Proteasome (prosome) subunit variations during the differentiation of myeloid U937 cells.
20S proteasomes (prosomes/multicatalytic proteinase) are protein particles built of 28 subunits in variable composition. We studied the changes in proteasome subunit composition during the differentiation of U937 cells induced by phorbol-myristate-acetate or retinoic acid plus 1,25-dihydroxy-cholecalciferol by western blot, flow cytometry and immuno-fluoresence. p25K (C3), p27K (IOTA) and p30/33K (C2) subunits were detected in both the nucleus and cytoplasm of undifferentiated cells. Flow cytometry demonstrated a biphasic decrease in proteasome subunits detection during differentiation induced by RA + VD. PMA caused an early transient decrease in these subunits followed by a return to their control level, except for p30/33K, which remained low. Immuno-fluorescence also showed differences in the cytolocalization of the subunits, with a particular decrease in antigen labeling in the nucleus of RA + VD-induced cells, and a scattering in the cytoplasm and a reorganization in the nucleus of PMA-induced cells. Small amounts of proteasomal proteins were seen on the outer membrane of non-induced cells; these membrane proteins disappeared when treated with RA + VD, whereas some increased on PMA-induced cells. The differential changes in the distribution and type of proteasomes in RA + VD and PMA-induced cells indicate that, possibly, 20S proteasomes may play a role in relation to the mechanisms of differentiation and the inducer used.
Henry
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Laboratoire de Biologie Cellulaire et Cytogénétique Moléculaire (UPRES-JE 1952), Faculté de Médecine de Montpellier-Nîmes, Université Montpellier I, Nîmes, France.
Baz
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Château
M T
MT
Caravano
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Scherrer
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Bureau
J P
JP
D000818:Animals; D000954:Antigens, Surface / Q000032:analysis; D015153:Blotting, Western; D002453:Cell Cycle / Q000502:physiology; D002454:Cell Differentiation; D003546:Cysteine Endopeptidases / Q000032:analysis* / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D051379:Mice / Q000276:immunology; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000032:analysis* / Q000276:immunology; D046988:Proteasome Endopeptidase Complex; D013347:Subcellular Fractions / Q000276:immunology; D014407:Tumor Cells, Cultured / Q000737:chemistry* / Q000166:cytology* / Q000648:ultrastructure
D000954:Antigens, Surface; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex