Failure to Guard: Mitochondrial Protein Quality Control in Cancer

Causal relationships between mitochondrial proteins and different pathological types of lung cancer: a bidirectional mendelian randomization study

An increasing number of studies point to an association between mitochondrial proteins (MPs) and lung cancer (LC). However, the causal relationship between MPs and LC remains unclear. Consequently, our study employed a bidirectional Mendelian randomization (MR) analysis to explore the causal association between MPs and different pathological types of LC. A two-sample MR study was performed using the genome-wide association study (GWAS) data publicly available. We applied the primary inverse variance weighted (IVW) method along with additional MR methods to validate the causality between MPs and different pathological types of LC. To ensure the robustness of our findings, sensitivity analyses were employed. Moreover, we performed a bi-directional MR analysis to determine the direction of the causal association. We identified a total of seven MPs had significant causal relationships on overall LC, lung squamous cell carcinoma (LUSC), and small cell lung carcinoma (SCLC). We found two MPs had significant associations with overall LC, four MPs had significant associations with LUSC, and four MPs had significant associations with SCLC. Additionally, an MP was found to have a nominal relationship with LUSC. Moreover, no causality was found between MPs and lung adenocarcinoma (LUAD). Bidirectional MR showed no reverse effect between identified MPs and different pathological types of LC. In general, our findings of this MR study suggest causal associations of specific MPs with overall LC, LUSC, and SCLC. However, no such causality was found in LUAD.

Mitochondrial quality control alterations and placenta-related disorders

Mitochondria are ubiquitous in eukaryotic cells. Normal maintenance of function is the premise and basis for various physiological activities. Mitochondrial dysfunction is commonly observed in a wide range of pathological conditions, such as neurodegenerative, metabolic, cardiovascular, and various diseases related to foetal growth and development. The placenta is a highly energy-dependent organ that acts as an intermediary between the mother and foetus and functions to maintain foetal growth and development. Recent studies have demonstrated that mitochondrial dysfunction is associated with placental disorders. Defects in mitochondrial quality control mechanisms may lead to preeclampsia and foetal growth restriction. In this review, we address the quality control mechanisms of mitochondria and the relevant pathologies of mitochondrial dysfunction in placenta-related diseases, such as preeclampsia and foetal growth restriction. This review also investigates the relation between mitochondrial dysfunction and placental disorders.

Risk of Neurodegenerative Diseases in Elderly Koreans with an Initial Diagnosis of Type 2 Diabetes: A Nationwide Retrospective Cohort Study

Type 2 diabetes (T2D) and neurodegenerative diseases (NDs) are common among elderly individuals. Growing evidence has indicated a strong link between T2D and NDs, such as Alzheimer's disease. However, previous studies have limitations in exploring the epidemiological relationship among these diseases as a group of NDs rather than as a specific type of ND. We aimed to investigate the risk of NDs in elderly Koreans who were first diagnosed with T2D and determine the association between T2D and NDs. We conducted a retrospective longitudinal cohort study of patients with who were initially diagnosed with T2D using the Korean National Health Information Database. The study participants were categorized into a T2D group (n = 155,459) and a control group (n = 155,459), aged 60-84 years, that were matched for age, sex, and comorbidities. We followed the participants for 10 years to investigate the incidence of NDs. The Cox proportional hazards regression model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) for NDs. The numbers of patients diagnosed with ND at the end of follow-up were as follows: 51,096/155,459 (32.9%) in the T2D group and 44,673/155,459 (28.7%) in the control group (χ2 = 622.53, p < 0.001). The incidences of NDs in the T2D and control groups were 44.68 (95% CI: 44.29, 45.07) and 36.89 (95% CI: 36.55, 37.24) cases per 1,000 person-years at risk, respectively. The overall incidence of NDs was higher in the T2D group than that in the control group (HR: 1.23, 95% CI: 1.22, 1.25, p < 0.001). This study revealed a higher incidence of NDs in elderly Koreans who were initially diagnosed with T2D. This suggests that T2D is a risk factor for NDs in elderly Koreans.

