Mortalin (HSPA9) facilitates BRAF-mutant tumor cell survival by suppressing ANT3-mediated mitochondrial membrane permeability

Multi-omics analysis reveals the sensitivity of immunotherapy for unresectable non-small cell lung cancer

Background

To construct a prediction model consisting of metabolites and proteins in peripheral blood plasma to predict whether patients with unresectable stage III and IV non-small cell lung cancer can benefit from immunotherapy before it is administered.

Methods

Peripheral blood plasma was collected from unresectable stage III and IV non-small cell lung cancer patients who were negative for driver mutations before receiving immunotherapy. Then we classified samples according to the follow-up results after two courses of immunotherapy and non-targeted metabolomics and proteomics analyses were performed to select different metabolites and proteins. Finally, potential biomarkers were picked out by applying machine learning methods including random forest and stepwise regression and prediction models were constructed by logistic regression.

Results

The presence of metabolites and proteins in peripheral blood plasma was causally associated with both non-small cell lung cancer and PD-L1/PD-1 expression levels. A total of 2 differential metabolites including 5-sulfooxymethylfurfural and Anthranilic acid and 2 differential proteins including Immunoglobulin heavy variable 1-45 and Microfibril-associated glycoprotein 4 were selected as reliable biomarkers. The area under the curve (AUC) of the prediction model built on clinical risks was merely 0.659. The AUC of metabolomics prediction model was 0.977 and the AUC of proteomics was 0.875 while the AUC of the integrative-omics prediction model was 0.955.

Conclusions

Metabolic and protein biomarkers in peripheral blood both have high efficacy and reliability in the prediction of immunotherapy sensitivity in unresectable stage III and IV non-small cell lung cancer, but validation in larger population-based cohorts is still needed.

Role of mitochondria and potential of mitochondria-targeted therapy in BRAF mutant cancer: A review

The classical mitogen-activated protein kinase (MAPK) signaling pathway, the Ras/Raf/MEK (mitogen-activated protein kinase/ERK kinase)/ERK protein kinase cascade, is a conserved cascade that regulates cell growth, differentiation, and proliferation. The significance of BRAF in cancer was established with the discovery of cancer-activating mutations in BRAF in several human tumors in 2002. Currently, BRAF is recognized as a driver mutation that affects cancer phenotypes in different ways, making it an important therapeutic target for cancer. BRAF-selective inhibitors have shown promise in clinical trials involving patients with metastatic melanoma. However, resistance mechanisms to BRAF inhibitors therapy have resulted in short-lived therapeutic responses. Further in-depth research is imperative to explore resistance mechanisms that oppose the effectiveness of BRAF inhibitors. Metabolic reprogramming has emerging role in BRAF-mutant cancers. In particular, mitochondrial metabolism and its closely related signaling pathways mediated by mitochondria have become recognized as potential new targets for treating BRAF-mutant cancers. This review, examines the progress in understanding BRAF mutations in cancer, the clinicopathological correlation of BRAF inhibitors, and recent advances in mitochondrial metabolism, mitochondrial dynamics and mitochondrial mediated death in BRAF-mutant cancer. This review will inform future cancer research and lay the foundation for novel treatment combinations of BRAF-mutant cancers.

ERK1/2 interaction with DHPS regulates eIF5A deoxyhypusination independently of ERK kinase activity

This study explores a non-kinase effect of extracellular regulated kinases 1/2 (ERK1/2) on the interaction between deoxyhypusine synthase (DHPS) and its substrate, eukaryotic translation initiation factor 5A (eIF5A). We report that Raf/MEK/ERK activation decreases the DHPS-ERK1/2 interaction while increasing DHPS-eIF5A association in cells. We determined the cryoelectron microscopy (cryo-EM) structure of the DHPS-ERK2 complex at 3.5 Å to show that ERK2 hinders substrate entrance to the DHPS active site, subsequently inhibiting deoxyhypusination in vitro. In cells, impairing the ERK2 activation loop, but not the catalytic site, prolongs the DHPS-ERK2 interaction irrespective of Raf/MEK signaling. The ERK2 Ser-Pro-Ser motif, but not the common docking or F-site recognition sites, also regulates this complex. These data suggest that ERK1/2 dynamically regulate the DHPS-eIF5A interaction in response to Raf/MEK activity, regardless of its kinase function. In contrast, ERK1/2 kinase activity is necessary to regulate the expression of DHPS and eIF5A. These findings highlight an ERK1/2-mediated dual kinase-dependent and -independent regulation of deoxyhypusination.

