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Ilona Linnoila, M.D.
Molecular Pathology of Lung Carcinogenesis and Differentiation
The major research objectives of the Experimental Pathology Section are directed toward understanding the molecular pathology of transformation, differentiation, and early neoplasia in the lung. We study the molecular basis of these events in their actual anatomic context featuring topographic genotyping through imaging coupled with interactive morphometric analysis, confocal microscopy, laser capture, microdissection, and molecular analysis. We utilize material obtained through clinical studies from patients with and without lung cancer as well as several experimental models including transgenic animals. Our current efforts focus on the potential tumor suppressor role of Clara cell-specific protein (CC10) in lung carcinogenesis and the family of achaete-scute basic helix-loop-helix transcription factors, exemplified by hASH1, in pulmonary neuroendocrine (NE) differentiation and tumorigenesis.
Several years ago we made the observation that the proportion of lung adenocarcinomas was increasing while the data on the precursor lesions was scanty. CC10 is a major product of the metabolically active airway cells that are progenitor cells for the nonneoplastic and neoplastic epithelium, including many adenocarcinomas. Our data from humans and animal models demonstrate that CC10 expression is markedly downregulated during early carcinogenesis. To address whether CC10 expression is compatible with the neoplastic phenotype, CC10 cDNA was overexpressed in cancer cells and immortalized normal bronchial epithelial cells. Enhanced expression in a nonsmall cell cancer cell line resulted in decreased clonogenic survival, decreased invasiveness, and decreased metalloproteinase expression. These data suggest that downregulation of CC10 contributes to neoplastic progression. We are further evaluating the potential tumor suppressor role of CC10 by investigating CC10 knockout animals during experimental lung carcinogenesis.
In our second approach, our laboratory used clinical lung cancer resection specimens to screen for precursors for adenocarcinoma. Systematic review of the three lung compartments revealed that in the alveolar region of the lung, marked changes in CC10 expression patterns were associated with metaplasia and atypia, such as bronchialization of alveoli and atypical alveolar hyperplasia. These areas also demonstrated a number of molecular abnormalities including loss of heterozygosity of 3p, a site of putative tumor suppressor gene, increased c-myc expression, and p53 abnormalities, suggesting that these abnormalities may in fact be early neoplastic changes.
We have previously shown that early changes and field cancerization in the lung are also characterized by alterations in the neuroendocrine (NE) differentiation. A minority of normal bronchial epithelial cells and many lung cancers, especially small cell lung cancer (SCLC), which is the most lethal form of human lung cancer, exhibit a NE phenotype that may reflect a common precursor cell population. The family of achaete-scute basic helix-loop-helix transcription factors, exemplified by hASH1, plays a pivotal role in the neurosensory development in Drosophila and vertebrates. We have shown hASH1 is selectively expressed in normal pulmonary NE cells and their precursors as well as in various lung cancers with NE features. A disruption of the gene in mice caused a complete lack of pulmonary NE cells. Depletion of hASH1 from lung cancer cells by antisense oligonucleotides resulted in a significant decrease in NE markers. To determine whether hASH1 overexpression is sufficient to drive NE differentiation in heterologous airway epithelial cells or is associated with aberrant growth, we established a transgenic mouse system where hASH1 was expressed under CC10 promoter. Overexpression of hASH1 alone led to hyperplasia of airway epithelium with metaplasia. When coupled with SV40 Large T antigen, greatly enhanced epithelial growth resulted in massive tumors with NE differentiation. Thus, a homolog of Drosophila neural fate determination genes appears necessary for progression of lung epithelial cells through a NE differentiation pathway and carcinogenesis that is characteristic for approximately one-third of human lung cancers.
The significance of our project is that the results will provide a rational basis for early detection and intervention in human lung carcinogenesis by identifying specific markers and models for multistep epithelial carcinogenesis.
We have collaborated with Douglas Ball and Stephen Baylin, Johns Hopkins University; Francesco DeMayo, Baylor College of Medicine; Bruce Johnson, Harvard University; Anil Mukherjee, Seth Steinberg, and Sandra Swain, NIH; and Hanspeter Witschi, University of California at Davis.
This page was last updated on 2/20/2013.