Mitochondria-to-nucleus stress signaling induces phenotypic changes, tumor progression and cell invasion

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Abstract
Recently we showed that partial depletion of mitochondrial DNA (genetic stress) or treatment with mitochondrial‐specific inhibitors (metabolic stress) induced a stress signaling that was associated with increased cytoplasmic‐free Ca2+ [Ca2+]c. In the present study we show that the mitochondria‐to‐nucleus stress signaling induces invasive phenotypes in otherwise non‐invasive C2C12 myoblasts and human pulmonary carcinoma A549 cells. Tumor‐specific markers cathepsin L and transforming growth factor β (TGFβ) are overexpressed in cells subjected to mitochondrial genetic as well as metabolic stress. C2C12 myoblasts subjected to stress showed 4‐ to 6‐fold higher invasion through reconstituted Matrigel membrane as well as rat tracheal xenotransplants in Scid mice. Activation of Ca2+‐dependent protein kinase C (PKC) under both genetic and metabolic stress conditions was associated with increased cathepsin L gene expression, which contributes to increased invasive property of cells. Reverted cells with ∼70% of control cell mtDNA exhibited marker mRNA contents, cell morphology and invasive property closer to control cells. These results provide insights into a new pathway by which mitochondrial DNA and membrane damage can contribute to tumor progression and metastasis.