Six-transmembrane epithelial antigen of the prostate 1 protects against increased oxidative stress via a nuclear erythroid 2-related factor pathway in colorectal cancer

Isolation and characterisation of secondary metabolites from Trifolium vesiculosum Savi and their antiproliferative activities

One unreported flavonol namely morin-7-O-methyl ether (1) along with seven known compounds were isolated from the aerial parts of Trifolium vesiculosum Savi which were elucidated by using extensive spectroscopic methods such as 1D and 2D NMR and HR-MS. According to the cell viability assay (MTS) on the purified compounds (1-8), quercetin-3-O-(6''-trans-p-coumaroyl)-β-galactoside (4) revealed remarkable antiproliferative activity most particularly against breast cancer cells (IC50  = 2.90 ± 0.25 µM in HCC1937 and 7.98 ± 0.57 µM in MCF7) while moderate inhibitory activity (IC50  = 17.96 ± 0.51-51.70 ± 2.69 µM) on prostate, colorectal and liver cancer cell viability was observed. Further mechanistic examinations (Annexin V/PI staining, DNA content and detection of reactive oxygen species analyses) showed that compound 4 significantly induced apoptosis, enhanced mitochondrial reactive oxygen species (ROS) accumulation, and caused cell cycle arrest in cancer cells by increasing accumulation of cells at G0/G1 and/or G2/M phases of the cell cycle.

Role of Oxidative Stress Signaling, Nrf2, on Survival and Stemness of Human Adipose-Derived Stem Cells Exposed to X-rays, Protons and Carbon Ions

Some cancers have a poor prognosis and often lead to local recurrence because they are resistant to available treatments, e.g., glioblastoma. Attempts have been made to increase the sensitivity of resistant tumors by targeting pathways involved in the resistance and combining it, for example, with radiotherapy (RT). We have previously reported that treating glioblastoma stem cells with an Nrf2 inhibitor increases their radiosensitivity. Unfortunately, the application of drugs can also affect normal cells. In the present study, we aim to investigate the role of the Nrf2 pathway in the survival and differentiation of normal human adipose-derived stem cells (ADSCs) exposed to radiation. We treated ADSCs with an Nrf2 inhibitor and then exposed them to X-rays, protons or carbon ions. All three radiation qualities are used to treat cancer. The survival and differentiation abilities of the surviving ADSCs were studied. We found that the enhancing effect of Nrf2 inhibition on cell survival levels was radiation-quality-dependent (X-rays > proton > carbon ions). Furthermore, our results indicate that Nrf2 inhibition reduces stem cell differentiation by 35% and 28% for adipogenesis and osteogenesis, respectively, using all applied radiation qualities. Interestingly, the results show that the cells that survive proton and carbon ion irradiations have an increased ability, compared with X-rays, to differentiate into osteogenesis and adipogenesis lineages. Therefore, we can conclude that the use of carbon ions or protons can affect the stemness of irradiated ADSCs at lower levels than X-rays and is thus more beneficial for long-time cancer survivors, such as pediatric patients.

Inflammatory response in gastrointestinal cancers: Overview of six transmembrane epithelial antigens of the prostate in pathophysiology and clinical implications

Chronic inflammation is known to increase the risk of gastrointestinal cancers (GICs), the common solid tumors worldwide. Precancerous lesions, such as chronic atrophic inflammation and ulcers, are related to inflammatory responses in vivo and likely to occur in hyperplasia and tumorigenesis. Unfortunately, due to the lack of effective therapeutic targets, the prognosis of patients with GICs is still unsatisfactory. Interestingly, it is found that six transmembrane epithelial antigens of the prostate (STEAPs), a group of metal reductases, are significantly associated with the progression of malignancies, playing a crucial role in systemic metabolic homeostasis and inflammatory responses. The structure and functions of STEAPs suggest that they are closely related to intracellular oxidative stress, responding to inflammatory reactions. Under the imbalance status of abnormal oxidative stress, STEAP members are involved in cell transformation and the development of GICs by inhibiting or activating inflammatory process. This review focuses on STEAPs in GICs along with exploring their potential molecular regulatory mechanisms, with an aim to provide a theoretical basis for diagnosis and treatment strategies for patients suffering from these types of cancers.

