Knockdown of clusterin alters mitochondrial dynamics, facilitates necrosis in camptothecin-induced cancer stem cells

Clusterin: a marker and mediator of chemoresistance in colorectal cancer

Intra-tumoural heterogeneity and cancer cell plasticity in colorectal cancer (CRC) have been key challenges to effective treatment for patients. It has been suggested that a subpopulation of LGR5-expressing cancer stem cells (CSCs) is responsible for driving tumour relapse and therapy resistance in CRC. However, studies have revealed that the LGR5+ve CSC population is highly sensitive to chemotherapy. It has been hypothesised that another subset of tumour cells can phenotypically revert to a stem-like state in response to chemotherapy treatment which replenishes the LGR5+ve CSC population and maintains tumour growth. Recently, a unique stem cell population marked by enriched clusterin (CLU) expression and termed the revival stem cell (RevSC) was identified in the regenerating murine intestine. This CLU-expressing cell population is quiescent during homeostasis but has the ability to survive and regenerate other stem cells upon injury. More recently, the CLU+ve signature has been implicated in several adverse outcomes in CRC, including chemotherapy resistance and poor patient survival; however, the mechanism behind this remains undetermined. In this review, we discuss recent insights on CLU in CRC and its roles in enhancing the plasticity of cells and further consider the implications of CLU as a prospective target for therapeutic intervention.

CLU (clusterin) promotes mitophagic degradation of MSX2 through an AKT-DNM1L/Drp1 axis to maintain SOX2-mediated stemness in oral cancer stem cells

Mitophagy regulates cancer stem cell (CSC) populations affecting tumorigenicity and malignancy in various cancer types. Here, we report that cisplatin treatment led to the activation of higher mitophagy through regulating CLU (clusterin) levels in oral CSCs. Moreover, both the gain-of-function and loss-of-function of CLU indicated its mitophagy-specific role in clearing damaged mitochondria. CLU also regulates mitochondrial fission by activating the Ser/Thr kinase AKT, which triggered phosphorylation of DNM1L/Drp1 at the serine 616 residue initiating mitochondrial fission. More importantly, we also demonstrated that CLU-mediated mitophagy positively regulates oral CSCs through mitophagic degradation of MSX2 (msh homeobox 2), preventing its nuclear translocation from suppressing SOX2 activity and subsequent inhibition of cancer stemness and self-renewal ability. However, CLU knockdown disturbed mitochondrial metabolism generating excessive mitochondrial superoxide, which improves the sensitivity to cisplatin in oral CSCs. Notably, our results showed that CLU-mediated cytoprotection relies on SOX2 expression. SOX2 inhibition through genetic (shSOX2) and pharmacological (KRX-0401) strategies reverses CLU-mediated cytoprotection, sensitizing oral CSCs toward cisplatin-mediated cell death.

3D bioprinted drug-resistant breast cancer spheroids for quantitative in situ evaluation of drug resistance

Drug-resistant cancer spheroids were fabricated by three-dimensional (3D) bioprinting for the quantitative evaluation of drug resistance of cancer cells, which is a very important issue in cancer treatment. Cancer spheroids have received great attention as a powerful in vitro model to replace animal experiments because of their ability to mimic the tumor microenvironment. In this work, the extrusion printing of gelatin-alginate hydrogel containing MCF-7 breast cancer stem cells successfully provided 3D growth of many single drug-resistant breast cancer spheroids in a cost-effective 3D-printed mini-well dish. The drug-resistant MCF-7 breast cancer spheroids were able to maintain their drug-resistant phenotype of CD44^high/CD24^low/ALDH1^high in the gelatin-alginate media during 3D culture and exhibited higher expression levels of drug resistance markers, such as GRP78 chaperon and ABCG2 transporter, than bulk MCF-7 breast cancer spheroids. Furthermore, the effective concentration 50 (EC₅₀) values for apoptotic and necrotic spheroid death could be directly determined from the 3D printed-gelatin-alginate gel matrix based on in situ 3D fluorescence imaging of cancer spheroids located out of the focal point and on the focal point. The EC₅₀ values of anti-tumor agents (camptothecin and paclitaxel) for apoptotic and necrotic drug-resistant cancer spheroid death were higher than those for bulk cancer spheroid death, indicating a greater drug resistance. STATEMENT OF SIGNIFICANCE: This study proposed a novel 3D bioprinting-based drug screening model, to quantitatively evaluate the efficacy of anticancer drugs using drug-resistant MCF-7 breast cancer spheroids formed within a 3D-printed hydrogel. Quantitative determination of anticancer drug efficacy using EC₅₀, which is extremely important in drug discovery, was achieved by 3D printing that enables concurrent growth of many single spheroids efficiently. This study verified whether drug-resistant cancer spheroids grown within 3D-printed gelatin-alginate hydrogel could maintain and present drug resistance. Also, the EC₅₀ values of the apoptotic and necrotic cell deaths were directly acquired in 3D-embedded spheroids based on in situ fluorescence imaging. This platform provides a single-step straightforward strategy to cultivate and characterize drug-resistant spheroids to facilitate anticancer drug screening.

