Pancreatic cancer cells express CD44 variant 9 and multidrug resistance protein 1 during mitosis
Introduction
Pancreatic cancer is one of the most lethal cancers with a 5-year survival rate less than 5%. This discouraging outcome is assumed to be due to the intrinsic biologic aggressiveness and robustness of pancreatic cancer cells (PCCs), characterized by extensive local invasion and strong resistance to conventional therapies (Li et al., 2004). Consequently, there have been no improvements of survival in patients with advanced pancreatic cancer even after the introduction of gemcitabine (Burris et al., 1997, Li et al., 2004).
Cancer stem cells (CSCs) are defined as a small fraction of tumor cells that display properties of self-renewal, high tumorigenicity and drug resistance, resulting in cancer metastasis and recurrence (Huntly and Gilliland, 2005, Mani et al., 2008). Accumulating evidence indicates the existence of pancreatic CSCs (Li et al., 2007). CD44, an important marker for CSCs, is a membrane glycoprotein involved in cell–cell and cell–extracellular matrix adhesion as well as cell migration, differentiation and survival (Zöller, 2011) and can directly reprogram stem cell properties in colon cancer cells (Su et al., 2011). The CD44 gene is encoded by 20 exons and generates a standard isoform (CD44s) and many variant isoforms (CD44v) by alternative splicing (Zöller, 2011). Importantly, expression of alternatively spliced variants reflects the grade of malignancy in gastric and breast cancers (Brown et al., 2011, Lau et al., 2014), with CD44s signaling the acquisition of a mesenchymal phenotype (Mima et al., 2012, Okabe et al., 2014). In breast cancer, splicing isoforms are switched from CD44v to CD44s as cancer cells undergo epithelial–mesenchymal transition (EMT) (Brown et al., 2011).
Although the precise functions of variant isoforms still remain to be elucidated, a recent study has shown that expression of the CD44 variant containing exons 8–10 (CD44v8-10 or CD44v9) contributes to the defense against reactive oxygen species by upregulating the synthesis of a major antioxidant, glutathione (Ishimoto et al., 2011), thereby making cancer cells resistant to chemotherapy and radiotherapy. CD44v9 also interacts with the death receptor FAS in lipid rafts, and interferes with death receptor signaling, leading to apoptosis resistance (Mielgo et al., 2006). Clinically, CD44v9 expression represents a potential predictive marker for recurrence in patients with colorectal (Yamaguchi et al., 1996) and multiple early gastric cancers (Hirata et al., 2013).
We demonstrate here that PCC lines with an epithelial phenotype upregulate the expression of CD44v9 and multidrug resistance protein 1 (MDR1) during the mitotic phases of the cell cycle. This observation suggests that the upregulated expression of CD44v9 and MDR1 might contribute to the intractable nature of PCCs with high proliferative activity.
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Cells
Five human PCC lines, PCI-24, PCI-43, PCI-55, PANC-1 and MIA PaCa-2, were used. PCI-24, PCI-43 and PCI-55 were established in our laboratory from pancreatic ductal adenocarcinoma tissues of primary sites surgically resected at Hokkaido University Hospital (Kishimoto et al., 1996). MIA PaCa-2 cells were obtained from the RIKEN Bio-Resource Center (Tsukuba, Japan). PCC lines were maintained in Dulbecco's minimal essential medium supplemented with 10% fetal bovine serum and penicillin/streptomycin.
PCI-24, PCI-43 and PCI-55 cells exhibit an epithelial phenotype, and PANC-1 and MIA PaCa-2 cells show a mesenchymal phenotype
We first analyzed the expression patterns of EMT markers in the following PCC lines: PCI-24, PCI-43, PCI-55, PANC-1 and MIA PaCa-2 (Fig. 1A). Transcriptional expression of E-cadherin, a prototypical epithelial cell marker (Zeisberg and Neilson, 2009), was observed in PCI-24, PCI-43 and PCI-55 cells. By contrast, PANC-1 and MIA PaCa-2 cells did not express E-cadherin, but expressed vimentin (Vuoriluoto et al., 2011) and ZEB1, a zinc finger transcription factor suppressing E-cadherin expression (
Discussion
In the present study, we have demonstrated that PCC lines with an epithelial phenotype strongly upregulate CD44v9 expression during mitosis (Fig. 2, Fig. 3, Fig. 4). Cell surface expression of CD44v8-10 plays an important role in the defense against reactive oxygen species, leading to ultimate survival of CSCs (Ishimoto et al., 2011). Therefore, our observation suggests that dividing PCCs can acquire strong resistance against oxidative stress. The malignant features of pancreatic cancer depend
Conflicts of interest
The authors declare that there are no conflicts of interest.
Acknowledgments
This work was supported by Grants-in-Aid for Scientific Research Grant Number 26460464 from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
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2021, Mutation Research - Reviews in Mutation ResearchCitation Excerpt :The role of CD44v9 expression during the pathogenicity of the pancreatic cancer cell was analyzed. The findings showed that this variant has high expression in the pancreatic cancer cells and can be considered as a resistant factor to chemotherapy [142]. These results were further supported by another research on a group of HCC patients positive for hepatitis C virus with liver cancer.
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These authors contributed equally to this work.