Non-invasive detection of fecal protein kinase C β(I)I and ζ messenger RNA: Putative biomarkers for colon cancer

Abstract

We have developed a non-invasive method utilizing feces, containing sloughed colonocytes, as a sensitive technique for detecting diagnostic colonic biomarkers. In this study, we used the rat colon carcinogenesis model to determine if changes in fecal protein kinase C (PKC) expression have predictive value in monitoring the neoplastic process. Weanling rats were injected with saline or azoxymethane (AOM) and 36 weeks later fecal samples and mucosa were collected, poly A+ RNA isolated, and quantitative RT-PCR performed using primers to PKC β(I)I, and ζ. Fecal PKC β(I)I and ζ mRNA levels were altered by the presence of a tumor, with tumor-bearing animals having a 3-fold higher (P < 0.05) PKC β(I)I expression as compared with animals without tumors. In addition, AOM-injection increased mucosal PKC β(I)I mRNA expression compared with saline controls. No effect of tumor incidence on mucosal PKC β(I)I expression was observed. In contrast, fecal PKC ζ expression was 2.5-fold lower (P < 0.05) in animals injected with azoxymethane versus saline. Since tumor incidence exerts a reciprocal effect on fecal PKC β(I)I and ζ mRNA expression, data were also expressed as the ratio between PKC β(I)I and ζ. The isozyme ratio was strongly related to tumor incidence, i.e. ratio for animals with tumors was 2.18 ± 1.25, animals without tumors was 0.50 ± 0.16, P = 0.025. We demonstrate that the expression of fecal PKC β(I)I and ζ may serve as a noninvasive marker for development of colon tumors. A sensitive technique for the detection of colon cancer is of importance since early diagnosis can substantially reduce mortality.