**The Role of Tissue-Specific Ubiquitin Ligases, RNF183, RNF186, RNF182 and RNF152, in Disease and Biological Function**

### **Takumi Okamoto** †**, Kazunori Imaizumi and Masayuki Kaneko \*,**†

Department of Biochemistry, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan; toka@hiroshima-u.ac.jp (T.O.); imaizumi@hiroshima-u.ac.jp(K.I.)

 **\*** Correspondence: mkaneko@hiroshima-u.ac.jp; Tel.: +81-82-257-5131

† These authors contributed equally to this work.

Received: 8 May 2020; Accepted: 28 May 2020; Published: 30 May 2020

**Abstract:** Ubiquitylation plays multiple roles not only in proteasome-mediated protein degradation but also in various other cellular processes including DNA repair, signal transduction, and endocytosis. Ubiquitylation is mediated by ubiquitin ligases, which are predicted to be encoded by more than 600 genes in humans. RING finger (RNF) proteins form the majority of these ubiquitin ligases. It has also been predicted that there are 49 RNF proteins containing transmembrane regions in humans, several of which are specifically localized to membrane compartments in the secretory and endocytic pathways. Of these, *RNF183*, *RNF186*, *RNF182*, and *RNF152* are closely related genes with high homology. These genes share a unique common feature of exhibiting tissue-specific expression patterns, such as in the kidney, nervous system, and colon. The products of these genes are also reported to be involved in various diseases such as cancers, inflammatory bowel disease, Alzheimer's disease, and chronic kidney disease, and in various biological functions such as apoptosis, endoplasmic reticulum stress, osmotic stress, nuclear factor-kappa B (NF-κB), mammalian target of rapamycin (mTOR), and Notch signaling. This review summarizes the current knowledge of these tissue-specific ubiquitin ligases, focusing on their physiological roles and significance in diseases.

**Keywords:** RNF183; RNF186; RNF182; RNF152; ubiquitin ligase; RING finger; mTOR; NF-κB; endoplasmic reticulum stress; osmotic stress
