Defining the role of ZEB1 in the pathogenesis of lung cancer

Using an in vitro model for malignant transformation of human bronchial epithelial cells (HBECs) we have found epithelial-to-mesenchymal transition (EMT) and expression of the EMT-transcription factor ZEB1 are early and critical events. Specifically, we found preexisting oncogenic mutations in TP53 and KRAS were required for HBECs to engage EMT machinery in response to microenvironmental (serum/TGFβ) or specific oncogenetic (MYC) EMT-inducing factors, which induce EMT through distinct TGFβ-dependent and vitamin D receptor (VDR)-dependent pathways, respectively, with both requiring ZEB1. Functional studies demonstrated ZEB1 causally promotes the malignant progression of HBECs and tumorigenicity of NSCLC and small cell lung cancer (SCLC) lines. Mechanistically ZEB1 directly represses ESRP1 leading to increased mesenchymal splicing of CD44, which drives a switch to CD44hi status and defines a highly transformed subpopulation. This was supported by finding ZEB1 is expressed in early-stage primary non-small cell lung cancers (NSCLC), as early as stage IB tumors, and its expression correlates with TNM stage. We conclude that: ZEB1-induced EMT and associated ESRP1 and CD44 molecular changes are important biomarkers for lung cancer pathogenesis; TGFβ and VDR are EMT chemoprevention targets; and as such, ZEB1 represents an important therapeutic target in NSCLC and SCLC. Human bronchial epithelial cells (HBECs) immortalized with cdk4 and hTERT and subsequently transformed with various oncogenetic manipulations (p53 knockdown, KrasV12, cMYC and ZEB1 over-expression) and/or growth conditions (10%FBS) were profiled on Illumina HumanHT-12 V4.0 expression beadchips. All cell lines were grown in KSFM (defined, serum-free medium) except HBEC3-KTRL53(R10), which was grown in RPMI1640 with 10% FBS.