Comparison of rapid changes in surface morphology and coated pit formation of PC12 cells in response to nerve growth factor, epidermal growth factor, and dibutyryl cyclic AMP

Scanning and transmission electron microscopic studies were carried out on the rapid cell surface response of PC12 pheochromocytoma cells to treatment with nerve growth factor (NGF), epidermal growth factor (EGF), and dibutyryl cyclic AMP. EGF induced a rapidly initiated series of surface changes identical to those previously observed with NGF. Ruffles appear over the dorsal surface of the cells by 30 s, are prominent at 3 min, and are absent by 7 min. Microvilli disappear as dorsal ruffles become prominent. Peripheral ruffles are seen by 3 min, are prominent on most of the cells by 7 min, and are virtually absent by 15 min. Large blebs are present on 50% of the cells by 2 h and are markedly decreased by 4 h. Within 30 s after NGF or EGF addition, an increase in the density of 60-130-nm coated pits per unit membrane is detectable. This reaches a maximum of two- to threefold in from 1 to 3 min and gradually decreases. Combined treatment with NGF and EGF increases surface ruffling and, after an early peak in coated pits which at 3 min is similar in magnitude to that observed for the separately administered factors, maintains a greater number of pits per unit area than either treatment alone. 3-d pretreatment with NGF greatly reduces the response of the cells to EGF both with respect to surface ruffling and coated pit formation while 4-h NGF pretreatment has no effect on the EGF response. Dibutyryl cyclic AMP induced none of the rapidly onsetting changes caused by NGF or EGF, and therefore it seems unlikely that cyclic AMP mediates these surface changes. Changes in cell surface architecture induced by NGF and EGF on PC12 cells and by NGF in normal sympathetic neurons (as previously described) indicates that such responses may be a widespread phenomenon associated with the interaction of at least some peptide growth factors/hormones with their receptors. These responses may represent or reflect primary events in the mechanism by which these factors act.