Breast Cancer Cell Survival Research Articles

Insulin-like growth factor binding protein-6 modulates proliferative antagonism in response to progesterone in breast cancer.

Breast cancer is one of the most diagnosed cancers worldwide. The insulin-like growth factor (IGF) system promotes proliferation and survival in breast cancer cells and is regulated by 6 insulin-like growth factor binding proteins (IGFBPs). The IGFBPs sequester IGFs to prolong their half-life and attenuate binding to insulin-like growth factor 1 receptor (IGF1R). While IGFBP-6 has been studied in some cancers it has not been studied extensively in hormone receptor positive breast cancer. Survival analysis using available databases indicated that high IGFBP-6 levels improve overall survival in progesterone receptor positive breast cancers. IGFBP-6 is transcriptionally induced by progesterone in T47D breast cancer cells resulting in increased intracellular and extracellular IGFBP-6 protein. Knockdown of IGFBP-6 resulted in reduced proliferative antagonism when estradiol stimulated T47D cells were cotreated with progesterone and protein levels of both progesterone receptor isoforms (PR-A and PR-B) were decreased following knockdown of IGFBP-6. P21(Cip1/Waf1), which is progesterone responsive, was not induced in response to progesterone following knockdown of IGFBP-6. Cyclin E2, a cell cycle regulator, is induced by progesterone only when IGFBP-6 is knocked down. Stable overexpression of IGFBP-6 in MCF-7 cells resulted in an increase in Epidermal Growth Factor Receptor (EGFR) and this expression was further enhanced when cells were cotreated with progesterone and estradiol. These results indicate that IGFBP-6 is a regulator of progesterone action, and that PR is required for the observed protective effects of IGFBP-6 in breast cancer.

Combinatorial effects of cannabinoid receptor 1 and 2 agonists on characteristics and proteomic alteration in MDA-MB-231 breast cancer cells.

Breast cancer is the most common cancer diagnosed in women worldwide. However, the effective treatment for breast cancer progression is still being sought. The activation of cannabinoid receptor (CB) has been shown to negatively affect breast cancer cell survival. Our previous study also reported that breast cancer cells responded to various combinations of CB1 and CB2 agonists differently. Nonetheless, the mechanism underlying this effect and whether this phenomenon can be seen in other cancer characteristics remain unknown. Therefore, this study aims to further elucidate the effects of highly selective CB agonists and their combination on triple-negative breast cancer proliferation, cell cycle progression, invasion, lamellipodia formation as well as proteomic profile of MDA-MB-231 breast cancer cells. The presence of CB agonists, specifically a 2:1 (ACEA: GW405833) combination, prominently inhibited colony formation and induced the S-phase cell cycle arrest in MDA-MB-231 cells. Furthermore, cell invasion ability and lamellipodia formation of MDA-MB-231 were also attenuated by the exposure of CB agonists and their 2:1 combination ratio. Our proteomic analysis revealed proteomic profile alteration in MDA-MB-231 upon CB exposure that potentially led to breast cancer suppression, such as ZPR1/SHC1/MAPK-mediated cell proliferation and AXL/VAV2/RAC1-mediated cell motility pathways. Our findings showed that selective CB agonists and their combination suppressed breast cancer characteristics in MDA-MB-231 cells. The exposure of CB agonists also altered the proteomic profile of MDA-MB-231, which could lead to cell proliferation and motility suppression.

Inhibitors of the mTOR signaling pathway can play an important role in breast cancer immunopathogenesis.