Targeting Aggressive B-cell Lymphomas through Pharmacological Activation of the Mitochondrial Protease OMA1

DLBCL are aggressive, rapidly proliferating tumors that critically depend on the ATF4-mediated integrated stress response (ISR) to adapt to stress caused by uncontrolled growth, such as hypoxia, amino acid deprivation, and accumulation of misfolded proteins. Here, we show that ISR hyperactivation is a targetable liability in DLBCL. We describe a novel class of compounds represented by BTM-3528 and BTM-3566, which activate the ISR through the mitochondrial protease OMA1. Treatment of tumor cells with compound leads to OMA1-dependent cleavage of DELE1 and OPA1, mitochondrial fragmentation, activation of the eIF2α-kinase HRI, cell growth arrest, and apoptosis. Activation of OMA1 by BTM-3528 and BTM-3566 is mechanistically distinct from inhibitors of mitochondrial electron transport, as the compounds induce OMA1 activity in the absence of acute changes in respiration. We further identify the mitochondrial protein FAM210B as a negative regulator of BTM-3528 and BTM-3566 activity. Overexpression of FAM210B prevents both OMA1 activation and apoptosis. Notably, FAM210B expression is nearly absent in healthy germinal center B-lymphocytes and in derived B-cell malignancies, revealing a fundamental molecular vulnerability which is targeted by BTM compounds. Both compounds induce rapid apoptosis across diverse DLBCL lines derived from activated B-cell, germinal center B-cell, and MYC-rearranged lymphomas. Once-daily oral dosing of BTM-3566 resulted in complete regression of xenografted human DLBCL SU-DHL-10 cells and complete regression in 6 of 9 DLBCL patient-derived xenografts. BTM-3566 represents a first-of-its kind approach of selectively hyperactivating the mitochondrial ISR for treating DLBCL.

Mitochondrial quality control proteases and their modulation for cancer therapy

Mitochondria, the main provider of energy in eukaryotic cells, contains more than 1000 different proteins and is closely related to the development of cells. However, damaged proteins impair mitochondrial function, further contributing to several human diseases. Evidence shows mitochondrial proteases are critically important for protein maintenance. Most importantly, quality control enzymes exert a crucial role in the modulation of mitochondrial functions by degrading misfolded, aged, or superfluous proteins. Interestingly, cancer cells thrive under stress conditions that damage proteins, so targeting mitochondrial quality control proteases serves as a novel regulator for cancer cells. Not only that, mitochondrial quality control proteases have been shown to affect mitochondrial dynamics by regulating the morphology of optic atrophy 1 (OPA1), which is closely related to the occurrence and progression of cancer. In this review, we introduce mitochondrial quality control proteases as promising targets and related modulators in cancer therapy with a focus on caseinolytic protease P (ClpP), Lon protease (LonP1), high-temperature requirement protein A2 (HrtA2), and OMA-1. Further, we summarize our current knowledge of the advances in clinical trials for modulators of mitochondrial quality control proteases. Overall, the content proposed above serves to suggest directions for the development of novel antitumor drugs.

With or without You: Co-Chaperones Mediate Health and Disease by Modifying Chaperone Function and Protein Triage

Heat shock proteins (HSPs) are a family of molecular chaperones that regulate essential protein refolding and triage decisions to maintain protein homeostasis. Numerous co-chaperone proteins directly interact and modify the function of HSPs, and these interactions impact the outcome of protein triage, impacting everything from structural proteins to cell signaling mediators. The chaperone/co-chaperone machinery protects against various stressors to ensure cellular function in the face of stress. However, coding mutations, expression changes, and post-translational modifications of the chaperone/co-chaperone machinery can alter the cellular stress response. Importantly, these dysfunctions appear to contribute to numerous human diseases. Therapeutic targeting of chaperones is an attractive but challenging approach due to the vast functions of HSPs, likely contributing to the off-target effects of these therapies. Current efforts focus on targeting co-chaperones to develop precise treatments for numerous diseases caused by defects in protein quality control. This review focuses on the recent developments regarding selected HSP70/HSP90 co-chaperones, with a concentration on cardioprotection, neuroprotection, cancer, and autoimmune diseases. We also discuss therapeutic approaches that highlight both the utility and challenges of targeting co-chaperones.

The San1 Ubiquitin Ligase Avidly Recognizes Misfolded Proteins through Multiple Substrate Binding Sites

Cellular homeostasis depends on robust protein quality control (PQC) pathways that discern misfolded proteins from functional ones in the cell. One major branch of PQC involves the controlled degradation of misfolded proteins by the ubiquitin-proteasome system. Here ubiquitin ligases must recognize and bind to misfolded proteins with sufficient energy to form a complex and with an adequate half-life to achieve poly-ubiquitin chain formation, the signal for protein degradation, prior to its dissociation from the ligase. It is not well understood how PQC ubiquitin ligases accomplish these tasks. Employing a fully reconstituted enzyme and substrate system to perform quantitative biochemical experiments, we demonstrate that the yeast PQC ubiquitin ligase San1 contains multiple substrate binding sites along its polypeptide chain that appear to display specificity for unique misfolded proteins. The results are consistent with a model where these substrate binding sites enable San1 to bind to misfolded substrates avidly, resulting in high affinity ubiquitin ligase-substrate complexes.