Correlation of induction of ATP binding cassette transporter A5 (ABCA5) and ABCB1 mRNAs with differentiation state of human colon tumor.

The ATP binding cassette transporter subtype A5 (ABCA5)-like transporters ABCA5, ABCA6, ABCA8, ABCA9 and ABCA10 form a unique gene cluster within the ABC transporter superfamily, though their function is still poorly understood. The purpose of this study is to examine whether ABCA5-like transporters may play a role in tumor development by measuring their mRNA levels in human tissues and tumors. Intense mRNA expression of human ABCA5-like transporters was detected in the brain. ABCA5 and ABCA8 mRNAs were detected in spleen, testis and ovary. ABCA5 mRNA was also detected in liver and pancreas. ABCA6 mRNA was detected in lung and liver, and ABCA8 was detected in lung. ABCA6, ABCA7 and ABCA8 mRNAs were not detected in any tumors, but weak mRNA expression of ABCA10 was detected in all tumors examined. ABCA5 mRNA was detected in poorly differentiated colon adenocarcinoma (GI-112) and undifferentiated ovarian carcinoma (GI-102), but not in normal colon. ABCB1 mRNA was also detected in GI-112, while ABCC1 and ABCA2 mRNAs were not. In contrast, ABCC1 and ABCA2 mRNAs, but not ABCA5 or ABCB1 mRNA, were detected in well differentiated colon adenocarcinoma (CX-1). Thus, induction of ABCA5, together with ABCB1, appears to be correlated with the differentiation state of human colon tumors, and may have a role in tumor development.