Persistent activation of Nrf2 through p62 in hepatocellular carcinoma cells

Inami, Yoshihiro; Waguri, Satoshi; Sakamoto, Ayako; Kouno, Tsuguka; Nakada, Kazuto; Hino, Okio; Watanabe, Sumio; Ando, Jin; Iwadate, Manabu; Yamamoto, Masayuki; Lee, Myung-Shik; Tanaka, Keiji; Komatsu, Masaaki

doi:10.1084/jem2085oia12

Cited by 53 publications

(83 citation statements)

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“…Recent studies have suggested that impaired autophagy may predispose an individual to tumorigenesis LC3A gene is involved in autophagy H Bai et al (Rubinsztein, 2006;Mathew et al, 2007;Fleming et al, 2011). This is supported by an increased incidence of tumors in mouse models with a haploinsufficiency or deficiency of autophagy-related genes such as Becn1, Atg5, Atg7, Atg4c and Zbtb24 (Qu et al, 2003;Yousefi et al, 2006;Marin˜o et al, 2007;Takahashi et al, 2007;Inami et al, 2011;Komatsu, 2011;Takamura et al, 2011). Thus, genetic aberrations affecting autophagy may be a factor in human cancers.…”

Section: Discussionmentioning

confidence: 99%

A transcriptional variant of the LC3A gene is involved in autophagy and frequently inactivated in human cancers

et al. 2012

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Microtubule-associated protein 1 light chain 3 has an important role in autophagy. The human LC3 gene family has five members, LC3A (variant-1: v1 and -2: v2), LC3B, LC3B2 and LC3C. Although a form of LC3B modified by phosphatidylethanolamine (form-II) is localized in autophagosomes, it is not clear whether other LC3 proteins also function in autophagy. Here, we examined the association between autophagy and human LC3 proteins during starvation-or p53-induced autophagy in Saos-2 cells. In an analysis of the intracellular distribution of each LC3 protein fused with GFP, GFP-LC3Av1 was frequently localized in autophagosomes with a punctate pattern, similar to GFP-LC3B. Further, endogenous LC3Av1 generated form-II and mostly localized in LC3B-positive autophagosomes during the induced autophagy. Interestingly, LC3Av1, not LC3B, was frequently inactivated at the transcriptional level in various human cancer cell lines (111/244 cell lines, 45.5%) and its inactivation was due to aberrant DNA methylation in esophageal squamous cell carcinoma (ESCC) cell lines and primary tumors. Restoration of LC3Av1 expression in KYSE170 cells, an LC3Av1-inactivated ESCC cell line, showed the inhibition of tumor growth in vivo. These results suggest that LC3Av1, not only LC3B, functions in autophagy and further, LC3Av1 may be crucial in carcinogenesis.

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Section: Discussionmentioning

confidence: 99%

A transcriptional variant of the LC3A gene is involved in autophagy and frequently inactivated in human cancers

et al. 2012

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“…However, once hepatocarcinogenesis had been initiated, it was also required to suppress the expression of tumor suppressors to promote the development of HCC. It does not appear likely that these effects were due to other nonspecific activities of Atg5, as mice with liver-specific KO of Atg7 was also found to develop benign liver tumors in another study, 9,10 and the treatment of rats with chloroquine, which inhibits autophagy, 24 enhanced the development of liver tumors induced by DEN in the early dysplastic stage and suppressed tumor progression in the later stage. 25 Our finding that the ablation of autophagy induced the expression of multiple tumor suppressors in the liver tumors of L-Atg5-KO mice is interesting (Figure 5b).…”

Section: Discussionmentioning

confidence: 99%

“…It has been shown that the monoallelic deletion of the Beclin-1 gene in mice induced tumor lesions in various tissues, 7 Atg4C-knockout (KO) mice had increased susceptibility to carcinogens for the development of fibrosarcomas 8 and the systemic mosaic KO of Atg5 and the liver-specific KO of Atg7 in mice led to the development of benign liver adenomas. 9,10 Autophagy has also been shown to promote tumor growth. It has been shown that autophagy can enhance the survival of tumor cells in the hypoxic regions of solid tumors.…”

