Figure 1.

Mkp1 mRNA levels increase in sympathetic neurons after NGF withdrawal, and this requires MLK activity. Sympathetic neurons from 1-d-old rats were cultured for 6 d in vitro and then rinsed and refed with medium containing NGF (+NGF), or lacking NGF (−NGF), or lacking NGF but containing 400 nm CEP-11004 (−NGF+CEP-11004) for 16 h. RNA was then isolated using an RNeasy mini kit. A, Affymetrix Rat Exon 1.0ST microarray analysis of gene expression in sympathetic neurons at the whole gene level. c-jun, bim, dp5, and atf3 are induced after NGF withdrawal, and this is reduced by CEP-11004 validating them as known targets of the MLK-JNK-c-Jun pathway. mkp1 induction after NGF withdrawal (4.51-fold) is reduced by CEP-11004 to 1.42-fold, suggesting that it too may be a transcriptional target of the JNK pathway. B, c-jun, bim, and mkp1 mRNA levels were measured by real-time PCR and normalized to the housekeeping genes gapdh and hprt1. Similar results were obtained in both cases. The data shown represents the average of three independent experiments ± SEM. Statistical comparisons were made between +NGF and −NGF or −NGF and −NGF+CEP for each gene. ^#p < 0.001; *p < 0.01; ⁺p = 0.02.