Identification of p53 in mitochondria

From Cell Populations to Molecular Complexes: Multiplexed Multimodal Microscopy to Explore p53-53BP1 Molecular Interaction

Surpassing the diffraction barrier revolutionized modern fluorescence microscopy. However, intrinsic limitations in statistical sampling, the number of simultaneously analyzable channels, hardware requirements, and sample preparation procedures still represent an obstacle to its widespread diffusion in applicative biomedical research. Here, we present a novel pipeline based on automated multimodal microscopy and super-resolution techniques employing easily available materials and instruments and completed with open-source image-analysis software developed in our laboratory. The results show the potential impact of single-molecule localization microscopy (SMLM) on the study of biomolecules' interactions and the localization of macromolecular complexes. As a demonstrative application, we explored the basis of p53-53BP1 interactions, showing the formation of a putative macromolecular complex between the two proteins and the basal transcription machinery in situ, thus providing visual proof of the direct role of 53BP1 in sustaining p53 transactivation function. Moreover, high-content SMLM provided evidence of the presence of a 53BP1 complex on the cell cytoskeleton and in the mitochondrial space, thus suggesting the existence of novel alternative 53BP1 functions to support p53 activity.

The Role of Oxidative Stress in Tumorigenesis and Progression

Oxidative stress refers to the imbalance between the production of reactive oxygen species (ROS) and the endogenous antioxidant defense system. Its involvement in cell senescence, apoptosis, and series diseases has been demonstrated. Advances in carcinogenic research have revealed oxidative stress as a pivotal pathophysiological pathway in tumorigenesis and to be involved in lung cancer, glioma, hepatocellular carcinoma, leukemia, and so on. This review combs the effects of oxidative stress on tumorigenesis on each phase and cell fate determination, and three features are discussed. Oxidative stress takes part in the processes ranging from tumorigenesis to tumor death via series pathways and processes like mitochondrial stress, endoplasmic reticulum stress, and ferroptosis. It can affect cell fate by engaging in the complex relationships between senescence, death, and cancer. The influence of oxidative stress on tumorigenesis and progression is a multi-stage interlaced process that includes two aspects of promotion and inhibition, with mitochondria as the core of regulation. A deeper and more comprehensive understanding of the effects of oxidative stress on tumorigenesis is conducive to exploring more tumor therapies.

Loss of Mitochondrial AAA Proteases AFG3L2 and YME1L Impairs Mitochondrial Structure and Respiratory Chain Biogenesis

Mitochondrial protein quality control is crucial for the maintenance of correct mitochondrial homeostasis. It is ensured by several specific mitochondrial proteases located across the various mitochondrial subcompartments. Here, we focused on characterization of functional overlap and cooperativity of proteolytic subunits AFG3L2 (AFG3 Like Matrix AAA Peptidase Subunit 2) and YME1L (YME1 like ATPase) of mitochondrial inner membrane AAA (ATPases Associated with diverse cellular Activities) complexes in the maintenance of mitochondrial structure and respiratory chain integrity. We demonstrate that loss of AFG3L2 and YME1L, both alone and in combination, results in diminished cell proliferation, fragmentation of mitochondrial reticulum, altered cristae morphogenesis, and defective respiratory chain biogenesis. The double AFG3L2/YME1L knockdown cells showed marked upregulation of OPA1 protein forms, with the most prominent increase in short OPA1 (optic atrophy 1). Loss of either protease led to marked elevation in OMA1 (OMA1 zinc metallopeptidase) (60 kDa) and severe reduction in the SPG7 (paraplegin) subunit of the m-AAA complex. Loss of the YME1L subunit led to an increased Drp1 level in mitochondrial fractions. While loss of YME1L impaired biogenesis and function of complex I, knockdown of AFG3L2 mainly affected the assembly and function of complex IV. Our results suggest cooperative and partly redundant functions of AFG3L2 and YME1L in the maintenance of mitochondrial structure and respiratory chain biogenesis and stress the importance of correct proteostasis for mitochondrial integrity.

LACE1 interacts with p53 and mediates its mitochondrial translocation and apoptosis

p53 is a major cellular tumor suppressor that in addition to its nuclear, transcription-dependent activity is also known to function extranuclearly. Cellular stressors such as reactive oxygen species can promote translocation of p53 into mitochondria where it acts to protect mitochondrial genome or trigger cell death via transcription-independent manner. Here we report that the mammalian homologue of yeast mitochondrial Afg1 ATPase (LACE1) promotes translocation of p53 into mitochondria. We further show that LACE1 exhibits significant pro-apoptotic activity, which is dependent on p53, and that the protein is required for normal mitochondrial respiratory function. LACE1 physically interacts with p53 and is necessary for mitomycin c-induced translocation of p53 into mitochondria. Conversely, increased expression of LACE1 partitions p53 to mitochondria, causes reduction in nuclear p53 content and induces apoptosis. Thus, LACE1 mediates mitochondrial translocation of p53 and its transcription-independent apoptosis.

