Overexpression of lipocalins and pro-inflammatory chemokines and altered methylation of PTGS2 and APC2 in oral squamous cell carcinomas induced in rats by 4-nitroquinoline-1-oxide

Abstract

Oral squamous cell carcinomas (OSCC) induced in F344 rats by 4-nitroquinoline-1-oxide (4-NQO) demonstrate considerable phenotypic similarity to human oral cancers. Gene expression studies (microarray and PCR) were coupled with methylation analysis of selected genes to identify molecular markers of carcinogenesis in this model and potential biochemical and molecular targets for oral cancer chemoprevention. Microarray analysis of 11 pairs of OSCC and site-matched phenotypically normal oral tissues from 4-NQO-treated rats identified more than 3500 differentially expressed genes; 1735 genes were up-regulated in rat OSCC versus non-malignant tissues, while 1803 genes were down-regulated. In addition to several genes involved in normal digestion, genes demonstrating the largest fold increases in expression in 4-NQO-induced OSCC include three lipocalins (VEGP1, VEGP2, LCN2) and three chemokines (CCL, CXCL2, CXCL3); both classes are potentially druggable targets for oral cancer chemoprevention and/or therapy. Down-regulated genes in 4-NQO-induced OSCC include numerous keratins and keratin-associated proteins, suggesting that alterations in keratin expression profiles may provide a useful biomarker of oral cancer in F344 rats treated with 4-NQO. Confirming and extending our previous results, PTGS2 (cyclooxygenase-2) and several cyclooxygenase-related genes were significantly up-regulated in 4-NQO-induced oral cancers; up-regulation of PTGS2 was associated with promoter hypomethylation. Rat OSCC also demonstrated increased methylation of the first exon of APC2; the increased methylation was correlated with down-regulation of this tumor suppressor gene. Overexpression of pro-inflammatory chemokines, hypomethylation of PTGS2, and hypermethylation of APC2 may be causally linked to the etiology of oral cancer in this model.

Figure 1. Histology of normal and neoplastic oral (tongue) epithelium in F344 rats treated with 4-NQO.

A. Phenotypically normal oral epithelium in F344 rat treated with 4-NQO (H&E, x100). B. Non-invasive squamous cell papilloma (Score 0) induced by 4-NQO. The tumor is confined to the mucosal epithelium of the tongue (H&E, x40). C. Invasive OSCC (Score +1) induced by 4-NQO. The cancer extends through the mucosal epithelial basement membrane into the lamina propria (H&E, x100). D. Invasive OSCC (Score +2) induced by 4-NQO. The cancer extends into the upper muscle layers of the tongue (H&E, x100). E. Invasive OSCC (Score +3) induced by 4-NQO. The cancer demonstrates extensive invasion into the underlying muscle layers of the tongue (H&E, x40).