Demonstration that some of the nonhistone proteins, inducible to translocate into the nucleus, are glycosylated

Con A, NaF, and eserine (lysosomotropic agents) induced marked translocation of acidic [3H] nonhistone proteins (NHP) from the cytoplasm to the nucleus in lymphocytes prelabeled with [3H]-2-mannose. The nuclear [3H] NHP contents were 38-120% higher in cells treated with these agents than in control cells. Tunicamycin, a strong inhibitor of N-glycosylation via the dolichol pathway, caused a concentration-dependent inhibition of [3H]-2-mannose incorporation into the nuclear [3H] NHP. Considerable amounts of nuclear [3H] NHP from lymphocytes labeled with either [3H]-2-mannose or [3H] leucine, bound specifically to Con A-Sepharose and could be eluted by alpha-methyl mannoside. Con A and NaF caused also nuclear translocation of acidic [3H] NHP in cells labeled with [3H] glucosamine, [3H] galactose, or [3H] fucose. Fractionation of the nuclear proteins by isoelectric focusing in a pH gradient of 2.5-6.5 showed that multiple species of acidic NHP were labeled with each of the four 3H-sugars. These results indicate that a fraction of the acidic nuclear NHP are N-glycosylated proteins and that gene activation and mitogenesis are associated with the translocation of these glycoproteins to the nucleus. Considering the known intracellular traffic of nascent glycoproteins our results suggest that at least some of the acidic NHP are synthesized and glycosylated in the endoplasmic reticulum and the Golgi (secretory pathway). It is likely that these proteins, after completion of synthesis and glycosylation, emerge from the trans-stack of the Golgi packaged in vesicles and accumulate in the cytoplasm. Induction of nuclear translocation of such NHP by various agents may be mediated by a vesicular transport mechanism.