Mucinous adenocarcinoma of the lung is a subtype of highly invasive pulmonary tumors and is associated with decreased or absent expression of the transcription factor NK2 homeobox 1 (NKX2-1; also known as TTF-1). Here, we show that haploinsufficiency of Nkx2-1 in combination with oncogenic Kras G12D , but not with oncogenic EGFR L858R , caused pulmonary tumors in transgenic mice that were phenotypically similar to human mucinous adenocarcinomas. Gene expression patterns distinguished tumor goblet (mucous) cells from nontumorigenic airway and intestinal goblet cells. Expression of NKX2-1 inhibited urethane and oncogenic Kras G12D -induced tumorigenesis in vivo. Haploinsufficiency of Nkx2-1 enhanced Kras G12D -mediated tumor progression, but reduced EGFR L858R -mediated progression. Genome-wide analysis of gene expression demonstrated that a set of genes induced in mucinous tumors was shared with genes induced in a nontumorigenic chronic lung disease, while a distinct subset of genes was specific to mucinous tumors. ChIP with massively parallel DNA sequencing identified a direct association of NKX2-1 with the genes induced in mucinous tumors. NKX2-1 associated with the AP-1 binding element as well as the canonical NKX2-1 binding element. NKX2-1 inhibited both AP-1 activity and tumor colony formation in vitro. These data demonstrate that NKX2-1 functions in a context-dependent manner in lung tumorigenesis and inhibits Kras G12D -driven mucinous pulmonary adenocarcinoma. IntroductionMucinous adenocarcinoma of the lung (formerly known as mucinous bronchioalveolar cancer) is pathologically classified as tumor cells with goblet cell morphology containing abundant intracytoplasmic mucin (1). Invasive mucinous adenocarcinoma of the lung has a higher malignant potential than do the more common types of lung adenocarcinoma, such as acinar or papillary adenocarcinoma. Mucinous adenocarcinoma of the lung is associated with decreased or absent expression of the transcription factor NK2 homeobox 1 (NKX2-1; also known as TTF-1) and the expression of mucins, including mucin 5AC, oligomeric mucus/gel-forming (MUC5AC). Genetically, approximately 76% of mucinous adenocarcinomas of the lung have KRAS mutations, a frequent mutation in lung adenocarcinoma associated with tobacco use (2), but mucinous adenocarcinoma of the lung is rarely associated with EGFR mutations. In contrast, nonmucinous lung adenocarcinoma is frequently associated with EGFR mutations (∼45%), but less frequently with KRAS mutations (∼13%; ref. 1).NKX2-1 plays a critical role in lung morphogenesis and respiratory epithelial-specific gene expression, including activation of surfactant proteins and repression of mucins (3, 4). The potential oncogenic role of NKX2-1 in the pathogenesis of adenocarcinoma of the lung was proposed by findings that a region of 14q13.3 containing NKX2-1, NKX2-8, and PAX9 was amplified in approximately 10% of human lung adenocarcinoma (5-7). Loss-offunction and gain-of-function studies in human lung carcinoma and transformed cells supporte...

The bronchioles of the murine lung are lined by a simple columnar epithelium composed of ciliated, Clara, and goblet cells that together mediate barrier function, mucociliary clearance and innate host defense, vital for pulmonary homeostasis. In the present work, we demonstrate that expression of Sox2 in Clara cells is required for the differentiation of ciliated, Clara, and goblet cells that line the bronchioles of the postnatal lung. The gene was selectively deleted in Clara cells utilizing Scgb1a1-Cre, causing the progressive loss of Sox2 in the bronchioles during perinatal and postnatal development. The rate of bronchiolar cell proliferation was decreased and associated with the formation of an undifferentiated, cuboidal-squamous epithelium lacking the expression of markers of Clara cells (Scgb1a1), ciliated cells (FoxJ1 and α-tubulin), and goblet cells (Spdef and Muc5AC). By adulthood, bronchiolar cell numbers were decreased and Sox2 was absent in extensive regions of the bronchiolar epithelium, at which time residual Sox2 expression was primarily restricted to selective niches of CGRP staining neuroepithelial cells. Allergen-induced goblet cell differentiation and mucus production was absent in the respiratory epithelium lacking Sox2. In vitro, Sox2 activated promoter-luciferase reporter constructs for differentiation markers characteristic of Clara, ciliated, and goblet cells, Scgb1a1, FoxJ1, and Agr2, respectively. Sox2 physically interacted with Smad3 and inhibited TGF-β1/Smad3-mediated transcriptional activity in vitro, a pathway that negatively regulates proliferation. Sox2 is required for proliferation and differentiation of Clara cells that serve as the progenitor cells from which Clara, ciliated, and goblet cells are derived.

No abstract

No abstract