect on this degradation, demonstrating a nonlysosomal pre-trans-Golgi process. In addition, the degradation is of endoglycosidase H-sensitive assembled sIgM molecules. We conclude that the degradation of sIgM in 38C B lymphocytes is a postendoplasmic reticulum, pre-trans-Golgi process. We suggest that this degradation process plays a role in the post-translational regulation of expression of soluble lumenal sIgM.
Amitay
R
R
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Bar-Nun
S
S
Haimovich
J
J
Rabinovich
E
E
Shachar
I
I
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D015152:Blotting, Northern; D002738:Chloroquine / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D006056:Golgi Apparatus / Q000378:metabolism*; D006596:Hexosaminidases; D007075:Immunoglobulin M / Q000235:genetics*; D016393:Lymphoma, B-Cell / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D008985:Monensin / Q000494:pharmacology; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D012313:RNA / Q000032:analysis; D013696:Temperature; D014407:Tumor Cells, Cultured
D007075:Immunoglobulin M; C033027:secretory IgM; D012313:RNA; D002738:Chloroquine; D008985:Monensin; D006596:Hexosaminidases