| This dissertation describes an observation that tunicamycin (TM), a specific inhibitor of protein glycosylation, prevents the mitogenic activation of murine lymphocytes. Lymphocyte mitogenesis results in both cellular proliferation and differentiation. The results presented here demonstrate that TM inhibits cellular proliferation induced by lipopolysaccharide (LPS) and Concanavalin A (Con A). In contrast, tunicamycin does not inhibit the cellular proliferation of unactivated lymphocytes, BW147.3 lymphatic leukemic cells, H4-II-E-C3 hepatoma cells, or Escherichia coli B bacteria. Evidence is presented which suggests that tunicamycin is not acting by: (1) inhibiting the initial interaction of LPS with the lymphocyte membrane, (2) inhibiting the transport of thymidine inside the cell, (3) inhibiting protein synthesis, or (4) inhibiting deoxyribonucleic acid (DNA) synthesis in general.;Tunicamycin specifically blocks protein glycosylations occurring via the lipid intermediate pathway. Evidence is presented demonstrating that murine lymphocytes contain enzymes catalyzing the formation of lipid saccharides. In particular, it is shown that lymphocyte membranes synthesize dolichyl phosphoryl-(beta)-D-mannose and dolichyl phosphoryl-(beta)-D-glucose from exogenous dolichyl phosphate and nucleotide sugar. An endogenous polyisoprenyl phosphoryl-(beta)-D-mannose is also synthesized with properties identical to dolichyl phosphoryl-(beta)-D-mannose.;This dissertation demonstrates that in murine lymphocytes tunicamycin also blocks the incorporation of saccharides into protein. It therefore appears that tunicamycin is inhibiting cellular proliferation by blocking protein glycosylation. Moreover, it is suggested that tunicamycin blocks the glycosylation of a proliferation associated glycoprotein(s) found on the surface of differentiating cells. The expression of a transformation (and proliferation) associated membrane protein on cells infected with Abelson murine leukemia virus has recently been reported. Abelson murine leukemia virus is thought to specifically transform cells of the B lymphocyte lineage. This proliferation associated protein is also expressed on untransformed hematopoietic precursor cells to B lymphocytes. The results presented in this work suggest the possibility that a membrane glycoprotein, analogous to the Abelson protein, is essential for the proliferation of differentiating cells. |