This study explores the critical role of inhibitors targeting the mammalian target of rapamycin (mTOR) signaling pathway in breast cancer research and treatment. The mTOR pathway, a central regulator of cellular processes, has been identified as a crucial factor in the development and progression of breast cancer. The essay explains the complex molecular mechanisms through which mTOR inhibitors, such as rapamycin and its analogs, exert their anticancer effects. These inhibitors can stop cell growth, proliferation, and survival in breast cancer cells by blocking critical signaling pathways within the mTOR pathway. Furthermore, the essay discusses the implications of using mTOR inhibitors as a comprehensive therapeutic strategy. It emphasizes the potential benefits of combining mTOR inhibitors with other treatment approaches to enhance the effectiveness of breast cancer treatment. The evolving landscape of breast cancer research underscores the significance of mTOR as a therapeutic target and highlights ongoing efforts to improve and optimize mTOR inhibitors for clinical use. In conclusion, the essay asserts that inhibitors of the mTOR signaling pathway offer a promising approach in the fight against breast cancer. These inhibitors provide a focused and effective intervention targeting specific dysregulations within the mTOR pathway. As research advances, the integration of mTOR inhibitors into customized combination therapies holds excellent potential for shaping a more effective and personalized approach to breast cancer treatment, ultimately leading to improved outcomes for individuals affected by this complex and diverse disease.

Pan-cancer Analysis Combined with Experiments Deciphers PHB Regulation for Breast Cancer Cell Survival and Predicts Biomarker Function.

Breast carcinoma has become the leading fatal disease among women. The location of prohibitin in the chromosome is close to the breast cancer susceptibility gene 1 (BRCA1). Accumulated research reported that prohibitin could interact with a variety of transcription factors and cell cycle-regulating proteins. This present study aims to comprehensively explore and reveal the biological functions of prohibitin on breast cancer via The Cancer Genome Atlas (TCGA) and validation experiment in vitro. Exploring the expression level of prohibitin across 27 tumors based on the TGGA database by bioinformatic methods and its relationship with tumor immune infiltration. Furthermore, we thus analyzed the biological roles of prohibitin on human breast cancer cell line MCF- 7 with pEGFP-prohibitin overexpression plasmid by western blotting and transwell-assay. Firstly, we found prohibitin is overexpressed in most tumors based on The Cancer Genome Atlas database, and the negative relationships between prohibitin and tumors infiltrating lymphocytes including B lymphocyte, CD4 T lymphocyte, CD8 T lymphocyte, Neutrophil, Macrophage and Dendritic, and its significant correlation with the prognosis of human cancer. In vitro, expression not only inhibited cell viability and invasive abilities but also increased the apoptosis percentage of cells with a decreased percentage of the S phase and an increased G2 phase. The reduction of Bcl-2 was observed when prohibitin was upregulated, although the expression of E2F-1 did not change. Although prohibitin is over-expressed in various cancer types, it functions as an important tumor suppressor that may suppress breast cancer cell proliferation and the invasive ability of MCF-7 by influencing its DNA synthesis and promoting cell apoptosis. All these may be likely associated with P53, erbB-2, and Bcl-2.

The Influence of Physical Training on Breast Cancer: The Role of Exercise-Induced Myokines in Regulating Breast Cancer Cell Growth and Survival.

The beneficial impact of physical training in lowering cancer risk is well known. However, the precise mechanisms linking physical training and cancer are not fully understood. Skeletal muscle releases various myokines that seem to possess a direct anti-tumor effect. Although breast cancer (BC) is the prevalent form of cancer among women on a global scale, only limited data are available about the secretion of myokines following exercise in patients with BC. To study the effects of exercise on BC, the blood samples of patients with varied stages of BC were analyzed after 12 weeks of resistance training with whole-body electromyostimulation (WB-EMS). Following the training period, we observed that resistance training helps these patients to improve their physical characteristics and performance function by increasing skeletal muscle mass and strengthening their hand grip. Notably, the patient's serum was found to inhibit the growth and promote the apoptosis of BC cells in vitro. Moreover, the conditioned medium collected from in vitro stimulated human myotubes using electric pulse stimulation (EPS), an in vitro simulation of WB-EMS training, induced the cell death of BC cells. These results highlighted the direct cancer-protective effects of activated skeletal muscle. In line with our observed effects of serum from exercise-trained pancreatic and prostate cancer patients, the growth of BC cells was notably inhibited when supplemented directly with recombinant myokines C-X-C motif ligand 1 (CXCL1), Interleukin 10 (IL10), and C-C motif chemokine ligand 4 (CCL4). Notably, treatment with these myokines also increased the expression of caspase 3/7 (Casp3/7), resulting in enhanced BC cell death. Our data strongly suggest that physical exercise has a positive impact on skeletal muscle mass and hand grip strength in BC patients, along with a significant anti-tumor effect in BC cells. This shows promising potential for considering sports and physical training as supportive therapies for achieving more impactful cancer treatment.

