BACKGROUNDTo determine the binding activity of nuclear factor-kappa B (NF-kappa B) and the transcription of transforming growth factor-beta 1 (TGF-beta 1) induced by oxidized low density lipoprotein (Ox-LDL) in rat mesangial cells and to elucidate the mechanism of renal injury of Ox-LDL.

METHODSNF-kappa B binding activity was measured by gel shift assay in mesangial cells with or without inducement of Ox-LDL. Protein kinase inhibitors and activators were then used to determine the signal transduction pathways. In this course I kappa B protein expression was analyzed by Western blot assay. TGF-beta 1 mRNA was measured in mesangial cells exposed to Ox-LDL by RT-PCR assay. TGF-beta 1 promoter from -1551 to +57 were constructed into a pGL3-Basic vector with a luciferase reporting gene. A putative binding site of NF-kappa B was mutated. The wild and mutant promoters activity was analyzed by transfection into mesangial cells.

RESULTSNF-kappa B was activated by Ox-LDL persistently and rebounded in the early period. Ox-LDL induced NF-kappa B activation in a dose dependent way. It also induced I kappa B degradation in 2 hours and resumed to normal levels. NF-kappa B activation was not alleviated by inhibitors of protein kinase A (PKA), extracellular signal-regulated kinase (ERK), and p38 MAP kinase (p38MAPK). Inhibitors of protein kinase C (PKC) and proteinsome inhibited the enhancement of NF-kappa B binding activity. Ox-LDL induced the transcription of TGF-beta1 in a time and dose dependent manner. Mutation of the putative binding site of NF-kappa B reduced the activity of TGF-beta1 promoter.

CONCLUSIONOx-LDL induced activation of NF-kappa B persistently. It was probably regulated by the degradation of I kappa B mediated by PKC pathway. NF-kappa B may be involved in the enhancement of TGF-beta 1 induced by Ox-LDL in rat mesangial cells.