NSCA-1-a novel N-substituted coumalamide derivative-increases Adriamycin sensitivity in HepG2/adriamycin cells through modulating Akt/GSK-3β signaling and p53-dependant apoptotic pathway

Coumalamide derivatives are one of 2-pyrones derivatives, exerting multifunctional bioactivity. An array of coumalamide derivatives have been developed and presented good antiproliferative properties on cancer cells. However, the synthesis of 5-substituted coumalamide derivatives has not yet been published. Resistance to chemotherapeutic drugs is a major obstacle in hepatocellular carcinoma therapy. Recent evidence suggests that overexpression of constitutively active Akt confers on cancer cells resistance to chemotherapy. In this study, we report the synthesis and biological evaluation of a novel N-substituted coumalamide derivative (NSCA-1). The results indicated that NSCA-1 exerts synergistic cytotoxicity with Adriamycin in HepG2/ADR (HepG2/adriamycin) cells. Furthermore, both of the Akt kinase activity and phosphorylated Akt (Ser473) were found to be inhibited by NSCA-1 and subsequently resulting in decreased phosphorylation of GSK-3β. The intracellular accumulation of Adriamycin was also boosted by NSCA-1 via reducing the expression of p-gp. In addition, we found that combined treatment with NSCA-1 enhance cell apoptosis induced by Adriamycin via p53-dependant apoptotic pathway.

Mitochondrial BMI1 maintains bioenergetic homeostasis in cells

The polycomb complex proto-oncogene BMI1 [B lymphoma Mo-MLV insertion region 1 homolog (mouse)] is essential for self-renewal of normal and cancer stem cells. BMI1-null mice show severe defects in growth, development, and survival. Although BMI1 is known to exert its effect in the nucleus via repression of 2 potent cell-cycle regulators that are encoded by the Ink4a/Arf locus, deletion of this locus only partially rescues BMI1-null phenotypes, which is indicative of alternate mechanisms of action of BMI1. Here, we show that an extranuclear pool of BMI1 localizes to inner mitochondrial membrane and directly regulates mitochondrial RNA (mtRNA) homeostasis and bioenergetics. These mitochondrial functions of BMI1 are independent of its previously described nuclear functions because a nuclear localization-defective mutant BMI1 rescued several bioenergetic defects that we observed in BMI1-depleted cells, for example, mitochondrial respiration, cytochrome c oxidase activity, and ATP production. Mechanistically, BMI1 coprecipitated with polynucleotide phosphorylase, a ribonuclease that is responsible for decay of mtRNA transcripts. Loss of BMI1 enhanced ribonuclease activity of polynucleotide phosphorylase and reduced mtRNA stability. These findings not only establish a novel extranuclear role of BMI1 in the regulation of mitochondrial bioenergetics, but also provide new mechanistic insights into the role of this proto-oncogene in stem cell differentiation, neuronal aging, and cancer.-Banerjee Mustafi, S., Aznar, N., Dwivedi, S. K. D., Chakraborty, P. K., Basak, R., Mukherjee, P., Ghosh, P., Bhattacharya, R. Mitochondrial BMI1 maintains bioenergetic homeostasis in cells.

Heart mitochondria and calpain 1: Location, function, and targets

Calpain 1 is an ubiquitous Ca(2+)-dependent cysteine protease. Although calpain 1 has been found in cardiac mitochondria, the exact location within mitochondrial compartments and its function remain unclear. The aim of the current review is to discuss the localization of calpain 1 in different mitochondrial compartments in relationship to its function, especially in pathophysiological conditions. Briefly, mitochondrial calpain 1 (mit-CPN1) is located within the intermembrane space and mitochondrial matrix. Activation of the mit-CPN1 within intermembrane space cleaves apoptosis inducing factor (AIF), whereas the activated mit-CPN1 within matrix cleaves complex I subunits and metabolic enzymes. Inhibition of the mit-CPN1 could be a potential strategy to decrease cardiac injury during ischemia-reperfusion.

The large conductance calcium-activated potassium channel affects extrinsic and intrinsic mechanisms of apoptosis

The large-conductance calcium-activated K(+) or BK channel underlies electrical signals in a number of different cell types. Studies show that BK activity can also serve to regulate cellular homeostasis by protecting cells from apoptosis resulting from events such as ischemia. Recent coimmunoprecipitation studies, combined with mass spectrometry, suggest putative protein partners that interact with BK to regulate intrinsic and extrinsic apoptotic pathways. This study tests two of those partners to determine the effects on these two signaling pathways. Through reciprocal coimmunoprecipitation (coIP) experiments, we show that BK interacts with p53 and fas-associated protein with death domain (FADD) in mouse brain and when overexpressed in a heterologous expression system, such as HEK293 cells. Moreover, coIP experiments with N- and C-terminal fragments reveal that FADD interacts with the C-terminus of BK, whereas p53 interacts with either the N- or the C-terminus. Immunolocalization studies show that BK colocalizes with p53 and FADD in the mitochondrion and plasmalemma, respectively. HEK cells that stably express BK are more resistant to apoptosis when p53 or FADD is overexpressed or when their intrinsic and extrinsic pathways are stimulated via mitomycin C or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), respectively. Moreover, when stimulating with TRAIL, caspase-8 activation decreases in BK-expressing cells. These data suggest that BK is part of a larger complex of proteins that protects against apoptosis by interacting with proapoptotic proteins, such as p53 and FADD.

