BIRD-2, a BH4-domain-targeting peptide of Bcl-2, provokes Bax/Bak-independent cell death in B-cell cancers through mitochondrial Ca2+-dependent mPTP opening

Crosstalk between mitochondria-ER contact sites and the apoptotic machinery as a novel health meter

Mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) function as transient signaling platforms that regulate essential cellular functions. MERCS are enriched in specific proteins and lipids that connect mitochondria and the ER together and modulate their activities. Dysregulation of MERCS is associated with several human pathologies including Alzheimer's disease (AD), Parkinson's disease (PD), and cancer. BCL-2 family proteins can locate at MERCS and control essential cellular functions such as calcium signaling and autophagy in addition to their role in mitochondrial apoptosis. Moreover, the BCL-2-mediated apoptotic machinery was recently found to trigger cGAS-STING pathway activation and a proinflammatory response, a recognized hallmark of these diseases that requires mitochondria-ER interplay. This review underscores the pivotal role of MERCS in regulating essential cellular functions, focusing on their crosstalk with BCL-2 family proteins, and discusses how their dysregulation is linked to disease.

Recent advances in canonical versus non-canonical Ca2+-signaling-related anti-apoptotic Bcl-2 functions and prospects for cancer treatment

Cell fate is tightly controlled by a continuous balance between cell survival and cell death inducing mechanisms. B-cell lymphoma 2 (Bcl-2)-family members, composed of effectors and regulators, not only control apoptosis at the level of the mitochondria but also by impacting the intracellular Ca2+ homeostasis and dynamics. On the one hand, anti-apoptotic protein Bcl-2, prevents mitochondrial outer membrane permeabilization (MOMP) by scaffolding and neutralizing proapoptotic Bcl-2-family members via its hydrophobic cleft (region composed of BH-domain 1-3). On the other hand, Bcl-2 suppress pro-apoptotic Ca2+ signals by binding and inhibiting IP3 receptors via its BH4 domain, which is structurally exiled from the hydrophobic cleft by a flexible loop region (FLR). As such, Bcl-2 prevents excessive Ca2+ transfer from ER to mitochondria. Whereas regulation of both pathways requires different functional regions of Bcl-2, both seem to be connected in cancers that overexpress Bcl-2 in a life-promoting dependent manner. Here we discuss the anti-apoptotic canonical and non-canonical role, via calcium signaling, of Bcl-2 in health and cancer and evolving from this the proposed anti-cancer therapies with their shortcomings. We also argue how some cancers, with the major focus on diffuse large B-cell lymphoma (DLBCL) are difficult to treat, although theoretically prime marked for Bcl-2-targeting therapeutics. Further work is needed to understand the non-canonical functions of Bcl-2 also at organelles beyond the mitochondria, the interaction partners outside the Bcl-2 family as well as their ability to target or exploit these functions as therapeutic strategies in diseases.

Targeting androgen receptor (AR) with a synthetic peptide increases apoptosis in triple negative breast cancer and AR-expressing prostate cancer cell lines

BACKGROUND

The androgen receptor (AR) has been studied as an approach to cancer therapy.

AIMS

We used human breast cancer-derived cells with high, low, and very low expression levels of AR, in addition to prostate cancer-derived LNCaP and DU-145 cells as a positive and negative controls to examine apoptosis caused by a synthetic peptide that targets ARs.

METHODS AND RESULTS

The peptide was produced to inhibit AR transactivation in breast cancer cell lines. We then measured cell viability, caspase-3 activity, and the ratio of Bax/Bcl-2. The findings indicated that the peptide (100-500 nM) in the presence of dihydrotestosterone (DHT) reduced cell growth in cells with high and low expression level of AR (p < .001), but not in cells with very low levels of AR. Treatment with 100-500 nM of peptide activated caspase-3 and increased the ratio of Bax/Bcl-2 in cells with high and low expression levels of AR. Also, increasing concentrations of the peptide (100-500 nM) reduced BrdU incorporation in the presence of DHT and promoted apoptosis in cells with high and low expression levels of AR (p < .001).

CONCLUSION

The findings indicate the peptide significantly increased apoptosis in cancer cells.

Adenosine triphosphate induced cell death: Mechanisms and implications in cancer biology and therapy

Adenosine triphosphate (ATP) induced cell death (AICD) is a critical cellular process that has garnered substantial scientific interest for its profound relevance to cancer biology and to therapeutic interventions. This comprehensive review unveils the intricate web of AICD mechanisms and their intricate connections with cancer biology. This review offers a comprehensive framework for comprehending the multifaceted role of AICD in the context of cancer. This is achieved by elucidating the dynamic interplay between systemic and cellular ATP homeostasis, deciphering the intricate mechanisms governing AICD, elucidating its intricate involvement in cancer signaling pathways, and scrutinizing validated key genes. Moreover, the exploration of AICD as a potential avenue for cancer treatment underscores its essential role in shaping the future landscape of cancer therapeutics.

