ABSTRACT
When macrophage (like the RAW264.7 cell line) was stimulated with lipopolysaccharide (LPS), factors that bind specifically to the LPS responsive element (LRE) of murine Rantes gene appeared in the nucleus. An electrophoretic mobility shift assay (EMSA) detected 2 specific bands, designated as S (slow) and M (middle). The S band appeared within 15 min of LPS stimulation, and reached its highest intensity within 2 h. The M band was present in unstimulated cells, but after stimulation its intensity increased and reached its highest intensity also in about 2 h. Significantly, in LPS hyporesponsive 10-9 macrophage like cells, the S band was absent. The M band was present in equal amounts in stimulated and unstimulated cells. The results suggest that the S band was induced by LPS stimulation. In the nuclear extract, the native molecular weight of the S band-forming factor was approximately 270 kDa, and that of the M bands-forming factor was approximately 140 kDa. U.V. cross linking studies consistently showed at least 2 different polypeptides of approximate molecular mass of 70 kDa, both in the S band-forming factor (complex) and the M band-forming factor (complex). In the nuclear extracts of both the LPS stimulated and unstimulated cells, we detected a factor with approximate molecular mass of 120 kDa that could convert the S band-forming complex to the M band-forming complex. This factor, designated as a converting factor, is a protein phosphatase since its activity was blocked by okadaic acid, an inhibitor of Ser/Thr protein phosphatase. Also, purified protein phosphatase type 1 (PP-1) could convert the S band-forming complex to the M band-forming complex.
