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MO04 - Lung Cancer Biology I (ID 86)
- Event: WCLC 2013
- Type: Mini Oral Abstract Session
- Track: Biology
- Presentations: 1
MO04.05 - Tracheal basal cells in the lung squamous dysplasia: moving proximal. (ID 1700)
16:15 - 17:45 | Author(s): L.D. Nield
Squamous cell carcinoma (SCC) is the second most common form of lung cancer, a disease primarily observed in smokers. Studies have shown that preneoplastic dysplasias are the precursors for SCC. However, only a subset of these lesions progress to invasive carcinoma and predicting the fate of individual lesions is difficult. Understanding the processes associated with the development of dysplasia would therefore have significant impact on preventative therapy for high-risk lesions. To this goal we have studied N-nitroso-tris chloroethyl urea (NTCU) model of premalignant murine squamous dysplasia. Bi-weekly topical application of NTCU for 32-weeks caused endobronchial dysplasias that were pathologically similar to dysplasias encountered in human smokers. In the current study we used NTCU model to identify the events that precede dysplastic changes in murine airways.
Immunofluorescence analysis of NTCU treated airways showed abundant expression of keratin 5 positive (K5+) basal cells. In normal mouse respiratory epithelium K5+ cells are confined only in the trachea and are absent in the bronchial epithelium. Ectopic expressions of K5+ cells in the mouse bronchial epithelium therefore suggested a role for tracheal basal cells in the pathogenesis of NTCU-induced dysplasia. To explore this possibility we analyzed tracheal and bronchial histology after vehicle and 20mM NTCU treatment at 4, 8, 12, 16, 25 and 32 weeks.
Low-grade dysplasia of the tracheal epithelium was observed as early as 4 weeks of NTCU exposure. On the contrary, squamous metaplasia or low-grade dysplasia of the bronchial epithelium was not seen until 25 weeks. Morphometric analysis of immunostained tracheal tissue showed a time-dependent increase in the numbers of K5+ cells and a concomitant loss of cells expressing Clara cell secretory protein (CCSP) and ciliated cells. We have shown previously that injury to the trachea upregulates expression of keratin 14 (K14) in basal cells. Consistent with this phenomenon, NTCU exposure showed a time-dependent increase in the number of K5/K14 dual-positive basal cells. To understand the mechanism by which NTCU treatment mediates ectopic expression of basal cells in the lung, we used flow-cytometry to analyze cell-surface markers expressed by tracheal basal cells. These studies revealed a time-dependent decrease in the level of integrin a6b4 (CD49f). CD49f is a hemidesmosomal protein that facilitates attachment of basal cells to the basement membrane. These findings suggested that NTCU treatment might promote migration of tracheal basal cells by destabilizing their adherence to the basement membrane.
Collectively, our results showed an early involvement of tracheal basal cells in the generation of dysplastic lung lesions in a murine model of SCC. By moving the focus proximal, we have discovered a realm of biological developments in the trachea that had not been previously examined. Further research of these processes will aid in the elucidation of dysplastic development in SCC.
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