CD44 is an adhesion molecule expressed in cancer stem-like cells. Here, we show that a CD44 variant (CD44v) interacts with xCT, a glutamate-cystine transporter, and controls the intracellular level of reduced glutathione (GSH). Human gastrointestinal cancer cells with a high level of CD44 expression showed an enhanced capacity for GSH synthesis and defense against reactive oxygen species (ROS). Ablation of CD44 induced loss of xCT from the cell surface and suppressed tumor growth in a transgenic mouse model of gastric cancer. It also induced activation of p38(MAPK), a downstream target of ROS, and expression of the gene for the cell cycle inhibitor p21(CIP1/WAF1). These findings establish a function for CD44v in regulation of ROS defense and tumor growth.

In cancer metastasis, various environmental stressors attack the disseminating cells. The successful colonization of cancer cells in secondary sites therefore requires the ability of the cells to avoid the consequences of such exposure to the stressors. Here we show that orthotopic transplantation of a CD44 variant isoform-expressing (CD44v + ) subpopulation of 4T1 breast cancer cells, but not that of a CD44v − subpopulation, in mice results in efficient lung metastasis accompanied by expansion of stem-like cancer cells. such metastasis is dependent on the activity of the cystine transporter xCT, and the stability of this protein is controlled by CD44v. We find that epithelial splicing regulatory protein 1 regulates the expression of CD44v, and knockdown of epithelial splicing regulatory protein 1 in CD44v + cells results in an isoform switch from CD44v to CD44 standard (CD44s), leading to reduced cell surface expression of xCT and suppression of lung colonization. The epithelial splicing regulatory protein 1-CD44v-xCT axis is thus a potential therapeutic target for the prevention of metastasis.

An increased glycolytic flux accompanied by activation of the pentose phosphate pathway (PPP) is implicated in chemoresistance of cancer cells. In this study, we found that CD44, a cell surface marker for cancer stem cells, interacts with pyruvate kinase M2 (PKM2) and thereby enhances the glycolytic phenotype of cancer cells that are either deficient in p53 or exposed to hypoxia. CD44 ablation by RNA interference increased metabolic flux to mitochondrial respiration and concomitantly inhibited entry into glycolysis and the PPP. Such metabolic changes induced by CD44 ablation resulted in marked depletion of cellular reduced glutathione (GSH) and increased the intracellular level of reactive oxygen species in glycolytic cancer cells. Furthermore, CD44 ablation enhanced the effect of chemotherapeutic drugs in p53-deficient or hypoxic cancer cells. Taken together, our findings suggest that metabolic modulation by CD44 is a potential therapeutic target for glycolytic cancer cells that manifest drug resistance. Cancer Res; 72(6); 1438-48. Ó2012 AACR.