A bird's eye view of mitochondrial unfolded protein response in cancer: mechanisms, progression and further applications

Mitochondria are essential organelles that play critical roles in energy metabolism, apoptosis and various cellular processes. Accumulating evidence suggests that mitochondria are also involved in cancer development and progression. The mitochondrial unfolded protein response (UPRmt) is a complex cellular process that is activated when the protein-folding capacity of the mitochondria is overwhelmed. The core machinery of UPRmt includes upstream regulatory factors, mitochondrial chaperones and proteases. These components work together to eliminate misfolded proteins, increase protein-folding capacity, and restore mitochondrial function. Recent studies have shown that UPRmt is dysregulated in various cancers and contributes to tumor initiation, growth, metastasis, and therapeutic resistance. Considering the pivotal role of the UPRmt in oncogenesis, numerous compounds and synthetic drugs targeting UPRmt-related components induce cancer cell death and suppress tumor growth. In this review, we comprehensively summarize recent studies on the molecular mechanisms of UPRmt activation in C. elegans and mammals and elucidate the conceptual framework, functional aspects, and implications of the UPRmt for cancer therapy. In summary, we paint a developmental landscape of the UPRmt in different types of cancer and offer valuable insights for the development of novel cancer treatment strategies by targeting the UPRmt.

SUMO E3 ligase MUL1 inhibits lymph node metastasis of bladder cancer by mediating mitochondrial HSPA9 translocation

Lymph node (LN) metastasis is the dominant cause of death in bladder cancer (BCa) patients, but the underlying mechanism remains largely unknown. In recent years, accumulating studies have confirmed that bidirectional mitochondria-nucleus communication is essential for sustaining multiple function of mitochondria. However, little has been studied regarding whether and how the translocation of mitochondrial proteins is involved in LN metastasis. In this study, we first identified that the SUMO E3 ligase MUL1 was significantly downregulated in LN-metastatic BCa tissues and correlated with a good prognosis. Mechanistically, MUL1 SUMOylated HSPA9 at the K612 residue, leading to HSPA9 export from mitochondria and interaction with SUZ12 and in the nucleus. Consequently, MUL1 induced the ubiquitination-mediated degradation of SUZ12 and EZH2 and induced downstream STAT3 pathway inhibition in a HSPA9-dependent manner. Importantly, mutation of HSPA9 SUMO-conjugation motifs limited the translocation of mitochondrial HSPA9 and blocked the HSPA9-SUZ12 and HSPA9-EZH2 interactions. With mutation of the HSPA9 K612 site, the suppressive role of MUL1 overexpression was lost in BCa cells. Further in vitro and in vivo assays revealed that MUL1 inhibits the metastasis and proliferation of BCa cells. Overall, our study reveals a novel function and molecular mechanism of SUMO E3 ligases in LN metastasis.

Estrogen-related receptor alpha promotes thyroid tumor cell survival via a tumor subtype-specific regulation of target gene networks

Mortalin (encoded by HSPA9) is a mitochondrial chaperone often overexpressed in cancer through as-yet-unknown mechanisms. By searching different RNA-sequencing datasets, we found that ESRRA is a transcription factor highly correlated with HSPA9 in thyroid cancer, especially in follicular, but not C cell-originated, tumors. Consistent with this correlation, ESRRA depletion decreased mortalin expression only in follicular thyroid tumor cells. Further, ESRRA expression and activity were relatively high in thyroid tumors with oncocytic characteristics, wherein ESRRA and mortalin exhibited relatively high functional overlap. Mechanistically, ESRRA directly regulated HSPA9 transcription through a novel ESRRA-responsive element located upstream of the HSPA9 promoter. Physiologically, ESRRA depletion suppressed thyroid tumor cell survival via caspase-dependent apoptosis, which ectopic mortalin expression substantially abrogated. ESRRA depletion also effectively suppressed tumor growth and mortalin expression in the xenografts of oncocytic or ESRRA-overexpressing human thyroid tumor cells in mice. Notably, our Bioinformatics analyses of patient data revealed two ESRRA target gene clusters that contrast oncocytic-like and anaplastic features of follicular thyroid tumors. These findings suggest that ESRRA is a tumor-specific regulator of mortalin expression, the ESRRA-mortalin axis has higher significance in tumors with oncocytic characteristics, and ESRRA target gene networks can refine molecular classification of thyroid cancer.

Peptidyl-prolyl isomerase F as a prognostic biomarker associated with immune infiltrates and mitophagy in lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD) is among the most prevalent malignancies worldwide, with unfavorable treatment outcomes. Peptidyl-prolyl isomerase F (PPIF) is known to influence the malignancy traits of tumor progression by modulating the bioenergetics and mitochondrial permeability in cancer cells; however, its role in LUAD remains unclear. Our study seeks to investigate the clinical significance, tumor proliferation, and immune regulatory functions of PPIF in LUAD.

