The role of GSTP1 in non-small cell lung cancer

Abstract

The unsatisfactory outcomes often encountered in the treatment of non-small cell lung cancers can be attributed to multiple drug resistance, tumour metastases, and tumour recrudescence. Recently, these features are suggested to be modulated by cancer stem cells (CSC) which is a subpopulation of tumour cells with special phenotypic characteristics such as enhanced survival, resistance to toxicity, cell invasion and migration, as well as maintenance of low intracellular levels of reactive oxygen species (ROS). Targeting CSC has been suggested as an essential approach for long-term eradication of tumours. Previous data have demonstrated Ca2+and calmodulin-dependent protein kinase Ⅱα (CaMKⅡα) could regulate CSC, and CSC isolated from NSCLC cell lines using well recognized surface markers contained lower levels of ROS. Accordingly, this study hypothesizes CaMKⅡα could play a role in the control of ROS levels through regulation of REDOX enzymes. To investigate this possibility, the effects of CaMKⅡα on the expression of the master ROS regulator nuclear factor erythroid-2-related factor 2 (NFR2) and its downstream targets were examined using in vitro models. Results from western blot analysis showed a higher level of activated, nuclear NRF2in cells over-expressing CaMKⅡα than that in control cells. Furthermore, amongst five NRF2 downstream targets, glutathione S-transferase P1 (GSTP1) showed the most consistent change in mRNA expression upon CaMKⅡα manipulation by pharmacologic or genetic approaches. In the literature, GSTP1 has not been shown to affect CSC properties. Thus, the in vitro analysis of self-renewal ability was studied in NSCLC cells with transient GSTP1 knockdown, which led to reduced cell sphere and colony formation, respectively. Together, the data showed maintenance of low intracellular ROS levels by regulation of NRF2/GSTP1 expression is a potential mechanism through which CaMKⅡα modulates CSC self-renewal capacity. The anti-oxidant action of CaMKⅡα/NRF2/GSTP1 pathway might be a novel treatment for NSCLC. Further studies using stable genetic manipulation of GSTP1 and in vivo models would provide further support for this hypothesis.