Activation of the murine B cell lymphoma M12.4.1 by LPS or taxol increases GM-CSF mRNA expression. Since taxol, which stabilizes tubulin dimers, induced GM-CSF expression we examined whether any perturbation of microtubules would induce GM-CSF mRNA expression. Colchicine, a microtubule dissociation compound, was examined to see if it would mimic the induction of GM-CSF mRNA by taxol. Our studies show that treatment of M12.4.1 cells with colchicine (1 microm) did not induce GM-CSF mRNA. However, pre-treatment of M12.4.1 cells with colchicine enhanced LPS-induced GM-CSF mRNA expression in a time-dependent manner with maximal induction (20-fold) observed when added 4 hr prior to LPS. Studies were performed to dissect the molecular and signal transduction events associated with colchicine-enhanced expression of GM-CSF mRNA. Actinomycin D chase experiments showed that colchicine pretreatment did not alter the half-life (t1/2) of LPS-induced GM-CSF mRNA. Since studies have shown that LPS activates protein kinase c (PKC) in macrophages, we sought to determine whether PKC played a role in the induction of GM-CSF mRNA expression in B cells. M12.4.1 cells were cultured for 1 hr with the PKC inhibitor calphostin-c (150-300nM) followed by colchicine and/or LPS. Although calphostin c did not effect the induction of GM-CSF mRNA expression in response to LPS, it significantly inhibited the enhanced expression of GM-CSF mRNA in a dose-dependent manner following colchicine pre-treatment. Thus, super-induction of GM-CSF mRNA expression by colchicine may involve activation of PKC while induction by LPS alone does not.
