Injury-triggered Akt phosphorylation of Cx43: A ZO-1-driven molecular switch that regulates gap junction size

Translational Research Program, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States
Journal of Cell Science (Impact Factor: 5.43). 11/2013; 127(2). DOI: 10.1242/jcs.142497
Source: PubMed


The proteins that form vertebrate gap junctions, the connexins, are highly regulated and have short (< 2 h) half-lives. Phosphorylation of connexin43 (Cx43) is generally known to affect gap junction assembly, channel gating and turnover. After finding dramatic effects on gap junctions with Akt inhibitors, we created an antibody specific for Cx43 phosphorylated on S373, a potential Akt substrate. We found S373 phosphorylation in cells and skin or heart almost exclusively in larger gap junctional structures that increased dramatically after wounding or hypoxia. We were able to mechanistically show that Akt-dependent S373 phosphorylation increases gap junction size and communication by completely eliminating interaction between Cx43 and ZO-1. Thus, phosphorylation on S373 acts as a molecular "switch" to rapidly increase gap junctional communication potentially leading to initiation of activation and migration of keratinocytes or ischemic injury response in skin and heart, respectively.

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    • "Although the effects of hypoxia on GBM gap junctions have not been investigated , several studies in other preparations point to a possible modulatory role. In cardiac tissue and MDCK epithelial cells expressing Cx43, hypoxia rapidly activates Akt, which leads to Cx43 phosphorylation and to larger gap junctions (Dunn and Lampe, 2014). Also in human mesenchymal stem cells Cx43 expression is increased by hypoxia (Grayson et al., 2007). "
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    ABSTRACT: The malignancy of glioblastoma multiform (GBM), the most common and aggressive form of human brain tumors, strongly correlates with the presence of hypoxic areas, but the mechanisms controlling the hypoxia-induced aggressiveness are still unclear. GBM cells express a number of ion channels whose activity supports cell volume changes and increases in the cytosolic Ca(2+) concentration, ultimately leading to cell proliferation, migration or death. In several cell types it has previously been shown that low oxygen levels regulate the expression and activity of these channels, and more recent data indicate that this also occurs in GBM cells. Based on these findings, it may be hypothesized that the modulation of ion channel activity or expression by the hypoxic environment may participate in the acquisition of the aggressive phenotype observed in GBM cells residing in a hypoxic environment. If this hypothesis will be confirmed, the use of available ion channels modulators may be considered for implementing novel therapeutic strategies against these tumors.
    Full-text · Article · Jan 2015 · Frontiers in Cellular Neuroscience
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    • "Previously, Akt and MAPK have demonstrated to modulate Cx43 phosphorylation and subsequently increase gap junction activity. Active Akt has been found to stabilize gap junctions and active p44/42 MAPK has been shown to increase GJIC [12,13]. This study was also determined whether the increase of gap junction activity by PQ1 was due to the activation of Akt and MAPK. "
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    ABSTRACT: Background Colorectal cancer is one of the most common cancers in the United States with an early detection rate of only 39%. Colorectal cancer cells along with other cancer cells exhibit many deficiencies in cell-to-cell communication, particularly gap junctional intercellular communication (GJIC). GJIC has been reported to diminish as cancer cells progress. Gap junctions are intercellular channels composed of connexin proteins, which mediate the direct passage of small molecules from one cell to the next. They are involved in the regulation of the cell cycle, cell differentiation, and cell signaling. Since the regulation of gap junctions is lost in colorectal cancer cells, the goal of this study is to determine the effect of GJIC restoration in colorectal cancer cells. Methods Gap Junction Activity Assay and protein analysis were performed to evaluate the effects of overexpression of connexin 43 (Cx43) and treatment of PQ1, a small molecule, on GJIC. Results Overexpression of Cx43 in SW480 colorectal cancer cells causes a 6-fold increase of gap junction activity compared to control. This suggests that overexpressing Cx43 can restore GJIC. Furthermore, small molecule like PQ1 directly targeting gap junction channel was used to increase GJIC. Gap junction enhancers, PQ1, at 200 nM showed a 4-fold increase of gap junction activity in SW480 cells. A shift from the P0 to the P2 isoform of Cx43 was seen after 1 hour treatment with 200 nM PQ1. Conclusion Overexpression of Cx43 and treatment of PQ1 can directly increase gap junction activity. The findings provide an important implication in which restoration of gap junction activity can be targeted for drug development.
    Full-text · Article · Jul 2014 · BMC Cancer
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    • "The aCT1 peptide binds in the PDZ domain of ZO-1 and inhibits Cx43-ZO-1 interactions [151]. The recent reports by Dunn et al. [36], again emphasise the importance of Cx43 interactions with ZO-1, via adhesive properties and interaction with the cytoskeleton, in epidermal integrity and repair [36]. "
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    ABSTRACT: Gap junction proteins (connexins) are differentially expressed throughout the multiple layers of the epidermis. A variety of skin conditions arise with aberrant connexin expression or function and suggest that maintaining the epidermal gap junction network has many important roles in preserving epidermal integrity and maintaining homeostasis. Mutations in a number of connexins lead to epidermal dysplasias giving rise to a range of dermatological disorders of differing severity. 'Gain of function' mutations reveal connexin-mediated roles in calcium signalling within the epidermis. Connexins are intrinsically involved in epidermal innate immunity and inflammation control, and in wound repair. The therapeutic potential of targeting connexins to improve wound healing responses is now clear. This review discusses the role of connexins in epidermal integrity, and examines the emerging evidence that connexins act as epidermal sensors to a variety of mechanical, temperature, pathogen-induced and chemical stimuli. Connexins thus act as an integral component of the skin's protective barrier.
    Full-text · Article · Mar 2014 · FEBS letters
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