A Non-genetic Mechanism Involving the Integrin b4/Paxillin Axis Contributes to Chemoresistance in Lung Cancer

Tumor heterogeneity and cisplatin resistance are major causes of tumor relapse and poor survival. Here, we show that in lung cancer, interaction between paxillin (PXN) and integrin b4 (ITGB4), components of the focal adhesion (FA) complex, contributes to cisplatin resistance. Knocking down PXN and ITGB4 attenuated cell growth and improved cisplatin sensitivity, both in 2D and 3D cultures. PXN and ITGB4 independently regulated expression of several genes. In addition, they also regulated expression of common genes including USP1 and VDAC1 that are required for maintaining genomic stability and mitochondrial function, respectively. Mathematical modelling suggested that bistability could lead to stochastic phenotypic switching between cisplatin-sensitive and resistant states in these cells. Consistently, purified subpopulations of sensitive and resistant cells recreated the mixed parental population when cultured separately. Altogether, these data point to an unexpected role of the FA complex in cisplatin resistance, and highlight a novel non-genetic mechanism. Knockdown of ITGB4 (Cat #: SR302473C) at the mRNA level was executed using siRNAs purchased from OriGene Technologies (Rockville, MD, USA). Knockdown of PXN was achieved by siRNA purchased from Life Technologies Corporation (Cat #: 4392421). JetPRIME transfection reagent (Polyplus Transfection, Illkirch, France) was used to transfect the siRNAs according to the manufacturer’s protocol. Cells were seeded in 6-well plates (200,000 cells/well) and allowed to adhere overnight. Next day, 10 nM siRNA was transfected with 4 μl jetPRIME reagent in complete growth medium for each well. Cell growth medium was changed the next day and expression was detected 72 h post-transfection by qPCR and immunoblot. The RNA extracted at 72hr of transfection was sent to the core for RNA sequencing. The experiments were repeated two times with SiRNA ITGB4 or SiRNA PXN or both SiRNA ITGB4 and PXN.