Mitochondrial protein alterations in a familial peripheral neuropathy caused by the V144D amino acid mutation in the sphingolipid protein, SPTLC1

Axonal degeneration is the final common path in many neurological disorders. Subsets of neuropathies involving the sensory neuron are known as hereditary sensory neuropathies (HSNs). Hereditary sensory neuropathy type I (HSN-I) is the most common subtype of HSN with autosomal dominant inheritance. It is characterized by the progressive degeneration of the dorsal root ganglion (DRG) with clinical symptom onset between the second or third decade of life. Heterozygous mutations in the serine palmitoyltransferase (SPT) long chain subunit 1 (SPTLC1) gene were identified as the pathogenic cause of HSN-I. Ultrastructural analysis of mitochondria from HSN-I patient cells has displayed unique morphological abnormalities that are clustered to the perinucleus where they are wrapped by the endoplasmic reticulum (ER). This investigation defines a small subset of proteins with major alterations in abundance in mitochondria harvested from HSN-I mutant SPTLC1 cells. Using mitochondrial protein isolates from control and patient lymphoblasts, and a combination of 2D gel electrophoresis, immunoblotting and mass spectrometry, we have shown the increased abundance of ubiquinol-cytochrome c reductase core protein 1, an electron transport chain protein, as well as the immunoglobulin, Ig kappa chain C. The regulation of these proteins may provide a new route to understanding the cellular and molecular mechanisms underlying HSN-I.

Phospho-aspirin-2 (MDC-22) inhibits estrogen receptor positive breast cancer growth both in vitro and in vivo by a redox-dependent effect

Phospho-aspirin (PA-2) is a novel aspirin derivative that exhibits promising anticancer properties and is considerably safer than conventional aspirin. In this study, we investigated the chemotherapeutic efficacy of PA-2 in preclinical models of estrogen receptor positive (ER+) breast cancer and elucidated its mechanism of action. PA-2 inhibited the growth of ER+ cells more potently than aspirin in vitro, and exerted a triple cytokinetic effect that includes induction of apoptosis and cell cycle arrest as well as the inhibition of cell proliferation. PA-2 is highly efficacious in vivo, as treatment of established MCF7 xenografts with PA-2 induced tumor stasis (98.2% inhibition, p<0.01). PA-2 triggered the activation of p53-dependent apoptosis via two distinct mechanisms: 1) acetylation of p53 (at K373), which disrupts its interaction with its transcription repressor MDM2, and 2) translocation of p53 to the mitochondria leading to the dissipation of mitochondrial transmembrane potential (ΔΨ(m)). Consistent with these observations, both the RNAi-mediated knockdown of p53 and forced deactylation via HDAC1 over-expression attenuated the anticancer effect of PA-2 in MCF7 cells. An upstream mediator of the signaling effects of PA-2 is RONS. PA-2 induced oxidative stress in vitro and in mice bearing MCF7 xenografts; its induction effect appears to be tumor-specific. Crucially, administration of N-acetylcysteine, a ROS scavenger, abrogated the effect of PA-2 on p53 acetylation and mitochondria translocation, thus identifying RONS as proximal molecules mediating the anticancer effect of PA-2. In summary, our findings demonstrate that PA-2 is a promising antineoplastic compound against ER+ breast cancer, warranting further evaluation as an anticancer agent.

Release of targeted p53 from the mitochondrion as an early signal during mitochondrial dysfunction

Increased accumulation of p53 tumor suppressor protein is an early response to low-level stressors. To investigate the fate of mitochondrial-sequestered p53, mouse embryonic fibroblast cells (MEFs) on a p53-deficient genetic background were transfected with p53-EGFP fusion protein led by a sense (m53-EGFP) or antisense (c53-EGFP) mitochondrial import signal. Rotenone exposure (100nM, 1h) triggered the translocation of m53-EGFP from the mitochondrion to the nucleus, thus shifting the transfected cells from a mitochondrial p53 to a nuclear p53 state. Antibodies for p53 serine phosphorylation or lysine acetylation indicated a different post-translational status of recombinant p53 in the nucleus and mitochondrion, respectively. These data suggest that cycling of p53 through the mitochondria may establish a direct pathway for p53 signaling from the mitochondria to the nucleus during mitochondrial dysfunction. PK11195, a pharmacological ligand of mitochondrial TSPO (formerly known as the peripheral-type benzodiazepine receptor), partially suppressed the release of mitochondria-sequestered p53. These findings support the notion that p53 function mediates a direct signaling pathway from the mitochondria to nucleus during mitochondrial dysfunction.