Clonal variants of PC12 pheochromocytoma cells with altered response to nerve growth factor.

We describe the isolation and characterization of clonal variants of PC12 pheochromocytoma cells which have been selected for loss of response to nerve growth factor (NGF). PC12 cells mutagenized with ethyl methanesulfonate were cultured in the presence of NGF, causing normal cells to cease proliferation and allowing the isolation of cell clones which do not show growth inhibition by NGF. Some but not all of these clones also failed to respond morphologically to NGF. Forty clones were isolated and characterized. Many exhibited altered morphologies of a variety of types, including clones with an NGF-independent formation of neurites and clones with various types of flattened epithelial morphology. Variant clones appeared to be mutants since their frequency of occurrence was increased by mutagen, the clones were generally phenotypically stable and no alteration in chromosomal composition was observed. Three clones lacked NGF receptor. Some clones responded morphologically to NGF (by forming neurites) without inhibition of proliferation. Several clones which did not otherwise respond to NGF nevertheless responded with transient membrane ruffling. Thus transient changes in cell surface morphology caused by NGF binding do not necessarily lead to subsequent responses. Several alternative hypotheses concerning the nature of the mutations induced are discussed.