Proteins IEF (isoelectric focusing) 31 and IEF 46 are keratin-type components of the intermediate-sized filaments: keratins of various human cultured epithelial cells.

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Abstract
Mouse polyclonal antibodies have been raised against 2 human proteins (IEF [isoelectric focusing] 31, MW = 50,000; IEF 46, MW = 43,500), previously shown to be present in HeLa [cervical carcinoma cell line] cytoskeletons enriched in intermediate-sized filaments. Immunoprecipitation studies show that both proteins share common antigenic determinants with each other and with the putative human keratins IEF 36 and 44, also present in HeLa cytoskeletons. Indirect immunofluorescence studies showed that both antibodies revealed similar filamentous networks in various cultured epithelial cells of human origin. These included AMA (transformed amnion), HeLa, normal amnion cells, Fl-amnion (transformed amnion), WISH-amnion (transformed amnion), Chang liver (liver), and Detroid-98 (sternal marrow). Human cells that did not react with both antibodies included skin fibroblasts, lung fibroblasts (WI-38), SV40-transformed lung fibroblasts, Molt 4 (leukemia), lymphocytes and monocytes. Results agreed with the presence or absence of both proteins in 2-dimensional gels of the different cell types. Exposure of AMA cells to demecolcine (24 h; 10 .mu.g/ml) caused the total collapse of vimentin filaments but, as seen by indirect immunofluorescence, caused only a partial redistribution of the IEF 31 and 46 filaments. Probably, both proteins are components of the intermediate-sized filaments of the keratin type. The antibodies could be clearly differentiated by staining human bladder carcinoma EJ 19 cells, as only the IEF 46 antibody stained a filamentous network in these cells. The occurrence of keratins IEF 31, 36, 44 and 46 in different cultured human epithelial cells was studied using 2-dimensional gel electrophoresis.