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In cancer patients, treatment modalities like chemotherapy and radiation exert their anticancer effects by inducing DNA damage. The cancer cells can survive under genotoxic stress by inducing DNA damage response (DDR) or can undergo cell death. The process of autophagy is emerging as crucial regulator of cell survival during different stress conditions. Post translational modification through ubiquitin plays an essential role in DDR during genotoxic stress conditions. Ubiquitin ligases regulate autophagy and cell death pathways however their role during genotoxic stress conditions is not understood. In the current study we identified TRIM8, RING E3 Ligase, as a novel regulator of autophagy during DDR. TRIM8 regulates lysosomal biogenesis and autophagy flux. The turnover of TRIM8 is high and is stabilized during genotoxic stress conditions. TRIM8 regulated autophagy is essential for its cytoprotective role during genotoxic stress induced cell death. TRIM8 stabilizes the turnover of XIAP during genotoxic stress and forms complex with XIAP and caspase-3 to inhibit its activation in presence of etoposide. TRIM8 mediated autophagy promotes degradation of cleaved caspase-3 subunits. This study described TRIM8, as a novel regulator of DDR-autophagy crosstalk, which may play role in survival of cancer cells in presence of genotoxic agents. [ABSTRACT FROM AUTHOR]

The emerging evidences suggest that posttranslational modification of target protein by ubiquitin (Ub) not only regulate its turnover through ubiquitin proteasome system (UPS) but is a critical regulator of various signaling pathways. During ubiquitination, E3 ligase recognizes the target protein and determines the topology of ubiquitin chains. In current study, we studied the role of TRIM4, a member of the TRIM/RBCC protein family of RING E3 ligase, in regulation of hydrogen peroxide (H 2 O 2 ) induced cell death. TRIM4 is expressed differentially in human tissues and expressed in most of the analyzed human cancer cell lines. The subcellular localization studies showed that TRIM4 forms distinct cytoplasmic speckle like structures which transiently interacts with mitochondria. The expression of TRIM4 induces mitochondrial aggregation and increased level of mitochondrial ROS in the presence of H 2 O 2 . It sensitizes the cells to H 2 O 2 induced death whereas knockdown reversed the effect. TRIM4 potentiates the loss of mitochondrial transmembrane potential and cytochrome c release in the presence of H 2 O 2 . The analysis of TRIM4 interacting proteins showed its interaction with peroxiredoxin 1 (PRX1), including other proteins involved in regulation of mitochondrial and redox homeostasis. TRIM4 interaction with PRX1 is critical for the regulation of H 2 O 2 induced cell death. Collectively, the evidences in the current study suggest the role of TRIM4 in regulation of oxidative stress induced cell death. [ABSTRACT FROM AUTHOR]

Abstract: The emerging evidences suggest that endoplasmic (ER) stress is involved in onset of many pathological conditions like cancer and neurodegeneration. The persistent ER stress results in misfolded protein aggregates, which are degraded through the process of autophagy or lead to cell death through activation of caspases. The regulation of crosstalk of autophagy and cell death during ER stress is emerging. Ubiquitination plays regulatory role in crosstalk of autophagy and cell death. In the current study, we describe the role of TRIM13, RING E3 ubiquitin ligase, in regulation of ER stress induced cell death. The expression of TRIM13 sensitizes cells to ER stress induced death. TRIM13 induced autophagy is essential for ER stress induced caspase activation and cell death. TRIM13 induces K63 linked poly-ubiquitination of caspase-8, which results in its stabilization and activation during ER stress. TRIM13 regulates translocation of caspase-8 to autophagosome and its fusion with lysosome during ER stress. This study first time demonstrated the role of TRIM13 as novel regulator of caspase-8 activation and cell death during ER stress. [Copyright &y& Elsevier]

Abstract: The cellular processes are controlled by a narrow range of mRNA and proteins levels, where small RNAs (sRNAs) known as miRNAs play a critical role. The spatial and temporal regulation of miRNA processing components and mature miRNA is emerging. The recent studies suggest that mitochondria are one of the destinations of pre as well as mature miRNAs. The role of mitochondria extends beyond energy metabolism to many other cellular processes like metabolism, cell death and inflammation. The new found destination of miRNAs suggest the role of mitochondria in monitoring site specific regulations of proteins as well as the function of mitochondria. The studies in this direction will decipher the novel role of mitochondria-associated miRNAs in different cellular processes. This review is focussed on the recent studies demonstrating the presence of miRNAs in mitochondria and its possible significance in different cellular and physiological conditions. [Copyright &y& Elsevier]

The discovery of MICU1 as gatekeeper of mitochondrial calcium (m Ca2+) entry has transformed our understanding of m Ca2+ flux. Recent studies revealed an additional role of MICU1 as a Ca2+ sensor at MICOS (mitochondrial contact site and cristae organizing system). MICU1's presence at MICOS suggests its involvement in coordinating Ca2+ signaling and mitochondrial ultrastructure. Besides its role in Ca2+ regulation, MICU1 influences cellular signaling pathways including transcription, epigenetic regulation, metabolism, and cell death, thereby affecting human health. Here, we summarize recent findings on MICU1's canonical and noncanonical functions, and its relevance to human health and diseases. • MICU1, a mitochondrial Ca2+ sensor, plays a key role in decoding cytoplasmic Ca2+ signals. • Through the mtCU, MICU1 modulates mitochondrial Ca2+ influx. • MICU1 functions extend beyond mtCU, impacting mitochondrial ultrastructure via MICOS. • Loss of MICU1 leads to bioenergetics failure and increased susceptibility to various cell death pathways. • MICU1 mutations are linked to neuromuscular, cognitive, and cardiac impairments. [ABSTRACT FROM AUTHOR]

