Differential induction of primary-response (TIS) genes in PC12 pheochromocytoma cells and the unresponsive variant PC12nnr5

Abstract

As a measure of the transmembrane signals that they transduce, two neurotrophic agents, nerve growth factor (NGF) and basic fibroblast growth factor (bFGF), and the muscarinic agonist carbachol were compared for their ability to induce TIS (tetradecanoyl phorbol acetate-inducible sequences) transcripts, representing a family of immediate early response genes, in the rat pheochromocytoma cell line PC12 and the morphologically unresponsive variant PC12nnr5. Three genes, TIS1 (also designated NGFIB), TIS8 (also designated NGFIA), and TIS21, induced in these cells by NGF (Kujubu, D.A., Lim, R.W., Varnum, B.C., and Herschman, H.R. (1987) Oncogene 1, 257-262, 1987), are also induced by bFGF and carbachol. In native PC12 cells the level of expression of TIS8 and TIS21 is similar for all three stimuli, as well as for tetradecanoyl phorbol acetate (TPA). In contrast, the induction of TIS1 by NGF and TPA is slight and is only just detectable after stimulation by bFGF, but is strong for carbachol. Thus, although all of these agents can stimulate protein kinase (PK-C), at least one TIS gene can apparently be differentially regulated by these ligands, suggesting that alternative signaling pathways must also exist. In keeping with this view, bFGF, and to a lesser degree NGF, can elicit a TIS gene response in PC12 cells in which PK-C has been down-regulated with TPA. The response to carbachol (and TPA) is effectively blocked under these conditions. Since both NGF and bFGF stimulate neurite outgrowth in such cells, PK-C is apparently not essential, i.e. does not represent the sole mechanism, for signal transduction leading to modulation of gene expression for these factors. Consistent with this model, putative protein kinase inhibitors, K252a and sphingosine, did not inhibit the TIS gene responses to bFGF. However, these agents also failed to block TIS gene responses to carbachol and TPA indicating that they were ineffective as PK-C inhibitors under these conditions. The NGF-induced response was, however, blocked by K252a indicating a unique step in the mechanism of this factor not shared by the other ligands. Sphingosine did not block TIS induction with NGF. The mutant cell line PC12 nnr5 does not respond morphologically to either NGF or bFGF. However, TIS gene responses to bFGF are unaffected, whereas those to NGF are completely abolished. The response to TPA is altered quantitatively but not qualitatively; the induction by carbachol is largely eliminated, apparently as a result of a 90% reduction in muscarinic receptors.(ABSTRACT TRUNCATED AT 400 WORDS)