The Complex Effects of PKM2 and PKM2:IP3R Disruption on Intracellular Ca2+ Handling and Cellular Functions

Pyruvate kinase M (PKM) 2 was described to interact with the inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and suppress its activity. To further investigate the physiological importance of the PKM2:IP3R interaction, we developed and characterized HeLa PKM2 knockout (KO) cells. In the HeLa PKM2 KO cells, the release of Ca2+ to the cytosol appears to be more sensitive to low agonist concentrations than in HeLa wild-type (WT) cells. However, upon an identical IP3-induced Ca2+ release, Ca2+ uptake in the mitochondria is decreased in HeLa PKM2 KO cells, which may be explained by the smaller number of contact sites between the ER and the mitochondria. Furthermore, in HeLa PKM2 KO cells, mitochondria are more numerous, though they are smaller and less branched and have a hyperpolarized membrane potential. TAT-D5SD, a cell-permeable peptide representing a sequence derived from IP3R1 that can disrupt the PKM2:IP3R interaction, induces Ca2+ release into the cytosol and Ca2+ uptake into mitochondria in both HeLa WT and PKM2 KO cells. Moreover, TAT-D5SD induced apoptosis in HeLa WT and PKM2 KO cells but not in HeLa cells completely devoid of IP3Rs. These results indicate that PKM2 separately regulates cytosolic and mitochondrial Ca2+ handling and that the cytotoxic effect of TAT-D5SD depends on IP3R activity but not on PKM2. However, the tyrosine kinase Lck, which also interacts with the D5SD sequence, is expressed neither in HeLa WT nor PKM2 KO cells, and we can also exclude a role for PKM1, which is upregulated in HeLa PKM2 KO cells, indicating that the TAT-D5SD peptide has a more complex mode of action than anticipated.

TGR5 supresses cGAS/STING pathway by inhibiting GRP75-mediated endoplasmic reticulum-mitochondrial coupling in diabetic retinopathy

Diabetic retinopathy (DR) is a serious and relatively under-recognized complication of diabetes. Müller glial cells extend throughout the retina and play vital roles in maintaining retinal homeostasis. Previous studies have demonstrated that TGR5, a member of the bile acid-activated GPCR family, could ameliorate DR. However, the role of TGR5 in regulating Müller cell function and the underlying mechanism remains to be ascertained. To address this, high glucose (HG)-treated human Müller cells and streptozotocin-treated Sprague-Dawley rats were used in the study. The IP3R1-GRP75-VDAC1 axis and mitochondrial function were assessed after TGR5 ablation or agonism. Cytosolic mitochondrial DNA (mtDNA)-mediated cGAS-STING activation was performed. The key markers of retinal vascular leakage, apoptosis, and inflammation were examined. We found that mitochondrial Ca2+ overload and mitochondrial dysfunction were alleviated by TGR5 agonist. Mechanically, TGR5 blocked the IP3R1-GRP75-VDAC1 axis mediated Ca2+ efflux from the endoplasmic reticulum into mitochondria under diabetic condition. Mitochondrial Ca2+ overload led to the opening of the mitochondrial permeability transition pore and the release of mitochondrial DNA (mtDNA) into the cytosol. Cytoplasmic mtDNA bound to cGAS and upregulated 2'3' cyclic GMP-AMP. Consequently, STING-mediated inflammatory responses were activated. TGR5 agonist prevented retinal injury, whereas knockdown of TGR5 exacerbated retinal damage in DR rats, which was rescued by the STING inhibitor. Based on the above results, we propose that TGR5 might be a novel therapeutic target for the treatment of DR.

Transient receptor potential ankyrin 1 (TRPA1) mediates reactive oxygen species-induced Ca2+ entry, mitochondrial dysfunction, and caspase-3/7 activation in primary cultures of metastatic colorectal carcinoma cells

