Acute Regulation of the Epidermal Growth Factor Receptor in Response to Nerve Growth Factor

Abstract

PC12 cells possess specific receptors for both nerve growth factor and epidermal growth factor, and by an unknown mechanism, nerve growth factor is able to attenuate the propagation of a mitogenic response to epidermal growth factor. The differentiation response of PC12 cells to nerve growth factor, therefore, predominates over the proliferative response to epidermal growth factor. We have observed that the addition of nerve growth factor to PC12 cells rapidly produces a decrease in surface 125I-epidermal growth factor binding capacity. Unlike previously described nerve growth factor effects on 125I-epidermal growth factor binding capacity, which required several days of nerve growth factor exposure, the decreases we report occur within minutes of nerve growth factor addition: A 50% decrease in 125I-epidermal growth factor binding capacity is evident at 10 min. This rapid nerve growth factor response is concentration dependent; inhibition of 125I-epidermal growth factor binding is detectable at nerve growth factor levels as low as 0.2 ng/ml and is maximal at approximately 50 ng/ml, consistent with known ranges of biological activity. No demonstrable differences in the rate of epidermal growth factor receptor synthesis or degradation were observed in cells acutely exposed to nerve growth factor. Scatchard analysis revealed that acute nerve growth factor treatment decreased the number of both high- and low-affinity 125I-epidermal growth factor binding sites, while the receptor affinity remained unchanged. We have also investigated the involvement of various potential intracellular mediators of nerve growth factor action and of known intracellular modulatory systems of the epidermal growth factor receptor for their capacity to participate in this nerve growth factor activity.