TRANSCRIPTIONAL REGULATION OF LDL RECEPTOR-RELATED PROTEIN BY IFN-GAMMA AND THE ANTAGONISTIC ACTIVITY OF TGF-BETA-1 IN THE RAW-264.7 MACROPHAGE-LIKE CELL-LINE

Low density lipoprotein receptor-related protein (LRP) is a major rece ptor for multiple ligands, including chylomicron and VLDL remnants, ba cterial toxins, viruses, proteinases, lipoprotein lipase, and activate d alpha(2)-macroglobulin (alpha(2)M). In this study, we used Northern blot analyses and nuclear run-on experiments to demonstrate that inter feron-gamma (IFN-gamma) causes a concentration-dependent decrease in s teady-state LRP mRNA expression and gene transcription rate in RAW 264 .7 cells, IFN-gamma also markedly increased expression of inducible ni tric oxide synthase (NOS), as expected; however, the increase in nitri c oxide was not responsible for the down-regulation of LRP expression since the NOS inhibitor, N-G-monomethyl-L-arginine, did not preserve L RP expression in IFN-gamma-treated cells, Transforming growth factor-b eta 1 (TGF-beta 1; 2.5 ng/mL) had no independent effect on LRP express ion and did not modify the response to IFN-gamma when the two cytokine s were added simultaneously to cultures, When TGF-beta 1 was added 24 h prior to IFN-gamma, the extent of LRP down-regulation was significan tly reduced, Specific binding of the LRP ligand, activated I-125-alpha (2)M, was decreased by 76 +/- 5% in cells treated with 100 U/mL IFN-ga mma, but only by 45 +/- 7% in cells treated with 100 U/mL IFN-gamma af ter TGF-beta 1-pretreatment, The antagonistic activity of TGF-beta 1 o n the IFN-gamma response in RAW 264.7 cells did not result from a chan ge in LRP mRNA stability or IFN-gamma receptor expression, as determin ed by Northern blot analyses and I-125-IFN-gamma binding experiments, The studies presented here suggest that the balance between IFN-gamma and TGF-beta 1 may be critical in determining LRP expression at sites of infection and inflammation.