Colorectal carcinoma (CRC) represents the fourth most common cancer worldwide and is the third most common cause of malignancy-associated mortality. Distant metastases to the liver and lungs are the main drivers of CRC-dependent death. Pro-oxidant therapies, which halt disease progression by exacerbating oxidative stress, represent an antitumour strategy that is currently exploited by chemotherapy and ionizing radiation. A more selective strategy to therapeutically exploit reactive oxygen species (ROS) signaling would consist in targeting a redox sensor that is up-regulated in metastatic cells and is tightly coupled to the stimulation of cancer cell death programs. The non-selective cation channel, Transient Receptor Potential Ankyrin 1 (TRPA1), serves as a sensor of the cellular redox state, being activated to promote extracellular Ca²⁺ entry by an increase in oxidative stress. Recent work demonstrated that TRPA1 channel protein is up-regulated in several cancer types and that TRPA1-mediated Ca²⁺ signals can either engage an antiapoptotic pro-survival signaling pathway or to promote mitochondrial Ca²⁺ dysfunction and apoptosis. Herein, we sought to assess for the first time the outcome of TRPA1 activation by ROS on primary cultures of metastatic colorectal carcinoma (mCRC cells). We found that TRPA1 channel protein is up-regulated and mediates enhanced hydrogen peroxide (H₂O₂)-induced Ca²⁺ entry in mCRC cells as compared to non-neoplastic control cells. The lipid peroxidation product 4-hydroxynonenal (4-HNE) is the main ROS responsible for TRPA1 activation upon mCRC cell exposure to oxidative stress. TRPA1-mediated Ca²⁺ entry in response to H₂O₂ and 4-HNE results in mitochondrial Ca²⁺ overload, followed by mitochondrial depolarization and caspase-3/7 activation. Therefore, targeting TRPA1 could represent an alternative strategy to eradicate metastatic CRC by enhancing its sensitivity to oxidative stress.

Bmal1 downregulation leads to diabetic cardiomyopathy by promoting Bcl2/IP3R-mediated mitochondrial Ca2+ overload

Brain and muscle arnt-like protein 1 (Bmal1) is a crucial transcription factor, regulating circadian rhythm and involved in multiple heart diseases. However, it is unknown whether Bmal1 promotes diabetic cardiomyopathy (DCM) pathogenesis. The objective of this investigation was to ascertain the vital role of Bmal1 in the progression of DCM. Mice with T2D and H9c2 cardiomyoblasts exposed to high glucose and palmitic acid (HGHP) were used. Cardiomyocyte-specific knockout mouse of Bmal1 (CKB) was also generated, and cardiac Bmal1 was overexpressed in type 2 diabetes (T2D) mice using an adeno-associated virus. Bmal1 gene recombinant adenovirus was used to either knockdown or overexpress in H9c2 cardiomyoblasts. Bmal1 expression was significantly altered in diabetic mice hearts. Bmal1 downregulation in CKB and T2D mice heart accelerated cardiac hypertrophy and diastolic dysfunction, while Bmal1 overexpression ameliorated these pathological changes in DCM mice. Furthermore, DCM mice had significant mitochondrial ultrastructural defects, reactive oxygen species accumulation, and apoptosis, which could be alleviated by overexpressing Bmal1. In H9c2 cardiomyoblasts, genetic downregulation of Bmal1 or HGHP markedly decreased the binding of Bcl2 to IP3R, thus increasing Ca²⁺ release to mitochondria through mitochondria-associated endoplasmic reticulum membranes. Importantly, chromatin immunoprecipitation revealed Bmal1 could bind directly to the Bcl2 gene promoter region. Bmal1 overexpression augmented the Bmal1/Bcl2 binding, enhancing the inhibition of Bcl2 on IP3R activity, thus alleviating mitochondrial Ca²⁺ overload and subsequent cell apoptosis. These results show that Bmal1 is involved in the DCM development through Bcl2/IP3R-mediated mitochondria Ca²⁺ overload. Therapy targeting the circadian clock (Bmal1) can treat DCM.

The ER-mitochondria interface, where Ca2+ and cell death meet

Endoplasmic reticulum (ER)-mitochondria contact sites are crucial to allow Ca²⁺ flux between them and a plethora of proteins participate in tethering both organelles together. Inositol 1,4,5-trisphosphate receptors (IP₃Rs) play a pivotal role at such contact sites, participating in both ER-mitochondria tethering and as Ca²⁺-transport system that delivers Ca²⁺ from the ER towards mitochondria. At the ER-mitochondria contact sites, the IP₃Rs function as a multi-protein complex linked to the voltage-dependent anion channel 1 (VDAC1) in the outer mitochondrial membrane, via the chaperone glucose-regulated protein 75 (GRP75). This IP₃R-GRP75-VDAC1 complex supports the efficient transfer of Ca²⁺ from the ER into the mitochondrial intermembrane space, from which the Ca²⁺ ions can reach the mitochondrial matrix through the mitochondrial calcium uniporter. Under physiological conditions, basal Ca²⁺ oscillations deliver Ca²⁺ to the mitochondrial matrix, thereby stimulating mitochondrial oxidative metabolism. However, when mitochondrial Ca²⁺ overload occurs, the increase in [Ca²⁺] will induce the opening of the mitochondrial permeability transition pore, thereby provoking cell death. The IP₃R-GRP75-VDAC1 complex forms a hub for several other proteins that stabilize the complex and/or regulate the complex's ability to channel Ca²⁺ into the mitochondria. These proteins and their mechanisms of action are discussed in the present review with special attention for their role in pathological conditions and potential implication for therapeutic strategies.

