TRIM21 Ubiquitylates SQSTM1/p62 and Suppresses Protein Sequestration to Regulate Redox Homeostasis.

TRIM21 is a RING finger domain-containing ubiquitin E3 ligase whose expression is elevated in autoimmune disease. While TRIM21 plays an important role in immune activation during pathogen infection, little is known about its inherent cellular function. Here we show that TRIM21 plays an essential role in redox regulation by directly interacting with SQSTM1/p62 and ubiquitylating p62 at lysine 7 (K7) via K63-linkage. As p62 oligomerizes and sequesters client proteins in inclusions, the TRIM21-mediated p62 ubiquitylation abrogates p62 oligomerization and sequestration of proteins including Keap1, a negative regulator of antioxidant response. TRIM21-deficient cells display an enhanced antioxidant response and reduced cell death in response to oxidative stress. Genetic ablation of TRIM21 in mice confers protection from oxidative damages caused by arsenic-induced liver insult and pressure overload heart injury. Therefore, TRIM21 plays an essential role in p62-regulated redox homeostasis and may be a viable target for treating pathological conditions resulting from oxidative damage.

Autophagy mediates degradation of nuclear lamina.

Macroautophagy (hereafter referred to as autophagy) is a catabolic membrane trafficking process that degrades a variety of cellular constituents and is associated with human diseases. Although extensive studies have focused on autophagic turnover of cytoplasmic materials, little is known about the role of autophagy in degrading nuclear components. Here we report that the autophagy machinery mediates degradation of nuclear lamina components in mammals. The autophagy protein LC3/Atg8, which is involved in autophagy membrane trafficking and substrate delivery, is present in the nucleus and directly interacts with the nuclear lamina protein lamin B1, and binds to lamin-associated domains on chromatin. This LC3-lamin B1 interaction does not downregulate lamin B1 during starvation, but mediates its degradation upon oncogenic insults, such as by activated RAS. Lamin B1 degradation is achieved by nucleus-to-cytoplasm transport that delivers lamin B1 to the lysosome. Inhibiting autophagy or the LC3-lamin B1 interaction prevents activated RAS-induced lamin B1 loss and attenuates oncogene-induced senescence in primary human cells. Our study suggests that this new function of autophagy acts as a guarding mechanism protecting cells from tumorigenesis.

SCCA1/SERPINB3 promotes oncogenesis and epithelial-mesenchymal transition via the unfolded protein response and IL6 signaling.

The serine/cysteine protease inhibitor SCCA1 (SERPINB3) is upregulated in many advanced cancers with poor prognosis, but there is limited information about whether it makes functional contributions to malignancy. Here, we show that SCCA1 expression promoted oncogenic transformation and epithelial-mesenchymal transition (EMT) in mammary epithelial cells, and that SCCA1 silencing in breast cancer cells halted their proliferation. SCCA1 overexpression in neu(+) mammary tumors increased the unfolded protein response (UPR), IL6 expression, and inflammatory phenotypes. Mechanistically, SCCA1 induced a prolonged nonlethal increase in the UPR that was sufficient to activate NF-κB and expression of the protumorigenic cytokine IL6. Overall, our findings established that SCCA1 contributes to tumorigenesis by promoting EMT and a UPR-dependent induction of NF-κB and IL6 autocrine signaling that promotes a protumorigenic inflammation.

The impact of the P2X7 receptor antagonist A-804598 on neuroimmune and behavioral consequences of stress.

Stress leads to neuroinflammatory and behavioral consequences through upregulation of inflammatory-related cytokines within the central nervous system such as interleukin-1ß (IL-1ß), which may be indicative of microglial priming/activation. Evidence suggests that the P2X7 receptor (P2X7R) may play an important role in the synthesis and conversion of IL-1ß. In a series of six experiments, adult male rats were intubated with a highly selective P2X7R antagonist (A-804598) before footshock exposure. As expected, footshock increased IL-1ß and CD14 mRNA in the paraventricular nucleus, and A-804598 (25 mg/kg) partially attenuated these effects. Footshock also increased hypothalamic IL-1 protein in whole hypothalamic blocks, but no effect was observed on the formation of pro-IL-1ß or IL-1ß in the paraventricular nucleus as assessed using western blotting. A-804598 also did not reverse the suppression in exploration produced by stress exposure. The present findings support the use of the footshock paradigm as a method for inducing stress-related neuroimmune and behavioral changes, but the evidence to support the role of A-804598 as a potential tool to reverse such changes remains modest. This study is the first to examine the role of P2X7R in vivo following footshock exposure. Further characterization of P2X7R may have implications for understanding the relationship between stress and inflammation.

NRBF2 regulates autophagy and prevents liver injury by modulating Atg14L-linked phosphatidylinositol-3 kinase III activity.

