COLCHICINE DOWN-REGULATES LIPOPOLYSACCHARIDE-INDUCED GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR PRODUCTION IN MURINE MACROPHAGES

Activation of macrophages by LPS and taxol results in production of IL -1, IL-6, TNF-alpha, and granulocyte-macrophage CSF (GM-CSF), which ar e involved in regulating hemopoiesis, inflammation, and immune respons es, Microtubules are proposed as a target site for LPS interaction(s), based on similarities between the effects of the tubulin-binding drug taxol and LPS. To clarify the role of microtubules in LPS-induced GM- CSF expression in macrophages, we examined whether microtubule depolym erizing agents affect GM-CSF production in macrophages, Pretreatment w ith colchicine impaired LPS induction of GM-CSF in RAW 264 cells, and studies using stable transfectants revealed that colchicine impaired t he transcriptional responsiveness of a reporter gene driven by a GM-CS F promoter sequence. Colchicine inhibition of the GM-CSF response corr elated with decreases in the mRNA levels of beta-tubulin; maximal inhi bition of both events was observed 4 h after addition of colchicine. M icrotubule agents inhibited LPS induction of IL-6 and TNF-alpha, while the induction of both IL-1 beta and inducible nitric oxide synthase w as unaltered, suggesting that LPS activates microtubule-dependent and -independent pathways, Interestingly, LPS stimulation of macrophages d own-regulated levels of beta-tubulin transcripts, implying that LPS in teracts with an element(s) of the microtubule network in vivo, activat ing pathways regulating transcription of beta-tubulin. The ability of both colchicine and LPS to modulate transcription of beta-tubulin sugg ests that this event does not per se underlie the inhibitory effect of colchicine on LPS-induced CM-CSF expression. These data led us to con clude that colchicine inhibits LPS induction of CM-CSF by affecting mi crotubule-dependent costimulatory signaling pathways that synergize wi th primary LPS-triggered responses.