Dinuclear nitrido-bridged osmium complexes inhibit the mitochondrial calcium uniporter and protect cortical neurons against lethal oxygen-glucose deprivation

Dysregulation of mitochondrial calcium uptake mediated by the mitochondrial calcium uniporter (MCU) is implicated in several pathophysiological conditions. Dinuclear ruthenium complexes are effective inhibitors of the MCU and have been leveraged as both tools to study mitochondrial calcium dynamics and potential therapeutic agents. In this study, we report the synthesis and characterization of Os245 ([Os2(μ-N)(NH3)8Cl2]3+) which is the osmium-containing analogue of our previously reported ruthenium-based inhibitor Ru265. This complex and its aqua-capped analogue Os245' ([Os2(μ-N)(NH3)8(OH2)2]5+) are both effective inhibitors of the MCU in permeabilized and intact cells. In comparison to the ruthenium-based inhibitor Ru265 (k obs = 4.92 × 10-3 s-1), the axial ligand exchange kinetics of Os245 are two orders of magnitude slower (k obs = 1.63 × 10-5 s-1) at 37 °C. The MCU-inhibitory properties of Os245 and Os245' are different (Os245 IC50 for MCU inhibition = 103 nM; Os245' IC50 for MCU inhibition = 2.3 nM), indicating that the axial ligands play an important role in their interactions with this channel. We further show that inhibition of the MCU by these complexes protects primary cortical neurons against lethal oxygen-glucose deprivation. When administered in vivo to mice (10 mg kg-1), Os245 and Os245' induce seizure-like behaviors in a manner similar to the ruthenium-based inhibitors. However, the onset of these seizures is delayed, a possible consequence of the slower ligand substitution kinetics for these osmium complexes. These findings support previous studies that demonstrate inhibition of the MCU is a promising therapeutic strategy for the treatment of ischemic stroke, but also highlight the need for improved drug delivery strategies to mitigate the pro-convulsant effects of this class of complexes before they can be implemented as therapeutic agents. Furthermore, the slower ligand substitution kinetics of the osmium analogues may afford new strategies for the development and modification of this class of MCU inhibitors.

Antimicrobial Peptides Mediate Apoptosis by Changing Mitochondrial Membrane Permeability

Changes in mitochondrial membrane permeability are closely associated with mitochondria-mediated apoptosis. Antimicrobial peptides (AMPs), which have been found to enter cells to exert physiological effects, cause damage to the mitochondria. This paper reviews the molecular mechanisms of AMP-mediated apoptosis by changing the permeability of the mitochondrial membrane through three pathways: the outer mitochondrial membrane (OMM), inner mitochondrial membrane (IMM), and mitochondrial permeability transition pore (MPTP). The roles of AMPs in inducing changes in membrane permeability and apoptosis are also discussed. Combined with recent research results, the possible application prospects of AMPs are proposed to provide a theoretical reference for the development of AMPs as therapeutic agents for human diseases.

Deregulated calcium signaling in blood cancer: Underlying mechanisms and therapeutic potential

Intracellular calcium signaling regulates diverse physiological and pathological processes. In solid tumors, changes to calcium channels and effectors via mutations or changes in expression affect all cancer hallmarks. Such changes often disrupt transport of calcium ions (Ca2+) in the endoplasmic reticulum (ER) or mitochondria, impacting apoptosis. Evidence rapidly accumulates that this is similar in blood cancer. Principles of intracellular Ca2+ signaling are outlined in the introduction. We describe different Ca2+-toolkit components and summarize the unique relationship between extracellular Ca2+ in the endosteal niche and hematopoietic stem cells. The foundational data on Ca2+ homeostasis in red blood cells is discussed, with the demonstration of changes in red blood cell disorders. This leads to the role of Ca2+ in neoplastic erythropoiesis. Then we expand onto the neoplastic impact of deregulated plasma membrane Ca2+ channels, ER Ca2+ channels, Ca2+ pumps and exchangers, as well as Ca2+ sensor and effector proteins across all types of hematologic neoplasms. This includes an overview of genetic variants in the Ca2+-toolkit encoding genes in lymphoid and myeloid cancers as recorded in publically available cancer databases. The data we compiled demonstrate that multiple Ca2+ homeostatic mechanisms and Ca2+ responsive pathways are altered in hematologic cancers. Some of these alterations may have genetic basis but this requires further investigation. Most changes in the Ca2+-toolkit do not appear to define/associate with specific disease entities but may influence disease grade, prognosis, treatment response, and certain complications. Further elucidation of the underlying mechanisms may lead to novel treatments, with the aim to tailor drugs to different patterns of deregulation. To our knowledge this is the first review of its type in the published literature. We hope that the evidence we compiled increases awareness of the calcium signaling deregulation in hematologic neoplasms and triggers more clinical studies to help advance this field.

