Cul3 overexpression depletes Nrf2 in breast cancer and is associated with sensitivity to carcinogens, to oxidative stress, and to chemotherapy

Abstract

Nrf2 is the key transcription factor for cytoprotective gene programs. Nrf2 is normally maintained at very low concentrations by proteasomal degradation, through its interaction with the adapter protein Keap1 and the Cul3 E3 ligase. Increased Nrf2 concentration resulting from loss of function Keap1 mutations has been described in chemoresistant non-small cell lung cancer. Previous studies in breast cancer showed low levels of some Nrf2-regulated detoxification genes, but the mechanism has not been systematically examined. We found that half of the breast cancer cell lines examined have decreased concentration of Nrf2 compared with normal mammary epithelial cell lines, associated with variable but detectable levels in Keap1 levels, and consistently increased Cul3 mRNA and protein.

miR-200a Regulates Nrf2 Activation by Targeting Keap1 mRNA in Breast Cancer Cells

“…2A) (26,27). Because down-regulation of Nrf2 has been found in breast cancers and is often preceded by the dysregulation of Keap1 (9,45,47), we investigated the possible relationship between these two phenomena and found that loss of miR-200a correlated with Keap1 up-regulation and Nrf2 down-regulation in breast cancer cell lines.…”

“…Nrf2 is found down-regulated in breast cancer cell lines and breast cancer patient samples when compared to healthy mammary epithelial cells (9). However, Nrf2 is not down-regulated in all cancers.…”

“…Previously, Nrf2 has been found down-regulated in multiple breast cancer cell lines and patient samples (9). To determine if miRs might play some role in the dysregulation of the Keap1/Nrf2 pathway, we first examined the expression profile of 88 highly characterized miRs in metastatic breast cancer cell line MDA-MB-231 compared with that of the MCF-10A non-tumorigenic mammary epithelial cell line.…”

Cullin-3 protein expression levels correlate with breast cancer progression

“…[9][10][11] Among these seven family members, Cullin-3 and Cullin-4 have been directly linked to breast cancer. [12][13][14][15] In a study done by Chen et al Cullin-4A was shown to be amplified and overexpressed in 600PE, MDA-MB-157 and SKBR3 cells. Cullin-4A mRNA expression was detected in 14 of 30 (47%) primary breast tumors analyzed, but not in the adjacent normal breast tissues, indicating that Cullin-4A might function as an oncogene.…”

“…15 Silencing of Cullin-3, which would stabilize Nrf2, resulted in increased resistance to oxidative stress, as well as to benzo(a)pyrene, doxorubicin and paclitaxel treatments. 14 It has also been shown that a cysteine to tyrosine mutation at position 23 in Keap1 (Keap1C23Y), which functions in Cullin-3 substrate recognition, impairs the ability of Keap1 to ubiquitylate Nrf2 and repress its activity via proteasomal degradation. 15 This mutation has been found in breast cancers and suggests that the resulting Figure 4, compared with normal breast tissue, which showed no Cullin-3 expression, both tumor number 904 and tumor number 281 showed high levels of Cullin-3 protein.…”