Molecular mechanisms underlying the effects of the small molecule AMC-04 on apoptosis: Roles of the activating transcription factor 4-C/EBP homologous protein-death receptor 5 pathway

A novel bystander effect in tamoxifen treatment: PPIB derived from ER+ cells attenuates ER- cells via endoplasmic reticulum stress-induced apoptosis

Tamoxifen (TAM) is the frontline therapy for estrogen receptor-positive (ER+) breast cancer in premenopausal women that interrupts ER signaling. As tumors with elevated heterogeneity, amounts of ER-negative (ER-) cells are present in ER+ breast cancer that cannot be directly killed by TAM. Despite complete remissions have been achieved in clinical practice, the mechanism underlying the elimination of ER- cells during TAM treatment remains an open issue. Herein, we deciphered the elimination of ER- cells in TAM treatment from the perspective of the bystander effect. Markable reductions were observed in tumorigenesis of ER- breast cancer cells by applying both supernatants from TAM-treated ER+ cells and a transwell co-culture system, validating the presence of a TAM-induced bystander effect. The major antitumor protein derived from ER+ cells, peptidyl-prolyl cis-trans isomerase B (PPIB), is the mediator of the TAM-induced bystander effect identified by quantitative proteomics. The attenuation of ER- cells was attributed to activated BiP/eIF2α/CHOP axis and promoted endoplasmic reticulum stress (ERS)-induced apoptosis, which can also be triggered by PPIB independently. Altogether, our study revealed a novel TAM-induced bystander effect in TAM treatment of ER+ breast cancer, raising the possibility of developing PPIB as a synergistic antitumor agent or even substitute endocrine therapy.

Metformin combined with glucose starvation synergistically suppress triple-negative breast cancer by enhanced unfolded protein response

Metformin (MET) is a well-documented drug used in the treatment of type II diabetes. Recent studies have revealed its potential anti-tumor effects in various types of cancer. However, the dosage of MET required to exhibit anti-tumor activity is considerably higher than the clinically recommended dosage. In this study, we investigated the synergistical anti-tumor effect of glucose deprivation and MET in MDA-MB-231 cells, which represents a triple-negative breast cancer subtype (TNBC). Our findings demonstrate that glucose deprivation significantly enhances the anti-tumor activity of MET by reducing cell proliferation and increasing cell apoptosis. RNA-seq was performed to identify the key molecules involved in this process. Our results indicate that unfolded protein response of endoplasmic reticulum (UPRER) was significantly activated upon glucose starvation combining with MET compared to glucose starvation alone. Notably, the combined treatment significantly activated UPRER signaling pathway through ATF4/ATF3/CHOP axis, due to enhanced UPRER stress. In conclusion, our study suggests that the synergistic effects of MET and glucose deprivation suppress cell proliferation in TNBC by activating pro-apoptotic molecules through UPRER stress. These findings have potential implications for the anti-tumor application of MET in TNBC.

A new cyclin-dependent kinase-9 inhibitor A09-003 induces apoptosis in acute myeloid leukemia cells with reduction of myeloid cell leukemia sequence-1 protein

Acute myeloid leukemia (AML) is the most common type of hematological disease in adults, and has a very poor outcome [1]. Based on its wide range of efficacy in AML models, a small-molecule inhibitor of the anti-apoptotic protein BCL-2, venetoclax (ABT-199/GDC-0199), was developed for clinical trials. However, venetoclax showed limited monotherapy activity [2]. The overexpression of myeloid cell leukemia sequence-1 protein (Mcl-1)-due to mutations in Fms-like tyrosine kinase 3 internal tandem duplication (FLT-3 ITD)-was considered to be the main reason for low efficacy of venetoclax in clinical trials [3-5]. To achieve venetoclax sensitization in AML, targeting CDK-9 with venetoclax is a promising therapeutic strategy. In this study, we developed A09-003 as a potent inhibitor of CDK-9, with an IC50 value of 16 nM. A09-003 inhibited cell proliferation in various leukemia cell lines. In particular, the proliferation inhibitory effect of A09-003 was most potent in MV4-11 and Molm-14 cells, harboring the FLT-3 ITD mutation with a high expression profile of Mcl-1. Marker analysis revealed that A09-003 reduced CDK-9 phosphorylation and reduced RNA polymerase II activity with decreased Mcl-1 expression. Finally, combining A09-003 with venetoclax induced apoptotic cell death in a synergistic manner. In summary, this study shows the potential of A09-003 in AML therapy.

