LEYDIG TUMOR-CELL PROTEIN PHOSPHORYLATED IN RESPONSE TO STIMULATION WITH CHORIOGONADOTROPIN OR EPIDERMAL GROWTH-FACTOR IS IDENTIFIED AS STATHMIN

Although hCG and mouse epidermal growth factor activate different sign aling systems in a clonal strain of Leydig tumor cells (designated MA- 10), both compounds are capable of increasing steroidogenesis, decreas ing transcription of the LH/CG receptor gene, and attenuating adenylyl cyclase. We have recently identified a 21-kilodalton protein (p21) th at is a potential intermediary in the actions of mouse epidermal growt h factor and hCG. Characterization of p21 revealed similarities to sta thmin, a ubiquitous phosphoprotein whose phosphorylation is associated with diverse second messenger pathways. Using two different experimen tal approaches, Western blotting and immunoprecipitation, we present d ata that identify p21 as stathmin.