METHODS

The expression of PPIF in LUAD tissues and cells was assessed using bioinformatics analysis, immunohistochemistry (IHC), and Western blotting. Survival curve analysis was conducted to examine the prognostic association between PPIF expression and LUAD. The immunomodulatory role of PPIF in LUAD was assessed through the analysis of PPIF expression and immune cell infiltration. A series of gain- and loss-of-function experiments were conducted on PPIF to investigate its biological functions in LUAD both in vitro and in vivo. The mechanisms underlying PPIF's effects on LUAD were delineated through functional enrichment analysis and Western blotting assays.

RESULTS

PPIF exhibited overexpression in LUAD tissues compared to normal controls. Survival curve analysis revealed that patients with LUAD exhibiting higher PPIF expression demonstrated decreased overall survival and a shorter progression-free interval. PPIF was implicated in modulating immune cell infiltration, particularly in regulating the T helper 1-T helper 2 cell balance. Functionally, PPIF was discovered to promote tumor cell proliferation and advance cell-cycle progression. Furthermore, PPIF could impede mitophagy by targeting the FOXO3a/PINK1-Parkin signaling pathway.

CONCLUSIONS

The findings of this study indicate that the prognosis-related gene PPIF may have a significant role in the regulation of LUAD cell proliferation, tumor-associated immune cell infiltration, and mitophagy, and thus PPIF may be a promising therapeutic target of LUAD.

Prenatal to preimplantation genetic diagnosis of a novel compound heterozygous mutation in HSPA9 associated with Even-Plus syndrome

BACKGROUND

Heat shock protein family A member 9 (HSPA9) prevents unfolded and dysfunctional protein accumulation, with genetic variants known to be pathogenic. Here, we determined the genetic cause of Even-Plus syndrome (OMIM: 616854) in a Chinese family.

METHODS

We collected samples from two affected and two normal individuals. Whole-exome sequencing was performed to identify their genetic profiles. Potential variants were validated using Sanger sequencing. Assisted reproduction with mutation-free embryos successfully blocked the transmission of mutations.

RESULTS

We identified novel inherited pathogenic complex heterozygous variations in the HSPA9 gene in the two affected fetuses. Three-dimensional spatial simulation of the HSPA9 protein after prediction of the mutated RNA splicing pattern abolished part of the substrate-binding domain of the protein. According to ACMG guidelines, c. 1822-1G>A and c. 1411-3T>G were classified as pathogenic and likely pathogenic, respectively. Mutation-free embryos were selected for transplantation and reconfirmed to possess no mutations. A healthy daughter was successfully born into the family.

CONCLUSIONS

This study is the first to report complex heterozygous variations in the HSPA9 gene that influence alternative splicing in early pregnancy. Our findings expand on the mutational spectrum leading to Even-Plus syndrome and provide a basis for genetic counseling and future embryonic studies.

HSP70 Family in Cancer: Signaling Mechanisms and Therapeutic Advances

The 70 kDa heat shock proteins (HSP70s) are a group of highly conserved and inducible heat shock proteins. One of the main functions of HSP70s is to act as molecular chaperones that are involved in a large variety of cellular protein folding and remodeling processes. HSP70s are found to be over-expressed and may serve as prognostic markers in many types of cancers. HSP70s are also involved in most of the molecular processes of cancer hallmarks as well as the growth and survival of cancer cells. In fact, many effects of HSP70s on cancer cells are not only related to their chaperone activities but rather to their roles in regulating cancer cell signaling. Therefore, a number of drugs directly or indirectly targeting HSP70s, and their co-chaperones have been developed aiming to treat cancer. In this review, we summarized HSP70-related cancer signaling pathways and corresponding key proteins regulated by the family of HSP70s. In addition, we also summarized various treatment approaches and progress of anti-tumor therapy based on targeting HSP70 family proteins.

Distinct mechanism of cervical cancer cell death caused by the investigational new drug SHetA2