Modulation of Ca2+ signaling by antiapoptotic Bcl-2 versus Bcl-xL: From molecular mechanisms to relevance for cancer cell survival

Members of the Bcl-2-protein family are key controllers of apoptotic cell death. The family is divided into antiapoptotic (including Bcl-2 itself, Bcl-xL, Mcl-1, etc.) and proapoptotic members (Bax, Bak, Bim, Bim, Puma, Noxa, Bad, etc.). These proteins are well known for their canonical role in the mitochondria, where they control mitochondrial outer membrane permeabilization and subsequent apoptosis. However, several proteins are recognized as modulators of intracellular Ca²⁺ signals that originate from the endoplasmic reticulum (ER), the major intracellular Ca²⁺-storage organelle. More than 25 years ago, Bcl-2, the founding member of the family, was reported to control apoptosis through Ca²⁺ signaling. Further work elucidated that Bcl-2 directly targets and inhibits inositol 1,4,5-trisphosphate receptors (IP₃Rs), thereby suppressing proapoptotic Ca²⁺ signaling. In addition to Bcl-2, Bcl-xL was also shown to impact cell survival by sensitizing IP₃R function, thereby promoting prosurvival oscillatory Ca²⁺ release. However, new work challenges this model and demonstrates that Bcl-2 and Bcl-xL can both function as inhibitors of IP₃Rs. This suggests that, depending on the cell context, Bcl-xL could support very distinct Ca²⁺ patterns. This not only raises several questions but also opens new possibilities for the treatment of Bcl-xL-dependent cancers. In this review, we will discuss the similarities and divergences between Bcl-2 and Bcl-xL regarding Ca²⁺ homeostasis and IP₃R modulation from both a molecular and a functional point of view, with particular emphasis on cancer cell death resistance mechanisms.

ER-mitochondria contact sites; a multifaceted factory for Ca2+ signaling and lipid transport

Membrane contact sites (MCS) between organelles of eukaryotic cells provide structural integrity and promote organelle homeostasis by facilitating intracellular signaling, exchange of ions, metabolites and lipids and membrane dynamics. Cataloguing MCS revolutionized our understanding of the structural organization of a eukaryotic cell, but the functional role of MSCs and their role in complex diseases, such as cancer, are only gradually emerging. In particular, the endoplasmic reticulum (ER)-mitochondria contacts (EMCS) are key effectors of non-vesicular lipid trafficking, thereby regulating the lipid composition of cellular membranes and organelles, their physiological functions and lipid-mediated signaling pathways both in physiological and diseased conditions. In this short review, we discuss key aspects of the functional complexity of EMCS in mammalian cells, with particular emphasis on their role as central hubs for lipid transport between these organelles and how perturbations of these pathways may favor key traits of cancer cells.

Cyclosporine A regulates PMN-MDSCs viability and function through MPTP in acute GVHD: Old medication, new target

Myeloid-derived suppressor cells (MDSCs), a population of myeloid lineage cells with immunosuppressive capacity, can mitigate acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We previously found that the immunosuppressive function of polymorphonuclear population (PMN-MDSCs) was impaired in aGVHD milieu. The aim of this study was to explore the intrinsic mechanism regulating the fate and function of donor-derived PMN-MDSCs during allo-HSCT. We firstly found that mitochondrial permeability transition pore (MPTP) opened in the PMN-MDSCs in response to the intense inflammatory environment of aGVHD, which induced mitochondrial damage, oxidative stress, and apoptosis of PMN-MDSCs. Inhibiting MPTP opening by a traditional immunosuppressant, cyclosporine A (CsA), could restore the immunosuppressive function and viability of PMN-MDSCs in vitro and in vivo, which reveals a new mechanism of CsA application.

