A radicicol-related macrocyclic nonaketide compound, antibiotic LL-Z1640-2, inhibits the JNK/p38 pathways in signal-specific manner

Macrocyclic nonaketide compounds, radicicol and its two analogues, 87-250904-F1 and LL-Z1640-2, have various biological activities. Here we show that these compounds inhibit signal-dependent transcriptional activation with different specificity with distinct mechanism. Although all three compounds inhibited PMA-induced AP-1 transcriptional activity in cell-based reporter assay, these compounds exhibited differential effects in separate transcriptional reporter assays for NF-kappaB and Glucocorticoid Receptor. Next we found that one of these compounds, LL-Z1640-2, was a signal-specific inhibitor of the JNK/p38 pathways. In contrast to LL-Z1640-2, radicicol and 87-250904-F1 did not inhibit JNK/p38 activation. Recently, radicicol was reported as an inhibitor of activated-Ras-induced ERK activation. These results indicated that radicicol and LL-Z1640-2 showed distinct specificity to various MAP kinase pathways despite their structural similarity. Furthermore, LL-Z-1640-2 inhibited anisomycin-induced but not TNF-induced JNK/p38 activation, indicating that the inhibition mechanism is signal-specific.