On the role of the low-affinity neurotrophin receptor p75(LNTR) in nerve growth factor induction of differentiation and AP 1 binding activity in PC12 cells

Three clones of PC12 cells that differ with respect to their nerve growth factor (NGF) receptors were examined: wild-type PC12 cells that have both trkA and p75(LNTR) receptors; the MR-1 clone that possesses a normal trk3, receptor and a truncated form of p75(LNTR) without the extracellular NGF-binding part; and a new PC12 variant, called v-clone, that is partly characterized here. The v-clone had no demonstrable binding to trkA, but displayed binding to p75(LNTR) as assessed by chemical crosslinking. NGF did not induce any change in the tyrosine phosphorylation of phosphatidy-3'-kinase in the v-clone. NGF induced neurite extension in wild-type cells, induced it more rapidly in mR-1, but not at all in v-clone cells. The v-clone lacked the b-form of protein kinase C, but transfection with this enzyme did not restore responsiveness to NGF. Neurite extension in response to staurosporine and basic fibroblast growth factor was equal in wild-type and v-clone cells. All three clones responded to forskolin, with the mR-1 clone the most responsive. NGF stimulated AP 1 binding activity in all clones. The response was transient in the MR-1 clone but prolonged in the wild-type and v-clone cells. Ln the wild-type and MR-1 clone cells, AP 1 binding activity was reduced by a tyrphostin analog, whereas in the v-clone cells it was inhibited by staurosporine. NGF increased inositol (1,4,5)-trisphosphate (InsP(3)) formation in all clones. In the wild-type and v-clone cells the InsP(3) responses were followed by [Ca2+](i) increases. It is concluded that although trkA is required for differentiation in response to NGF in PC12 cells, the concomitant stimulation, by NGF, of p75(LNTR) may affect phospholipase C and AP 1. This may be important for the reported ability of p75(LNTR) to modify the phenotypic changes induced in PC12 cells by NGF.