A novel prodrug and its nanoformulation suppress cancer stem cells by inducing immunogenic cell death and inhibiting indoleamine 2, 3-dioxygenase

Cancer stem cells (CSCs) present grand challenges for triple-negative breast cancer (TNBC). Conventional chemotherapy drugs, including Camptothecin (CPT), not only cannot eradicate CSCs but also foster a suppressive immune microenvironment for the initiation and proliferation of CSCs. Herein, we report a novel prodrug CPT-SS-NLG919 (CN) and its nanoformulation CN@PLA-HES-FA (CN@PHF), which potently suppress CSCs by regulating CSCs niche in murine TNBC 4T1 tumors. Via inducing immunogenic cell death (ICD) and simultaneous inhibiting indoleamine 2, 3-dioxygenase (IDO), CN and CN@PHF promote DC maturation, decrease Treg cells, mitigate tryptophan consumption, and reduce the amount of IL-6, IL-13, and TGF-β, converting CSCs niche to a hostile condition for CSCs to live in and eliminating CSCs efficiently, thereby inducing efficient tumor inhibition in 4T1 tumor models. Our work represents a new paradigm of eliminating CSCs by regulating tumor immune microenvironment and suggests that CN and its nanoformulation CN@PHF are promising candidates for the treatment of intractable TNBC.

Dysregulation of mitophagy and mitochondrial homeostasis in cancer stem cells: Novel mechanism for anti-cancer stem cell-targeted cancer therapy

Despite the potential of cancer medicine, cancer stem cells (CSCs) associated with chemoresistance and disease recurrence are the significant challenges currently opposing the efficacy of available cancer treatment options. Mitochondrial dynamics involving the fission-fusion cycle and mitophagy are the major contributing factors to better adaptation, enabling CSCs to survive and grow better under tumour micro-environment-associated stress. Moreover, mitophagy is balanced with mitochondrial biogenesis to maintain mitochondrial homeostasis in CSCs, which are necessary for the growth and maintenance of CSCs and regulate metabolic switching from glycolysis to oxidative phosphorylation. In this review, we discuss different aspects of mitochondrial dynamics, mitophagy, and mitochondrial homeostasis and their effects on modulating CSCs behaviour during cancer development. Moreover, the efficacy of pharmacological targeting of these cellular processes using anti-CSC drugs in combination with currently available chemotherapeutic drugs improves the patient's survival of aggressive cancer types.

Recent progress in the use of mitochondrial membrane permeability transition pore in mitochondrial dysfunction-related disease therapies

Mitochondria have various cellular functions, including ATP synthesis, calcium homeostasis, cell senescence, and death. Mitochondrial dysfunction has been identified in a variety of disorders correlated with human health. Among the many underlying mechanisms of mitochondrial dysfunction, the opening up of the mitochondrial permeability transition pore (mPTP) is one that has drawn increasing interest in recent years. It plays an important role in apoptosis and necrosis; however, the molecular structure and function of the mPTP have still not been fully elucidated. In recent years, the abnormal opening up of the mPTP has been implicated in the development and pathogenesis of diverse diseases including ischemia/reperfusion injury (IRI), neurodegenerative disorders, tumors, and chronic obstructive pulmonary disease (COPD). This review provides a systematic introduction to the possible molecular makeup of the mPTP and summarizes the mitochondrial dysfunction-correlated diseases and highlights possible underlying mechanisms. Since the mPTP is an important target in mitochondrial dysfunction, this review also summarizes potential treatments, which may be used to inhibit pore opening up via the molecules composing mPTP complexes, thus suppressing the progression of mitochondrial dysfunction-related diseases.

