GPR37 is processed in the N-terminal ectodomain by ADAM10 and furin.

GPR37 is an orphan G protein-coupled receptor (GPCR) implicated in several neurological diseases and important physiological pathways in the brain. We previously reported that its long N-terminal ectodomain undergoes constitutive metalloprotease-mediated cleavage and shedding, which have been rarely described for class A GPCRs. Here, we demonstrate that the protease that cleaves GPR37 at Glu167↓Gln168 is a disintegrin and metalloprotease 10 (ADAM10). This was achieved by employing selective inhibition, RNAi-mediated downregulation, and genetic depletion of ADAM10 in cultured cells as well as in vitro cleavage of the purified receptor with recombinant ADAM10. In addition, the cleavage was restored in ADAM10 knockout cells by overexpression of the wild type but not the inactive mutant ADAM10. Finally, postnatal conditional depletion of ADAM10 in mouse neuronal cells was found to reduce cleavage of the endogenous receptor in the brain cortex and hippocampus, confirming the physiological relevance of ADAM10 as a GPR37 sheddase. Additionally, we discovered that the receptor is subject to another cleavage step in cultured cells. Using site-directed mutagenesis, the site (Arg54↓Asp55) was localized to a highly conserved region at the distal end of the ectodomain that contains a recognition site for the proprotein convertase furin. The cleavage by furin was confirmed by using furin-deficient human colon carcinoma LoVo cells and proprotein convertase inhibitors. GPR37 is thus the first multispanning membrane protein that has been validated as an ADAM10 substrate and the first GPCR that is processed by both furin and ADAM10. The unconventional N-terminal processing may represent an important regulatory element for GPR37.

USP28 Deficiency Promotes Breast and Liver Carcinogenesis as well as Tumor Angiogenesis in a HIF-independent Manner.

Recent studies suggest that the ubiquitin-specific protease USP28 plays an important role in cellular repair and tissue remodeling, which implies that it has a direct role in carcinogenesis. The carcinogenic potential of USP28 was investigated in a comprehensive manner using patients, animal models, and cell culture. The findings demonstrate that overexpression of USP28 correlates with a better survival in patients with invasive ductal breast carcinoma. Mouse xenograft experiments with USP28-deficient breast cancer cells also support this view. Furthermore, lack of USP28 promotes a more malignant state of breast cancer cells, indicated by an epithelial-to-mesenchymal (EMT) transition, elevated proliferation, migration, and angiogenesis as well as a decreased adhesion. In addition to breast cancer, lack of USP28 in mice promoted an earlier onset and a more severe tumor formation in a chemical-induced liver cancer model. Mechanistically, the angio- and carcinogenic processes driven by the lack of USP28 appeared to be independent of HIF-1α, p53, and 53BP1.Implications: The findings of this study are not limited to one particular type of cancer but are rather applicable for carcinogenesis in a more general manner. The obtained data support the view that USP28 is involved in tumor suppression and has the potential to be a prognostic marker. Mol Cancer Res; 16(6); 1000-12. ©2018 AACR.

Mitochondrial Dysfunction Due to Lack of Manganese Superoxide Dismutase Promotes Hepatocarcinogenesis.

AIMS: One of the cancer hallmarks is mitochondrial dysfunction associated with oxidative stress. Among the first line of defense against oxidative stress is the dismutation of superoxide radicals, which in the mitochondria is carried out by manganese superoxide dismutase (MnSOD). Accordingly, carcinogenesis would be associated with a dysregulation in MnSOD expression. However, the association studies available so far are conflicting, and no direct proof concerning the role of MnSOD as a tumor promoter or suppressor has been provided. Therefore, we investigated the role of MnSOD in carcinogenesis by studying the effect of MnSOD deficiency in cells and in the livers of mice. RESULTS: We found that loss of MnSOD in hepatoma cells contributed to their conversion toward a more malignant phenotype, affecting all cellular properties generally associated with metabolic transformation and tumorigenesis. In vivo, hepatocyte-specific MnSOD-deficient mice showed changed organ architecture, increased expression of tumor markers, and a faster response to carcinogenesis. Moreover, deficiency of MnSOD in both the in vitro and in vivo model reduced ß-catenin and hypoxia-inducible factor-1α levels. INNOVATION: The present study shows for the first time the important correlation between MnSOD presence and the regulation of two major pathways involved in carcinogenesis, the Wnt/ß-catenin and hypoxia signaling pathway. CONCLUSION: Our study points toward a tumor suppressive role of MnSOD in liver, where the Wnt/ß-catenin and hypoxia pathway may be crucial elements.

Manganese superoxide dismutase in carcinogenesis: friend or foe?

Superoxide and its derived ROS (reactive oxygen species) have been considered for a long time to be generated as toxic by-products of metabolic events. Although ROS generated in low amounts are able to act as signalling molecules, ROS appear to also play a major role in aging and in the pathogenesis of diseases such as inflammation, diabetes and cancer. Since superoxide formation, in particular in mitochondria, is often considered to be an initial step in the pathogenesis of these diseases, improper function of the MnSOD (mitochondrial superoxide dismutase; SOD2) may be critical for tissue homoeostasis. However, the underlying regulatory mechanisms appear to be multiple and this article summarizes current aspects by which MnSOD can regulate carcinogenesis under various conditions.