Retrograde Ca2+ signaling in C2C12 skeletal myocytes in response to mitochondrial genetic and metabolic stress: a novel mode of inter-organelle crosstalk

Abstract

We have investigated the mechanism of mitochondrialnuclear crosstalk during cellular stress in mouse C2C12 myocytes. For this purpose, we used cells with reduced mitochondrial DNA (mtDNA) contents by ethidium bromide treatment or myocytes treated with known mitochondrial metabolic inhibitors, including carbonyl cyanide m-chlorophenylhydrazone (CCCP), antimycin, valinomycin and azide. Both genetic and metabolic stresses similarly affected mitochondrial membrane potential (Δψ m ) and electron transport-coupled ATP synthesis, which was also accompanied by an elevated steady-state cytosolic Ca 2⍣ level ([Ca 2⍣ ] i ). The mitochondrial stress resulted in: (i) an enhanced expression of the sarcoplasmic reticular ryanodine receptor-1 (RyR-1), hence potentiating the Ca 2⍣ release in response to its modulator, caffeine; (ii) enhanced levels of Ca 2⍣ -responsive factors calineurin, calcineurindependent NFATc (cytosolic counterpart of activated T-cell-specific nuclear factor) and c-Jun N-terminal kinase (JNK)-dependent ATF2 (activated transcription factor 2); (iii) reduced levels of transcription factor, NF-κB; and (iv) enhanced transcription of cytochrome oxidase Vb (COX Vb) subunit gene. These cellular changes, including the steady-state [Ca 2⍣ ] i were normalized in genetically reverted cells which contain near-normal mtDNA levels. We propose that the mitochondria-to-nucleus stress signaling occurs through cytosolic [Ca 2⍣ ] i changes, which are likely to be due to reduced ATP and Ca 2⍣ efflux. Our results indicate that the mitochondrial stress signal affects a variety of cellular processes, in addition to mitochondrial membrane biogenesis.

Mitochondrial stress-induced calcium signaling, phenotypic changes and invasive behavior in human lung carcinoma A549 cells

“…This change in Dc m was accompanied by elevated cytosolic free [Ca 2+ ] c and activation of calcium responsive transcription factors (Biswas et al, 1999). Our results also demonstrated that the mitochondria-to-nucleus stress signaling induces invasive phenotypes in otherwise non-invasive C2C12 rhabdomyoblasts (Amuthan et al, 2001).…”

“…This change in Dc m was accompanied by elevated cytosolic free [Ca 2+ ] c and activation of calcium responsive transcription factors (Biswas et al, 1999). Our results also demonstrated that the mitochondria-to-nucleus stress signaling induces invasive phenotypes in otherwise non-invasive Tumor-specific markers cathepsin L and transforming growth factor b1 (TGFb1) were shown to be among the several genes that are overexpressed in cells subjected to mitochondrial genetic and metabolic stress.…”

“…In a recent study we showed that mitochondrial stress conditions, which disrupt Dc m , cause a steady and sustained increase in cytoplasmic free Ca 2+ ([Ca 2+ ] c ) (Biswas et al, 1999). These changes in C2C12 myocytes were also associated with increased expression of RyR1 Ca 2+ channel gene expression and increased steady state levels of RyR1 protein.…”

“…We generated mtDNA-depleted A549 cell line by culturing cells in the presence of 100 ng/ml of ethidium bromide (EtBr) for 30 division cycles, essentially as described before for C2C12 rhabdomyoblasts (Biswas et al, 1999). EtBr, a phenanthredine dye, selectively inhibits the mtDNA replication.…”

RTG-dependent Mitochondria-to-Nucleus Signaling Is Regulated by MKS1 and Is Linked to Formation of Yeast Prion [URE3]

“…In animal cells, for example, compromises in mitochondrial function or certain external cues can lead to increased expression of genes encoding components of the mitochondrial oxidative phosphorylation apparatus and, in some instances, lead to a general increase in the biogenesis of mitochondria (Lunardi and Attardi, 1991;Scarpulla, 1997;Biswas et al, 1999;Heddi et al, 1999;Murdock et al, 1999;Wu et al, 1999;Amuthan et al, 2001). These events are controlled, in part, by transcriptional activators and coactivators whose targets include nuclear genes encoding mitochondrial proteins.…”