Clusterin as modulator of carcinogenesis: A potential avenue for targeted cancer therapy

Clusterin (CLU) is an evolutionary conserved molecular chaperone present in different human tissues and fluids and established to be a significant cancer regulator. It controls several cancer-associated cellular events, including cancer cell proliferation, stemness, survival, metastasis, epithelial-mesenchymal transition, therapy resistance, and inhibition of programmed cell death to support cancer growth and recurrence. This multifunctional role of CLU makes it an ideal target for cancer control. More importantly, genetic and antisense-mediated (OGX-011) inhibition of CLU enhances the anticancer potential of different FDA-approved chemotherapeutic drugs at the clinical level, improving patient's survival. In this review, we have discussed the detailed mechanism of CLU-mediated modulation of different cancer-associated signaling pathways. We have also provided updated information on the current preclinical and clinical findings that drive trials in various cancer types for potential targeted cancer therapy.

Secretory clusterin promotes oral cancer cell survival via inhibiting apoptosis by activation of autophagy in AMPK/mTOR/ULK1 dependent pathway

AIMS

Secretory clusterin (sCLU) plays an important role in tumor development and cancer progression. However, the molecular mechanisms and physiological functions of sCLU in oral cancer is unclear. We examined the impact of sCLU-mediated autophagy in cell survival and apoptosis inhibition in oral cancer.

MAIN METHODS

Immunohistochemical analysis was performed to analyze protein expression in patient samples. Autophagy and mitophagy was studied by immunofluorescence microscopy and Western blot. The gain and loss of function was studied by overexpression of plasmid and siRNA approaches respectively. Cellular protection against nutrient starvation and therapeutic stress by sCLU was studied by cell viability, caspase assay and meta-analysis.

KEY FINDINGS

The data from oral cancer patients showed that the expression levels of sCLU, ATG14, ULK1, and PARKIN increased in grade-wise manners. Interestingly, sCLU overexpression promoted autophagy through AMPK/Akt/mTOR signaling pathway leading to cell survival and protection from long exposure serum starvation induced-apoptosis. Additionally, sCLU was demonstrated to interact with ULK1 and inhibition of ULK1 activity by SBI206965 was found to abolish sCLU-induced autophagy indicating critical role of ULK1 in induction of autophagy. Furthermore, sCLU was observed to promote expression of mitophagy-associated proteins in serum starvation conditions to protect cells from nutrient deprivation. The meta-analysis elucidated that high CLU expression is associated with therapy resistance in cancer and we demonstrated that sCLU-mediated mitophagy was revealed to inhibit cell death by cisplatin.

SIGNIFICANCE

The present investigation has highlighted the probable implications of the clusterin-induced autophagy in cell survival and inhibition of apoptosis in oral cancer.

Tumour Cell Secretome in Chemoresistance and Tumour Recurrence

Chemoresistance is a major factor driving tumour relapse and the high rates of cancer-related deaths. Understanding how cancer cells overcome chemotherapy-induced cell death is critical in promoting patient survival. One emerging mechanism of chemoresistance is the tumour cell secretome (TCS), an array of protumorigenic factors released by tumour cells. Chemotherapy exposure can also alter the composition of the TCS, known as therapy-induced TCS, and can promote tumour relapse and the formation of an immunosuppressive tumour microenvironment (TME). Here, we outline how the TCS can protect cancer cells from chemotherapy-induced cell death. We also highlight recent evidence describing how therapy-induced TCS can impact cancer stem cell (CSC) expansion and tumour-associated immune cells to enable tumour regrowth and antitumour immunity.