Abstract: Emerging evidences suggest that chronic inflammation is one of the major causes of tumorigenesis. The role of inflammation in regulation of breast cancer progression is not well established. Recently Mediator of IRF3 Activation (MITA) protein has been identified that regulates NF-κB and IFN pathways. Role of MITA in the context of inflammation and cancer progression has not been investigated. In the current report, we studied the role of MITA in the regulation of cross talk between cell death and inflammation in breast cancer cells. The expression of MITA was significantly lower on in estrogen receptor (ER) positive breast cancer cells than ER negative cells. Similarly, it was significantly down regulated in tumor tissue as compared to the normal tissue. The overexpression of MITA in MCF-7 and T47D decreases the cell proliferation and increases the cell death by activation of caspases. MITA positively regulates NF-κB transcription factor, which is essential for MITA induced cell death. The activation of NF-κB induces TNF-α production which further sensitizes MITA induced cell death by activation of death receptor pathway through capsase-8. MITA expression decreases the colony forming units and migration ability of MCF-7 cells. Thus, our finding suggests that MITA acts as a tumor suppressor which is down regulated during tumorigenesis providing survival advantage to tumor cell. [Copyright &y& Elsevier]

The physiological cardiac hypertrophy is an adaptive condition without myocyte cell death, while pathological hypertrophy is a maladaptive condition associated with myocyte cell death. This study explores the miRNome of α-2M-induced physiologically hypertrophied cardiomyocytes and the role of miRNA-99 family during cardiac hypertrophy. Physiological and pathological cardiac hypertrophy was induced in H9c2 cardiomyoblast cell lines using α-2M and isoproterenol respectively. Total RNA isolation and small RNA sequencing were executed for physiological hypertrophy model. The differentially expressed miRNAs and its target mRNAs were validated in animal models. Transcription factor binding sites were predicted in the promoter of specific miRNAs and validated by ChIP-PCR. Subsequently, the selected miRNA was functionally characterized by overexpression and silencing. The effects of silencing of upstream regulator and downstream target gene were studied. Analysis of small RNA reads revealed the differential expression of a large set of miRNAs during hypertrophy, of which miR-99 family was highly downregulated upon α-2M treatment. However, this miR-99 family expression was upregulated during pathological hypertrophy and confirmed in animal models. ChIP-PCR confirms the binding of Egr-1 transcription factor to the miR-99 promoter. Further, silencing of Egr-1 decreased the expression of miR-99. The overexpression or silencing of miR-99 diverges the physiological hypertrophy to pathological hypertrophy and vice versa by regulating Akt-1 pathway. Silencing of Akt-1 replicates the effect of overexpression of miR-99. Conclusion The results proved Egr-1 mediated regulation of miR-99 family that plays a key role in determining the fate of cardiac hypertrophy by regulating Akt-1 signaling. [ABSTRACT FROM AUTHOR]

Summary Calcium (Ca 2+ ) flux into the matrix is tightly controlled by the mitochondrial Ca 2+ uniporter (MCU) due to vital roles in cell death and bioenergetics. However, the precise atomic mechanisms of MCU regulation remain unclear. Here, we solved the crystal structure of the N-terminal matrix domain of human MCU, revealing a β-grasp-like fold with a cluster of negatively charged residues that interacts with divalent cations. Binding of Ca 2+ or Mg 2+ destabilizes and shifts the self-association equilibrium of the domain toward monomer. Mutational disruption of the acidic face weakens oligomerization of the isolated matrix domain and full-length human protein similar to cation binding and markedly decreases MCU activity. Moreover, mitochondrial Mg 2+ loading or blockade of mitochondrial Ca 2+ extrusion suppresses MCU Ca 2+ -uptake rates. Collectively, our data reveal that the β-grasp-like matrix region harbors an MCU-regulating acidic patch that inhibits human MCU activity in response to Mg 2+ and Ca 2+ binding. [ABSTRACT FROM AUTHOR]

Summary Mitochondrial permeability transition is a phenomenon in which the mitochondrial permeability transition pore (PTP) abruptly opens, resulting in mitochondrial membrane potential (ΔΨ m ) dissipation, loss of ATP production, and cell death. Several genetic candidates have been proposed to form the PTP complex, however, the core component is unknown. We identified a necessary and conserved role for spastic paraplegia 7 (SPG7) in Ca 2+ - and ROS-induced PTP opening using RNAi-based screening. Loss of SPG7 resulted in higher mitochondrial Ca 2+ retention, similar to cyclophilin D (CypD, PPIF ) knockdown with sustained ΔΨ m during both Ca 2+ and ROS stress. Biochemical analyses revealed that the PTP is a heterooligomeric complex composed of VDAC, SPG7, and CypD. Silencing or disruption of SPG7-CypD binding prevented Ca 2+ - and ROS-induced ΔΨ m depolarization and cell death. This study identifies an ubiquitously expressed IMM integral protein, SPG7, as a core component of the PTP at the OMM and IMM contact site. [ABSTRACT FROM AUTHOR]