Microheterogeneity of human interleukin 6 synthesized by transfected NIH/3T3 cells: Comparison with human monocytes, fibroblasts and endothelial cells

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Abstract
A cDNA containing the entire coding region of human interleukin 6 (IL 6) was stably expressed in murine NIH/3T3 fibroblasts using a bovine papilloma virus‐based expression vector with a metallothionein promoter. Expression of IL 6 in transfected cells was highly inducible by heavy metals like cadmium as measured at mRNA and protein levels. Cadmium‐stimulated transfected NIH/3T3 cells synthesized and exported biologically active IL 6 (1.7 × 104 U/106 cells/24 h). IL 6 from the culture medium of transfected NIH/3T3 cells exhibited at least eight bands on Western blots after sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, indicating that human IL 6 expressed in NIH/3T3 cells shows a complex glycosylation pattern. Using glycosidases and the N‐glycosylation inhibitor tunicamycin it was possible to discriminate between five species carrying N‐linked carbohydrate side chains and two species carrying only O‐linked side chains. In addition, a substantial amount of unglycosylated IL 6 was observed. IL 6 from transfected NIH/3T3 cells differed markedly in its glycosylation pattern from those of stimulated human monocytes, fibroblasts and endothelial cells.