The Use of Nucleotide-Sugar: Glycoprotein Glycosyltransferases to Assess Golgi Apparatus Function in Morris Hepatomas

Enzymatic assays for CMP-sialic acid: glycoprotein sialyltransferase and UDP-N-acetylglucosamine: glycoprotein N-acetylglucosaminyltransferase were performed on crude homogenates of three Morris hepatomas (7777, 7800, and 5123D), and on liver homogenates from the host animals and normal Buffalo strain rats. It was found that sialyltransferase activities were greatly decreased in the most rapidly growing tumor (hepatoma 7777) and were decreased to a lesser extent in the more slowly growing hepatoma 7800; enzyme activities in hepatoma 5123D, another relatively slow growing tumor, were not significantly different from control values. Sialyltransferase activities were significantly elevated in the livers of all the tumor-bearing animals and were especially high in the livers of animals carrying hepatoma 7777; these elevations may be related to increased plasma glycoprotein synthesis by liver secondary to the inflammatory stimulus generated by the tumors. In contrast to the sialyltransferase analyses, N-acetylglucosaminyltransferase activities in tumor homogenates were very similar to control values for all three hepatomas. When the data are expressed as ratios of sialyltransferase activity to N-acetylglucosaminyltransferase activity, two of the three tumors show highly significant decreases of this ratio compared to either control or host livers. Since these glycosyltransferases have previously been shown to be located in the Golgi apparatus of normal rat liver where they function in the biosynthesis of glycoproteins, the above results have been interpreted to indicate a shift in the function of the Golgi apparatus in certain Morris hepatomas as compared to normal livers. Finally, glycosyltransferase assays and electron microscopy have been used to demonstrate the feasibility of preparing Golgi-enriched fractions from all three hepatomas by methods previously applied to normal rat liver.