Mechanism of colchicine-induced steroidogenesis in rat adrenocortical cells

Conflicting data for the effects of colchicine on cholesterol transport and steroidogenesis raise the question of the role of microtubules in choleste rol transport from the lipid droplet to mitochondria in steroidogenic cells . In this study, using corticosterone radioimmunoassay and immunofluorescen ce microscopy, we re-evaluated the effects of colchicine on hormone product ion and morphological changes of lipid droplets' and studied the signaling pathway involved in colchicine-induced steroidogenesis. Colchicine stimulat ed steroid production in a dose- and time-dependent manner. The structural integrity of both the microtubules and the lipid droplet capsule was destro yed by colchicine treatment. Disruption of the lipid droplet capsule occurr ed later than microtubule depolymerization. After cessation of colchicine t reatment and a 3 h recovery in fresh medium, capsular protein relocated to the droplet surface before the cytoplasmic microtubule network was re-estab lished. beta -lumicolchicine, an inactive analogue of colchicine, disrupted the capsule and increased hormone production without affecting microtubula r structure. Thus, microtubule depolymerization is not required for the inc rease in steroid production and capsular disruption. To explore the signali ng pathway involved in colchicine-induced steroidogenesis, we measured intr acellular cAMP levels. Unlike ACTH, colchicine did not increase cAMP levels , suggesting that the cAMP-PKA system is not involved. Colchicine and ACTH had additive effects on corticosterone production, whereas colchicine and P MA did not, implying that part of the PKC signaling mechanism may be involv ed in colchicine-induced steroidogenesis. Cycloheximide, a protein synthesi s inhibitor, completely inhibited colchicine-induced steroidogenesis and ca psular disruption. These results demonstrate that the steroid production an d lipid droplet capsule detachment induced by colchicine are both protein n eosynthesis-dependent and microtubule-independent. (C) 2001 Wiley-Li is, In c.