CHOP promotes coelomocyte apoptosis through p38-MAPK pathway in Vibrio splendidus-challenged sea cucumber Apostichopus japonicus

CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) belongs to the C/EBP family of transcription factors that has been proven to regulate apoptosis in many vertebrate species. However, the functional role of CHOP in invertebrates is largely unknown. In this paper, the open reading frame of CHOP was cloned and characterized in the sea cucumber Apostichopus japonicus (AjCHOP). The deuced amino acid of AjCHOP shared a conserved RTP801_C domain from 63 to 171 aa. Phylogenetic analysis indicated that AjCHOP clustered with CHOPs from Lytechinus variegatus and Strongylocentrotus purpuratus. To confirm the immune function of AjCHOP, the time-course expression profiles of AjCHOP were investigated, and the findings revealed AjCHOP was significantly induced in coelomocytes at mRNA and protein levels after Vibro splendidus challenge. Furthermore, knockdown of AjCHOP in coelomocyes by siRNA transfection significantly decreased the apoptosis level induced by V. splendidus. Mechanically, AjCHOP-mediated apoptosis was dependent on the activation of p38-MAPK pathway but not JNK/ERK-MAPK. Overall, our results supported that V. splendidus triggers apoptosis among the coelomocytes, whereas AjCHOP mediates through the p38-MAPK pathway in A. japonicus.

Improved Sleep, Memory, and Cellular Pathological Features of Tauopathy, Including the NLRP3 Inflammasome, after Chronic Administration of Trazodone in rTg4510 Mice

Several cellular pathways contribute to neurodegenerative tauopathy-related disorders. Microglial activation, a major component of neuroinflammation, is an early pathologic hallmark that correlates with cognitive decline, while the unfolded protein response (UPR) contributes to synaptic pathology. Sleep disturbances are prevalent in tauopathies and may also contribute to disease progression. Few studies have investigated whether manipulations of sleep influence cellular pathologic and behavioral features of tauopathy. We investigated whether trazodone, a licensed antidepressant with hypnotic efficacy in dementia, can reduce disease-related cellular pathways and improve memory and sleep in male rTg4510 mice with a tauopathy-like phenotype. In a 9 week dosing regimen, trazodone decreased microglial NLRP3 inflammasome expression and phosphorylated p38 mitogen-activated protein kinase levels, which correlated with the NLRP3 inflammasome, the UPR effector ATF4, and total tau levels. Trazodone reduced theta oscillations during rapid eye movement (REM) sleep and enhanced REM sleep duration. Olfactory memory transiently improved, and memory performance correlated with REM sleep duration and theta oscillations. These findings on the effects of trazodone on the NLRP3 inflammasome, the unfolded protein response and behavioral hallmarks of dementia warrant further studies on the therapeutic value of sleep-modulating compounds for tauopathies.SIGNIFICANCE STATEMENT Dementia and associated behavioral symptoms such as memory loss and sleep disturbance are debilitating. Identifying treatments that alleviate symptoms and concurrently target cellular pathways contributing to disease progression is paramount for the patients and their caregivers. Here we show that a chronic treatment with trazodone, an antidepressant with positive effects on sleep, has beneficial effects on several cellular pathways contributing to neuroinflammation and tau pathology, in tauopathy-like rTg4510 mice. Trazodone also improved rapid eye movement (REM) sleep, the slowing of brain oscillations, and olfactory memory disturbances, which are all early symptoms observed in Alzheimer's disease. Thus, trazodone and compounds with REM sleep-promoting properties may represent a promising treatment approach to reduce the early symptoms of tauopathy and slow down disease progression.

Inhibition of histone demethylase KDM4 by ML324 induces apoptosis through the unfolded protein response and Bim upregulation in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is an extremely aggressive malignancy that ranks as the sixth-leading cause of cancer-associated death worldwide. Recently, various epigenetic mechanisms including gene methylation were reported to be potential next era HCC therapeutics and biomarkers. Although inhibition of epigenetic enzymes including histone lysine demethylase 4 (KDM4) enhanced cell death in HCC cells, the detailed mechanism of cell death machinery is poorly understood. In this study, we found that ML324, a small molecule KDM4-specific inhibitor, induced the death of HCC cells in a general cell culture system and 3D spheroid culture with increased cleavage of caspase-3. Mechanistically, we identified that unfolded protein responses (UPR) were involved in ML324-induced HCC cell death. Incubation of HCC cells with ML324 upregulated death receptor 5 (DR5) expression through the activation transcription factor 3 (ATF3)-C/EBP homologous protein (CHOP)-dependent pathway. Moreover, we identified BIM protein as a mediator of ML324-induced apoptosis using CRISPR/Cas9 knockout analysis. We showed that the loss of Bim suppressed ML324-induced apoptosis by flow cytometry analysis, colony formation assay, and caspase-3 activation assay. Interestingly, BIM protein expression by ML324 was regulated by ATF3, CHOP, and DR5 which are factors involved in UPR. Specifically, we confirmed the regulating roles of KDM4E in Bim and CHOP expression using a chromatin immune precipitation (ChIP) assay. Physical binding of KDM4E to Bim and CHOP promoters decreased the response to ML324. Our findings suggest that KDM4 inhibition is a potent anti-tumor therapeutic strategy for human HCC, and further studies of UPR-induced apoptosis and the associated epigenetic functional mechanisms may lead to the discovery of novel target for future cancer therapy.

Melatonin relieves heat-induced spermatocyte apoptosis in mouse testes by inhibition of ATF6 and PERK signaling pathways

Normal spermatogenic processes require the scrotal temperature to be lower than that of the body as excessive heat affects spermatogenesis in the testes, reduces sperm quality and quantity, and even causes infertility. Endoplasmic reticulum stress (ERS) is a crucial factor in many pathologies. Although several studies have linked ERS to heat stress, researchers have not yet determined which ERS signaling pathways contribute to heat-induced testicular damage. Melatonin activates antioxidant enzymes, scavenges free radicals, and protects the testes from inflammation; however, few studies have reported on the influence of melatonin on heat-induced testicular damage. Using a murine model of testicular hyperthermia, we observed that heat stress causes both ERS and apoptosis in the testes, especially in the spermatocytes. These observations were confirmed using the mouse spermatocyte cell line GC2, where the Atf6 and Perk signaling pathways were activated during heat stress. Knockout of the above genes effectively reduced spermatocyte damage caused by heat stress. Pretreatment with melatonin alleviated heat-induced apoptosis by inhibiting the Atf6 and Perk signaling pathways. This mitigation was dependent on the melatonin receptors. In vivo experiments verified that melatonin treatment relieved heat-induced testicular damage. In conclusion, our results demonstrated that ATF6 and PERK are important mediators for heat-induced apoptosis, which can be prevented by melatonin treatment. Thus, our study highlights melatonin as a potential therapeutic agent in mammals for subfertility/infertility induced by testicular hyperthermia.

LCT-3d Induces Oxidative Stress-Mediated Apoptosis by Upregulating Death Receptor 5 in Gastric Cancer Cells

Gastric cancer is a global health problem. In this study, we investigate the role of a novel Indole derivative, named LCT-3d, in inhibiting the growth of gastric cancer cells by MTT assay. The Western blotting results showed that LCT-3d modulated the mitochondrial-related proteins and Cleaved-Caspases 3/9, to induce cell apoptosis. The up-regulation of Death receptor 5 (DR5) in MGC803 cells was observed with LCT-3d treatment. Knockdown of DR5 on MGC803 cells partially reversed the LCT-3d-induced mitochondrial apoptosis. The level of Reactive Oxygen Species (ROS) in MGC803 cells was increased with LCT-3d treatment and could be blocked with the pretreatment of the ROS inhibitor N-Acetylcysteine (NAC). The results demonstrate that the elevating ROS can up-regulate the expression of DR5, resulting in apoptosis via mitochondrial pathway. Although the nuclear factor erythroid-2 related factor 2 (Nrf2) pathway served an important role in protecting gastric cancer cells against the injury of ROS, it can’t reverse LCT-3d-induced cell apoptosis. Taken together, our study showed that LCT-3d induced apoptosis via DR5-mediated mitochondrial apoptotic pathway in gastric cancer cells. LCT-3d could be a novel lead compound for development of anti-cancer activity in gastric cancer.