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Published on: April 29, 2016
Manganese superoxide dismutase-mediated inside-out signaling in HaCaT human keratinocytes and SKH-1 mouse skin
Aaron K Holley1, Yong Xu, Teresa Noel
11 Graduate Center for Toxicology, University of Kentucky , Lexington, Kentucky.
Aims:
Inside-out signaling occurs when changes in organellar activity lead to alterations in cell signaling that culminate at the cell surface. Mitochondria are vital signaling platforms in cells that participate in radiation-induced inside-out signaling. However, the importance of the reactive oxygen species (ROS)-scavenging ability of mitochondria through manganese superoxide dismutase (MnSOD) is not established. Here, we used MnSOD heterozygous knockout and transgenic SKH-1 hairless, albino mice and MnSOD knockdown and overexpressing HaCaT human keratinocytes to study the effects of MnSOD on ultraviolet (UV) radiation-induced inside-out signaling.
Results And Innovation:
There is an inverse correlation between MnSOD expression and UV-induced activation of epidermal growth factor receptor (EGFR), as determined by phosphorylation at Tyr1068, both in vitro and in vivo, which correlates with increased ROS production (as measured by dihydroethidium fluorescence). EGFR activation is dependent on Nox4 expression and Src kinase activation, with Src activation upstream of Nox4 in regulation of EGFR activation. Enhanced EGFR activation in MnSOD knockdown cells is abrogated by treatment with the SOD mimetic MnTnBuOE-2-PyP(5+).
Conclusions:
Our data demonstrate that the ROS-scavenging ability of mitochondria, through the expression of MnSOD, is important for UV-induced inside-out signaling. Decreased MnSOD expression enhances UV-induced activation of different oncogenic signaling pathways through an inside-out signaling-mediated mechanism. Inhibition of inside-out signaling by MnTnBuOE-2-PyP(5+) mimics the effect of endogenous MnSOD, suggesting that pharmacological intervention by SOD mimetics could play an important role in the prevention of aberrant cell signaling, which may contribute to carcinogenesis and may prove valuable for the treatment or prevention of cancer in the future.
Insights
Mitochondrial manganese superoxide dismutase (MnSOD) is crucial for preventing ultraviolet (UV) radiation-induced cell signaling. Lower MnSOD levels enhance UV-driven oncogenic pathway activation, suggesting SOD mimetics as potential cancer prevention agents.
Area of Science:
- Mitochondrial signaling and cell surface communication.
- Reactive oxygen species (ROS) and antioxidant defense mechanisms.
- Molecular mechanisms of UV radiation-induced cellular responses.
Background:
- Inside-out signaling describes how organelle activity influences cell surface signaling.
- Mitochondria act as critical signaling platforms during radiation exposure.
- The role of mitochondrial manganese superoxide dismutase (MnSOD) in UV-induced signaling remains unclear.
Purpose of the Study:
- To investigate the impact of MnSOD's ROS-scavenging function on UV radiation-induced inside-out signaling.
- To elucidate the molecular pathways linking MnSOD, ROS, and cell surface receptor activation following UV exposure.
Main Methods:
- Utilized MnSOD heterozygous knockout and transgenic mice (SKH-1 hairless, albino).
- Employed MnSOD knockdown and overexpressing HaCaT human keratinocytes.
- Assessed epidermal growth factor receptor (EGFR) activation via phosphorylation at Tyr1068.
- Measured ROS production using dihydroethidium fluorescence.
- Investigated the roles of Nox4 and Src kinase in EGFR activation.
- Evaluated the effect of the SOD mimetic MnTnBuOE-2-PyP(5+) on EGFR activation.
Main Results:
- An inverse correlation was observed between MnSOD expression and UV-induced EGFR activation (p-Tyr1068).
- Increased ROS production correlated with enhanced EGFR activation in conditions of lower MnSOD.
- EGFR activation was dependent on Nox4 expression and Src kinase activation, with Src preceding Nox4.
- MnSOD knockdown led to enhanced EGFR activation, which was reversed by MnTnBuOE-2-PyP(5+) treatment.
Conclusions:
- Mitochondrial MnSOD's ROS-scavenging activity is essential for regulating UV-induced inside-out signaling.
- Reduced MnSOD expression promotes UV-induced activation of oncogenic signaling pathways via inside-out signaling.
- Pharmacological inhibition of inside-out signaling using SOD mimetics, like MnTnBuOE-2-PyP(5+), mimics endogenous MnSOD function.
- SOD mimetics hold potential for preventing aberrant cell signaling, cancer development, and may aid in cancer treatment.
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