Cyclosporine A loaded brain targeting nanoparticle to treat cerebral ischemia/reperfusion injury in mice

BACKGROUND

Ischemic stroke is one of the main causes of death and disability in the world. The treatment for ischemic stroke is to restore blood perfusion as soon as possible. However, when ischemic brain tissue is re-perfused by blood, the mitochondrial permeability transition pore (mPTP) in neuron and microglia is excessively opened, resulting in the apoptosis of neuron and nerve inflammation. This aggravates nerve injury. Cyclosporine A (CsA) inhibits the over-opening of mPTP, subsequently reducing the release of ROS and the apoptosis of cerebral ischemia/reperfusion injured neuron and microglia. However, CsA is insoluble in water and present in high concentrations in lymphatic tissue. Herein, cerebral infarction tissue targeted nanoparticle (CsA@HFn) was developed to treat cerebral ischemia/reperfusion injury.

RESULTS

CsA@HFn efficiently penetrated the blood-brain barrier (BBB) and selectively accumulated in ischemic area, inhibiting the opening of mPTP and ROS production in neuron. This subsequently reduced the apoptosis of neuron and the damage of BBB. Consequently, CsA@HFn significantly reduced the infarct area. Moreover, CsA@HFn inhibited the recruitment of astrocytes and microglia in ischemic region and polarized microglia into M2 type microglia, which subsequently alleviated the nerve inflammation.

CONCLUSIONS

CsA@HFn showed a significant therapeutic effect on cerebral ischemia/reperfusion injury by alleviating the apoptosis of neuron, nerve inflammation and the damage of BBB in ischemic area. CsA@HFn has great potential in the treatment of ischemic stroke.

Anti-cancer peptide-based therapeutic strategies in solid tumors

BACKGROUND

Nowadays, conventional medical treatments such as surgery, radiotherapy, and chemotherapy cannot cure all types of cancer. A promising approach to treat solid tumors is the use of tumor-targeting peptides to deliver drugs or active agents selectively.

RESULT

Introducing beneficial therapeutic approaches, such as therapeutic peptides and their varied methods of action against tumor cells, can aid researchers in the discovery of novel peptides for cancer treatment. The biomedical applications of therapeutic peptides are highly interesting. These peptides, owing to their high selectivity, specificity, small dimensions, high biocompatibility, and easy modification, provide good opportunities for targeted drug delivery. In recent years, peptides have shown considerable promise as therapeutics or targeting ligands in cancer research and nanotechnology.

CONCLUSION

 This study reviews a variety of therapeutic peptides and targeting ligands in cancer therapy. Initially, three types of tumor-homing and cell-penetrating peptides (CPPs) are described, and then their applications in breast, glioma, colorectal, and melanoma cancer research are discussed.

The diagnostic significance of 64-slice spiral CT combined with serological CA19-9, Bcl-2, CYFRA21-1 detection in thoracic esophageal carcinoma

BACKGROUND

To analyze the clinical value of multi-slice spiral computed tomography (MSCT) combined with carbohydrate antigen 19-9 (CA19-9), B-cell leukemia/lymphoma-2 protein (Bcl-2), and cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) detection in the diagnosis of thoracic esophageal cancer.

METHODS

The clinical data of 74 patients with thoracic esophageal cancer admitted to the Dazu District People's Hospital in Chonqing, China, from December 2019 to December 2020 were collected (esophageal cancer group), and their computed tomography (CT) signs were analyzed. Another 55 healthy people who underwent physical examination during the same period in the hospital were selected for the healthy group. The serum levels of CA19-9, Bcl-2, and CYFRA21-1 in the different populations were compared, using the receiver operating characteristic (ROC) curve to analyze the value of MSCT combined with CA19-9, Bcl-2, and CYFRA21-1 detection in the diagnosis of thoracic esophageal cancer.

RESULTS

The serum levels of CA19-9, Bcl-2, and CYFRA21-1 in patients of the esophageal cancer group were significantly higher than those in the healthy group (P<0.05). The serum levels of CA19-9, Bcl-2, and CYFRA21-1 in patients with poorly differentiated, stage III-IV carcinoma and lymph node metastasis were significantly higher than in those patients with moderately well-differentiated, stage I-II carcinoma and no lymph node metastasis (P<0.05). The CT scans of patients in the esophageal cancer group showed esophageal walls with irregular, needle-shaped, circular, or localized eccentric thickening and narrowed lumens, which were dilated above the cancerous lesions. Some tumors compressed adjacent organs to deform and shift the organs, resulting in the disappearance of surrounding fat layers. Enhanced scans showed mild or moderate enhancement, with large-diameter lesions unable to enhance central, low-density, necrotic areas. The ROC curve showed that the area under the curve (AUC) and the sensitivity and specificity of MSCT combined with CA19-9, Bcl-2, and CYFRA21-1 detection were all higher than for esophageal lesions detected by individual indicators.

