TAK1 Regulates the Nrf2 Antioxidant System Through Modulating p62/SQSTM1.

AIMS: Nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) is the master transcriptional regulator of antioxidant gene expression. On increased oxidative stress, an adaptor for Nrf2 degradation, Kelch-like ECH-associated protein 1 (Keap1), is directly modulated by oxidants in the cytoplasm, which results in stabilization and activation of Nrf2. Nrf2 is also constitutively active, to some extent, in the absence of exogenous oxidative stress. We have previously demonstrated that intestinal epithelium-specific TGF-ß-activated kinase 1 (TAK1) deletion downregulates the level of Nrf2 protein, resulting in an increase of reactive oxygen species (ROS) in a mouse model. We aim at determining the mechanism by which TAK1 modulates the level of Nrf2. RESULTS: We found that TAK1 upregulated serine 351 phosphorylation of an autophagic adaptor protein, p62/Sequestosome-1 (SQSTM1), which facilitates interaction between p62/SQSTM1 and Keap1 and subsequent Keap1 degradation. This, ultimately, causes increased Nrf2. Tak1 deficiency reduced the phosphorylation of p62/SQSTM1, resulting in decreased steady-state levels of Nrf2 along with increased Keap1. We also found that this regulation is independent of the canonical redox-mediated Nrf2 activation mechanism. In Tak1-deficient intestinal epithelium, a synthetic phenolic electrophile, butylated hydroxyanisole still effectively upregulated Nrf2 and reduced ROS. INNOVATION: Our results identify for the first time that TAK1 is a modulator of p62/SQSTM1-dependent Keap1 degradation and maintains the steady state-level of Nrf2. CONCLUSION: TAK1 regulates Nrf2 through modulation of Keap-p62/SQSTM1 interaction. This regulation is important for homeostatic antioxidant protection in the intestinal epithelium. Antioxid. Redox Signal. 25, 953-964.

Recruitment of the oncoprotein v-ErbA to aggresomes.

Aggresome formation, a cellular response to misfolded protein aggregates, is linked to cancer and neurodegenerative disorders. Previously we showed that Gag-v-ErbA (v-ErbA), a retroviral variant of the thyroid hormone receptor (TRα1), accumulates in and sequesters TRα1 into cytoplasmic foci. Here, we show that foci represent v-ErbA targeting to aggresomes. v-ErbA colocalizes with aggresomal markers, proteasomes, hsp70, HDAC6, and mitochondria. Foci have hallmark characteristics of aggresomes: formation is microtubule-dependent, accelerated by proteasome inhibitors, and they disrupt intermediate filaments. Proteasome-mediated degradation is critical for clearance of v-ErbA and T(3)-dependent TRα1 clearance. Our studies highlight v-ErbA's complex mode of action: the oncoprotein is highly mobile and trafficks between the nucleus, cytoplasm, and aggresome, carrying out distinct activities within each compartment. Dynamic trafficking to aggresomes contributes to the dominant negative activity of v-ErbA and may be enhanced by the viral Gag sequence. These studies provide insight into novel modes of oncogenesis across multiple cellular compartments.

Molecular discrimination of multiple primary versus metastatic squamous cell cancers of the head/neck and lung.

Patients with squamous cell carcinoma (SqCa) arising in the head and neck (H/N) commonly develop solitary pulmonary metastases that mimic the clinical, radiographic, and pathologic presentation of new primary lung SqCa. Primary pulmonary and metastatic SqCas cannot be differentiated from each other histologically. However, distinguishing multiple independent primary neoplasms from a primary H/N SqCa with pulmonary metastasis has prognostic significance due to its impact on tumor stage, the most important determinant of prognosis. Since genomic instability is a common feature of cancer, we hypothesized that independently-arising neoplasms in an individual patient would exhibit measurable genomic variation, enabling discrimination of tumor lineage and relatedness. In this study, we describe a molecular approach for analysis of genetic variation among multiple tumors from a single patient that does not rely on collection of normal tissue, and which can be performed with minimal tumor samples. Genomic DNA from H/N and lung SqCas from individual patients were analyzed by microsatellite PCR to identify discordant allelic variation. This method is rapid, sensitive, does not require constitutional DNA for comparison, and can be applied to the analysis of archival tumor DNA. Our results demonstrate that microsatellite PCR can identify discordant genetic variation among multiple tumors from a single patient, facilitating the molecular discrimination of metachronous primary SqCa versus solitary pulmonary metastasis from a H/N primary SqCa.