Am. Colangelo et al., INDUCTION OF NERVE GROWTH-FACTOR RESPONSIVENESS IN C6-2B GLIOMA-CELLSBY EXPRESSION OF TRKA PROTOONCOGENE, Glia, 12(2), 1994, pp. 117-127
Cells that lack the high affinity receptor component (trkA) for nerve
growth factor (NGF) are unresponsive to NGF. We investigated whether C
6-2B cells, a rat glioma derived cell line, express trkA and, as a con
sequence, are responsive to NGF. In these cells, NGF (100 ng/ml) faile
d to induce the mRNA encoding for c-fos protooncogene and the low affi
nity NGF receptor p75(NGFR), two NGF-responsive genes. In contrast, bo
th mRNAs were induced in PC12 cells by NGF. Using a RNase protection a
ssay with a cRNA probe for rat trkA, the expected trkA RNA protected f
ragment was detected in PC12 but not in C6-2B glioma cells, indicating
that C6-2B cells either do not express the gene or express it only in
low amounts. Cross-linking of I-125-labeled NGF to PC12 cells identif
ied two major bands with an apparent molecular weight of 158 kDa and 1
00 kDa corresponding to trkA and p75(NGFR), respectively. In contrast,
only the 100 kDa band could be detected in C6-2B cells by cross-linki
ng analysis. In C6-2B cells stably transfected with the rat trkA cDNA,
NGF increased c-fos mRNA, induced tyrosine phosphorylation of gp140(t
rk), and SNT (suc-associated neurotrophic factor-induced tyrosine-phos
phorylated target), and caused morphological changes within 72 h. All
of these effects of NGF were blocked by the protein kinase inhibitor K
-252a suggesting that NGF signal transduction was restored by trkA exp
ression. Most important, in C6trk(+) cells, NGF was a weaker (2-fold)
inducer of [H-3]thymidine incorporation when compared to bFGF (5-fold)
, suggesting that expression of trkA fails to confer to NGF a strong m
itogenic effect. Our findings indicate that C6-2B glioma cells do not
possess high affinity NGF receptor and thus are unresponsive to NGF an
d that expression of trkA in neuroectoderm derived cells elicits some
of the NGF responses characteristic of neuronal cells. (C) 1994 Wiley-
Liss, Inc.