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Ion Channels in Immune Cells
Published in Shyam S. Bansal, Immune Cells, Inflammation, and Cardiovascular Diseases, 2022
Devasena Ponnalagu, Shridhar Sanghvi, Shyam S. Bansal, Harpreet Singh
Even intracellular ion channels localized to mitochondria and other organelles have been established to contribute to immune cell activation by regulating key cellular signaling pathways, including mitochondrial pathways, as summarized in a recent review1. A family of anion channel proteins called chloride intracellular channel (CLIC) proteins has been identified in the mitochondria of cardiomyocytes, in which these proteins were shown to be important in maintaining cardiac mitochondrial physiology117. Their function is also implicated in macrophage activation and the formation of inflammasome complex118–120. CLICs contain glutathione S-transferase (GST) omega fold and are therefore classified under the GST super-family of proteins121–124. CLICs are an evolutionarily conserved unique class of ion channel proteins that can exist in both soluble and integral membrane forms123–126. There are six main paralogs of CLIC proteins that are identified in mammals. They are referred to as CLIC1–CLIC6127–135. Some of the CLICs, such as CLIC5 and CLIC6, also seem to exhibit splice variation126. Other than mammals, CLIC orthologs are also observed in plants136, invertebrates137,138, and prokaryotes139, in which they have been shown to exhibit channel-like activity139,140. Similar to GST, some of the CLIC members, CLIC1, CLIC2, and CLIC4, exhibit glutaredoxin-like activity122. CLICs, through either their channel activity or other regulatory mechanisms, have been demonstrated to play a role in many of the physiological and pathophysiological processes125,141.
Chloride intracellular channel protein 2 in cancer and non-cancer human tissues: relationship with tight junctions
Published in Tissue Barriers, 2019
Yoshitomo Ueno, Saya Ozaki, Akihiro Umakoshi, Hajime Yano, Mohammed E. Choudhury, Naoki Abe, Yutaro Sumida, Jun Kuwabara, Rina Uchida, Afsana Islam, Kohei Ogawa, Kei Ishimaru, Toshihiro Yorozuya, Takeharu Kunieda, Yuji Watanabe, Yasutsugu Takada, Junya Tanaka
Endothelia in the blood vessels of non-cancer tissues express tight junction proteins claudins 1 and 5, ZO-1 and occludin in addition to CLIC2 as revealed by immunohistochemical staining. By contrast, most blood vessel endothelia in cancer tissues did not or only faintly expressed these proteins. Furthermore, CD31+/CD45− endothelial cells isolated from non-cancer tissues expressed CLIC2 as well as claudin 1, ZO-1, and occludin at high levels. However, the same cell fraction from cancer tissues expressed these proteins at much lower levels. These results suggest that CLIC2 may be involved in the formation and/or maintenance of tight junctions between endothelial cells of blood vessels in non-cancer tissues. Furthermore, the intimate colocalization of CLIC2 and CD31 suggests the involvement of CLIC2 in CD31-mediated cell-cell contact between endothelial cells. Lymphatic endothelial cells normally form different types of cell-cell junctions from tight junctions22 The simultaneous lack of CLIC2 and tight junction proteins in lymphatic vessels suggests the specific involvement of CLIC2 in tight junction formation in blood vessel endothelia. However, the molecular mechanisms involved in the relationship between CLIC2 and tight junction proteins are unclear. Whether CLIC2 has direct binding to proteins that form tight junctions including the actin cytoskeleton, or whether CLIC2 regulates the expression of these proteins is unclear.