B-328 A Novel Pathway of Akt-Dependent PARP1 Activation Through the Nuclear Localization of EPRS1

Abstract Background Glutamyl-prolyl-tRNA synthetase (EPRS1) is the only bifunctional aminoacyl-tRNA synthetase (aaRS) and is essential for interpreting the genetic code. EPRS1, along with seven other aaRSs, forms the multi-tRNA synthetase complex (MSC). EPRS1 consists of two catalytic domains, GluRS and ProRS, connected by a linker region. Several aaRSs within the MSC, including EPRS1, can dissociate from the MSC in response to specific stimuli. This dissociation enables non-canonical activities distinct from their primary role in protein synthesis. Breast cancer cells harboring a loss-of-function mutation in phosphatase and tensin homolog (PTEN) are known to have more activity in the serine/threonine kinase Akt. Poly-(ADP)-ribose polymerase 1 (PARP1), plays a vital role in DNA damage repair (DDR). PARP1 deposits one or more ADP-Ribose moieties onto damaged DNA or other proteins in a process referred to as PARylation. We hope to connect Akt activation and PARP1 activity through the nuclear localization and noncanonical function of EPRS1. We hypothesize, that when Akt is activated, either through the loss of PTEN function or through stimuli such as heat shock or H2O2 treatment, will stimulate the nuclear localization of EPRS1 and modulate PARP1 activity. Methods To test our hypothesis, we evaluate Akt activation, EPRS1 localization, and PARP1 activity. Using pharmacological activators and inhibitors of Akt, we test if inhibitors and activators alone are sufficient to cause the nuclear localization of EPRS1. Biochemically, we isolate nuclear and cytosolic fractions used in various western blot analysis. We use a variety of assays for PARP1 activity and DDR that include immobilized histones, calculating IC50s of PARP1 inhibitors, comet assay, and confocal microscopy. To ascertain the connection between PARP1 and EPRS1 we use LC-MS/MS analysis and immunoprecipitation. Results We show, in both patient-derived and cultured breast cancer cells, elevated levels of EPRS1 not only in the cytoplasm, but also within the nucleus. We find that nuclear localization EPRS1 is facilitated by a nuclear localization sequence (NLS) located within the linker region of the protein. Breast cancer cells harboring a loss-of-function in PTEN exhibit higher levels of EPRS1 in the nucleus compared to PTEN-positive cells. In EPRS1 knockdown cells, there is diminished expression of multiple tumor-related transcription factors, DNA-damage repair, tumor cell survival, and PARP1 auto-PARylation. We demonstrate that nuclear EPRS1 binds to and shares an interactome with PARP1. Conclusions EPRS1-mediated regulation of PARP1 activity provides a new mechanistic link between PTEN loss in breast cancer cells, PARP1 activation, and cell survival and tumor growth. Targeting the non-canonical activity of EPRS1, without inhibiting canonical tRNA ligase activity, might provide a new therapeutic approach in breast and other forms of cancer, potentially supplementing existing cancer therapeutics.

IDH2 Inhibitors Gain a Wildcard Status in the Cancer Therapeutics Competition.

The metabolic reprogramming characteristic of cancer cells, including the Warburg effect, has long been recognized as a hallmark of malignancy. This commentary explores three recent investigations focusing on the role of wild-type IDH2 in cancer and immune cell function. The first publication identifies wild-type IDH2 as a crucial factor in the survival of triple-negative breast cancer (TNBC) cells, with its inhibition leading to disrupted energy metabolism, reduced tumor growth, and enhanced apoptosis. The second analysis examines the role of IDH2 in CD8+ T cells, revealing that its inhibition promotes the differentiation of memory T cells, thereby enhancing the efficacy of cell-based immunotherapies like CAR T cells. A third investigation supports these findings, demonstrating that IDH2 inhibition in CAR T cells reduces exhaustion, enhances memory T cell formation, and improves anti-tumor efficacy. Collectively, these reports highlight wild-type IDH2 as a promising therapeutic target, with potential applications as a two-edged sword in both cancer treatment and immunotherapy. The development of specific wild-type IDH2 inhibitors could offer new avenues for therapy, particularly in tumors reliant on IDH2 activity as well as in enhancing the effectiveness of CAR T cell therapies.

New Mitochondria-Targeted Fisetin Derivative Compromises Mitophagy and Limits Survival of Drug-Induced Senescent Breast Cancer Cells.

Mitochondria are considered as promising targets for cancer treatment. In the present study, triphenyl phosphonium cationic group-conjugated fisetin (mito-fisetin) was synthesized, and its anticancer activity was investigated in several cellular models of estrogen receptor (ER)-positive breast cancer in vitro and in vivo in proliferating and tamoxifen-promoted senescent states. Mito-fisetin, when used at low micromolar concentrations, stimulated the dissipation of mitochondrial membrane potential and oxidative stress, and affected mitochondrial function, resulting in apoptosis induction in senescent breast cancer cells. Mito-fisetin-mediated cytotoxicity was due to increased levels of phosphorylated AMPK, decreased levels of AKT and HSP90, and impaired mitophagic response, as judged by the analysis of the markers of mitophagosome formation. Senescent breast cancer cells were found to be more sensitive to mito-fisetin treatment than proliferating ones. We postulate that mitochondrial targeting in the case of fisetin may be considered as a promising anticancer and senotherapeutic strategy to eliminate drug-resistant senescent breast cancer cells.

Effects of pleiotrophin (PTN) on the FAK inhibitor Y15 in breast cancer cells

Overexpression of PTN (Pleiotrophin) in breast cancer cells stimulates breast cell proliferation and anti-apoptosis via the FAK/Src signaling pathway.1,2,4,5-Benzenetetramine tetrahydrochloride (C6H14Cl4N4) known as Y15 is an inhibitor that specifically blocks phosphorylation of Y397-FAK and total FAK phosphorylation. The exogenous PTN protein was induced to be expressed by a prokaryotic expression strain. The addition of PTN protein decreased the sensitivity of breast cancer cells to Y15, as shown by both MTT and flow cytometry assays. Breast cancer cells transfected with sh-RNA knockdown PTN were analyzed by real-time fluorescence quantitative PCR reaction (RT-PCR) and protein immunoblotting 24 h after transfection. MTT assay data showed a significant increase in the IC50 value of Y15 against breast cancer cells in the presence of PTN protein. Flow cytometry data confirmed the dose-dependent anti-apoptotic effect of PTN protein in Y15-treated breast cancer cells. After transfection with sh-RNA, Y15 further inhibited the FAK pathway, greatly reducing cell survival and promoting apoptosis. Western blotting analysis showed that knockdown of PTN protein with sh-RNA resulted in increased apoptosis and elevated levels of apoptotic proteins, such as cleaved PARP and cleaved caspase-3 in Y15-induced breast cancer cells. Finally, it was hypothesized that PTN and Y15 were associated with a significant increase in the IC50 value of PTN and Y15 in breast cancer cells by western blotting analysis. It was hypothesized that PTN and Y15 regulate the proliferation and apoptosis of breast cancer cells through the AKT/PI3K pathway. The results demonstrated that PTN affects the sensitivity of the kinase inhibitor Y15, and PTN silencing and Y15 may inhibit the survival of breast cancer cells through the AKT/PI3K pathway, which lays the foundation for subsequent in-depth research on the clinical treatment of breast cancer.

Three-dimensional analysis of mitochondria in a patient-derived xenograft model of triple negative breast cancer reveals mitochondrial network remodeling following chemotherapy treatments.

Mitochondria are hubs of metabolism and signaling and play an important role in tumorigenesis, therapeutic resistance, and metastasis in many cancer types. Various laboratory models of cancer demonstrate the extraordinary dynamics of mitochondrial structure, but little is known about the role of mitochondrial structure in resistance to anticancer therapy. We previously demonstrated the importance of mitochondrial structure and oxidative phosphorylation in the survival of chemotherapy-refractory triple negative breast cancer (TNBC) cells. As TNBC is a highly aggressive breast cancer subtype with few targeted therapy options, conventional chemotherapies remain the backbone of early TNBC treatment. Unfortunately, approximately 45% of TNBC patients retain substantial residual tumor burden following chemotherapy, associated with abysmal prognoses. Using an orthotopic patient-derived xenograft mouse model of human TNBC, we compared mitochondrial structures between treatment-naïve tumors and residual tumors after conventional chemotherapeutics were administered singly or in combination. We reconstructed 1,750 mitochondria in three dimensions from serial block-face scanning electron micrographs, providing unprecedented insights into the complexity and intra-tumoral heterogeneity of mitochondria in TNBC. Following exposure to carboplatin or docetaxel given individually, residual tumor mitochondria exhibited significant increases in mitochondrial complexity index, area, volume, perimeter, width, and length relative to treatment-naïve tumor mitochondria. In contrast, residual tumors exposed to those chemotherapies given in combination exhibited diminished mitochondrial structure changes. Further, we document extensive intra-tumoral heterogeneity of mitochondrial structure, especially prior to chemotherapeutic exposure. These results highlight the potential for structure-based monitoring of chemotherapeutic responses and reveal potential molecular mechanisms that underlie chemotherapeutic resistance in TNBC.

Bag-1-mediated HSF1 phosphorylation regulates expression of heat shock proteins in breast cancer cells.

According to the World Health Organization in 2022, 2.3 million women were diagnosed with breast cancer. Investigating the interaction networks between Bcl-2-associated athanogene (Bag)-1 and other chaperone proteins may further the current understanding of the regulation of protein homeostasis in breast cancer cells and contribute to the development of treatment options. The present study aimed to determine the interactions between Bag-1 and heat shock proteins (HSPs); namely, HSP90, HSP70 and HSP27, to elucidate their role in promoting heat shock factor-1 (HSF1)-dependent survival of breast cancer cells. HER2-negative (MCF-7) and HER2-positive (BT-474) cell lines were used to examine the impact of Bag-1 expression on HSF1 and HSPs. We demonstrated that Bag-1 overexpression promoted HER2 expression in breast cancer cells, thereby resulting in the concurrent constitutive activation of the HSF1-HSP axis. The activation of HSP results in the stabilization of several tumor-promoting HSP clients such as AKT, mTOR and HSF1 itself, which substantially accelerates tumor development. Our results suggest that Bag-1 can modulate the chaperone activity of HSPs, such as HSP27, by directly or indirectly regulating the phosphorylation of HSF1. This modulation of chaperone activity can influence the activation of genes involved in cellular homeostasis, thereby protecting cells against stress.

Decoding the Role of Insulin-like Growth Factor 1 and Its Isoforms in Breast Cancer.

Insulin-like Growth Factor-1 (IGF-1) is a crucial mitogenic factor with important functions in the mammary gland, mainly through its interaction with the IGF-1 receptor (IGF-1R). This interaction activates a complex signaling network that promotes cell proliferation, epithelial to mesenchymal transition (EMT) and inhibits apoptosis. Despite extensive research, the precise molecular pathways and intracellular mechanisms activated by IGF-1, in cancer, remain poorly understood. Recent evidence highlights the essential roles of IGF-1 and its isoforms in breast cancer (BC) development, progression, and metastasis. The peptides that define the IGF-1 isoforms-IGF-1Ea, IGF-1Eb, and IGF-1Ec-act as key points of convergence for various signaling pathways that influence the growth, metastasis and survival of BC cells. The aim of this review is to provide a detailed exami-nation of the role of the mature IGF-1 and its isoforms in BC biology and their potential use as possible therapeutical targets.

Advancements in targeting tumor suppressor genes (p53 and BRCA 1/2) in breast cancer therapy.

Globally, among numerous cancer subtypes, breast cancer (BC) is one of the mostprevalent forms of cancer affecting the female population. A female's family history significantly increases her risk of developing breast cancer. BC is caused by aberrant breast cells that proliferate and develop into tumors. It is estimated that 5-10% of breastcarcinomas are inherited and involve genetic mutations that ensure the survival and prognosis of breast cancer cells. The most common genetic variations are responsible for hereditary breast cancer but are not limited to p53, BRCA1, and BRCA2. BRCA1 and BRCA2 are involved in genomic recombination, cell cycle monitoring, programmed cell death, and transcriptional regulation. When BRCA1 and 2 genetic variations are present in breast carcinoma, p53 irregularities become more prevalent. Both BRCA1/2 and p53 genes are involved in cell cycle monitoring. The present article discusses the current status of breast cancer research, spotlighting the tumor suppressor genes (BRCA1/2 and p53) along with structural activity relationship studies, FDA-approved drugs, and several therapy modalities for treating BC. Breast cancer drugs, accessible today in the market, have different side effects includinganemia, pneumonitis, nausea, lethargy, and vomiting. Thus, the development of novel p53 and BRCA1/2 inhibitors with minimal possible side effects is crucial. We have covered compounds that have been examined subsequently (2020 onwards) in this overview which may be utilized as lead compounds. Further, we have covered mechanistic pathways to showcase the critical druggable targets and clinical and post-clinical drugs targeting them for their utility in BC.

MANF facilitates breast cancer cell survival under glucose-starvation conditions via prkn-mediated mitophagy regulation

ABSTRACT During tumor expansion, breast cancer (BC) cells often experience reactive oxygen species accumulation and mitochondrial damage because of glucose shortage. However, the mechanism by which BC cells deal with the glucose-shortage-induced oxidative stress remains unclear. Here, we showed that MANF (mesencephalic astrocyte derived neurotrophic factor)-mediated mitophagy facilitates BC cell survival under glucose-starvation conditions. MANF-mediated mitophagy also promotes fatty acid oxidation in glucose-starved BC cells. Moreover, during glucose starvation, SENP1-mediated de-SUMOylation of MANF increases cytoplasmic MANF expression through the inhibition of MANF’s nuclear translocation and hence renders mitochondrial distribution of MANF. MANF mediates mitophagy by binding to PRKN (parkin RBR E3 ubiquitin protein ligase), a key mitophagy regulator, in the mitochondria. Under conditions of glucose starvation, protein oxidation inhibits PRKN activity; nevertheless, the CXXC motif of MANF alleviates protein oxidation in RING II-domain of PRKN and restores its E3 ligase activity. Furthermore, MANF-PRKN interactions are essential for BC tumor growth and metastasis. High MANF expression predicts poor outcomes in patients with BC. Our results highlight the prosurvival role of MANF-mediated mitophagy in BC cells during glucose starvation, suggesting MANF as a potential therapeutic target.

Endocrine therapy for early breast cancer in the era of oral selective estrogen receptor degraders: challenges and future perspectives.

Growth and survival of hormone receptor positive breast cancer cells are dependent on circulating hormones (e.g., estrogen and progesterone). Endocrine therapy improved outcomes in both early and advanced hormone receptor positive breast cancer. These treatments include drugs with different mechanisms of action, namely selective estrogen receptor modulators (SERM), aromatase inhibitors, and selective estrogen receptor degraders (SERDs). SERDs represent estrogen receptor antagonists, favoring its degradation and thus interfering with proliferation genes transcription and activation. Fulvestrant is the first approved SERD, administered intramuscularly for treating advanced breast cancer. Oral SERDs have been tested to overcome the limitation of the intramuscular administration, and to increase SERD bioavailability. Recently, an oral SERD, Elacestrant, has been approved by the Food and Drug Administration (FDA) for patients carrying an ESR1 mutation. In fact, oral SERDs seem to be effective in tumors harboring ESR1 mutations, a well known mechanism of resistance to endocrine therapy (especially aromatase inhibitors). More recently, oral SERDs have been tested in patients with early hormone receptor positive breast cancer, although their impact on survival and in this curative setting compared to standard endocrine therapy still needs to be elucidated. The best timing and duration of SERD administration and specific biomarkers in (neo)adjuvant setting remain largely unknown.

The mevalonate pathway contributes to breast primary tumorigenesis and lung metastasis.

The mevalonate pathway plays an important role in breast cancer and other tumor types. However, many issues remain obscure as yet regarding its mechanism of regulation and action. In the present study, we report that the expression of mevalonate pathway enzymes is mediated by theRHO guanosine nucleotide exchange factors VAV2 and VAV3 in a RAC1- and sterol regulatory element-binding factor (SREBF)-dependent manner in breast cancer cells. Furthermore, in vivo tumorigenesis experiments indicated that the two most upstream steps of this metabolic pathway [3-hydroxy-3-methylglutaryl-coenzyme A synthase 1 (HMGCS1) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR)] are important for primary tumorigenesis, angiogenesis, and cell survival in breast cancer cells. HMGCR, but not HMGCS1, is also important for the extravasation and subsequent fitness of breast cancer cells in the lung parenchyma. Genome-wide expression analyses revealed that HMGCR influences the expression of gene signatures linked to proliferation, metabolism, and immune responses. The HMGCR-regulated gene signature predicts long-term tumor recurrence but not metastasis in cohorts of nonsegregated and chemotherapy-resistant breast cancer patients. These results reveal a hitherto unknown, VAV-catalysis-dependent mechanism involved in the regulation of the mevalonate pathway in breast cancer cells. They also identify specific mevalonate-pathway-dependent processes that contribute to the malignant features of breast cancer cells.

ERα Coregulator TRIM28 Promotes Breast Cancer Progression by Activating the AKT/GSK3β Pathway.

Estrogen receptor α (ERα) promotes the growth and survival of ER-positive breast cancer (BC) cells. ER regulates ER expression target genes by directly binding to specific estrogen response elements, upon activation by estrogens. In this study, 106 proteins interacting with endogenous chromatin-bound ER in a BC cell line MCF7 were identified using the RIME method. The interactome data showed that the tripartite motif containing 28 (TRIM28) is the most significantly enriched ER-associated protein. This study provides evidence that TRIM28 expression improves ER transcriptional activity and promotes the BC cells proliferation, migration, and invasion of BC cells. The high expression of TRIM28 is associated with poor clinical outcomes in patients with ER-positive BC. Mechanistic experiments indicate that TRIM28 expression activates the AKT/GSK3β pathway. To conclude, TRIM28 acts as a regulatory protein of ER and AKT signaling; therefore, it can be a target for the therapeutic interventions of BC.

CHD1L Regulates Cell Survival in Breast Cancer and Its Inhibition by OTI-611 Impedes the DNA Damage Response and Induces PARthanatos.

The Chromodomain helicase DNA-binding protein 1-like (CHD1L) is a nucleosome remodeling enzyme, which plays a key role in chromatin relaxation during the DNA damage response. Genome editing has shown that deletion of CHD1L sensitizes cells to PARPi, but the effect of its pharmacological inhibition has not been defined. Triple-negative breast cancer SUM149PT, HCC1937, and MDA-MB-231 cells were used to assess the mechanism of action of the CHD1Li OTI-611. Cytotoxicity as a single agent or in combination with standard-of-care treatments was assessed in tumor organoids. Immunofluorescence was used to assess the translocation of PAR and AIF to the cytoplasm or the nucleus and to study markers of DNA damage or apoptosis. Trapping of PARP1/2 or CHD1L onto chromatin was also assessed by in situ subcellular fractionation and immunofluorescence and validated by Western blot. We show that the inhibition of CHD1L's ATPase activity by OTI-611 is cytotoxic to triple-negative breast cancer tumor organoids and synergizes with PARPi and chemotherapy independently of the BRCA mutation status. The inhibition of the remodeling function blocks the phosphorylation of H2AX, traps CHD1L on chromatin, and leaves PAR chains on PARP1/2 open for hydrolysis. PAR hydrolysis traps PARP1/2 at DNA damage sites and mediates PAR translocation to the cytoplasm, release of AIF from the mitochondria, and induction of PARthanatos. The targeted inhibition of CHD1L's oncogenic function by OTI-611 signifies an innovative therapeutic strategy for breast cancer and other cancers. This approach capitalizes on CHD1L-mediated DNA repair and cell survival vulnerabilities, thereby creating synergy with standard-of-care therapies.

AKT-dependent nuclear localization of EPRS1 activates PARP1 in breast cancer cells

Glutamyl-prolyl-tRNA synthetase (EPRS1) is a bifunctional aminoacyl-tRNA-synthetase (aaRS) essential for decoding the genetic code. EPRS1 resides, with seven other aaRSs and three noncatalytic proteins, in the cytoplasmic multi-tRNA synthetase complex (MSC). Multiple MSC-resident aaRSs, including EPRS1, exhibit stimulus-dependent release from the MSC to perform noncanonical activities distinct from their primary function in protein synthesis. Here, we show EPRS1 is present in both cytoplasm and nucleus of breast cancer cells with constitutively low phosphatase and tensin homolog (PTEN) expression. EPRS1 is primarily cytosolic in PTEN-expressing cells, but chemical or genetic inhibition of PTEN, or chemical or stress-mediated activation of its target, AKT, induces EPRS1 nuclear localization. Likewise, preferential nuclear localization of EPRS1 was observed in invasive ductal carcinoma that were also P-Ser473-AKT+. EPRS1 nuclear transport requires a nuclear localization signal (NLS) within the linker region that joins the catalytic glutamyl-tRNA synthetase and prolyl-tRNA synthetase domains. Nuclear EPRS1 interacts with poly(ADP-ribose) polymerase 1 (PARP1), a DNA-damage sensor that directs poly(ADP-ribosyl)ation (PARylation) of proteins. EPRS1 is a critical regulator of PARP1 activity as shown by markedly reduced ADP-ribosylation in EPRS1 knockdown cells. Moreover, EPRS1 and PARP1 knockdown comparably alter the expression of multiple tumor-related genes, inhibit DNA-damage repair, reduce tumor cell survival, and diminish tumor sphere formation by breast cancer cells. EPRS1-mediated regulation of PARP1 activity provides a mechanistic link between PTEN loss in breast cancer cells, PARP1 activation, and cell survival and tumor growth. Targeting the noncanonical activity of EPRS1, without inhibiting canonical tRNA ligase activity, provides a therapeutic approach potentially supplementing existing PARP1 inhibitors.

The LDHC-STAT3 Signaling Network Is a Key Regulator of Basal-like Breast Cancer Cell Survival.

Breast cancer treatment has evolved drastically with the addition of immunotherapy and novel targeted drugs to the current treatment options. However, achieving long-term responses with minimal adverse events remains challenging. Cancer testis antigens (CTAs) offer novel opportunities for drug development thanks to their tumor specificity, immunogenicity, pro-tumorigenic functions, and negative prognostic connotations. We previously reported that lactate dehydrogenase C (LDHC) plays a key role in regulating genomic stability and that targeting LDHC significantly improved treatment response to DNA damage response drugs in breast cancer. Here, we explored the molecular mechanisms associated with LDHC silencing in two basal-like breast cancer cell lines, MDA-MB-468 and BT-549, and a Her2-enriched breast cancer cell line, HCC-1954. Transcriptomic analyses identified the cell line-dependent differential activation of the pro-survival STAT3 pathway following LDHC depletion. While LDHC silencing significantly compromised cell survival in basal-like breast cancer cells in conjunction with a downregulation of STAT3 signaling, the opposite effect was observed in Her2-enriched breast cancer cells, which demonstrated the enhanced activation of the pro-survival STAT3 signaling pathway. The inhibition of STAT3 not only reversed the unfavorable effect of LDHC silencing in the Her2-enriched cancer cells but also demonstrated significant anti-cancer activity when used as a single agent. Our findings suggest that the LDHC-STAT3 signaling axis plays a role in regulating breast tumor cell survival in a subtype-dependent manner. Thus, LDHC-targeted therapy could be a viable therapeutic approach for a subset of breast cancer patients, particularly patients with basal-like breast cancer, whereas patients carrying Her2-enriched tumors may likely benefit more from monotherapy with STAT3 inhibitors.