Analysis of gene expression profiles of forestomach tumors in rasH2 mice initiated with N-ethyl-N-nitrosourea

Abstract

To clarify the mechanisms underlying enhancement of carcinogenesis in transgenic mice carrying a human prototype c-Ha- ras gene (rasH2 mouse), animals received a single intraperitoneal injection of 120 mg/kg N-ethyl-N-nitrosourea (ENU) and at 20 weeks thereafter expression profiles in three induced forestomach squamous cell carcinomas were assessed using high-density oligonucleotide microarrays. In addition, the reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to assess mRNA expression of human c-Ha- ras gene and some molecules involved in the Ras-regulated mitogen-activated protein kinase (MAPK) pathway. Compared with normal forestomach tissue from control mice, 416 and 368 genes, respectively, were found to be commonly up- and down-regulated by 2-fold or more in the three tumors. Many genes involved in tumor invasion and metastasis such as transforming growth factor beta1 and matrix metalloproteinases were up-regulated, reflecting tumor progression. RT-PCR analysis confirmed up-regulation of transgene, mouse endogenous Ha- ras, N- ras, raf, Mekk2, c- fos, junB, c- myc and cyclin D1. These results suggest that activation of the Ras-MAPK cascade following up-regulation of both human and mouse endogenous ras genes is involved in the enhanced tumorigenesis of ENU-induced forestomach squamous cell carcinomas in rasH2 mice.