Tyrphostins are well-established selective inhibitors of protein tyrosine kinase activity of EGF receptor and other growth factor receptors. Unexpectedly, we found that, in U-937 monocytic cells, tyrphostin AG-126 augments the sensitivity of the corresponding genes to NO, in contrast to other protein tyrosine kinase inhibitors like genistein, PD 168393, PP2, and SU 11652. Moreover, by itself AG-126 appeared to be a potent activator of the expression of heme oxygenase 1 (HO-1), H-ferritin, activating transcription factor 3 (ATF3), interleukin 8 (IL-8), and several other NO- and redox-regulated genes. The most sensitive to AG-126 was the HO-1 gene, with a fold-change of expression reaching 300. Besides, we showed that AG-126 stimulated key elements of upstream signaling systems as p38 MAP kinase and AP-1 and Nrf2 transcription factors. Together with AG-126, structurally related benzylidenemalononitrile tyrphostins AG-9, AG-10, AG-18, and AG-1288 were able to up-regulate the expression of HO-1 and several other genes, although with relatively less efficacy. Conversely, tyrphostins AG-30 and AG-490 were ineffective regulators of gene expression. Comparison of the chemical structures of these compounds indicates that most important for transcriptional activation of target genes is the presence of either the 4-nitro or 4-methoxy group in the benzene ring and two CN-groups of the malononitrile residue. Several lines of evidence indicate that the gene induction capacity of AG-126-like tyrphostins is not related to the inhibition of protein tyrosine kinases.