CONCLUSIONS

CA19-9, Bcl-2, and CYFRA21-1, which are abnormally expressed in patients with esophageal cancer, may be related to the occurrence and development of esophageal cancer. MSCT combined with CA19-9, Bcl-2, and CYFRA21-1 detection appears to enhance the diagnosis of esophageal cancer.

Yes, MAM!

Regulation of cell life and death by members of the BCL-2 family of proteins occurs at the mitochondria. Large portions of the mitochondria's outer membrane are found in tight approximation with the endoplasmic reticulum (ER), known as mitochondria-associated membranes (MAMs) or mitochondria-ER contact sites (MERCs). We recently reported that BOK is present within MAMs where it regulates Ca²⁺ transfer from the ER to the mitochondria, appropriate MAM components and MERC structure, and apoptosis.

Dynamic control of mitochondria-associated membranes by kinases and phosphatases in health and disease

Membrane-contact sites are getting more and more credit for their indispensable role in maintenance of cell function and homeostasis. In the last decades, the ER-mitochondrial contact sites in particular received a lot of attention. While our knowledge of ER-mitochondrial contact sites increases steadily, the focus often lies on a static exploration of their functions. However, it is increasingly clear that these contact sites are very dynamic. In this review, we highlight the dynamic nature of ER-mitochondrial contact sites and the role of kinases and phosphatases therein with a focus on recent findings. Phosphorylation events allow for rapid integration of information on the protein level, impacting protein function, localization and interaction at ER-mitochondrial contact sites. To illustrate the importance of these events and to put them in a broader perspective, we connect them to pathologies like diabetes type II, Parkinson's disease and cancer.

Tracing the evolutionary history of Ca2+-signaling modulation by human Bcl-2: Insights from the Capsaspora owczarzaki IP3 receptor ortholog

Recently, a functional IP₃R ortholog (CO.IP₃R-A) capable of IP₃-induced Ca²⁺ release has been discovered in Capsaspora owczarzaki, a close unicellular relative to Metazoa. In contrast to mammalian IP₃Rs, CO.IP₃R-A is not modulated by Ca²⁺, ATP or PKA. Protein-sequence analysis revealed that CO.IP₃R-A contained a putative binding site for anti-apoptotic Bcl-2, although Bcl-2 was not detected in Capsaspora owczarzaki and only appeared in Metazoa. Here, we examined whether human Bcl-2 could form a complex with CO.IP₃R-A channels and modulate their Ca²⁺-flux properties using ectopic expression approaches in a HEK293 cell model in which all three IP₃R isoforms were knocked out. We demonstrate that human Bcl-2 via its BH4 domain could functionally interact with CO.IP₃R-A, thereby suppressing Ca²⁺ flux through CO.IP₃R-A channels. The BH4 domain of Bcl-2 was sufficient for interaction with CO.IP₃R-A channels. Moreover, mutating the Lys17 of Bcl-2's BH4 domain, the residue critical for Bcl-2-dependent modulation of mammalian IP₃Rs, abrogated Bcl-2's ability to bind and inhibit CO.IP₃R-A channels. Hence, this raises the possibility that a unicellular ancestor of animals already had an IP₃R that harbored a Bcl-2-binding site. Bcl-2 proteins may have evolved as controllers of IP₃R function by exploiting this pre-existing site, thereby counteracting Ca²⁺-dependent apoptosis.

Cobalt amine complexes and Ru265 interact with the DIME region of the mitochondrial calcium uniporter

We report our investigation into the MCU-inhibitory activity of Co3+ complexes in comparison to Ru265. These compounds reversibly inhibit the MCU with nanomolar potency. Mutagenesis studies and molecular docking simulations suggest that the complexes operate through interactions with the DIME motif of the MCU pore.

Cell death as a result of calcium signaling modulation: A cancer-centric prospective

Calcium ions (Ca²⁺) and the complex regulatory system governed by Ca²⁺ signaling have been described to be of crucial importance in numerous aspects related to cell life and death decisions, especially in recent years. The growing attention given to this second messenger is justified by the pleiotropic nature of Ca²⁺-binding proteins and transporters and their consequent involvement in cell fate decisions. A growing number of works highlight that deregulation of Ca²⁺ signaling and homoeostasis is often deleterious and drives pathological conditions; in particular, a disruption of the main Ca²⁺-mediated death mechanisms may lead to uncontrolled cell growth that results in cancer. In this work, we review the latest useful evidence to better understand the complex network of pathways by which Ca²⁺ regulates cell life and death decisions.