Drug-targetable vulnerabilities of cancer cells include their dependence on heat shock proteins (HSPs) to support elevated mitochondrial metabolism and counteract cell death factors. The investigational new drug SHetA2 targets these vulnerabilities in ovarian and endometrial cancer cells by disrupting complexes of the mortalin HSP with its client proteins (mitochondrial support proteins, metabolic enzymes, p53) leading to mitochondrial leakage of cytochrome c and apoptosis-inducing factor (AIF), and caspase-dependent apoptosis. Our objective was to evaluate the roles of mitochondrial damage and another SHetA2-target HSP protein, cytoplasmic heat shock cognate 70 (hsc70), in the mechanism of SHetA2 killing of cervical cancer cells. Cervical cancer cells responded to SHetA2 with excessive mitophagy that did not deter AIF leakage into the cytoplasm. Then, hsc70 was unable to prevent cytoplasmic AIF nuclear translocation and promotion of DNA damage and cell death, because SHetA2 disrupted hsc70/AIF complexes. The Cancer Genome Atlas analysis found that overexpression of hsc70, but not mortalin, was associated with worse cervical cancer patient survival. Use of specific inhibitors documented that AIF and mitophagy, but not caspases, contributed to the mechanism of SHetA2-induced cell death in cervical cancer cells. As validation, excessive mitophagy and lack of caspase activation were observed in SHetA2-inhibited xenograft tumors.

Identification of a new member of Mortaparib class of inhibitors that target mortalin and PARP1

Mortalin, a heat shock family protein enriched in cancer cells, is known to inactivate tumor suppressor protein p53. Abrogation of mortalin-p53 interaction and reactivation of p53 has been shown to trigger growth arrest/apoptosis in cancer cells and hence, suggested to be useful in cancer therapy. In this premise, we earlier screened a chemical library to identify potential disruptors of mortalin-p53 interaction, and reported two novel synthetic small molecules (5-[1-(4-methoxyphenyl) (1,2,3,4-tetraazol-5-yl)]-4-phenylpyrimidine-2-ylamine) and (4-[(1E)-2-(2-phenylindol-3-yl)-1-azavinyl]-1,2,4-triazole) called Mortaparib and Mortaparib^Plus, respectively. These compounds were shown to possess anticancer activity that was mediated through targeting mortalin and PARP1 proteins, essential for cancer cell survival and proliferation. Here, we report characterization of the third compound, {4-[(4-amino-5-thiophen-2-yl-1,2,4-triazol-3-yl)sulfanylmethyl]-N-(4-methoxyphenyl)-1,3-thiazol-2-amine}, isolated in the same screening. Extensive computational and molecular analyses suggested that the new compound has the capability to interact with mortalin, p53, and PARP1. We provide evidence that this new compound, although required in high concentration as compared to the earlier two compounds (Mortaparib and Mortaparib^Plus) and hence called Mortaparib^Mild, also downregulates mortalin and PARP1 expression and functions in multiple ways impeding cancer cell proliferation and migration characteristics. Mortaparib^Mild is a novel candidate anticancer compound that warrants further experimental and clinical attention.

Allosteric HSP70 inhibitors perturb mitochondrial proteostasis and overcome proteasome inhibitor resistance in multiple myeloma

Proteasome inhibitor (PI) resistance remains a central challenge in multiple myeloma. To identify pathways mediating resistance, we first mapped proteasome-associated genetic co-dependencies. We identified heat shock protein 70 (HSP70) chaperones as potential targets, consistent with proposed mechanisms of myeloma cells overcoming PI-induced stress. We therefore explored allosteric HSP70 inhibitors (JG compounds) as myeloma therapeutics. JG compounds exhibited increased efficacy against acquired and intrinsic PI-resistant myeloma models, unlike HSP90 inhibition. Shotgun and pulsed SILAC mass spectrometry demonstrated that JGs unexpectedly impact myeloma proteostasis by destabilizing the 55S mitoribosome. Our data suggest JGs have the most pronounced anti-myeloma effect not through inhibiting cytosolic HSP70 proteins but instead through mitochondrial-localized HSP70, HSPA9/mortalin. Analysis of myeloma patient data further supports strong effects of global proteostasis capacity, and particularly HSPA9 expression, on PI response. Our results characterize myeloma proteostasis networks under therapeutic pressure while motivating further investigation of HSPA9 as a specific vulnerability in PI-resistant disease.

The mitochondrial unfolded protein response (UPRmt): shielding against toxicity to mitochondria in cancer

Mitochondria are essential for tumor growth and progression. However, the heavy demand for mitochondrial activity in cancer leads to increased production of mitochondrial reactive oxygen species (mtROS), accumulation of mutations in mitochondrial DNA, and development of mitochondrial dysfunction. If left unchecked, excessive mtROS can damage and unfold proteins in the mitochondria to an extent that becomes lethal to the tumor. Cellular systems have evolved to combat mtROS and alleviate mitochondrial stress through a quality control mechanism called the mitochondrial unfolded protein response (UPR^mt). The UPR^mt system is composed of chaperones and proteases, which promote protein folding or eliminate mitochondrial proteins damaged by mtROS, respectively. UPR^mt is conserved and activated in cancer in response to mitochondrial stress to maintain mitochondrial integrity and support tumor growth. In this review, we discuss how mitochondria become dysfunctional in cancer and highlight the tumor-promoting functions of key components of the UPR^mt.

Cyclophilin D: Guardian or Executioner for Tumor Cells?

Cyclophilin D (CypD) is a peptide-proline cis-trans isomerase (PPIase) distributed in the mitochondrial matrix. CypD regulates the opening of the mitochondrial permeability conversion pore (mPTP) and mitochondrial bioenergetics through PPIase activity or interaction with multiple binding partners in mitochondria. CypD initially attracted attention due to its regulation of mPTP overopening-mediated cell death. However, recent studies on the effects of CypD on tumors have shown conflicting results. Although CypD has been proven to promote the aerobic glycolysis in tumor cells, its regulation of malignant characteristics such as the survival, invasion and drug resistance of tumor cells remains controversial. Here, we elaborate the main biological functions of CypD and its relationships with tumor progression identified in recent years, focusing on the dual role of CypD in tumors.

GRP75-faciliated Mitochondria-associated ER Membrane (MAM) Integrity controls Cisplatin-resistance in Ovarian Cancer Patients

Background: Control of ER-mitochondrial Ca2+ fluxes is a critical checkpoint to determine cell fate under stress. The 75-kDa glucose-regulated protein (GRP75) is a key tether protein facilitating mitochondria-associated ER membrane (MAM) formation through the IP3R-GRP75-VDAC1 complex. Although GRP75 contributes to cisplatin (CP)-resistance of ovarian cancer (OC), the underlying mechanisms are not clear. Methods: CP-resistant and -sensitive OC cell lines with GRP75 stable modulation were established. Confocal, PLA, co-IP, and TEM analysis were utilized to detect MAM integrity. Live cell Ca2+ imaging, intracellular ATP, ROS, and NAD+ assays were utilized to investigate ER-to-mitochondrial Ca2+ transfer and mitochondrial bioenergetics. Western blot, flow cytometry, CCK-8, Δψm, and mPTP assays were utilized to examine apoptotic cell death. Bioinformatics, patient's specimens, and immunohistochemistry were conducted to obtain the clinical relevance for GRP75-facilitated MAM formation. Results: GRP75-faciliated MAM formation was enriched in CP-resistant OC cells. CP-exposure only increased MAM formation in CP-sensitive OC cells, and enrichment of GRP75 and VDAC1 at MAMs is indispensable to CP-resistance. Diminishing MAM integrity by GRP75-deficiency reduced ER-to-mitochondria Ca2+ transfer, accelerated CP-induced mitochondrial dysfunction, provoked catastrophic ROS, and enhanced CP-triggered apoptotic cell death in OC cells. Clinical investigations confirmed the enrichment of GRP75-faciliated MAM formation in relapsed OC patients, and such enrichment was associated with the CP-resistance phenotype. Conclusion: GRP75-overexpression confers CP-resistance by distinctively managing MAM-facilitated Ca2+ fluxes and the pro-survival ROS signal, whereas GRP75-deficiency induces cell death via bioenergetic crisis and apoptotic ROS accumulation in OC cells. Our results show that GRP75-faciliated MAM formation is a potential target to overcome CP-resistance of OC.

Selective vulnerabilities in the proteostasis network of castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is associated with an increased reliance on heat shock protein 70 (HSP70), but it is not clear what other protein homeostasis (proteostasis) factors might be involved. To address this question, we performed functional and synthetic lethal screens in four prostate cancer cell lines. These screens confirmed key roles for HSP70, HSP90, and their co-chaperones, but also suggested that the mitochondrial chaperone, HSP60/HSPD1, is selectively required in CRPC cell lines. Knockdown of HSP60 does not impact the stability of androgen receptor (AR) or its variants; rather, it is associated with loss of mitochondrial spare respiratory capacity, partly owing to increased proton leakage. Finally, transcriptional data revealed a correlation between HSP60 levels and poor survival of prostate cancer patients. These findings suggest that re-wiring of the proteostasis network is associated with CRPC, creating selective vulnerabilities that might be targeted to treat the disease.

Analogs of the Heat Shock Protein 70 Inhibitor MKT-077 Suppress Medullary Thyroid Carcinoma Cells

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor mainly caused by mutations in the RET proto-oncogene. We previously demonstrated that depletion of the mitochondrial molecular chaperone, mortalin, can effectively suppress human MTC cells in culture and in mouse xenografts, by disrupting mitochondrial bioenergetics and subsequently inducing apoptosis and RET downregulation. Similar effects were induced by MKT-077, a water-soluble rhodocyanine dye analog known to inhibit mortalin, but with notable toxicity in animals. These observations led us to evaluate recently developed MKT-077 analogs that exhibited higher selectivity to HSP70 proteins and improved bioavailability. We validated the MTC cell-suppressive effects of mortalin depletion in three-dimensional cultures of the human MTC lines, TT, and MZ-CRC-1, and then evaluated different MKT-077 analogs in two- and three-dimensional cell cultures, to show that the MKT-077 analogs, JG-98 and JG-194, effectively and consistently inhibited propagation of TT and MZ-CRC-1 cells in these cultures. Of note, these compounds also effectively suppressed the viability of TT and MZ-CRC-1 progenies resistant to vandetanib and cabozantinib. Moreover, JG-231, an analog with improved microsomal stability, consistently suppressed TT and MZ-CRC-1 xenografts in mice. These data suggest that mortalin inhibition may have therapeutic potential for MTC.

The Role of Altered Mitochondrial Metabolism in Thyroid Cancer Development and Mitochondria-Targeted Thyroid Cancer Treatment

Thyroid cancer (TC) is the most common type of endocrine malignancy. Tumour formation, progression, and metastasis greatly depend on the efficacy of mitochondria-primarily, the regulation of mitochondria-mediated apoptosis, Ca²⁺ homeostasis, dynamics, energy production, and associated reactive oxygen species generation. Recent studies have successfully confirmed the mitochondrial aetiology of thyroid carcinogenesis. In this review, we focus on the recent progress in understanding the molecular mechanisms of thyroid cancer relating to altered mitochondrial metabolism. We also discuss the repurposing of known drugs and the induction of mitochondria-mediated apoptosis as a new trend in the development of anti-TC therapy.

Identification and Validation of a Proliferation-Associated Score Model Predicting Survival in Lung Adenocarcinomas

AIM

This study is aimed at building a risk model based on the genes that significantly altered the proliferation of lung adenocarcinoma cells and exploring the underlying mechanisms.

METHODS

The data of 60 lung adenocarcinoma cell lines in the Cancer Dependency Map (Depmap) were used to identify the genes whose knockout led to dramatical acceleration or deacceleration of cell proliferation. Then, univariate Cox regression was performed using the survival data of 497 patients with lung adenocarcinoma in The Cancer Genome Atlas (TCGA). The least absolute shrinkage and selection operator (LASSO) model was used to construct a risk prediction score model. Patients with lung adenocarcinoma from TCGA were classified into high- or low-risk groups based on the scores. The differences in clinicopathologic, genomic, and immune characteristics between the two groups were analyzed. The prognosis of the genes in the model was verified with immunohistochemical staining in 100 samples from the Department of Thoracic Surgery, Zhongshan Hospital, and the alteration in the proliferation rate was checked after these genes were knocked down in lung adenocarcinoma cells (A549 and H358).

RESULTS

A total of 55 genes were found to be significantly related to survival by combined methods, which were crucial to tumor progression in functional enrichment analysis. A six-gene-based risk prediction score, including the proteasome subunit beta type-6 (PSMB6), the heat shock protein family A member 9 (HSPA9), the deoxyuridine triphosphatase (DUT), the cyclin-dependent kinase 7 (CDK7), the polo-like kinases 1 (PLK1), and the folate receptor beta 2 (FOLR2), was built using the LASSO method. The high-risk group classified with the score model was characterized by poor overall survival (OS), immune infiltration, and relatively higher mutation load. A total of 9864 differentially expressed genes and 138 differentially expressed miRNAs were found between the two groups. Also, a nomogram comparing score model, age, and the stage was built to predict OS for patients with lung adenocarcinoma. Using immunohistochemistry, the expression levels of PSMB6, HSPA9, DUT, CDK7, and PLK1 were found to be higher in lung adenocarcinoma tissues of patients, while the expression of FOLR2 was low, which was consistent with survival prediction. The knockdown of PSMB6 and HSPA9 by siRNA significantly downregulated the proliferation of A549 and H358 cells.

CONCLUSION

The proposed score model may function as a promising risk prediction tool for patients with lung adenocarcinoma and provide insights into the molecular regulation mechanism of lung adenocarcinoma.

