The role of the organic anion transporting polypeptide OATP4A1 in immunactivation in colorectal cancer and inflammatory colon disease.

Abstract

481 Background: OATP-transporter proteins, such as OATP4A1, present influence cancer progression by providing compounds (hormones, prostaglandins, cyclic nucleotides, second messenger proteins, drugs) which either inhibit or stimulate tumor cells growth. Therefore, OATP expression in cancer cells and in the stroma, i.e., the microenvironment surrounding the epithelial cells can become a critical parameter. Methods: OATP4A1 was investigated in paraffin-embedded specimens from 148 patients with colorectal cancer and 20 with diverticulitis by immunohistochemistry (IHC) on an automatic quantitative microscopic image analysis system (TissuesFaxs). With the Histoquest program, the immunoreactive score (IRS), was calculated from the degree of the staining intensity and the number of OATP4A1-positive cells. To identify OATP4A1+-cells, double-immunofluorescence staining (IF) was done with antibodies against appropriate cellular markers. Results: OATP4A1 was located in the membrane and cytosol of colon cancer cells and immune cells, while membranous OATP4A1staining was seen in normal mucosa. OATP4A1 levels were higher in cancer cells in patients without tumor recurrence for up to 5 years (NR) than in patients with an early relapse (R) having IRS of 4391±231 and 3026±373 (Mean±SEM), respectively. Highest OATP4A1 levels were observed in immune cells in the tumors of Rs (IRS, 5712 ±254, while in NRs they were lower (IRS: 3549±358; p=0.05). In both groups, OATP4A1 levels in stroma cells were low (288±54 vs. 611±82). OATP4A1 expressing immune cell subtypes in cancer and diverticulitis sections were identified as CD45+ leukocytes, CD3+ T- and CD20+ B-cells, CD68+ macrophages, CD34+precursor cells. OATP4A1 was not detectable in Conclusions: High levels of OATP4A1 in immune cells in malignant and non-malignant colon disease suggest a role of the transporter in the activation of the immune system in malignant and non-malignant colon disease. Whether OATP4A1 might be a therapeutical target has to be established.