FIG. 9.

Role of JNK in retinoid resistance in lung cancer. (A) JNK levels and activity in NSCLC and HBE cells. NSCLC cell lines and the simian virus 40-immortalized HBE cell line BEAS2B were treated (+) or not treated (−) with SP600125 (15 μM) for 16 h. JNK was immunoprecipitated from cell lysates and subjected to immune complex kinase assays with GST-c-Jun as a substrate. The same lysates were analyzed for JNK protein levels by Western blotting (bottom). (B) Effect of RA on BEAS-2B and H322 cell growth. BEAS2B and H322 cells were treated for 6 days with medium alone or 1 μM RA and subjected to MTT assays. Results are expressed as the means ± standard deviations from three identical wells. (C) Effect of JNK and p38 inhibitors on RAR levels. H322 cells were treated for 16 h with medium alone, the JNK inhibitor SP600125 (SP) (15 μM), or the p38 inhibitor SB203580 (SB) (10 μM) and lysed, after which the cell lysates were subjected to Western blotting. (D) Effect of RA and SP600125 on RARE activity. H322 and Calu-6 cells were transiently cotransfected with β-Gal vector and DR5TK-luc reporter constructs. Transfectants were treated for 16 h with medium alone, RA (1 μM), SP600125 (1 μM), or both and subjected to luciferase assays. Values were corrected for differences in transfection efficiency and expressed as the means ± standard deviations from three identical wells. (E) Effect of RA and SP600125 on H322 cell growth. H322 cells were treated for 4 days with medium alone, RA (1 μM), SP600125 (5 μM), or both, and cell density was measured by MTT assays. Values were expressed as the means ± standard deviations from three identical wells.