Phorbol ester and interleukin-1 induce interleukin-6 gene expression in vascular smooth muscle cells via independent pathways.
Previous studies using bioassays suggest that interleukin 6 (IL-6) is a major secretory product of vascular smooth muscle cells (VSMC), which is induced by proinflammatory cytokines. This study investigated whether activation of the protein kinase C (PKC) pathway induces IL-6 gene expression and release in VSMC, by using both bioassay and specific immunoassay methods to measure IL-6 release. Activation of PKC with a phorbol ester, PMA (phorbol myristate acetate), induced a rapid and transient (1-4 h) increase in the levels of both 1.2- and 2.4-kb IL-6 transcripts in rat aortic SMCs (RASMC), as determined by Northern analysis, which was followed by increased release of bioactive IL-6, as determined by a B9 cell-proliferation assay. IL-1, a physiological activator of PKC, induced a rapid increase in IL-6 messenger RNA (mRNA) levels, which was sustained at 24 h. PMA-induced IL-6 mRNA levels in RASMC were markedly attenuated after downregulation of PKC with PMA and by the selective PKC inhibitor, bisindolylmaleimide. In contrast, IL-1-induced increases in IL-6 mRNA were not affected by either PKC downregulation or bisindolylmaleimide. Angiotensin II (Ang II), also known to activate PKC, likewise induced a rapid increase in IL-6 mRNA levels and IL-6 release in RASMC, but the effect was not blocked by PKC downregulation. VSMC derived from human saphenous vein (HSVSMC) released substantial amounts of immunoreactive IL-6 in the absence of stimulation by exogenous growth factors, and both PMA and IL-1 markedly increased IL-6 release. Furthermore, downregulation of PKC and bisindolylmaleimide blocked the effect of PMA but not that of IL-1 in HSVSMC. These results suggest that activation of phorbol ester-responsive PKC induces IL-6 gene expression in both rat and human VSMC. In contrast, IL-1 and Ang II activate IL-6 gene expression by a pathway distinct from that of phorbol ester-responsive PKC.
Beasley
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Department of Medicine, New England Medical Center Hospitals, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D015152:Blotting, Northern; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D006825:Hybridomas; D066298:In Vitro Techniques; D007375:Interleukin-1 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000235:genetics*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011493:Protein Kinase C / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012501:Saphenous Vein / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D007375:Interleukin-1; D015850:Interleukin-6; D012333:RNA, Messenger; D000804:Angiotensin II; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate