The chaperone Hsp70 is a BH3 receptor activated by the pro-apoptotic Bim to stabilize anti-apoptotic clients

Transcranial Magnetic Stimulation Alleviates Spatial Learning and Memory Impairment by Inhibiting the Expression of SARM1 in Rats with Cerebral Ischemia-Reperfusion Injury

The cognitive impairment resulting from stroke is purported to be associated with impaired neuronal structure and function. Transcranial Magnetic Stimulation (TMS) modulates neuronal or cortical excitability and inhibits cellular apoptosis, thereby enhancing spatial learning and memory in middle cerebral artery occlusion/reperfusion (MCAO/R) rats. In this study, we aimed to investigate whether Sterile alpha and Toll/interleukin receptor motif-containing protein 1 (SARM1), a pivotal Toll-like receptor adaptor molecule and its related mechanisms are involved in the ameliorating effect of TMS on cognitive function post-cerebral ischemia. We evaluated hippocampal injury in MCAO/R rats after one week of treatment with 10-Hz TMS at an early stage. The effect of SARM1 was more effectively assessed through lentivirus-mediated SARM1 overexpression. Various techniques, including FJB staining, HE staining, western blot, immunofluorescence, imunohistochemistry, and transmission electron microscopy, were employed to investigate the molecular biological and morphological alterations of axons, myelin sheaths and apoptosis in the hippocampus. Ultimately, Morris Water Maze was employed to evaluate the spatial learning and memory capabilities of the rats. We observed that TMS significantly reduced the levels of SARM1, NF-κB, and Bax following MCAO/R, while elevating the levels of HSP70, Bcl-2, GAP-43, NF-200, BDNF, and MBP. Overexpression of SARM1 not only reversed the neuroprotective effects induced by TMS but also exacerbated spatial learning and memory impairments in rats. Our results demonstrate that TMS mitigates hippocampal cell apoptosis via the SARM1/HSP70/NF-κB signaling pathway, thus fostering the regeneration of hippocampal axons and myelin sheaths, as well as the improvement of spatial learning and memory.

A kinase-independent Bcr-Abl function mediating an Hsp70-Bim protein-protein interaction in chronic myeloid leukemia

Despite the transformative impact of tyrosine kinase inhibitors (TKIs) on chronic myeloid leukemia (CML), a subset of TKIs-resistant CML cells survives independent of Bcr-Abl kinase activity, forming a persistent therapeutic challenge. In this study, we present the first direct evidence that Bcr-Abl, through its DNA-binding domain (DBD), interacts with the nucleotide-binding domain (NBD) of Hsp70 to mediate the formation of a Bcr-Abl/Hsp70/Bim tri-complex, independent of its kinase function. Using a combination of in vitro biophysical assays-including fluorescent polarization assays (FPAs), isothermal titration calorimetry (ITC), circular dichroism spectroscopy, ATPase activity measurement, and rhodanese aggregation suppression-and cell-based co-immunoprecipitation (Co-IP), we demonstrate that this interaction induces a conformational change in Hsp70 that enhances its affinity for Bim and significantly elevates its ATPase activity. The resulting complex stabilizes oncogenic survival proteins such as AKT and eIF4E, thereby protecting TKIs-resistant CML cells from apoptosis in a Bcr-Abl kinase-independent manner. Importantly, pharmacologic disruption of this complex using the Hsp70/Bim inhibitor S1g-10 or Bcr-Abl PROTAC molecule effectively suppresses TKIs-resistant CML cell proliferation. These findings reveal a novel non-canonical function of Bcr-Abl and provide a new therapeutic strategy for overcoming TKIs-resistance in CML.

Advances in the structures, mechanisms and targeting of molecular chaperones

Molecular chaperones, a class of complex client regulatory systems, play significant roles in the prevention of protein misfolding and abnormal aggregation, the modulation of protein homeostasis, and the protection of cells from damage under constantly changing environmental conditions. As the understanding of the biological mechanisms of molecular chaperones has increased, their link with the occurrence and progression of disease has suggested that these proteins are promising targets for therapeutic intervention, drawing intensive interest. Here, we review recent advances in determining the structures of molecular chaperones and heat shock protein 90 (HSP90) chaperone system complexes. We also describe the features of molecular chaperones and shed light on the complicated regulatory mechanism that operates through interactions with various co-chaperones in molecular chaperone cycles. In addition, how molecular chaperones affect diseases by regulating pathogenic proteins has been thoroughly analyzed. Furthermore, we focus on molecular chaperones to systematically discuss recent clinical advances and various drug design strategies in the preclinical stage. Recent studies have identified a variety of novel regulatory strategies targeting molecular chaperone systems with compounds that act through different mechanisms from those of traditional inhibitors. Therefore, as more novel design strategies are developed, targeting molecular chaperones will significantly contribute to the discovery of new potential drugs.

Induction of Chaperone Synthesis in Human Neuronal Cells Blocks Oxidative Stress-Induced Aging

Oxidative stress accompanies many pathologies that are characterized by neuronal degradation leading to a deterioration of the disease. The main causes are the disruption of protein homeostasis and activation of irreversible processes of cell cycle disruption and deterioration of cellular physiology, leading to senescence. In this paper, we propose a new approach to combating senescence caused by oxidative stress. This approach is based on the use of a low-molecular inducer of chaperone synthesis, one of the cell protective systems regulating proteostasis and apoptosis. We present data demonstrating the ability of the pyrrolylazine derivative PQ-29 to induce chaperone accumulation in human neuronal cells and prevent oxidative stress-induced aging.

Selective degradation of mutant FMS-like tyrosine kinase-3 requires BIM-dependent depletion of heat shock proteins

Internal tandem duplications in the FMS-like tyrosine kinase-3 (FLT3-ITD) are common mutations in acute myeloid leukemia (AML). Proteolysis-targeting chimeras (PROTACs) that induce proteasomal degradation of mutated FLT3 emerge as innovative pharmacological approach. Molecular mechanisms that control targeted proteolysis beyond the ubiquitin-proteasome-system are undefined and PROTACs are the only known type of FLT3 degraders. We report that the von-Hippel-Lindau ubiquitin-ligase based FLT3 PROTAC MA49 (melotinib-49) and the FLT3 hydrophobic tagging molecule MA50 (halotinib-50) reduce endoplasmic reticulum-associated, oncogenic FLT3-ITD but spare FLT3. Nanomolar doses of MA49 and MA50 induce apoptosis of human leukemic cell lines and primary AML blasts with FLT3-ITD (p < 0.05-0.0001), but not of primary hematopoietic stem cells and differentiated immune cells, FLT3 wild-type cells, retinal cells, and c-KIT-dependent cells. In vivo activity of MA49 against FLT3-ITD-positive leukemia cells is verified in a Danio rerio model. The degrader-induced loss of FLT3-ITD involves the pro-apoptotic BH3-only protein BIM and a previously unidentified degrader-induced depletion of protein-folding chaperones. The expression levels of HSP90 and HSP110 correlate with reduced AML patient survival (p < 0.1) and HSP90, HSP110, and BIM are linked to the expression of FLT3 in primary AML cells (p < 0.01). HSP90 suppresses degrader-induced FLT3-ITD elimination and thereby establishes a mechanistically defined feed-back circuit.

Heat shock proteins as hallmarks of cancer: insights from molecular mechanisms to therapeutic strategies

Heat shock proteins are essential molecular chaperones that play crucial roles in stabilizing protein structures, facilitating the repair or degradation of damaged proteins, and maintaining proteostasis and cellular functions. Extensive research has demonstrated that heat shock proteins are highly expressed in cancers and closely associated with tumorigenesis and progression. The "Hallmarks of Cancer" are the core features of cancer biology that collectively define a series of functional characteristics acquired by cells as they transition from a normal state to a state of tumor growth, including sustained proliferative signaling, evasion of growth suppressors, resistance to cell death, enabled replicative immortality, the induction of angiogenesis, and the activation of invasion and metastasis. The pivotal roles of heat shock proteins in modulating the hallmarks of cancer through the activation or inhibition of various signaling pathways has been well documented. Therefore, this review provides an overview of the roles of heat shock proteins in vital biological processes from the perspective of the hallmarks of cancer and summarizes the small-molecule inhibitors that target heat shock proteins to regulate various cancer hallmarks. Moreover, we further discuss combination therapy strategies involving heat shock proteins and promising dual-target inhibitors to highlight the potential of targeting heat shock proteins for cancer treatment. In summary, this review highlights how targeting heat shock proteins could regulate the hallmarks of cancer, which will provide valuable information to better elucidate and understand the roles of heat shock proteins in oncology and the mechanisms of cancer occurrence and development and aid in the development of more efficacious and less toxic novel anticancer agents.

Discovery of Biphenyl Derivatives to Target Hsp70-Bim Protein-Protein Interaction in Chronic Myeloid Leukemia by Scaffold Hopping Strategy

Hsp70-Bim protein-protein interaction (PPI) is the most recently identified specific target in chronic myeloid leukemia (CML) therapy. Herein, we developed a new class of Hsp70-Bim PPI inhibitors via scaffold hopping of S1g-10, the most potent Hsp70-Bim PPI inhibitor thus far. Through structure-activity relationship (SAR) study, we obtained a biphenyl scaffold compound JL-15 with a 5.6-fold improvement in Hsp70-Bim PPI suppression (Kd = 123 vs 688 nM) and a 4-fold improvement in water solubility (29.42 vs 7.19 μg/mL) compared to S1g-10. It maintains comparable apoptosis induction capability with S1g-10 against both TKI-sensitive and TKI-resistant CML cell lines in an Hsp70-Bim-dependent manner. Additionally, through SAR, 1H-15N TRSOY-NMR, and molecular docking, we revealed that Lys319 is a "hot spot" in the Hsp70-Bim PPI interface. Collectively, these results provide a novel chemical scaffold and structural insights for the rational design of Hsp70-Bim PPI inhibitors.

Yeast Bxi1/Ybh3 mediates conserved mitophagy and apoptosis in yeast and mammalian cells: convergence in Bcl-2 family

The process of degrading unwanted or damaged mitochondria by autophagy, called mitophagy, is essential for mitochondrial quality control together with mitochondrial apoptosis. In mammalian cells, pan-Bcl-2 family members including conical Bcl-2 members and non-conical ones are involved in and govern the two processes. We have illustrated recently the BH3 receptor Hsp70 interacts with Bim to mediate both apoptosis and mitophagy. However, whether similar pathways exist in lower eukaryotes where conical Bcl-2 members are absent remained unclear. Here, a specific inhibitor of the Hsp70-Bim PPI, S1g-10 and its analogs were used as chemical tools to explore the role of yeast Bxi1/Ybh3 in regulating mitophagy and apoptosis. Using Om45-GFP processing assay, we illustrated that yeast Ybh3 mediates a ubiquitin-related mitophagy pathway in both yeast and mammalian cells through association with Hsp70, which is in the same manner with Bim. Moreover, by using Bax/Bak double knockout MEF cells, Ybh3 was identified to induce apoptosis through forming oligomerization to trigger mitochondrial outer membrane permeabilization (MOMP) like Bax. We not only illustrated a conserved ubiquitin-related mitophagy pathway in yeast but also revealed the multi-function of Ybh3 which combines the function of BH3-only protein and multi-domain Bax protein as one.

Hsp70-Bim incoherent feedforward loop contributes to cell-fate heterogeneity and fractional killing

BACKGROUND AND PURPOSE

Although chemotherapeutics or molecular targeted drugs often elicit profound initial responses, fractional killing capable of driving acquired resistance can persist. Identifying stress-induced negative feedback or an incoherent feedforward loop (IFFL), which may contribute to fractional killing, is urgently needed.

EXPERIMENTAL APPROACH

Mathematical modelling was used to identify how and to what extent a recently reported Hsp70-Bim protein-protein interaction (PPI) contributes to the adaptation of the Bcl-2 network. Experimental validation was made by using a specific inhibitor of Hsp70-Bim PPI, S1g-2, as chemical tool. Bifurcation analysis and stochastic simulation were used for the theoretical study of the impact of Hsp70-Bim PPI on cell-fate heterogeneity and factional killing.

KEY RESULTS

The Hsp70-Bim-AKT circuit forms an IFFL that greatly contributes to the adaptation of the Bcl-2-regulated apoptosis network, thus leading to fractional killing. This adaptive programme enhances noise-induced cell-fate heterogeneity by shifting from a saddle-node to a saddle-collision transition scenario.

CONCLUSION AND IMPLICATIONS

Hsp70-Bim IFFL serves as a molecular pathway induced by DNA damaging drugs or tyrosine kinase inhibitors that enabled fractional killing, whereby acquired resistance emerges. A synergistic strategy is unveiled for overcoming fractional killing by suppressing Hsp70-Bim PPI.

Small molecule inhibitor targeting the Hsp70-Bim protein-protein interaction in estrogen receptor-positive breast cancer overcomes tamoxifen resistance

INTRODUCTION

Estrogen receptor (ER) positive patients compromise about 70% of breast cancers. Tamoxifen, an antagonist of ERα66 (the classic ER), is the most effective and the standard first-line drug. However, its efficacy is limited by the development of acquired resistance.

METHODS

A specific inhibitor of Hsp70-Bim protein-protein interaction (PPI), S1g-2, together with an inhibitor of Hsp70-Bag3 PPI, MKT-077 and an ATP-competitive inhibitor VER155008, were used as chemical tools. Cell viability assays, co-immunoprecipitation and gene knockdown were used to investigate the role of Hsp70 in tamoxifen resistance. A xenograft model was established in which tamoxifen-resistant breast cancer (MCF-7/TAM-R) cells maintained in the presence of 5 μM tamoxifen were subcutaneously inoculated. The anti-tumor efficiency of S1g-2 was measured after a daily injection of 0.8 mg/kg for 14 days.

RESULTS

It was revealed that Hsp70-Bim PPI protects ERα-positive breast cancer from tamoxifen-induced apoptosis through binding and stabilizing ERα36, rather than ERα66, resulting in sustained EGFR mRNA and protein expression. Disruption of Hsp70-Bim PPI and downregulation of ERα36 expression in tumor samples are consistent with the in vitro functions of S1g-2, resulting in about a three-fold reduction in tumor volume.

CONCLUSIONS

The in vivo activity and safety of S1g-2 illustrated that it is a potential strategy for Hsp70-Bim disruption to overcome tamoxifen-resistant ER-positive breast cancer.

Exploring the binding mechanism of a small molecular Hsp70-Bim PPI inhibitor through molecular dynamic simulation

CONTEXT

The interface of Hsp70-Bim protein-protein interaction (PPI) has been identified as a specific target for Chronic Myeloid Leukemia (CML) therapy and the specific inhibitors were developed to exhibit in vivo anti-leukemia activities. Herein, we explored the binding mechanism of a Hsp70-Bim inhibitor, 6-(cyclohexylthio)-3-((2-morpholinoethyl) amino)-1-oxo-1H-phenalene-2-carbonitrile (S1g-6), to Hsp70 at the atomic level by MD simulation. TYR-149, THR-222, ALA-223, and GLY-224 on Hsp70 were identified as four key residues that contribute to Hsp70/S1g-6 complex. Moreover, the site mutation validation demonstrated the TYR-149 of Hsp70 is a "hot-spot" in the Hsp70-Bim PPI interface. These results could benefit the design of further inhibitors to occupy the Bim binding site on the Hsp70 surface.

METHODS

The binding mechanism of S1g-6 and Hsp70 was predicted through the molecular dynamics (MD) method by Gromacs-2021.3. The MD simulation was performed with 100-ps NVT and 100-ps NPT ensemble, and the force field was chosen as the Charmm36 force field. The temperature was set as 300 K, the time step was 2 fs and the total MD simulation time was 500 ns.

Exploiting the "Hot-Spots" of Hsp70Bim ProteinProtein Interaction to Optimize the 1-Oxo-1H-phenalene-2,3-dicarbonitrile Analogues as Specific Hsp70Bim Inhibitors

Selectively targeting the cancer-specific protein-protein interaction (PPI) between Hsp70 and Bim has been discovered as a promising strategy for treating chronic myeloid leukemia (CML). The first Hsp70-Bim PPI inhibitor, S1g-2, has been identified to overcome the on-target toxicity of known Hsp70 inhibitors when it induces apoptosis of CML cells. Herein, we carried out a hit-to-lead optimization of S1g-2, yielding S1g-10, which exhibited a 10-fold increase in Hsp70/Bim suppressing potency. Furthermore, S1g-10 not only exhibited a 5- to 10-fold stronger antitumor activity in the sub-μM range against CML cells than S1g-2 in vitro, but it also overcame BCR-ABL-independent tyrosine kinase inhibitor resistance in CML in vivo depending on the Hsp70-Bim signaling pathway. Moreover, through structure-activity relationship analysis, TROSY-HSQC NMR, molecular dynamics simulation, and point mutation validation, two hydrophobic pockets composed of eight key residues were demonstrated to produce predominant interactions with either Bim or S1g-10, regarded as the "hot-spots" in the Hsp70-Bim PPI interface.

Ectopic BH3-Only Protein Bim Associates with Hsp70 to Regulate Yeast Mitophagy

Mitophagy, a form of selective autophagy, plays an essential role to maintain a population of healthy and functional mitochondria for normal cellular metabolism. Acting mainly as one of the B-cell lymphoma 2 (Bcl-2) family pro-apoptotic members, Bim (also known as BCL2L11) was identified to be a co-chaperone of Hsp70 to promote mitophagy in mammalian cells. Herein, with the help of a specific Hsp70/Bim disruptor and Om45-GFP processing assay, we illustrated that ectopic BimEL is able to promote mitophagy through Hsp70/Bim interaction in yeast, where Bax/Bak is absent. The Hsp70/Bim-mediated mitophagy is conserved in eukaryotes, from yeast to humans.

Hsp70-Bim interaction facilitates mitophagy by recruiting parkin and TOMM20 into a complex

BACKGROUND

For cancer therapy, the identification of both selective autophagy targets and small molecules that specifically regulate autophagy is greatly needed. Heat shock protein 70 (Hsp70) is a recently discovered BH3 receptor that forms a protein‒protein interaction (PPI) with Bcl-2-interacting mediator of cell death (Bim). Herein, a specific inhibitor of the Hsp70-Bim PPI, S1g-2, and its analog S1, which is a Bcl-2-Bim disruptor, were used as chemical tools to explore the role of Hsp70-Bim PPI in regulating mitophagy.

METHODS

Co-immunoprecipitation and immunofluorescence assays were used to determine protein interactions and colocalization patterns. Organelle purification and immunodetection of LC3-II/LC3-I on mitochondria, endoplasmic reticulum (ER) and Golgi were applied to identify specific types of autophagy. Cell-based and in vitro ubiquitination studies were used to study the role of the Hsp70-Bim PPI in parkin-mediated ubiquitination of outer mitochondrial membrane 20 (TOMM20).

RESULTS

We found that after the establishment of their PPI, Hsp70 and Bim form a complex with parkin and TOMM20, which in turn facilitates parkin translocation to mitochondria, TOMM20 ubiquitination and mitophagic flux independent of Bax/Bak. Moreover, S1g-2 selectively inhibits stress-induced mitophagy without interfering with basal autophagy.

CONCLUSIONS

The findings highlight the dual protective function of the Hsp70-Bim PPI in regulating both mitophagy and apoptosis. S1g-2 is thus a newly discovered antitumor drug candidate that drives both mitophagy and cell death via apoptosis.

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.

Heat-Shock Proteins in Leukemia and Lymphoma: Multitargets for Innovative Therapeutic Approaches

Heat-shock proteins (HSPs) are powerful chaperones that provide support for cellular functions under stress conditions but also for the homeostasis of basic cellular machinery. All cancer cells strongly rely on HSPs, as they must continuously adapt to internal but also microenvironmental stresses to survive. In solid tumors, HSPs have been described as helping to correct the folding of misfolded proteins, sustain oncogenic pathways, and prevent apoptosis. Leukemias and lymphomas also overexpress HSPs, which are frequently associated with resistance to therapy. HSPs have therefore been proposed as new therapeutic targets. Given the specific biology of hematological malignancies, it is essential to revise their role in this field, providing a more adaptable and comprehensive picture that would help design future clinical trials. To that end, this review will describe the different pathways and functions regulated by HSP27, HSP70, HSP90, and, not least, HSP110 in leukemias and lymphomas.

BH3 mimetics and TKI combined therapy for Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) was considered for a long time one of the most hostile leukemia that was incurable for most of the patients, predominantly due to the extreme resistance to chemotherapy. Part of the resistance to cell death (apoptosis) is the result of increased levels of anti-apoptotic and decreased levels of pro-apoptotic member of the BCL-2 family induced by the BCR-ABL1 oncoprotein. BCR-ABL1 is a constitutively active tyrosine kinase responsible for initiating multiple and oncogenic signaling pathways. With the development of specific BCR-ABL1 tyrosine kinase inhibitors (TKIs) CML became a much more tractable disease. Nevertheless, TKIs do not cure CML patients and a substantial number of them develop intolerance or become resistant to the treatment. Therefore, novel anti-cancer strategies must be developed to treat CML patients independently or in combination with TKIs. Here, we will discuss the mechanisms of BCR-ABL1-dependent and -independent resistance to TKIs and the use of BH3-mimetics as a potential tool to fight CML.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Advances in the study of HSP70 inhibitors to enhance the sensitivity of tumor cells to radiotherapy

The 70 kDa heat shock protein (HSP70) is one of the most conserved proteins and a ubiquitous molecular chaperone that plays a role in the folding, remodeling, and degradation of various proteins to maintain proteostasis. It has been shown that HSP70 is abundantly expressed in cancer and enhances tumor resistance to radiotherapy by inhibiting multiple apoptotic pathways, such as interfering with the cellular senescence program, promoting angiogenesis, and supporting metastasis. Thus, HSP70 provides an effective target for enhancing the effects of radiation therapy in the clinical management of cancer patients. Inhibition of HSP70 enhances the radiation-induced tumor-killing effect and thus improves the efficacy of radiotherapy. This article reviews the sensitivity of Hsp70 and its related inhibitors to radiotherapy of tumor cells.

Bcr-Abl drives the formation of Hsp70/Bim PPI to stabilize oncogenic clients and prevent cells from undergoing apoptosis

Although tyrosine kinase inhibitors that inhibit Bcr-Abl kinase activity have shown excellent efficacy in the clinical application of CML patients, it still a challenge to discover alternative targets and novel therapies because of the emergence of Bcr-Abl-independent resistance. Most recently, Hsp70/Bim complex was revealed that driven by Bcr-Abl and testified as a specific target for CML because it folds and stabilizes many Hsp70 oncogenic substrates that mediate CML specific signaling pathways. However, the relationship between Bcr-Abl and Hsp70/Bim complex and how the chaperone complex contributes to Bcr-Abl-driven leukemogenic cells remain unclear. Herein, with the help of S1g-2, a specific small-molecule inhibitor of Hsp70/Bim complex, and Bcr-Abl knockdown to induce a panel of cancer cell lines apoptosis, we illustrated that Bcr-Abl could prevent cells from undergoing apoptosis mainly by driving the formation of Hsp70/Bim complex both in Bcr-Abl positive CML cells and ALL cells. Through cell-based Co-immunoprecipitation experiments, we identified that Bcr-Abl could stabilize oncogenic clients including AKT and eIF4E mainly by driving the formation of Hsp70/Bim complex in Bcr-Abl positive cells. Moreover, we identified that Bim mediates interactions of Hsp70 and Bak in Bcr-Abl positive cells. Together, the target identification of Hsp70/Bim complex could make it as a promising anticancer target for Bcr-Abl positive leukemia treatment.

Small-molecule inhibitor targeting the Hsp70-Bim protein-protein interaction in CML cells overcomes BCR-ABL-independent TKI resistance

Herein, we screened a novel inhibitor of the Hsp70-Bim protein-protein interaction (PPI), S1g-2, from a Bcl-2 inhibitor library; this compound specifically disrupted the Hsp70-Bim PPI by direct binding to an unknown site adjacent to that of an allosteric Hsp70 inhibitor MKT-077, showing binding affinity in sub-μM concentration range. S1g-2 exhibited overall 5-10-fold higher apoptosis-inducing activity in CML cells, primary CML blasts, and BCR-ABL-transformed BaF3 cells than other cancer cells, normal lymphocytes, and BaF3 cells, illustrating Hsp70-Bim PPI driven by BCR-ABL protects CML through oncoclient proteins that enriched in three pathways: eIF2 signaling, the regulation of eIF4E and p70S6K signaling, and the mTOR signaling pathways. Moreover, S1g-2 progressively enhanced lethality along with the increase in BCR-ABL-independent TKI resistance in the K562 cell lines and is more effective in primary samples from BCR-ABL-independent TKI-resistant patients than those from TKI-sensitive patients. By comparing the underlying mechanisms of S1g-2, MKT-077, and an ATP-competitive Hsp70 inhibitor VER-155008, the Hsp70-Bim PPI was identified to be a CML-specific target to protect from TKIs through the above three oncogenic signaling pathways. The in vivo activity against CML and low toxicity endows S1g-2 a first-in-class promising drug candidate for both TKI-sensitive and resistant CML.

Ectopic BH3-only protein Bim acts as a co-chaperone to positively regulate Hsp70 in yeast

The chaperone heat shock protein 70 (Hsp70) is conserved from bacteria to humans and is crucial for avoiding protein misfolding under stress. Bim functions mainly as one of the Bcl-2 family pro-apoptotic members, was identified to be a co-chaperone of Hsp70. Herein, we reported that ectopic Bim could constitute the interactions with intrinsic Hsp70 and translate its positive co-chaperone activity in vitro to the yeast growth promotion and help Hsp70 to fold its client Ras-like protein. With the help of a specific Hsp70/Bim disruptor, we illustrated that Hsp70/Bim dimers rescue yeast from heat shock. In an organism lacks apoptotic Bcl-2 factors, the pro-apoptotic Bim in mammalian cells exhibits pro-survival functions.

Bim transfer between Bcl-2-like protein and Hsp70 underlines Bcl-2/Hsp70 crosstalk to regulate apoptosis

The chaperone heat shock protein 70 (Hsp70) is crucial for avoiding protein misfolding under stress, but it is also upregulated in many kinds of cancers, where its ability to buffer cellular stress prevents apoptosis. Previous research has suggested that Bim, a BH3-only member of the Bcl-2 family proteins, also serves as a cochaperone for Hsp70, which modulates the folding and stabilization of many Hsp70 oncogenic substrates in tumor cells. However, a definitive demonstration of crosstalk between Bcl-2 and Hsp70 family proteins and molecular mechanism remain unclear. Herein, we examined the effects of pan-Bcl-2 inhibitor S1, Hsp70 inhibitor S1g-6 on the K562, U937, H23, HL-60 cell lines and these inhibitors synergistically induce mitochondrial apoptosis in cancer cell lines. Moreover, we identified that Bim transfer between Bcl-2-like protein and Hsp70 underlines Bcl-2/Hsp70 crosstalk in mitochondrial apoptosis pathway. Thus, the synergy of S1 and S1g-6 to induce a panel of cancer cell lines apoptosis by inhibiting free Bim and facilitating oncogenic client AKT folding and activation. Together, our results demonstrated the combination of Bcl-2 inhibitor and Hsp70 inhibitor showed synergistic effect in cancer cells and the potential to decrease tumor regression.

Synthesis and approbation of new neuroprotective chemicals of pyrrolyl- and indolylazine classes in a cell model of Alzheimer's disease

One of the major causes of neurodegeneration in the pathogenesis of Alzheimer's disease is the accumulation of cytotoxic amyloid species within the intercellular compartments of the brain. The efficacy of the anti-proteotoxic mechanism based on the molecular chaperones Hsp70 and Hsp90 in numerous types of neurons is often low, while its pharmacological enhancement has been shown to ameliorate the physiological and cognitive functions of the brain. Suggesting that the chemicals able to induce heat shock protein synthesis and therefore rescue neural cells from cytotoxicity associated with amyloid, we have synthesized a group of pyrrolyl- and indolylazines that cause the accumulation of heat shock proteins, using a novel method of photocatalysis that is employed in green chemistry. The selected compounds were tested in a cell model of Alzheimer's disease and demonstrated a pronounced neuroprotective effect. These substances increased the survival of neurons, blocked the activation of β-galactosidase, and prevented apoptosis in neurons cultured in the presence of β-amyloid.

A novel Hsp70 inhibitor specifically targeting the cancer-related Hsp70-Bim protein-protein interaction

Targeting cancer-related Hsp70-Bim protein-protein interactions (PPIs) offers a new strategy for the design of Hsp70 inhibitors. Herein, we discovered a novel Hsp70 inhibitor, S1g-6, based on the established BH3 mimetics. S1g-6 exhibited sub-μM binding affinity toward Hsp70 and selectively disrupted Hsp70-Bim PPI. The target specificity of S1g-6in situ was validated by affinity-based protein profiling, co-immunoprecipitation, and cell-based shRNA assays. S1g-6 specifically antagonized the ATPase activity of Hsp70 upon recruiting Bim and showed selective apoptosis induction in some cancer cell lines over normal ones through suppression of some oncogenic clients of Hsp70, representing a new class of antitumor candidates. Hsp70-Bim PPI exhibited cancer-dependent role as a potential anti-cancer target.