Endothelial lipase (LIPG) is a cell surface associated lipase that displays phospholipase A1 activity towards phosphatidylcholine present in high‐density lipoproteins (HDL). LIPG was recently reported to be expressed in breast cancer and to support proliferation, tumourigenicity and metastasis. Here we show that severe oxidative stress leading to AMPK activation triggers LIPG upregulation, resulting in intracellular lipid droplet accumulation in breast cancer cells, which supports survival. Neutralizing oxidative stress abrogated LIPG upregulation and the concomitant lipid storage. In human breast cancer, high LIPG expression was observed in a limited subset of tumours and was significantly associated with shorter metastasis‐free survival in node‐negative, untreated patients. Moreover, expression of PLIN2 and TXNRD1 in these tumours indicated a link to lipid storage and oxidative stress. Altogether, our findings reveal a previously unrecognized role for LIPG in enabling oxidative stress‐induced lipid droplet accumulation in tumour cells that protects against oxidative stress, and thus supports tumour progression.

Members of the receptor tyrosine kinase family (RTK) have been shown to be present in the nucleus of cells; however, the mechanisms underlying their trafficking to the nucleus, and their relevance once there are poorly understood. In the present study, we focus on the RTK ErbB3 and elucidate the mechanisms regulating its trafficking. We show that heregulin-stimulation induces trafficking of phosphorylated ErbB3 from the plasma membrane to the nucleus via a clathrin-independent mechanism. Nuclear import of ErbB3 occurs via importin ␤1, which drives the receptor through the nuclear pore complex. In the nucleus, ErbB3 interacts with transcription complexes, and thereby has a role in transcriptional regulation. Our results also demonstrate that ErbB3 nuclear localization is transient as it is exported out of the nucleus by the nuclear receptor protein crm-1. Analysis of normal, regenerating tissues, and tumors showed that ErbB3 nuclear translocation is a common event in proliferating tissues.The epidermal growth factor receptor family (EGFR,3 ErbB2, ErbB3, and ErbB4) comprises some of the best characterized members of the receptor tyrosine kinases (RTKs). Their activation influences cellular signaling via the mitogen-activated protein kinase (MAPK)/ERK and the phosphatidylinositol 3-kinase (PI3K)-AKT pathways, both of which regulate essential cellular mechanisms including cell proliferation, survival, and differentiation. Dysregulation of these pathways is regularly found in carcinogenesis, tumor progression, and metastasis (1, 2). Furthermore, overexpression of EGFR, ErbB2, and ErbB3 in tumor tissue is often associated with poor patient outcome (3). ErbB3 is the least studied member of the EGFR family, However, recent evidence supports a key role for ErbB3 in cell transformation and malignancy of tumors (4). In addition, therapeutic interventions directed toward EGFR family members lead to the activation of ErbB3, which in turn is associated with the development of chemoresistance (5-8). However, the consequences of signaling activation and trafficking of ErbB3, as well as its functional relevance are poorly understood.Previous reports have shown that EGFR family members are present in the nucleus, either as full-length molecules, as in the case of EGFR (9) and ErbB2 (10), or truncated as for ␥-secretase-cleaved ErbB4 (11). In the present study, we demonstrate that nuclear translocation of ErbB3 is not limited to cancer, but appears to be a general phenomenon in proliferating tissues. To clarify ErbB3 trafficking from the cell surface to the nucleus, and its function once there, we applied a comprehensive approach using subcellular fractionation, cell surface protein labeling, immunostaining, and live cell imaging to investigate the transfer of ErbB3 to the nucleus. In addition, we studied the activation state, the translocation mechanisms, and the nuclear entry of ErbB3. To understand its function in the nucleus, we investigated the prevalence of nuclear ErbB3 in both controlled and diseased tissues. Our findings ...

The pyrrolizidine alkaloid senecionine induces CYP-dependent destruction of sinusoidal endothelial cells and cholestasis in mice. Archives of Toxicology.

Binding of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to the plasma membrane TRAIL-R1/-R2 selectively kills tumor cells. This discovery led to evaluation of TRAIL-R1/-R2 as targets for anti-cancer therapy, yet the corresponding clinical trials were disappointing. Meanwhile, it emerged that many cancer cells are TRAIL-resistant and that TRAIL-R1/-R2-triggering may lead to tumor-promoting effects. Intriguingly, recent studies uncovered specific functions of long ignored intracellular TRAIL-R1/-R2, with tumor-promoting functions of nuclear (n)TRAIL-R2 as the regulator of let-7-maturation. As nuclear trafficking of TRAIL-Rs is not well understood, we addressed this issue in our present study. Cell surface biotinylation and tracking of biotinylated proteins in intracellular compartments revealed that nTRAIL-Rs originate from the plasma membrane. Nuclear TRAIL-Rs-trafficking is a fast process, requiring clathrin-dependent endocytosis and it is TRAIL-dependent. Immunoprecipitation and immunofluorescence approaches revealed an interaction of nTRAIL-R2 with the nucleo-cytoplasmic shuttle protein Exportin-1/CRM-1. Mutation of a putative nuclear export sequence (NES) in TRAIL-R2 or the inhibition of CRM-1 by Leptomycin-B resulted in the nuclear accumulation of TRAIL-R2. In addition, TRAIL-R1 and TRAIL-R2 constitutively localize to chromatin, which is strongly enhanced by TRAIL-treatment. Our data highlight the novel role for surface-activated TRAIL-Rs by direct trafficking and signaling into the nucleus, a previously unknown signaling principle for cell surface receptors that belong to the TNF-superfamily.

TNF-related apoptosis-inducing ligand (TRAIL) receptor 2 (TRAIL-R2) can induce apoptosis in cancer cells upon crosslinking by TRAIL. However, TRAIL-R2 is highly expressed by many cancers suggesting pro-tumor functions. Indeed, TRAIL/TRAIL-R2 also activate pro-inflammatory pathways enhancing tumor cell invasion, migration, and proliferation. In addition, nuclear TRAIL-R2 (nTRAIL-R2) promotes malignancy by inhibiting miRNA let-7-maturation. Here, we show that TRAIL-R2 interacts with the tumor suppressor protein p53 in the nucleus, assigning a novel pro-tumor function to TRAIL-R2. Knockdown of TRAIL-R2 in p53 wild-type cells increases the half-life of p53 and the expression of its target genes, whereas its re-expression decreases p53 protein levels. Interestingly, TRAIL-R2 also interacts with promyelocytic leukemia protein (PML), a major regulator of p53 stability. PML-nuclear bodies are also the main sites of TRAIL-R2/p53 co-localization. Notably, knockdown or destruction of PML abolishes the TRAIL-R2-mediated regulation of p53 levels. In summary, our finding that nTRAIL-R2 facilitates p53 degradation and thereby negatively regulates p53 target gene expression provides insight into an oncogenic role of TRAIL-R2 in tumorigenesis that particularly manifests in p53 wild-type tumors.