The alterations of mitochondrial DNA in coronary heart disease

Coronary heart disease (CHD) is the major cause of death in modern society. CHD is characterized by atherosclerosis, which could lead to vascular cavity stenosis or obstruction, resulting in ischemic cardiac conditions such as angina and myocardial infarction. In terms of the mitochondrion, the main function is to produce adenosine triphosphate (ATP) for cells. And the alterations (including mutations, altered copy number and haplogroups) of mitochondrial DNA (mtDNA) are associated with the abnormal expression of oxidative phosphorylation (OXPHOS) system, resulting in mitochondrial dysfunction, then leading to perturbation on the electron transport chain and increased ROS generation and reduction in ATP level, contributing to ATP-producing disorders and oxidative stress, which may further accelerate development or vulnerability of atherosclerosis and myocardial ischemic injury. Therefore, the mtDNA defects may play an important role in making an early diagnosis, identifying disease-specific biomarkers and therapeutic targets, and predicting outcomes for patients with atherosclerosis and CHD. In this review, we aim to summarize the contribution of mtDNA mutations, altered mtDNA copy number and mtDNA haplogroups on the occurrence and development of CHD.

Secretory clusterin promotes hepatocellular carcinoma progression by facilitating cancer stem cell properties via AKT/GSK-3β/β-catenin axis

Background

To explore the modulatory effects and mechanism of secretory clusterin (sCLU) on cancer stem cell (CSC) properties in hepatocellular carcinoma (HCC).

Methods

The effects of sCLU repression or overexpression on chemoresistance, migration, invasion, and tumor growth were detected by MTT, wound healing, transwell assays, and xenograft assay, respectively. The tumor sphere assay was performed to evaluate the self-renewal ability of HCC cells. In addition, the molecular regulation between sCLU and AKT/GSK-3β/β-catenin axis in HCC cells were discovered by western blotting, quantitative real-time PCR (qRT-PCR), and immunofluorescence. The expression status of sCLU and β-catenin in HCC tissues were investigated by immunohistochemistry.

Results

Knockdown or overexpressing sCLU remarkably inhibited or promoted the chemoresistance against sorafenib/doxorubicin, metastasis, and tumor growth of HCC cells, respectively. HepG2 and HCCLM3-derived spheroids showed higher expression of sCLU than that in attached cells. Additionally, repressing sCLU impaired the self-renewal capacity of HCC cells and CSC-related chemoresistance while overexpression of sCLU enhanced these CSC properties. Knockdown or overexpression of sCLU inhibited or increased the expressions of β-catenin, cyclinD1, MMP-2 and MMP-9, and the phosphorylation of AKT or GSK3β signaling, respectively. However, LiCl or LY294002 abrogated the effects mediated by sCLU silencing or overexpression on chemoresistance, metastasis, and CSC phenotype. Furthermore, co-expression of sCLU and β-catenin in HCC tissues indicated poor prognosis of HCC patients.

Conclusions

Taken together, the oncogenic sCLU might promote CSC phenotype via activating AKT/GSK3β/β-catenin axis, suggesting that sCLU was a potential molecular-target for HCC therapy.

Insights into new mechanisms and models of cancer stem cell multidrug resistance

The acquisition of genetic alterations, clonal evolution, and the tumor microenvironment promote cancer progression, metastasis and therapy resistance. These events correspond to the establishment of the great phenotypic heterogeneity and plasticity of cancer cells that contribute to tumor progression and resistant disease. Targeting resistant cancers is a major challenge in oncology; however, the underlying processes are not yet fully understood. Even though current treatments can reduce tumor size and increase life expectancy, relapse and multidrug resistance (MDR) ultimately remain the second cause of death in developed countries. Recent evidence points toward stem-like phenotypes in cancer cells, promoted by cancer stem cells (CSCs), as the main culprit of cancer relapse, resistance (radiotherapy, hormone therapy, and/or chemotherapy) and metastasis. Many mechanisms have been proposed for CSC resistance, such as drug efflux through ABC transporters, overactivation of the DNA damage response (DDR), apoptosis evasion, prosurvival pathways activation, cell cycle promotion and/or cell metabolic alterations. Nonetheless, targeted therapy toward these specific CSC mechanisms is only partially effective to prevent or abolish resistance, suggesting underlying additional causes for CSC resilience. This article aims to provide an integrated picture of the MDR mechanisms that operate in CSCs' behavior and to propose a novel model of tumor evolution during chemotherapy. Targeting the pathways mentioned here might hold promise and reveal new strategies for future clinical therapeutic approaches.