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confidence: 99%

Autophagy inhibits oxidative stress and tumor suppressors to exert its dual effect on hepatocarcinogenesis

et al. 2014

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The role of autophagy in carcinogenesis is controversial and apparently complex. By using mice with hepatocyte-specific knockout of Atg5, a gene essential for autophagy, we longitudinally studied the role of autophagy in hepatocarcinogenesis. We found that impairing autophagy in hepatocytes would induce oxidative stress and DNA damage, followed by the initiation of hepatocarcinogenesis, which could be suppressed by the antioxidant N-acetylcysteine. Interestingly, these mice developed only benign tumors with no hepatocellular carcinoma (HCC), even after the treatment with diethylnitrosamine, which induced HCC in wild-type mice. The inability of mice to develop HCC when autophagy was impaired was associated with the induction of multiple tumor suppressors including p53. Further analysis indicated that the induction of p53 was associated with the DNA-damage response. Tumorigenesis studies using an established liver tumor cell line confirmed a positive role of autophagy in tumorigenesis and a negative role of p53 in this process when autophagy was impaired. Our studies thus demonstrate that autophagy is required to maintain healthy mitochondria and to reduce oxidative stress and DNA damage to prevent the initiation of hepatocarcinogenesis. However, once hepatocarcinogenesis has been initiated, its presence is also required to suppress the expression of tumor suppressors to promote the development of HCC. Autophagy (i.e., macroautophagy) is important for cells to remove protein aggregates and damaged organelles. Its dysfunction can cause a variety of diseases including cancers. 1,2 However, its role in carcinogenesis is apparently complex, as it has been shown in different reports to positively or negatively regulate carcinogenesis. 3,4 Autophagy apparently can function as a tumor suppressor, as the gene encoding Beclin-1, a component of the phosphatidylinositol-3-kinase class III (PI3KC3) complex that is essential for the initiation of autophagy, is often monoallelically deleted or mutated in breast, ovarian and prostate cancers. 5 Frameshift mutations in Atg2B, Atg5, Atg9B and Atg12 autophagy genes are also often found in gastric and colorectal cancers with microsatellite instability. 6 The tumor suppressor role of autophagy is further supported by the studies using mouse models. It has been shown that the monoallelic deletion of the Beclin-1 gene in mice induced tumor lesions in various tissues, 7 Atg4C-knockout (KO) mice had increased susceptibility to carcinogens for the development of fibrosarcomas 8 and the systemic mosaic KO of Atg5 and the liver-specific KO of Atg7 in mice led to the development of benign liver adenomas. 9,10 Autophagy has also been shown to promote tumor growth. It has been shown that autophagy can enhance the survival of tumor cells in the hypoxic regions of solid tumors. 11 It has also been shown that in cells expressing oncogenic Ras, autophagy is required to promote tumorigenesis by maintaining oxidative metabolism or facilitating glycolysis. 12,13 Moreover, it has also been demonstrate...

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“…Recent experimental evidence showed that p62, a multidomain adapter protein, has a critical role in an oxidative stress response pathway by its direct interaction with the ubiquitin ligase adaptor Keap1, which resulted in constitutive activation of Nrf2 (38,39). Another study presented evidence that p62 was an Nrf2 target gene, which created a positive feedback loop in the Nrf2-mediated transcriptional response (40).…”

Section: Discussionmentioning

confidence: 99%

Knockdown of Nrf2 enhances autophagy induced by temozolomide in U251 human glioma cell line

et al. 2012

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Abstract. Glioblastoma multiforme (GBM) and oxidative stress are closely linked. Oxidative stress affects many signaling pathways and may cause the induction of autophagy. The NF-E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) signaling pathway is the main pathway responsible for cell defense against oxidative stress and Nrf2 is a critical transcription factor related with cancer multidrug resistance. However, the relation between Nrf2 and regulation of autophagy is not well understood. In this study, we used temozolomide (TMZ), which inhibited the viability of GBM cells mainly by inducing autophagic cell death and explored the role of Nrf2 downregulation on autophagy induced by TMZ in GBM cells. In U251-Si-Nrf2 48 h after transfection the protein levels of Nrf2 were significantly downregulated, while the protein levels of LC3B-II increased by western blot analysis. Knockdown of Nrf2 also led to a significant increase of autophagic vacuoles and acidic vesicular organelles (AVOs), revealed by trans mission electron microscopy (TEM) and acridine orange (AO) staining using flow cytometry. Collectively, these findings demonstrate that knockdown of Nrf2 can enhance the basal level of autophagy in the U251 glioma cell line. Furthermore, after the treatment with TMZ (100 µM) for 3 days, the U251-Si-Nrf2 transfected cells showed less viability rate by cell counting kit-8 (CCK-8) assay and the levels of autophagy increased obviously through analysis of western blot and AO staining using flow cytometry. Taken together, our results suggest that knockdown of Nrf2 may enhance autophagy induced by TMZ in the U251 glioma cell line, which should be further evaluated for novel anticancer activity.

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Persistent activation of Nrf2 through p62 in hepatocellular carcinoma cells

Cited by 53 publications

References 1 publication

A transcriptional variant of the LC3A gene is involved in autophagy and frequently inactivated in human cancers

A transcriptional variant of the LC3A gene is involved in autophagy and frequently inactivated in human cancers

Autophagy inhibits oxidative stress and tumor suppressors to exert its dual effect on hepatocarcinogenesis

Knockdown of Nrf2 enhances autophagy induced by temozolomide in U251 human glioma cell line

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