ATF3 regulates CDC42 transcription and influences cytoskeleton remodeling, thus inhibiting the proliferation, migration and invasion of malignant skin melanoma cells

Cutaneous malignant melanoma (CMM) is one of the most aggressive and lethal types of skin cancer. Cytoskeletal remodeling is a key factor in the progression of CMM. Previous research has shown that activating transcription factor 3 (ATF3) inhibits metastasis in bladder cancer by regulating actin cytoskeleton remodeling through gelsolin. However, whether ATF3 plays a similar role in cytoskeletal remodeling in CMM cells remains unknown. Various gene and protein expression analyses were performed using techniques such as reverse transcription quantitative PCR, western blot, immunofluorescent staining, and immunohistochemical staining. CMM viability, migration, and invasion were examined through cell counting kit-8 and transwell assays. The interactions between cell division cycle 42 (CDC42) and ATF3 were investigated using chromatin immunoprecipitation and dual-luciferase reporter assays. CDC42 was upregulated in CMM tissues and cells. Cytoskeletal remodeling of CMM cells, as well as CMM cell proliferation, migration, and invasion, were inhibited by CDC42 or ATF3. ATF3 targeted the CDC42 promoter region to regulate its transcriptional activity. ATF3 suppresses cytoskeletal remodeling in CMM cells, thereby inhibiting CMM progression and metastasis through CDC42. This research may provide a foundation for using ATF3 as a therapeutic target for CMM.

ATF family members as therapeutic targets in cancer: From mechanisms to pharmacological interventions

The activating transcription factor (ATF)/ cAMP-response element binding protein (CREB) family represents a large group of basic zone leucine zip (bZIP) transcription factors (TFs) with a variety of physiological functions, such as endoplasmic reticulum (ER) stress, amino acid stress, heat stress, oxidative stress, integrated stress response (ISR) and thus inducing cell survival or apoptosis. Interestingly, ATF family has been increasingly implicated in autophagy and ferroptosis in recent years. Thus, the ATF family is important for homeostasis and its dysregulation may promote disease progression including cancer. Current therapeutic approaches to modulate the ATF family include direct modulators, upstream modulators, post-translational modifications (PTMs) modulators. This review summarizes the structural domain and the PTMs feature of the ATF/CREB family and comprehensively explores the molecular regulatory mechanisms. On this basis, their pathways affecting proliferation, metastasis, and drug resistance in various types of cancer cells are sorted out and discussed. We then systematically summarize the status of the therapeutic applications of existing ATF family modulators and finally look forward to the future prospect of clinical applications in the treatment of tumors by modulating the ATF family.

Shikonin suppresses small cell lung cancer growth via inducing ATF3-mediated ferroptosis to promote ROS accumulation

Small cell lung cancer (SCLC) is a subtype of lung cancer with a very poor overall survival rate due to its extremely high proliferation and metastasis predilection. Shikonin is an active ingredient extracted from the roots of Lithospermum erythrorhizon, and exerts multiple anti-tumor functions in many cancers. In the present study, the role and underlying mechanism of shikonin in SCLC were investigated for the first time. We found that shikonin effectively suppressed cell proliferation, apoptosis, migration, invasion, and colony formation and slightly induced apoptosis in SCLC cells. Further experiment indicated the shikonin could also induced ferroptosis in SCLC cells. Shikonin treatment effectively suppressed the activation of ERK, the expression of ferroptosis inhibitor GPX4, and elevated the level of 4-HNE, a biomarker of ferroptosis. Both total ROS and lipid ROS were increased, while the GSH levels were decreased in SCLC cells after shikonin treatment. More importantly, our data identified that the function of shikonin was dependent on the up-regulation of ATF3 by performing rescue experiments using shRNA to silence the expression of ATF3, especially in the total and lipid ROS accumulaiton. Xenograft model was established using SBC-2 cells, and the results revealed that shikonin also significantly inhibited tumor growth by inducing ferroptosis. Finally, our data further confirmed that shikonin activated ATF3 transcription by impairing the recruitment of HDAC1 mediated by c-myc on the ATF3 promoter, and subsequently elevating of histone acetylation. Our data documented that shikonin suppressed SCLC by inducing ferroptosis in a ATF3-dependent manner. Shikonin upregulated the expression of ATF3 expression via promoting the histone acetylation by inhibiting c-myc-mediated HDAC1 binding on ATF3 promoter.

