Research demonstrated that differentiation of the mouse teratocarcinoma cell line F9 induced by retinoic acid is accompanied by major and specific alterations in the glycosylation of surface glycoproteins and suggest that the, changes may be due to modifications in activity of a few or perhaps a single glycosyltransferase. These studies do not, however, directly address many specific issues about the regulation of surface glycoprotein biosynthesis in animal cells. Little is actually known in detail about the structures of oligosaccharides at specific Asn-linked sugar sites of functional and normal cell surface glycoproteins (i.e. non- viral) and little is known about the factors that influence the glycosylation of surface proteins. Sugar addition is determined in part by the expression of appropriate glycosyltransferases an, glycosidases. However, several studies have shown that the primary sequences of protein can influence the glycosylation of the peptide at specific sites. To understand more about the factors regulating glycoprotein biosynthesis in F9 an, differentiated F9 cells, the glycosylation of a common surface glycoprotein, the transferrin receptor, will be investigated. The specific questions to be addressed in the proposed study are the following. (1) What are the structures of the chains at each Asn-linked glycosylation site on the receptor? (2) Does differentiation result in specific differences in the glycosylation of the receptor? (3) If changes are found to occur in the structures of the chain upon differentiation, how soon following the addition of retinoic acid are these change, observable? (4) Do the complex- type Asn-linked chains on the receptor have structures representative of the major types of chains derived from total glycoproteins? (5) If changes do occur in receptor glycosylation upon differentiation, do these changes affect the binding affinity of the receptor for transferrin or the turnover or recycling rate of the receptor? Answers to all these types of questions are not known for any surface glycoprotein in differentiating animal cells. Success in these studies will increase our knowledge of those factors influencing cell surface glycoprotein biosynthesis and should have broad implications for studies on other surface glycoproteins.
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