Colorectal cancer has a high incidence of morbidity and mortality in the North American population. Elevated levels of
plasmalogens have been reported in some neoplastic tissues including colon
tumors, but the mechanism for this increase has not been defined. Since changes in
plasmalogen level are usually associated with changes in the other
phospholipid subclasses, a general increase in all
phospholipid subclasses may also be found in
colonic neoplasms. In this study, the levels of the major
phospholipids, including their
plasmalogen and diacylphospholipid subclasses, were found to be elevated in human malignant colonic tissues. Since
phosphatidylcholine is the most prominent type of
phospholipid found in both malignant and control tissues, the mechanism for its accumulation during
malignancy was investigated. Decreases in
phospholipase C and D activities were observed in
tumor samples, but an enhancement of the
CTP: phosphocholine cytidylyltransferase activity was also detected. Immunoblotting analysis revealed that the elevated cytidylyltransferase activity was caused by a three-fold increase in the level of
enzyme protein during
tumor development. Based on these
enzyme studies, we conclude that the high level of
phosphatidylcholine in colon
tumors resulted from a decrease in its turnover and an increase in its expression.