The possible involvement of tubulin in transduction of the prolactin signal.

Prolactin has many different biological functions. It stimulates Nb2 cell multiplication through the kinase C transduction mechanism, casein secretion through the phospholipase A2-arachidonic acid-leukotrienes cascade and milk protein gene expression through an unknown mechanism. Colchicine and other tubulin binding drugs inhibit casein gene expression and DNA synthesis stimulated by prolactin whereas chemical compound which alter microtubule without binding tubulin exert no inhibitory effect. Myo-inositol which suppresses some of the colchicine actions in several biological systems does not restore prolactin action after an inhibition by the drug. These data suggest that a tubulin molecule in the vicinity of the prolactin receptor, rather than actual microtubules, is involved in the transduction of the prolactin message from its receptor to milk protein genes.