Studies on the role of organic cation transporter 3 (SLC22A3/OCT3) as a histamine transporter and on the pathophysiological significance of its interaction with the tetraspanin CD63

• Applicant: Professor Dr. Giuliano Ciarimboli
• Subject Area: Anatomy and Physiology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 490815291

The organic cation transporter 3 (OCT3) is a broadly distributed transporter with important endogenous (e.g. serotonine, histamine) and exogenous (e.g. cisplatin, metformin) substrates, whose pathophysiological importance is only partially described for neuronal processes. The main objective of this project is to study the physiological and eventual pathological significance of OCT3 as a histamine transporter and to characterize the effects of its interaction with CD63, whose function is, at least in part, known. The direct interaction of OCT3 with other proteins may change the function of the transporter, without influencing its mRNA and/or protein abundance. For this reason, the consequences of this type of regulation may remain undetected by quantitative measurement of transporter expression. The OCT3/CD63 interaction has a potential pathophysiological significance because CD63 is involved in allergic and inflammatory reactions associated with histamine which, in turn, is a substrate of OCT3. Trafficking of CD63 from intracellular vesicles to the plasma membrane is related to basophils and mast cells (MCs) activation and histamine release. Histamine is an essential player in the development of allergic-related inflammatory diseases and exerts various other immune regulatory functions by modulating the functions of monocytes, T cells, macrophages, neutrophils, eosinophils, B cells, and dendritic cells. Activation of histamine producing cells is not only important in allergic reactions but is also proposed to play a role in cardiovascular diseases and in transplantation rejection. No specific histamine transporter is known, suggesting that histamine transport is an important physiological role of OCT3 and that OCT3/CD63 interaction may represent an autocrine cellular loop for regulating histamine release. However, since activated basophils and MCs migrate and adhere to other cells which highly express OCT in the plasma membrane, the CD63/OCT interaction may also have a role in the adhesion process (heterocellular OCT3/CD63 interaction). The following aspects of OCT3 and OCT3/CD63 interaction will be investigated:1) Consequences of genetic deletion of OCT3 or CD63 for the development of allergic reaction in in vivo models. A model with specific OCT3-deletion in basophils will be also established 2) Consequences of OCT3/CD63 interaction for OCT3 function (focused on histamine transport) and intracellular transporter trafficking. This aspect will be investigated in cell lines, which endogenously express both OCT3 and CD63 and in Drosophila photoreceptors, studying whether the carcinine transporter (a fly organic cation transporter) by the CD63-homologue Sunglasses (sun) are here co-expressed. This approach in flies is important to understand whether the OCT3/CD63 interaction has a conserved biological significance. 3) Role of the OCT/CD63 interaction for adhesion of basophils to cells expressing OCT (heterocellular OCT3/CD63 interaction).

• DFG Programme: Research Grants