Heat Shock Proteins are Methylated in Avian and Mammalian Cells
Exposure of chicken cells grown in tissue culture to heat shock or sodium arsenite results in a dramatic increase in the synthesis of three major polypeptides with molecular weights of 83,000 (HSP 83), 68,000 (HSP 68; referred to here as "thermin"), and 25,000 (HSP 25). Incubation of BHK-21 or HeLa cells under the same conditions results in induction of HSP 68 and a 66,000-dalton polypeptide (HSP 66). Chicken thermin is resolved by isoelectric focusing into a major acidic and a more-basic component; mammalian thermin is resolved only into one major acidic component. HSP 83 and the acidic form of thermin are highly conserved in all avian and mammalian cells examined as judged by their electrophoretic mobilities, isoelectric points, and one-dimensional peptide maps. In addition, the acidic form of thermin is indistinguishable from a protein that copurifies with brain microtubules and that remains associated with the intermediate filament-enriched Triton/KCl cytoskeletons of cells grown in tissue culture. Thermin is also a component of skeletal myofibrils. HSP 83 and thermin are methylated in cells cultured under normal growth conditions. Induction of heat shock proteins by incubation of cells in the presence of sodium arsenite results in a marked methylation of the newly synthesized thermin. Under the same experimental conditions, no significant increase in methylation of the HSP 83 is observed. HSP 25 is not methylated in untreated cells or in cells treated with sodium arsenite. These results suggest that methylation of heat shock proteins may have an important role in regulating their function.
Additional Information© 1981 by the National Academy of Sciences Communicated by James F. Bonner, March 19, 1981 We thank Dr. Ignacio Sandoval and Dr. David L. Gard for their critical reading of the manuscript and Dr. Bruce L. Granger for providing us with the erythrocyte extracts used in the purification of thermin. We thank Dr. J.A. Weatherbee for providing us with a sample of purified 68,000-dalton protein from HeLa cells to compare with the proteins described here. This work was supported by grants from the National Institutes of Health (GM-06965), National Science Foundation, and Muscular Dystrophy Association of America and a Biomedical Research Support Grant to the Division of Biology. E.L. is a recipient of a Research Career Development Award. R.H.G. was also supported by a National Research Service Award from the National Institute of General Medical Sciences. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Published - WANpnas81.pdf