Nerve Growth Factor-induced Growth Arrest and Induction of p21 in NIH-3T3 Cells Expressing TrkA

Treatment of NIH-3T3 cells expressing human TrkA with nerve growth factor (NGF) resulted in a rapid cessation of growth. Cells stopped dividing within 24 h of NGF treatment and failed to divide as long as NGF was present, accumulating in the G1 stage of the cell cycle. NGF caused a prolonged activation of mitogen-activated protein kinase relative to EGF. NGF treatment of cells greatly increased levels of the p21Cip1/WAF1 protein, an inhibitor of cyclin-dependent kinases, without affecting levels of p27KIP1 or p16INK4. Levels of p21Cip1/WAF1 remained elevated for at least 48 h following NGF addition. EGF had little effect on p21Cip1/WAF1 expression in the same parental cells expressing the human EGF receptor. NGF treatment of cells completely inhibited the activity of the cyclin-dependent protein kinases CDK2 and CDK4. Inhibition correlated with a 10-20-fold increase in the amount of p21Cip1/WAF1 complexed with CDK2 and CDK4. Levels of CDK2 and CDK4 were decreased following NGF treatment of cells; however, levels of cyclin E and cyclin D were increased. These data indicate that NGF can induce cell cycle arrest of NIH-3T3, perhaps through modulation of p21Cip1/WAF1 levels. The data also show that distinct signals are generated by TrkA versus the EGF receptor in NIH-3T3 cells.