High CD44 expression mediates p62-associated NFE2L2/NRF2 activation in breast cancer stem cell-like cells: Implications for cancer stem cell resistance

Abstract

Cluster of differentiation 44 (CD44) is the most common cancer stem cell (CSC) marker and high CD44 expression has been associated with anticancer drug resistance, tumor recurrence, and metastasis. In this study, we aimed to investigate the molecular mechanism by which CD44 and nuclear factor erythroid 2-like 2 (NFE2L2; NRF2), a key regulator of antioxidant genes, are linked to CSC resistance using CD44high breast CSC-like cells. NRF2 expression was higher in CD44high cell populations isolated from doxorubicin-resistant MCF7 (ADR), as well as MCF7, MDA-MB231, and A549 cells, than in corresponding CD44low cells. High NRF2 expression in the CD44highCD24low CSC population (ADR44P) established from ADR cells depended on standard isoform of CD44. Silencing of CD44 or overexpression of CD44 resulted in the reduction or elevation of NRF2, respectively, and treatment with hyaluronic acid, a CD44 ligand, augmented NRF2 activation. As functional implications, NRF2 silencing rendered ADR44P cells to retain higher levels of reactive oxygen species and to be sensitive to anticancer drug toxicity. Moreover, NRF2-silenced ADR44P cells displayed tumor growth retardation and reduced colony/sphere formation and invasion capacity. In line with these, CD44 significantly colocalized with NRF2 in breast tumor clinical samples. The molecular mechanism of CD44-mediated NRF2 activation was found to involve high p62 expression. CD44 elevation led to an increase in p62, and inhibition of p62 resulted in NRF2 suppression in ADR44P. Collectively, our results showed that high CD44 led to p62-associated NRF2 activation in CD44high breast CSC-like cells. NRF2 activation contributed to the aggressive phenotype, tumor growth, and anticancer drug resistance of CD44high CSCs. Therefore, the CD44-NRF2 axis might be a promising therapeutic target for the control of stress resistance and survival of CD44high CSC population within breast tumors.

Loss of Xanthine Oxidoreductase Potentiates Propagation of Hepatocellular Carcinoma Stem Cells

“…In comparison with other cancer cells, CSCs have lower levels of intracellular ROS production and higher sensitivity to oxidant stress, which are considered beneficial for maintenance of CSC stemness . The low ROS levels are primarily due to the enhanced intercellular free radical scavenging system in CSCs . Increased ROS can induce antioxidant transcription factors and signal pathway activation in CSCs .…”

“…Current studies have revealed that Nrf2‐KEAP1 signaling could be regulated by several molecular mechanisms. The up‐regulation of p62 and p21 sustained enhancement of Nrf2 activity through competitive binding in several CSCs models . Likewise, Nrf2 signaling could be inhibited by USP15, which is part the ubiquitin‐specific processing protease family of deubiquitinating enzymes mediated by KEAP1 deubiquitination …”

p62/SQSTM1 – steering the cell through health and disease

“…Accordingly, in HCC, the SQSTM1-Keap1-Nrf2 axis promotes metabolic reprogramming that includes enhanced production of uridine diphosphate (UDP)-glucuronate and glutathione, both of which promote cancer development as well as its resistance to anticancer drugs (Saito et al, 2016;Umemura et al, 2016). This prominent role of the SQSTM1-Keap1-Nrf2 axis in tumorigenesis has been extended to other cancer forms, including ovarian (Xia et al, 2014), pancreatic (Todoric et al, 2017), breast (Ryoo et al, 2018;Xu et al, 2017), lung (Huang et al, 2016) and arsenic-induced skin cancers (Shah et al, 2017), as well as multiple myeloma (Riz et al, 2016) and esophageal squamous cell carcinoma (Shi et al, 2018). In the case of pancreatic ductal adenocarcinoma (PDAC), SQSTM1mediated activation of Nrf2 also results in the induction of the ubiquitin ligase MDM2, which further aggravates cancer progression by promoting degradation of p53 and inducing the Notch signaling pathway (Todoric et al, 2017).…”

Enhancer Remodeling Promotes Tumor-Initiating Activity in NRF2-Activated Non-Small Cell Lung Cancers

“…Tumor-initiating abilities of cancer cells are experimentally evaluated based on their capacity to generate grossly recognizable tumors. Thus, the self-renewal capacity of TICs is not easily separated from their proliferative and survival abilities, which are strongly enhanced by NRF2, and chemo-resistant populations expressing high levels of NRF2 are often regarded as TICs (Mizuno et al, 2015;Jia et al, 2015;Ryoo et al, 2018). More precisely, it remains to be elucidated whether NRF2 does more than merely enhance proliferation and survival in order to support the tumor-initiating activity of cancer cells.…”