Role of endocytosis in the transactivation of nuclear factor-kappaB by oxidized low-density lipoprotein.
Oxidized low-density lipoprotein (oxLDL) has been shown to modulate transactivation by the peroxisome proliferator-activated receptor (PPAR)-gamma and by nuclear factor-kappaB (NF-kappaB). In the present study, the oxLDL signalling pathways involved in NF-kappaB transactivation were investigated by utilizing a reporter construct driven by three upstream NF-kappaB binding sites, and various pharmacological inhibitors. OxLDL and its constituent lysophophatidylcholine (lysoPC) induced a rapid and transient increase in intracellular calcium and stimulated NF-kappaB transactivation in resting RAW264.7 macrophage cells in an oxidation-dependent manner. NF-kappaB activation by oxLDL or lysoPC was inhibited by inhibitors of protein kinase C or by a chelator of intracellular calcium. Tyrosine kinase or phosphatidylinositol 3-kinase inhibitors did not block NF-kappaB transactivation. Furthermore, oxLDL-induced NF-kappaB activity was abolished by PPAR-gamma ligands. When the endocytosis of oxLDL was blocked by cytochalasin B, NF-kappaB transactivation by oxLDL was synergistically increased, while PPAR transactivation was blocked. These results suggest that oxLDL activates NF-kappaB in resting macrophages via protein kinase C- and/or calcium-dependent pathways, and that this does not involve the endocytic processing of oxLDL. The endocytosis-dependent activation of PPAR-gamma by oxLDL may function as a route of inactivation of the oxLDL-induced NF-kappaB signal.
Han
C Y
CY
Division of Metabolic Disease Research, Department of Biomedical Sciences, National Institute of Health, Korea, Nokbun-Dong, Seoul 122-701, Korea.
Park
S Y
SY
Pak
Y K
YK
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004705:Endocytosis; D006801:Humans; D008077:Lipoproteins, LDL / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology*
D008077:Lipoproteins, LDL; D016328:NF-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C099252:oxidized low density lipoprotein; D011493:Protein Kinase C; D002118:Calcium