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Int. J. Mol. Sci. 2018, 19(4), 1159; doi:10.3390/ijms19041159

Conflicting Roles of Connexin43 in Tumor Invasion and Growth in the Central Nervous System

1
Laboratory of Clinical Pharmacology and Pharmacometrics, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba-shi, Chiba 263-8522, Japan
2
Division of Cancer Pathophysiology, National Cancer Center Research Institute, Chuo-ku, Tokyo 104-0045, Japan
3
Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
*
Author to whom correspondence should be addressed.
Received: 9 March 2018 / Revised: 5 April 2018 / Accepted: 9 April 2018 / Published: 11 April 2018
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Abstract

The tumor microenvironment is known to have increased levels of cytokines and metabolites, such as glutamate, due to their release from the surrounding cells. A normal cell around the tumor that responds to the inflammatory environment is likely to be subsequently altered. We discuss how these abnormalities will support tumor survival via the actions of gap junctions (GJs) and hemichannels (HCs) which are composed of hexamer of connexin43 (Cx43) protein. In particular, we discuss how GJ intercellular communication (GJIC) in glioma cells, the primary brain tumor, is a regulatory factor and its attenuation leads to tumor invasion. In contrast, the astrocytes, which are normal cells around the glioma, are “hijacked” by tumor cells, either by receiving the transmission of malignant substances from the cancer cells via GJIC, or perhaps via astrocytic HC activity through the paracrine signaling which enable the delivery of these substances to the distal astrocytes. This astrocytic signaling would promote tumor expansion in the brain. In addition, brain metastasis from peripheral tissues has also been known to be facilitated by GJs formed between cerebral vascular endothelial cells and cancer cells. Astrocytes and microglia are generally thought to eliminate cancer cells at the blood–brain barrier. In contrast, some reports suggest they facilitate tumor progression as tumor cells take advantage of the normal functions of astrocytes that support the survival of the neurons by exchanging nutrients and metabolites. In summary, GJIC is essential for the normal physiological function of growth and allowing the diffusion of physiological substances. Therefore, whether GJIC is cancer promoting or suppressing may be dependent on what permeates through GJs, when it is active, and to which cells. The nature of GJs, which has been ambiguous in brain tumor progression, needs to be revisited and understood together with new findings on Cx proteins and HC activities. View Full-Text
Keywords: connexin43; central nervous system; glioma; astrocyte; blood–brain barrier; neurovascular unit connexin43; central nervous system; glioma; astrocyte; blood–brain barrier; neurovascular unit
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Uzu, M.; Sin, W.C.; Shimizu, A.; Sato, H. Conflicting Roles of Connexin43 in Tumor Invasion and Growth in the Central Nervous System. Int. J. Mol. Sci. 2018, 19, 1159.

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