A new role of GRP75-USP1-SIX1 protein complex in driving prostate cancer progression and castration resistance

Prostate cancer (PC) is the second most common cancer with limited treatment option in males. Although the reactivation of embryonic signals in adult cells is one of the characteristics of cancer, the underlying protein degradation mechanism remains elusive. Here, we show that the molecular chaperone GRP75 is a key player in PC cells by maintaining the protein stability of SIX1, a transcription factor for embryonic development. Mechanistically, GRP75 provides a platform to recruit the deubiquitinating enzyme USP1 to inhibit K48-linked polyubiquitination of SIX1. Structurally, the C-terminus of GRP75 (433-679 aa) contains a peptide binding domain, which is required for the formation of GRP75-USP1-SIX1 protein complex. Functionally, pharmacological or genetic inhibition of the GRP75-USP1-SIX1 protein complex suppresses tumor growth and overcomes the castration resistance of PC cells in vitro and in xenograft mouse models. Clinically, the protein expression of SIX1 in PC tumor tissues is positively correlated with the expression of GRP75 and USP1. These new findings not only enhance our understanding of the protein degradation mechanism, but also may provide a potential way to enhance the anti-cancer activity of androgen suppression therapy.

Identification and Characterization of MortaparibPlus-A Novel Triazole Derivative That Targets Mortalin-p53 Interaction and Inhibits Cancer-Cell Proliferation by Wild-Type p53-Dependent and -Independent Mechanisms

p53 has an essential role in suppressing the carcinogenesis process by inducing cell cycle arrest/apoptosis/senescence. Mortalin/GRP75 is a member of the Hsp70 protein family that binds to p53 causing its sequestration in the cell cytoplasm. Hence, p53 cannot translocate to the nucleus to execute its canonical tumour suppression function as a transcription factor. Abrogation of mortalin-p53 interaction and subsequent reactivation of p53's tumour suppression function has been anticipated as a possible approach in developing a novel cancer therapeutic drug candidate. A chemical library was screened in a high-content screening system to identify potential mortalin-p53 interaction disruptors. By four rounds of visual assays for mortalin and p53, we identified a novel synthetic small-molecule triazole derivative (4-[(1E)-2-(2-phenylindol-3-yl)-1-azavinyl]-1,2,4-triazole, henceforth named Mortaparib^Plus). Its activities were validated using multiple bioinformatics and experimental approaches in colorectal cancer cells possessing either wild-type (HCT116) or mutant (DLD-1) p53. Bioinformatics and computational analyses predicted the ability of Mortaparib^Plus to competitively prevent the interaction of mortalin with p53 as it interacted with the p53 binding site of mortalin. Immunoprecipitation analyses demonstrated the abrogation of mortalin-p53 complex formation in Mortaparib^Plus-treated cells that showed growth arrest and apoptosis mediated by activation of p21^WAF1, or BAX and PUMA signalling, respectively. Furthermore, we demonstrate that Mortaparib^Plus-induced cytotoxicity to cancer cells is mediated by multiple mechanisms that included the inhibition of PARP1, up-regulation of p73, and also the down-regulation of mortalin and CARF proteins that play critical roles in carcinogenesis. Mortaparib^Plus is a novel multimodal candidate anticancer drug that warrants further experimental and clinical attention.

Mitochondrial protein import dysfunction: mitochondrial disease, neurodegenerative disease and cancer

The majority of proteins localised to mitochondria are encoded by the nuclear genome, with approximately 1500 proteins imported into mammalian mitochondria. Dysfunction in this fundamental cellular process is linked to a variety of pathologies including neuropathies, cardiovascular disorders, myopathies, neurodegenerative diseases and cancer, demonstrating the importance of mitochondrial protein import machinery for cellular function. Correct import of proteins into mitochondria requires the co-ordinated activity of multimeric protein translocation and sorting machineries located in both the outer and inner mitochondrial membranes, directing the imported proteins to the destined mitochondrial compartment. This dynamic process maintains cellular homeostasis, and its dysregulation significantly affects cellular signalling pathways and metabolism. This review summarises current knowledge of the mammalian mitochondrial import machinery and the pathological consequences of mutation of its components. In addition, we will discuss the role of mitochondrial import in cancer, and our current understanding of the role of mitochondrial import in neurodegenerative diseases including Alzheimer's disease, Huntington's disease and Parkinson's disease.

Mortalin depletion induces MEK/ERK-dependent and ANT/CypD-mediated death in vemurafenib-resistant B-RafV600E melanoma cells

Therapy resistance to a selective B-Raf inhibitor (BRAFi) poses a challenge in treating patients with BRAF-mutant melanomas. Here, we report that RNA interference of mortalin (HSPA9/GRP75), a mitochondrial molecular chaperone often upregulated and mislocalized in melanoma, can effectively induce death of vemurafenib-resistant progenies of human B-Raf^V600E melanoma cell lines, A375 and Colo-829. Mortalin depletion induced death of vemurafenib-resistant cells at similar efficacy as observed in vemurafenib-naïve parental cells. This lethality was correlated with perturbed mitochondrial permeability and was attenuated by knockdown of adenine nucleotide translocase (ANT) and cyclophilin D (CypD), the key regulators of mitochondrial permeability. Chemical inhibition of MEK1/2 and ERK1/2 also suppressed mortalin depletion-induced death and mitochondrial permeability in these cells. These data suggest that mortalin and MEK/ERK regulate an ANT/CypD-associated mitochondrial death mechanism(s) in B-Raf^V600E melanoma cells and that this regulation is conserved even after these cells develop BRAFi resistance. We also show that doxycycline-induced mortalin depletion can effectively suppress the xenografts of vemurafenib-resistant A375 progeny in athymic nude mice. These findings suggest that mortalin has potential as a candidate therapeutic target for BRAFi-resistant BRAF-mutant tumors.

