Pancreatic cancer cells express CD44 variant 9 and multidrug resistance protein 1 during mitosis.

Pancreatic cancer is one of the most lethal cancers with high metastatic potential and strong chemoresistance. Its intractable natures are attributed to high robustness in tumor cells for their survival. We demonstrate here that pancreatic cancer cells (PCCs) with an epithelial phenotype upregulate cell surface expression of CD44 variant 9 (CD44v9), an important cancer stem cell marker, during the mitotic phases of the cell cycle. Of five human CD44(+) PCC lines examined, three cell lines, PCI-24, PCI-43 and PCI-55, expressed E-cadherin and CD44 variants, suggesting that they have an epithelial phenotype. By contrast, PANC-1 and MIA PaCa-2 cells expressed vimentin and ZEB1, suggesting that they have a mesenchymal phenotype. PCCs with an epithelial phenotype upregulated cell surface expression of CD44v9 in prophase, metaphase, anaphase and telophase and downregulated CD44v9 expression in late-telophase, cytokinesis and interphase. Sorted CD44v9-negative PCI-55 cells resumed CD44v9 expression when they re-entered the mitotic stage. Interestingly, CD44v9(bright) mitotic cells expressed multidrug resistance protein 1 (MDR1) intracellularly. Upregulated expression of CD44v9 and MDR1 might contribute to the intractable nature of PCCs with high proliferative activity.