Re-expression of LKB1 in LKB1-mutant EKVX cells leads to resistance to paclitaxel through the up-regulation of MDR1 expression

The restoration of LKB1 in LKB1-null cells failed to promote paclitaxel-induced apoptosis in both p53-wild type and p53-mutant backgrounds, indicating that LKB1 was not required for paclitaxel-induced apoptosis. Interestingly, the re-establishment of LKB1 expression led to the up-regulation of class III beta-tubulin and MDR1 in EKVX cells. The up-regulation of MDR1 protein and transcripts in EKVX cells was specifically associated with the expression of wild-type LKB1 and mainly responsible for the increased cellular resistance to paclitaxel. However, the presence of LKB1 protein was not required to maintain this increased MDR1 expression even though there was no genetic amplification or promoter de-methylation of the ABCB1 locus in EKVX-LKB1-WT cells. These data suggest that LKB1 does not promote paclitaxel-induced apoptosis in most NSCLC cell lines. In contrast, in some NSCLC, the presence of LKB1 may facilitate increases in either MDR1 or class III beta-tubulin expression which can lead to paclitaxel resistance.