Tumor factors stimulate lysosomal degradation of tumor antigens and undermine their cross-presentation in lung cancer

Activities of dendritic cells (DCs) that present tumor antigens are often suppressed in tumors. Here we report that this suppression is induced by tumor microenvironment-derived factors, which activate the activating transcription factor-3 (ATF3) transcription factor and downregulate cholesterol 25-hydroxylase (CH25H). Loss of CH25H in antigen presenting cells isolated from human lung tumors is associated with tumor growth and lung cancer progression. Accordingly, mice lacking CH25H in DCs exhibit an accelerated tumor growth, decreased infiltration and impaired activation of intratumoral CD8+ T cells. These mice do not establish measurable long-term immunity against malignant cells that undergo chemotherapy-induced immunogenic cell death. Mechanistically, downregulation of CH25H stimulates membrane fusion between endo-phagosomes and lysosomes, accelerates lysosomal degradation and restricts cross-presentation of tumor antigens in the intratumoral DCs. Administration of STING agonist MSA-2 reduces the lysosomal activity in DCs, restores antigen cross presentation, and increases therapeutic efficacy of PD-1 blockade against tumour challenge in a CH25H-dependent manner. These studies highlight the importance of downregulation of CH25H in DCs for tumor immune evasion and resistance to therapy.

Emerging roles of activating transcription factor (ATF) family members in tumourigenesis and immunity: Implications in cancer immunotherapy

Activating transcription factors, ATFs, are a group of bZIP transcription factors that act as homodimers or heterodimers with a range of other bZIP factors. In general, ATFs respond to extracellular signals, indicating their important roles in maintaining homeostasis. The ATF family includes ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7. Consistent with the diversity of cellular processes reported to be regulated by ATFs, the functions of ATFs are also diverse. ATFs play an important role in cell proliferation, apoptosis, differentiation and inflammation-related pathological processes. The expression and phosphorylation status of ATFs are also related to neurodegenerative diseases and polycystic kidney disease. Various miRNAs target ATFs to regulate cancer proliferation, apoptosis, autophagy, sensitivity and resistance to radiotherapy and chemotherapy. Moreover, ATFs are necessary to maintain cell redox homeostasis. Therefore, deepening our understanding of the regulation and function of ATFs will provide insights into the basic regulatory mechanisms that influence how cells integrate extracellular and intracellular signals into genomic responses through transcription factors. Under pathological conditions, especially in cancer biology and response to treatment, the characterization of ATF dysfunction is important for understanding how to therapeutically utilize ATF2 or other pathways controlled by transcription factors. In this review, we will demonstrate how ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7 function in promoting or suppressing cancer development and identify their roles in tumour immunotherapy.

Conditioned Media of Adipose-Derived Stem Cells Suppresses Sidestream Cigarette Smoke Extract Induced Cell Death and Epithelial-Mesenchymal Transition in Lung Epithelial Cells

The role of the epithelial-mesenchymal transition (EMT) in lung epithelial cells is increasingly being recognized as a key stage in the development of COPD, fibrosis, and lung cancers, which are all highly associated with cigarette smoking and with exposure to second-hand smoke. Using the exposure of human lung cancer epithelial A549 cells and non-cancerous Beas-2B cells to sidestream cigarette smoke extract (CSE) as a model, we studied the protective effects of adipose-derived stem cell-conditioned medium (ADSC-CM) against CSE-induced cell death and EMT. CSE dose-dependently induced cell death, decreased epithelial markers, and increased the expression of mesenchymal markers. Upstream regulator analysis of differentially expressed genes after CSE exposure revealed similar pathways as those observed in typical EMT induced by TGF-β1. CSE-induced cell death was clearly attenuated by ADSC-CM but not by other control media, such as a pass-through fraction of ADSC-CM or A549-CM. ADSC-CM effectively inhibited CSE-induced EMT and was able to reverse the gradual loss of epithelial marker expression associated with TGF-β1 treatment. CSE or TGF-β1 enhanced the speed of A549 migration by 2- to 3-fold, and ADSC-CM was effective in blocking the cell migration induced by either agent. Future work will build on the results of this in vitro study by defining the molecular mechanisms through which ADSC-CM protects lung epithelial cells from EMT induced by toxicants in second-hand smoke.

