Elevated osteopontin expression and proliferative/apoptotic ratio in the colorectal adenoma-dysplasia-carcinoma sequence

Abstract

Colorectal cancer progression is characterized by altered epithelial proliferation and apoptosis and by changed expression of tumor development regulators. Our aims were to determine the proliferative/apoptotic epithelial cell ratio (PAR) in the adenoma-dysplasia-carcinoma sequence (ADCS), and to examine its association with osteopontin (OPN), a previously identified protein product related to cancer development. One mm diameter cores from 13 healthy colons, 13 adenomas and 13 colon carcinoma samples were included into a tissue microarray (TMA) block. TUNEL reaction and Ki-67 immunohistochemistry were applied to determine the PAR. The osteopontin protein was also immunodetected. Stained slides were semiquantitatively evaluated using digital microscope and statistically analyzed with logistic regression and Fisher's exact test. The PAR continuously increased along the ADCS. It was significantly (p < 0.001) higher in cancer epithelium (8.84 ± 7.01) than in adenomas (1.40 ± 0.78) and in normal controls (0.89 ± 0.21) (p < 0.001). Also, significant positive correlation was observed between elevated PAR and the expression of osteopontin. Cytoplasmic OPN expression was weak in healthy samples. In contrast, cytoplasmic immunoreaction was moderately intensive in adenomas, while in colon cancer strong, diffuse cytoplasmic immune staining was detected. Increasing PAR and OPN expression along ADCS may help monitoring colorectal cancer progression. The significantly elevated OPN protein levels we found during normal epithelium to carcinoma progression may contribute to the increased fibroblast-myofibroblast transition determining stem cell niche in colorectal cancer.