Intracellular Association between UDP-glucose:Glycoprotein Glucosyltransferase and an Incompletely Folded Variant of α1-Antitrypsin*
- From the ‡Departments of Pathology and Cell Biology, Baylor College of Medicine, and the §Department of Pathology, University of Texas, Houston, Texas 77030
Abstract
Genetic variants of human α1-antitrypsin unable to fold into the native structural conformation are poorly secreted from hepatocytes. The molecular chaperone calnexin coimmunoprecipitates with secretion-incompetent variant null(Hong Kong) retained in stably transfected mouse hepatoma cells (Le, A., Steiner, J. L., Ferrell, G. A., Shaker, J. F., and Sifers, R. N. (1994) J. Biol. Chem. 269, 7514–7519). Mobilization of intracellular Ca2+ stores with metabolic poisons diminished interaction with calnexin and coincided with coimmuoprecipitation of a 150-kDa protein (p150). Mobilization of endoplasmic reticulum lumenal Ca2+ with thapsigargin, an inhibitor of the microsomal Ca2+ATPase, gave a similar result. Coimmunoprecipitation of p150 was specifically disrupted in response to incubation of the cell lysate with exogenous CaCl2. Finally, in ECL Western blotting, p150 was recognized by polyclonal antiserum against UDP-glucose:glycoprotein glucosyltransferase that likely functions in glycoprotein folding and quality control (Sousa, M. C., Ferrero-Garcia, M. A., and Parodi, A. J. (1992) Biochemistry 31, 97–105). The data are consistent with a model in which perturbation of endoplasmic reticulum Ca2+ results in a stable physical association between unfolded human α1-antitrypsin and UDP-glucose:glycoprotein glucosyltransferase.
Footnotes
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↵* This work was supported in part by an American Heart Association grant-in-aid and an American Lung Association research career investigator award (to R. N. S.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ To whom correspondence should be addressed: Dept. of Pathology, Section of Molecular Pathobiology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Tel.: 713-798-3169; Fax: 713-798-5838; E-mail: rsifers{at}bcm.tmc.edu.
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↵1 The abbreviations used are: ER, endoplasmic reticulum; AAT, α1-antitrypsin; PAGE, polyacrylamide gel electrophoresis; UGTR, UDP-glucose:glycoprotein glucosyltransferase.
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↵2 R. Sifers, unpublished observations.
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↵3 P. Choudhury, unpublished observation.
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- Received November 14, 1996.
- Revision received February 10, 1997.
