GPR15 is an orphan G protein-coupled receptor (GPCR) that is found in lymphocytes. It functions as a co-receptor of simian immunodeficiency virus and HIV-2 and plays a role in the trafficking of T cells to the lamina propria in the colon and to the skin. We describe the purification from porcine colonic tissue extracts of an agonistic ligand for GPR15 and its functional characterization. In humans, this ligand, which we named GPR15L, is encoded by the gene C10ORF99 and has some features similar to the CC family of chemokines. GPR15L was found in some human and mouse epithelia exposed to the environment, such as the colon and skin. In humans, GPR15L was also abundant in the cervix. In skin, GPR15L was readily detected after immunologic challenge and in human disease, for example, in psoriatic lesions. Allotransplantation of skin from Gpr15l-deficient mice onto wild-type mice resulted in substantial graft protection, suggesting nonredundant roles for GPR15 and GPR15L in the generation of effector T cell responses. Together, these data identify a receptor-ligand pair that is required for immune homeostasis at epithelia and whose modulation may represent an alternative approach to treating conditions affecting the skin such as psoriasis.

Suply T, Hannedouche S, Carte N, et al. A natural ligand for the orphan receptor GPR15 modulates lymphocyte recruitment to epithelia. Sci Signal. 2017;10(496)

Chemoattractants control lymphocyte recruitment from the blood, contributing to the systemic organization of the immune system. The G protein-linked receptor GPR15 mediates lymphocyte homing to the large intestines and skin. Here we show that the 9  kDa CC-motif containing cationic polypeptide AP57/colon-derived sushi containing domain-2 binding factor (CSBF), encoded by C10orf99 in the human and 2610528A11Rik in the mouse, functions as a chemokine ligand for GPR15 (GPR15L). GPR15L binds GPR15 and attracts GPR15-expressing T cells including lymphocytes in colon-draining lymph nodes and V?3+ thymic precursors of dermal epithelial T cells. Patterns of GPR15L expression by epithelial cells in adult mice and humans suggest a homeostatic role for the chemokine in lymphocyte localization to the large intestines, as well as a role in homing to the epidermis during wound healing or inflammation. GPR15L is also significantly expressed in squamous mucosa of the oral cavity and esophagus with still poorly defined regulation. Identification of the chemotactic activity of GPR15L adds to its reported antibacterial and tumor cell growth regulatory functions and suggests the potential of targeting GPR15L–GPR15 interactions for modulation of mucosal and cutaneous inflammation.

Borja Ocón, Junliang Pan, Theresa Thu Dinh et al., Frontiers in Immunology. 2017;8

In situ gel-forming system as local drug delivery system in dermal traumas has generated a great interest. Accumulating evidence shows that antimicrobial peptides play pivotal roles in the process of wound healing. Here in this study, to explore the potential application of antimicrobial peptide in wound healing, biodegradable poly(L-lactic acid)-Pluronic L35-poly(L-lactic acid) (PLLA-L35-PLLA) was developed at first. Then based on this polymer, an injectable in situ gel-forming system composed of human antimicrobial peptides 57 (AP-57) loaded nanoparticles and thermosensitive hydrogel was prepared and applied for cutaneous wound healing. AP-57 peptides were enclosed with biocompatible nanoparticles (AP-57-NPs) with high drug loading and encapsulation efficiency. AP-57-NPs were further encapsulated in a thermosensitive hydrogel (AP-57-NPs-H) to facilitate its application in cutaneous wound repair. As a result, AP-57-NPs-H released AP-57 in an extended period and exhibited quite low cytotoxicity and high anti-oxidant activity in vitro. Moreover, AP-57-NPs-H was free-flowing liquid at room temperature, and can form non-flowing gel without any crosslink agent upon applied on the wounds. In vivo wound healing assay using full-thickness dermal defect model of SD rats indicated that AP-57-NPs-H could significantly promote wound healing. At day 14 after operation, AP-57-NPs-H treated group showed nearly complete wound closure of 96.78 ± 3.12%, whereas NS, NPs-H and AP-57-NPs group recovered by about 68.78 ± 4.93%, 81.96 ± 3.26% and 87.80 ± 4.62%, respectively. Histopathological examination suggested that AP-57-NPs-H could promote cutaneous wound healing through enhancing granulation tissue formation, increasing collagen deposition and promoting angiogenesis in the wound tissue. Therefore, AP-57-NPs-H might have potential application in wound healing.

