Upregulated Myc expression in N-methyl nitrosourea (MNU)- induced rat mammary tumours

Abstract

Background: The most common incident cancer and cause of cancer-related deaths in women is breast cancer. The Myc gene is upregulated in many cancer types including breast cancer, and it is considered as a potential anti-cancer drug target. The present study was conducted to evaluate the Myc (gene and protein) expression pattern in an experimental mammary tumour model in rats.

Materials and methods: Thirty six Sprague Dawley rats were divided into: Experimental group (26 animals), which received the chemical carcinogen N-methyl nitrosourea (MNU) and a control group (10 animals), which received vehicle only. c-Myc oncoprotein and its mRNA expression pattern were evaluated using immunohistochemistry (IHC) and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), respectively, in normal rat mammary tissue and mammary tumours. The rat glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene was used as internal control for semi-quantitative RT-PCR.

Results: Histopathological examination of mammary tissues and tumours from MNU treated animals revealed the presence of premalignant lesions, benign tumours, in situ carcinomas and invasive carcinomas. Immunohistochemical evaluation of tumour tissues showed upregulation and heterogeneous cellular localization of c-Myc oncoprotein. The expression levels of c-Myc oncoprotein were significantly elevated (75- 91%) in all the tumours. Semi-quantitative RT-PCR revealed increased expression of c-Myc mRNA in mammary tumours compared to normal mammary tissues.

Conclusions: Further large-scale investigation study is needed to adopt this experimental rat mammary tumour model as an in vivo model to study anti-cancer strategies directed against Myc or its downstream partners at the transcriptional or post-transcriptional level.