Loss of activating transcription factor 3 prevents KRAS-mediated pancreatic cancer

The unfolded protein response (UPR) is activated in pancreatic pathologies and suggested as a target for therapeutic intervention. In this study, we examined activating transcription factor 3 (ATF3), a mediator of the UPR that promotes acinar-to-ductal metaplasia (ADM) in response to pancreatic injury. Since ADM is an initial step in the progression to pancreatic ductal adenocarcinoma (PDAC), we hypothesized that ATF3 is required for initiation and progression of PDAC. We generated mice carrying a germline mutation of Atf3 (Atf3-/-) combined with acinar-specific induction of oncogenic KRAS (Ptf1acreERT/+KrasG12D/+). Atf3-/- mice with (termed APK) and without KRASG12D were exposed to cerulein-induced pancreatitis. In response to recurrent pancreatitis, Atf3-/- mice showed decreased ADM and enhanced regeneration based on morphological and biochemical analysis. Similarly, an absence of ATF3 reduced spontaneous pancreatic intraepithelial neoplasia (PanIN) formation and PDAC in Ptf1acreERT/+KrasG12D/+ mice. In response to injury, KRASG12D bypassed the requirement for ATF3 with a dramatic loss in acinar tissue and PanIN formation observed regardless of ATF3 status. Compared to Ptf1acreERT/+KrasG12D/+ mice, APK mice exhibited a significant decrease in pancreatic and total body weight, did not progress through to PDAC, and showed altered pancreatic fibrosis and immune cell infiltration. These findings suggest a complex, multifaceted role for ATF3 in pancreatic cancer pathology.

Inhibitory role of ATF3 in gastric cancer progression through regulating cell EMT and stemness

BACKGROUND

Gastric cancer (GC) is one of the most common cancers and the third leading cause of cancer related mortality worldwide. The 5-year survival rate is rather low owing to advanced unresectable and distant metastasis. The EMT has been widely implicated in the stemness, metastatic dormancy, and chemoresistance of different solid tumors. Given the fact that activating transcription factor-3 (ATF3) is a member of the ATF/CREB family of transcription factors and its role in regulation of GC recurrence and metastasis remain poorly understood, the aim of the present study was to investigate its potential impact in epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) properties and GC aggression.

METHODS

To elucidate the potential role of ATF3 in gastric cancer, we utilized SGC-7901 and MGC-803 gastric cancer cell lines as research models and constructed stable cell lines overexpressing ATF3. We conducted a series of assays including cell proliferation, colony formation, cell migration, tumorsphere formation, and invasion to investigate the functional roles of ATF3 in stemness of gastric cancer. The possible effect of ATF3 on epithelial-mesenchymal transition (EMT) was assessed through flow cytometry and qRT-PCR. In vivo functional effect of upregulation of ATF3 on tumor growth was examined in a mouse xenograft model.

RESULTS

We found that overexpression of ATF3 inhibited cell proliferation, colony formation, cell migration and invasion. In addition, up-regulation of ATF3 attenuated tumorsphere formation, cell stemness, and potentially decreased expression of EMT markers. Moreover, ATF3 overexpression inhibited tumorigenesis in mouse xenograft model.

CONCLUSION

Our data suggest a suppressive role of ATF3 in gastric cancer development. Our findings will provide a potential therapeutic strategy and novel drug target for gastric cancer.

Comparative pan-cancer DNA methylation analysis reveals cancer common and specific patterns

Abnormal DNA methylation is an important epigenetic regulator involving tumorigenesis. Deciphering cancer common and specific DNA methylation patterns is essential for us to understand the mechanisms of tumor development. The Cancer Genome Atlas (TCGA) project provides a large number of samples of different cancers that enable a pan-cancer study of DNA methylation possible. Here we investigate cancer common and specific DNA methylation patterns among 5480 DNA methylation profiles of 15 cancer types from TCGA. We first define differentially methylated CpG sites (DMCs) in each cancer and then identify 5450 hyper- and 4433 hypomethylated pan-cancer DMCs (PDMCs). Intriguingly, three adjacent hypermethylated PDMC constitute an enhancer region, which potentially regulates two tumor suppressor genes BVES and PRDM1 negatively. Moreover, we identify six distinct motif clusters, which are enriched in hyper- or hypomethylated PDMCs and are associated with several well-known cancer hallmarks. We also observe that PDMCs relate to distinct transcriptional groups. Additionally, 55 hypermethylated and 7 hypomethylated PDMCs are significantly associated with patient survival. Lastly, we find that cancer-specific DMCs are enriched in known cancer genes and cell-type-specific super-enhancers. In summary, this study provides a comprehensive investigation and reveals meaningful cancer common and specific DNA methylation patterns.