Li X, Fan R, Tong A, et al. Int J Pharm. 2015;495(1):560-71.

Antimicrobial peptides (AMPs) are an evolutionarily conserved component of the innate immune response that provides host defence at skin and mucosal surfaces. Here, we report the identification and characterization of a new type human AMPs, termed AP-57 (Antimicrobial Peptide with 57 amino acid residues), which is also known as C10orf99 (chromosome 10 open reading frame 99). AP-57 is a short basic amphiphilic peptide with four cysteines and a net charge +14 (MW = 6.52, PI = 11.28). The highest expression of AP-57 were detected in the mucosa of stomach and colon through immunohistochemical assay. Epithelium of skin and esophagus show obvious positive staining and strong positive staining were also observed in some tumor and/or their adjacent tissues, such as esophagus cancer, hepatocellular carcinoma, squamous cell carcinoma and invasive ductal carcinoma. AP-57 exhibited broad-spectrum antimicrobial activities against Gram-positive Staphylococcus aureus, Actinomyce, and Fungi Aspergillus niger as well as mycoplasma and lentivirus. AP-57 also exhibited DNA binding capacity and specific cytotoxic effects against human B-cell lymphoma Raji. Compared with other human AMPs, AP-57 has its distinct characteristics, including longer sequence length, four cysteines, highly cationic character, cell-specific toxicity, DNA binding and tissue-specific expressing patterns. Together, AP-57 is a new type of multifunctional AMPs worthy further investigation.

Yang M, Tang M, Ma X, et al. Biochem Biophys Res Commun. 2015;457(3):347-52.

Cytokines are soluble proteins that exert their functions by binding specific receptors. Many cytokines play essential roles in carcinogenesis and have been developed for the treatment of cancer. In this study, we identified a novel potential cytokine using immunogenomics designated colon-derived SUSD2 binding factor (CSBF), also known as chromosome 10 open reading frame 99 (C10orf99). CSBF/C10orf99 is a classical secreted protein with predicted molecular mass of 6.5 kDa, and a functional ligand of Sushi Domain Containing 2 (SUSD2). CSBF/C10orf99 has the highest expression level in colon tissue. Both CSBF/C10orf99 and SUSD2 are down-regulated in colon cancer tissues and cell lines with different regulation mechanisms. CSBF/C10orf99 interacts with SUSD2 to inhibit colon cancer cell growth and induce G1 cell cycle arrest by down-regulating cyclin D and cyclin-dependent kinase 6 (CDK6). CSBF/C10orf99 displays a bell-shaped activity curve with the optimal effect at ~10 ng/ml. Its growth inhibitory effects can be blocked by sSUSD2-Fc soluble protein. Our results suggest that CSBF/C10orf99 is a novel potential cytokine with tumor suppressor functions.

Pan W, Cheng Y, Zhang H, et al. Sci Rep. 2014;4:6812.

Psoriasis is an autoimmune disease, which symptoms can significantly impair the patient's life quality. It is mainly diagnosed through the visual inspection of the lesion skin by experienced dermatologists. Currently no cure for psoriasis is available due to limited knowledge about its pathogenesis and development mechanisms. Previous studies have profiled hundreds of differentially expressed genes related to psoriasis, however with no robust psoriasis prediction model available. This study integrated the knowledge of three feature sorting algorithms that revealed 21 features belonging to 18 genes as candidate markers. The final psoriasis classification model was established using the novel Incremental Feature sorting algorithm that utilizes only 3 features from 2 unique genes, IGFL1 and C10orf99. This model has demonstrated highly stable prediction accuracy (averaged at 99.81%) over three independent validation strategies. The two marker genes, IGFL1 and C10orf99, were revealed as the upstream components of growth signal transduction pathway of psoriatic pathogenesis.

Guo P, Luo Y, Mai G, et al. Genomics. 2014;103(1):48-55.