DOWN-REGULATION BUT NOT PHOSPHORYLATION OF STATHMIN IS ASSOCIATED WITH INDUCTION OF HL-60 CELL-GROWTH ARREST AND DIFFERENTIATION BY PHYSIOLOGICAL AGENTS

Stathmin is a cytosolic phosphoprotein that has an important but, as y et, undefined role in cell proliferation and differentiation. Inductio n of growth arrest and differentiation of HL60 cells to monocytes by p horbol 12-myristate 13-acetate is associated with rapid phosphorylatio n of the protein. Stathmin phosphorylation was not seen when HL60 cell s were induced to differentiate to monocytes, by 1 alpha,25-dihydroxyv itamin D3, and to neutrophils, by all-ir mls retinoic acid and granulo cyte colony stimulating factor. In all the above instances, stathmin e xpression was down-regulated. Thus, increased stathmin phosphorylation is not required for cell growth arrest or differentiation or down-reg ulation of stathmin expression.