Abstract
Mutp53 level is widely variable among individual cancer cells in tumor tissues, and within cells a higher level of mutp53 is usually observed in the nucleus as compared to the cytoplasm. This spatial heterogeneity in mutp53 expression has been well documented and likely plays an important role in tumor therapeutic resistance. However, its underlying mechanism remains poorly understood. In this study, we first revealed a critical role of micro-environmental reducing status in regulating mutp53 stability and spatially heterogeneous accumulation. Immunofluorescence and ThiolTracker Violet dye staining demonstrated a clear correlation between the cellular mutp53 level and the reducibility in the patient-derived tumor tissues and mutp53-expressing cancer cell lines. The nucleus exhibited both higher reducibility and more mutp53 accumulation than the cytoplasm did. Supplementing GSH exacerbated the accumulation of mutp53, while consuming GSH led to extensive depletion of mutp53, suggesting that the environmental reducing status kept mutp53 stability. Mechanistically, S-glutathionylation could trigger ubiquitination and proteasomal degradation of mutp53. A highly-reducing local environment preserved mutp53 stability by inhibiting glutathionylation and subsequent proteasomal degradation of mutp53, which also provided an explanation for the differential accumulation of mutp53 proteins in the nucleus and cytoplasm. Thirdly, we revealed that the expression level of glutathione reductase (GR) was positively correlated with mutp53 accumulation across the cultured mutp53-expressing cell lines, patient-derived tumor tissues and patient databases. Over-expression of GR reinforced the environmental reducibility, affected glutathionylation and improved mutp53 accumulation, while inhibiting GR either by chemical inhibitors or genetic approach induced massive clearance of a variety of mutp53 and effectively retarded the growth of p53-mutated cell-derived xenografts in mice. These studies provided an explanation for the widely-observed spatial heterogeneous accumulation of mutp53 proteins, and inhibiting GR or directly consuming GSH represented a promising strategy for mutp53 carrying cancer therapy.