Palmitoylated CKAP4 regulates mitochondrial functions through an interaction with VDAC2 at ER-mitochondria contact sites

Cytoskeleton-associated protein 4 (CKAP4) is a palmitoylated type II transmembrane protein localized to the endoplasmic reticulum (ER). Here, we found that knockout (KO) of CKAP4 in HeLaS3 cells induces the alteration of mitochondrial structures and increases the number of ER-mitochondria contact sites. To understand the involvement of CKAP4 in mitochondrial functions, the binding proteins of CKAP4 were explored, enabling identification of the mitochondrial porin voltage-dependent anion-selective channel protein 2 (VDAC2), which is localized to the outer mitochondrial membrane. Palmitoylation at Cys100 of CKAP4 was required for the binding between CKAP4 and VDAC2. In CKAP4 KO cells, the binding of inositol trisphosphate receptor (IP3R) and VDAC2 was enhanced, the intramitochondrial Ca2+ concentration increased and the mitochondrial membrane potential decreased. In addition, CKAP4 KO decreased the oxidative consumption rate, in vitro cancer cell proliferation under low-glucose conditions and in vivo xenograft tumor formation. The phenotypes were not rescued by expression of a palmitoylation-deficient CKAP4 mutant. These results suggest that CKAP4 plays a role in maintaining mitochondrial functions through the binding to VDAC2 at ER-mitochondria contact sites and that palmitoylation is required for this novel function of CKAP4.This article has an associated First Person interview with the first author of the paper.

Growth Inhibitory Signaling of the Raf/MEK/ERK Pathway

In response to extracellular stimuli, the Raf/MEK/extracellular signal-regulated kinase (ERK) pathway regulates diverse cellular processes. While mainly known as a mitogenic signaling pathway, the Raf/MEK/ERK pathway can mediate not only cell proliferation and survival but also cell cycle arrest and death in different cell types. Growing evidence suggests that the cell fate toward these paradoxical physiological outputs may be determined not only at downstream effector levels but also at the pathway level, which involves the magnitude of pathway activity, spatial-temporal regulation, and non-canonical functions of the molecular switches in this pathway. This review discusses recent updates on the molecular mechanisms underlying the pathway-mediated growth inhibitory signaling, with a major focus on the regulation mediated at the pathway level.

Mortalin/HSPA9 targeting selectively induces KRAS tumor cell death by perturbing mitochondrial membrane permeability

The mitochondrial HSP70 chaperone mortalin (HSPA9/GRP75) is often upregulated and mislocalized in MEK/ERK-deregulated tumors. Here, we show that mortalin depletion can selectively induce death of immortalized normal fibroblasts IMR90E1A when combined with K-Ras^G12V expression, but not with wild type K-Ras expression, and that K-Ras^G12V-driven MEK/ERK activity is necessary for this lethality. This cell death was attenuated by knockdown or inhibition of adenine nucleotide translocase (ANT), cyclophilin D (CypD), or mitochondrial Ca²⁺ uniporter (MCU), which implicates a mitochondria-originated death mechanism. Indeed, mortalin depletion increased mitochondrial membrane permeability and induced cell death in KRAS-mutated human pancreatic ductal adenocarcinoma (PDAC) and colon cancer lines, which were attenuated by knockdown or inhibition of ANT, CypD, or MCU, and occurred independently of TP53 and p21^CIP1. Intriguingly, JG-98, an advanced MKT-077 derivative, phenocopied the lethal effects of mortalin depletion in K-Ras^G12V-expressing IMR90E1A and KRAS-mutated tumor cell lines in vitro. Moreover, JG-231, a JG-98 analog with improved microsomal stability effectively suppressed the xenograft of MIA PaCa-2, a K-Ras^G12C-expressing human PDAC line, in athymic nude mice. These data demonstrate that oncogenic KRAS activity sensitizes cells to the effects of mortalin depletion, suggesting that mortalin has potential as a selective therapeutic target for KRAS-mutated tumors.