Bcl-2 Family of Proteins in the Control of Mitochondrial Calcium Signalling: An Old Chap with New Roles

Bcl-2 family proteins are considered as one of the major regulators of apoptosis. Indeed, this family is known to control the mitochondrial outer membrane permeabilization (MOMP): a central step in the mitochondrial pathway of apoptosis. However, in recent years Bcl-2 family members began to emerge as a new class of intracellular calcium (Ca²⁺) regulators. At mitochondria-ER contacts (MERCs) these proteins are able to interact with major Ca²⁺ transporters, thus controlling mitochondrial Ca²⁺ homeostasis and downstream Ca²⁺ signalling pathways. Beyond the regulation of cell survival, this Bcl-2-dependent control over the mitochondrial Ca²⁺ dynamics has far-reaching consequences on the physiology of the cell. Here, we review how the Bcl-2 family of proteins mechanistically regulate mitochondrial Ca²⁺ homeostasis and how this regulation orchestrates cell death/survival decisions as well as the non-apoptotic process of cell migration.

Bok binds to a largely disordered loop in the coupling domain of type 1 inositol 1,4,5-trisphosphate receptor

Bcl-2-related ovarian killer (Bok) binds tightly to inositol 1,4,5-trisphosphate receptors (IP₃Rs). To better understand this interaction, we sought to elucidate the Bok binding determinants in IP₃R1, focusing on the ∼75 amino acid loop (residues 1882-1957) between α helices 72 and 73. Bioinformatic analysis revealed that the majority of this loop is intrinsically disordered, with two flanking regions of high disorder next to a low disorder central region (∼residues 1914-1926) that is predicted to contain two fused, disjointed transient helical elements. Experiments with IP₃R1 mutants, combined with computational analysis, indicated that small deletions in this central region block Bok binding due to perturbation of the helical elements. Studies in vitro with purified Bok and IP₃R1-derived peptides revealed high affinity binding to amino acids 1898-1940 of IP₃R1 (K_d ∼65 nM) and that binding affinity is also dependent upon both of the high disorder flanking regions. The strength of the Bok-IP₃R1 interaction was demonstrated by the ability of IP₃R1 or Bok to recruit transmembrane domain-free Bok or IP₃R1 mutants, respectively, to membranes in intact cells, and that these two mutants can bind in the cytosol independently of membrane association. Overall, we show that Bok binding to IP₃R1 occurs within a largely disordered loop between α helices 72 and 73 and that high affinity binding is mediated by multivalent interactions.

Balancing ER-Mitochondrial Ca2+ Fluxes in Health and Disease

Organelles cooperate with each other to control cellular homeostasis and cell functions by forming close connections through membrane contact sites. Important contacts are present between the endoplasmic reticulum (ER), the main intracellular Ca²⁺-storage organelle, and the mitochondria, the organelle responsible not only for the majority of cellular ATP production but also for switching on cell death processes. Several Ca²⁺-transport systems focalize at these contact sites, thereby enabling the efficient transmission of Ca²⁺ signals from the ER toward mitochondria. This provides tight control of mitochondrial functions at the microdomain level. Here, we discuss how ER-mitochondrial Ca²⁺ transfers support cell function and how their dysregulation underlies, drives, or contributes to pathogenesis and pathophysiology, with a major focus on cancer and neurodegeneration but also with attention to other diseases such as diabetes and rare genetic diseases.

Cancer cell death strategies by targeting Bcl-2's BH4 domain

The Bcl-2-family proteins have long been known for their role as key regulators of apoptosis. Overexpression of various members of the family is associated with oncogenesis. Its founding member, anti-apoptotic Bcl-2 regulates cell death at different levels, whereby Bcl-2 emerged as a major drug target to eradicate cancers through cell death. This resulted in the development of venetoclax, a Bcl-2 antagonist that acts as a BH3 mimetic. Venetoclax already entered the clinic to treat relapse chronic lymphocytic leukemia patients. Here, we discuss the role of Bcl-2 as a decision-maker in cell death with focus on the recent advances in anti-cancer therapeutics that target the BH4 domain of Bcl-2, thereby interfering with non-canonical functions of Bcl-2 in Ca²⁺-signaling modulation. In particular, we critically discuss previously developed tools, including the peptide BIRD-2 (Bcl-2/IP₃R-disrupter-2) and the small molecule BDA-366. In addition, we present a preliminary analysis of two recently identified molecules that emerged from a molecular modeling approach to target Bcl-2's BH4 domain, which however failed to induce cell death in two Bcl-2-dependent diffuse large B-cell lymphoma cell models. Overall, antagonizing the non-canonical functions of Bcl-2 by interfering with its BH4-domain biology holds promise to elicit cell death in cancer, though improved tools and on-target antagonizing small molecules remain necessary and ought to be designed.