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Asialoglycoprotein Receptor Mediates the Toxic Effects of an Asialofetuin-Diphtheria Toxin Fragment A Conjugate on Cultured Rat Hepatocytes

Daniel B. Cawley, David L. Simpson and Harvey R. Herschman
Proceedings of the National Academy of Sciences of the United States of America
Vol. 78, No. 6, [Part 2: Biological Sciences] (Jun., 1981), pp. 3383-3387
Stable URL: http://www.jstor.org/stable/10837
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Asialoglycoprotein Receptor Mediates the Toxic Effects of an Asialofetuin-Diphtheria Toxin Fragment A Conjugate on Cultured Rat Hepatocytes
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Abstract

We have constructed a toxic hybrid protein that is recognized by asialoglycoprotein (ASGP) receptors of cultured rat hepatocytes. The conjugate consists of fragment A of diphtheria toxin (DTA) linked by a disulfide bond to asialofetuin (ASF). This conjugate is highly toxic, inhibiting protein synthesis in primary rat hepatocytes at concentrations as low as 10 pM. The ASF-DTA conjugate was 600 and 1800 times as toxic as diphtheria toxin and DTA, respectively, on primary rat hepatocytes. The ASGP receptor recognizes galactose-terminated proteins. We tested a series of glycoproteins for their ability to block the action of the ASF-DTA conjugate. Fetuin and orosomucoid, two glycoproteins with terminal sialic acid on their oligosaccharide chains, did not block the action of the conjugate. Their galactose-terminated asialo derivatives, ASF and asialoorosomucoid, as expected, did block the action of the conjugate. The N-acetylglucosaminyl-terminated derivative (asialoagalactoorosomucoid) had no appreciable effect on the activity of the conjugate. We tested the ASF-DTA conjugate on six cell types; except for primary rat hepatocytes, none of them were affected by a high concentration (10 nM) of ASF-DTA conjugate. A fetuin-DTA conjugate was less toxic by a factor of 300 than the ASF-DTA conjugate and exerted its effects primarily through non-receptor-mediated mechanisms. The highly toxic ASF-DTA conjugate is cell-type specific, and its action is mediated by a well-characterized receptor, whose mechanism of receptor-ligand internalization has been extensively investigated.

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