SUSTAINED TYROSINE PHOSPHORYLATION OF P140(TRKA) IN PC12H-R CELLS RESPONDING RAPIDLY TO NGF

The PC12h cell, a subclone of PC12 cells, has considerable activities of tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) and shows an NGF-induced increase in both enzyme activities. The TH activi ty and its inducibility by NGF in PC12h cells were stably maintained i n the passage of > 200 generations whereas the ChAT activity was not. We isolated a new cell line, PC12h-R (originally clone 8), from a long -term culture of PC12h cells. PC12h-R cells still showed the considera ble TH activity, but not the ChAT activity, and maintained the inducib ility of TH activity by NGF. Thus, the responses of PC12h-R cells to N GF were similar to those of chromaffin cells and sympathetic neurons. PC12h-R cells were found to extend neurites and differentiate into sym pathetic neuron-like cells in response to NGF much more rapidly than P C12h cells. In addition, PC12h-R cells showed sustained NGF-induced ty rosine phosphorylation of p140(trkA) and several cellular proteins, in cluding 42-, 44- and 54-kDa proteins, in comparison with PC12h cells. We suggest that the NGF-induced sustained tyrosine phosphorylation sig nal in PC12h-R cells may be correlated closely with their rapid NGF-in duced differentiation into neuron-like cells.