MA02.03 Expression of Oncofetal miRNAs Inactivates NFIB, a Developmental Transcription Factor Linked to Tumor Aggressiveness in Lung Adenocarcinoma

Abstract

Fetal and tumor development share striking similarities, such as intense cell proliferation, angiogenesis, increased cell motility, and immune evasion. Molecular regulators, including microRNAs (miRNAs), play important roles in both fetal lung development and in the malignant transformation of adult lung cells. Consequently, investigation of lung tumor biology in the context of lung development may reveal key regulatory mechanisms that tumors hijack from normal development, which potentially play critical roles in the pathology of lung cancer. 131 pairs of non-small cell lung cancer (NSCLC) tumor and non-malignant lung tissues and 15 human fetal lung tissue samples were profiled by miRNA-sequencing. Genes controlled by the oncofetal miRNAs identified were first investigated by miRNA-Data-Integration-Portal (mirDIP) prediction, followed by luciferase-reporter assays. Associations between patient survival and mRNA expression of oncofetal miRNA-gene targets were evaluated in independent samples (>1,400 cases) across multiple NSCLC cohorts. Immunohistochemical analysis of oncofetal miRNA targets was performed on 96 lung adenocarcinoma (LUAD) specimens. We describe for the first time a comprehensive characterization of miRNA expression in human fetal lung tissue, and identified numerous miRNAs that recapitulate their fetal expression patterns in NSCLC. Nuclear Factor I/B (NFIB), a transcription factor essential for lung development, was identified as being frequently targeted by these oncofetal miRNAs. Overexpression of the oncofetal miRNA miR-92b-3p, significantly reduced NFIB levels in vitro. Concordantly, analysis of NFIB expression in multiple NSCLC cohorts revealed its frequent underexpression in tumors (∼40-70%). This is in contrast with its recurrent oncogenic overexpression recently reported in SCLC. Low expression of NFIB was significantly associated with poorer survival in LUAD patients but not in squamous cell carcinoma patients, consistent with the functional role of NFIB in distal lung cell differentiation (i.e., precursor cells of LUAD). Furthermore, an NFIB-related gene signature was identified in LUAD tumors, comprising several well-known lung differentiation markers (e.g., TTF-1, SFTPB, ABCA3). The underexpression of NFIB protein was ultimately validated in LUAD specimens, which also revealed that tumors presenting lower levels of this transcription factor are associated with higher grade, biologically more aggressive LUAD (invasive mucinous, micropapillary and solid subtypes). This work has revealed a prominent mechanism for the downregulation of NFIB, a transcription factor essential for lung differentiation, which we found to be associated with aggressive phenotypes of LUAD and consequently, poor patient survival. Restoration of NFIB expression, specifically in LUAD, has the potential to induce lung cell differentiation and thereby reduce tumor aggressiveness.