ras-induced Up-regulation of CTP:Phosphocholine Cytidylyltransferase α Contributes to Malignant Transformation of Intestinal Epithelial Cells

Cancer cells have enhanced lipogenic capacity characterized by increased synthesis of fatty acids and complex lipids, including phosphatidylcholine (PC). As the rate-limiting enzyme in the CDP-choline pathway for PC synthesis, CTP:phosphocholine cytidylyltransferase alpha (CCT alpha) is implicated in the provision of membranes and bioactive lipids necessary of cell proliferation. In this study, we assessed the role of CCT alpha in malignant intestinal epithelial cells transformed with activated H-ras (IEC-ras). Three IEC-ras clones had significant up-regulation CCT alpha expression, but PC synthesis and in vitro activity of CCT alpha were similar to control IEC. RNA interference of CCT alpha in adherent IEC-ras did not affect PC synthesis, confirming that the enzyme was relatively inactive. However, CCT alpha silencing in ras-transformed IEC reduced anchorage-independent growth, a criterion for malignant transformation, as well as tumorigenicity in mice. Relative to their adherent counterparts, detached IEC-ras had increased PC synthesis that was attenuated by inducible CCT alpha silencing. Detachment of IEC-ras was accompanied by increased CCT alpha phosphorylation and cytosolic enzyme activity. We conclude that the expanded pool of CCT alpha in IEC-ras is activated by detachment. This provides the increased PC biosynthetic capacity that contributes to malignant transformation of intestinal epithelial cells when detached from the extracellular matrix.