Role of secretory clusterin in hepatocarcinogenesis

Secretory clusterin (sCLU) is a small stress-induced cytoprotective chaperone protein. Its biological functions are similar to those of a heat-shock protein. The sCLU plays a crucial role in cell proliferation, multiple drug resistance, metastasis, and tumor progression. Abnormal sCLU expression in tumor tissues or sera of patients with primary hepatic cancer has been considered a useful biomarker for diagnosis and surveillance. However, the exact relationship between sCLU overexpression and malignant transformation of hepatocytes is still unknown. The present review examines some novel advances of the knowledge about the oncogenic role of sCLU in hepatocarcinogenesis.

A Role for Clusterin in Exfoliation Syndrome and Exfoliation Glaucoma?

The multifunctional protein clusterin (CLU) is a secreted glycoprotein ubiquitously expressed throughout the body, including in the eye. Its primary function is to act as an extracellular molecular chaperone, preventing the precipitation and aggregation of misfolded extracellular proteins. Clusterin is commonly identified at fluid-tissue interfaces, and has been identified in most body fluids. It is a component of exfoliation material, and CLU mRNA is reduced in eyes with exfoliation syndrome compared with controls. SNPs located in the CLU genomic region have been associated with Alzheimer disease (AD) at the genome-wide level and several CLU SNPs located in an apparent regulatory region have been nominally associated with XFS/XFG in Caucasians with European ancestry and in south Indians. Interestingly, clusterin associates with altered elastic fibers in human photoaged skin and prevents UV-induced elastin aggregation in vitro. In light of the known geographic risk factors for XFS/XFG, which could include UV light, investigations of CLU-geographic interactions could be of interest. Future studies investigating rare CLU variation and other complex interactions including gene-gene interactions in XFS/XFG cases and controls may also be fruitful. Although CLU has been considered as a therapeutic target in AD, cancer and dry eye, a role for clusterin in XFS/XFG needs to be better defined before therapeutic approaches involving CLU can be entertained.

The Significance of Single-Cell Biomedicine in Stem Cells

Clinical application of stem cells (SCs) progresses significantly in the treatment of a large number of diseases, e.g. leukemia, respiratory diseases, kidney disease, cerebral palsy, autism, or autoimmune diseases. Of those, the population, biological phenotypes, and functions of individual SCs are mainly concerned, due to the lack of cell separation and purification processes. The single-cell technology, including microfluidic technology and single-cell genome amplification technology, is widely used to study SCs and gains some recognitions. The present review will address the importance of single-cell technologies in the recognition and heterogeneity of SCs and highlight the significance of current single-cell approaches in the understanding of SC phenotypes. We also discuss the values of single-cell studies to overcome the bottleneck in explore of biological mechanisms and reveal the therapeutic potentials of SCs in diseases, especially tumor-related diseases, as new diagnostic and therapeutic strategies.

Roles of Mitochondrial DNA Signaling in Immune Responses

Mitochondrial DNA (mtDNA) plays an important role in immune responses during the evolution. The present chapter systemically describes its role on immune-related diseases and its interaction on immune responses. It is important to explore the main function and mechanisms of mtDNA in immune responses by which mtDNA regulates the signaling pathways of Toll-like receptor 9, autophagy, and STING. There are potentials to discover therapeutic targets of mtDNA in immune diseases and inflammation. It will be more exciting if the CRISPR-Cas9 method can be applied for mtDNA gene editing to cure diseases and provide a novel insight of mtDNA in immune responses as well as new therapies.

The Role of DNA Repair in Maintaining Mitochondrial DNA Stability

Mitochondria are vital double-membrane organelles that act as a "powerhouse" inside the cell and have essential roles to maintain cellular functions, e.g., ATP production, iron-sulfur synthesis metabolism, and steroid synthesis. An important difference with other organelles is that they contain their own mitochondrial DNA (mtDNA). Such powerful organelles are also sensitive to both endogenous and exogenous factors that can cause lesions to their structural components and their mtDNA, resulting in gene mutations and eventually leading to diseases. In this review, we will mainly focus on mammalian mitochondrial DNA repair pathways that safeguard mitochondrial DNA integrity and several important factors involved in the repair process, especially on an essential pathway, base excision repair. We eagerly anticipate to explore more methods to treat related diseases by constantly groping for these complexes and precise repair mechanisms.