The Beclin 1-Vps34 complex, the core component of the class III phosphatidylinositol-3 kinase (PI3K-III), binds Atg14L or UVRAG to control different steps of autophagy. However, the mechanism underlying the control of PI3K-III activity remains elusive. Here we report the identification of NRBF2 as a component in the specific PI3K-III complex and a modulator of PI3K-III activity. Through its microtubule interaction and trafficking (MIT) domain, NRBF2 binds Atg14L directly and enhances Atg14L-linked Vps34 kinase activity and autophagy induction. NRBF2-deficient cells exhibit enhanced vulnerability to endoplasmic reticulum (ER) stress that is reversed by re-introducing exogenous NRBF2. NRBF2-deficient mice develop focal liver necrosis and ductular reaction, accompanied by impaired Atg14L-linked Vps34 activity and autophagy, although the mice show no increased mortality. Our data reveal a key role for NRBF2 in the assembly of the specific Atg14L-Beclin 1-Vps34-Vps15 complex for autophagy induction. Thus, NRBF2 modulates autophagy via regulation of PI3K-III and prevents ER stress-mediated cytotoxicity and liver injury.

Oncogenic Ras induces inflammatory cytokine production by upregulating the squamous cell carcinoma antigens SerpinB3/B4.

Mounting evidence indicates that oncogenic Ras can modulate cell autonomous inflammatory cytokine production, although the underlying mechanism remains unclear. Here we show that squamous cell carcinoma antigens 1 and 2 (SCCA1/2), members of the Serpin family of serine/cysteine protease inhibitors, are transcriptionally upregulated by oncogenic Ras via MAPK and the ETS family transcription factor PEA3. Increased SCCA expression leads to inhibition of protein turnover, unfolded protein response, activation of NF-κB and is essential for Ras-mediated cytokine production and tumour growth. Analysis of human colorectal and pancreatic tumour samples reveals a positive correlation between Ras mutation, enhanced SCCA expression and IL-6 expression. These results indicate that SCCA is a Ras-responsive factor that plays an important role in Ras-associated cytokine production and tumorigenesis.

Elevated expression of squamous cell carcinoma antigen (SCCA) is associated with human breast carcinoma.

Squamous cell carcinoma antigen (SCCA) belongs to the serine protease inhibitor (Serpin) family of proteins. Elevated expression of SCCA has been used as a biomarker for aggressive squamous cell carcinoma (SCC) in cancers of the cervix, lung, head and neck, and liver. However, SCCA expression in breast cancer has not been investigated. Immunohistochemical analysis of SCCA expression was performed on tissue microarrays containing breast tumor tissues (n = 1,360) and normal breast epithelium (n = 124). SCCA expression was scored on a tiered scale (0-3) independently by two evaluators blind to the patient's clinical status. SCCA expression was observed in Grade I (0.3%), Grade II (2.5%), and Grade III (9.4%) breast cancers (p<0.0001). Comparing tissues categorized into the three non-metastatic TNM stages, I-III, SCCA positivity was seen in 2.4% of Stage I cancers, 3.1% of Stage II cancers, and 8.6% of Stage III breast cancers (p = 0.0005). No positive staining was observed in normal/non-neoplastic breast tissue (0 out of 124). SCCA expression also correlated to estrogen receptor/progesterone receptor (ER/PR) double-negative tumors (p = 0.0009). Compared to SCCA-negative patients, SCCA-positive patients had both a worse overall survival and recurrence-free survival (p<0.0001 and p<0.0001, respectively). This study shows that SCCA is associated with both advanced stage and high grade human breast carcinoma, and suggests the necessity to further explore the role of SCCA in breast cancer development and treatment.

DNA alkylating therapy induces tumor regression through an HMGB1-mediated activation of innate immunity.

Dysregulation of apoptosis is associated with the development of human cancer and resistance to anticancer therapy. We have previously shown in tumor xenografts that DNA alkylating agents induce sporadic cell necrosis and regression of apoptosis-deficient tumors. Sporadic tumor cell necrosis is associated with extracellular release of cellular content such as the high mobility group box 1 (HMGB1) protein and subsequent recruitment of innate immune cells into the tumor tissue. It remained unclear whether HMGB1 and the activation of innate immunity played a role in tumor response to chemotherapy. In this study, we show that whereas DNA alkylating therapy leads to a complete tumor regression in an athymic mouse tumor xenograft model, it fails to do so in tumors deficient in HMGB1. The HMGB1-deficient tumors have an impaired ability to recruit innate immune cells including macrophages, neutrophils, and NK cells into the treated tumor tissue. Cytokine array analysis reveals that whereas DNA alkylating treatment leads to suppression of protumor cytokines such as IL-4, IL-10, and IL-13, loss of HMGB1 leads to elevated levels of these cytokines upon treatment. Suppression of innate immunity and HMGB1 using depleting Abs leads to a failure in tumor regression. Taken together, these results indicate that HMGB1 plays an essential role in activation of innate immunity and tumor clearance in response to DNA alkylating agents.