Targeting STEAP1 as an anticancer strategy

Although the six-transmembrane epithelial antigen of prostate 1 (STEAP1) was first identified in advanced prostate cancer, its overexpression is recognized in multiple types of cancer and associated with a poor prognosis. STEAP1 is now drawing attention as a promising therapeutic target because of its tumor specificity and membrane-bound localization. The clinical efficacy of an antibody-drug conjugate targeting STEAP1 in metastatic, castration-resistant, prostate cancer was demonstrated in a phase 1 trial. Furthermore, growing evidence suggests that STEAP1 is an attractive target for immunotherapies such as chimeric antigen receptor-T cell therapy. In this review, we summarize the oncogenic functions of STEAP1 by cancer type. This review also provides new insights into the development of new anticancer strategies targeting STEAP1.

Specific Six-Transmembrane Epithelial Antigen of the Prostate 1 Capture with Gellan Gum Microspheres: Design, Optimization and Integration

This work demonstrates the potential of calcium- and nickel-crosslinked Gellan Gum (GG) microspheres to capture the Six-Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) directly from complex Komagataella pastoris mini-bioreactor lysates in a batch method. Calcium-crosslinked microspheres were applied in an ionic exchange strategy, by manipulation of pH and ionic strength, whereas nickel-crosslinked microspheres were applied in an affinity strategy, mirroring a standard immobilized metal affinity chromatography. Both formulations presented small diameters, with appreciable crosslinker content, but calcium-crosslinked microspheres were far smoother. The most promising results were obtained for the ionic strategy, wherein calcium-crosslinked GG microspheres were able to completely bind 0.1% (v/v) DM solubilized STEAP1 in lysate samples (~7 mg/mL). The target protein was eluted in a complexed state at pH 11 with 500 mM NaCl in 10 mM Tris buffer, in a single step with minimal losses. Coupling the batch clarified sample with a co-immunoprecipitation polishing step yields a sample of monomeric STEAP1 with a high degree of purity. For the first time, we demonstrate the potential of a gellan batch method to function as a clarification and primary capture method towards STEAP1, a membrane protein, simplifying and reducing the costs of standard purification workflows.

Comprehensive Landscape of STEAP Family Members Expression in Human Cancers: Unraveling the Potential Usefulness in Clinical Practice Using Integrated Bioinformatics Analysis

The human Six-Transmembrane Epithelial Antigen of the Prostate (STEAP) family comprises STEAP1-4. Several studies have pointed out STEAP proteins as putative biomarkers, as well as therapeutic targets in several types of human cancers, particularly in prostate cancer. However, the relationships and significance of the expression pattern of STEAP1-4 in cancer cases are barely known. Herein, the Oncomine database and cBioPortal platform were selected to predict the differential expression levels of STEAP members and clinical prognosis. The most common expression pattern observed was the combination of the over- and underexpression of distinct STEAP genes, but cervical and gastric cancer and lymphoma showed overexpression of all STEAP genes. It was also found that STEAP genes’ expression levels were already deregulated in benign lesions. Regarding the prognostic value, it was found that STEAP1 (prostate), STEAP2 (brain and central nervous system), STEAP3 (kidney, leukemia and testicular) and STEAP4 (bladder, cervical, gastric) overexpression correlate with lower patient survival rate. However, in prostate cancer, overexpression of the STEAP4 gene was correlated with a higher survival rate. Overall, this study first showed that the expression levels of STEAP genes are highly variable in human cancers, which may be related to different patients’ outcomes.

Solute carrier family 16 member 5 downregulation and its methylation might serve as a prognostic indicator of prostate cancer

Prostate cancer (PCa), characterized by high invasion, metastasis, and recurrence, is the most prevalent malignant tumor in men worldwide. A clear understanding of the underlying molecular mechanisms and their role during PCa tumorigenesis can help develop prognostic and targeted therapies. We analyzed datasets from public databases, including the Cancer Genome Atlas (TCGA) and Oncomine and Gene Expression Profiling Interactive Analysis for differential expression of solute carrier family 16 member 5 (SLC16A5). We further investigated its relationship with clinical stage, pathological grade, and prognosis of PCa. The promoter methylation level of SLC16A5 in PCa was also investigated by UALCAN. We also utilized datasets from UCSC Xena to explore the prognostic role of SLC16A5 methylation levels and CpG site. Correlations between SLC16A5 and immune infiltration were discovered through TIMER. We observed significantly lower levels of SLC16A5 mRNA in PCa relative to normal tissues across six datasets from Oncomine database (p < .001) and 498 cases from TCGA database (p < .0001). SLC16A5 is strongly negatively regulated by its DNA methylation, with a Spearman of -0.81 and Pearson of -0.80 (p < .001). The aberrant SLC16A5 expression resulted in a significant relationship with clinical stage, pathological grade, and lower SLC16A5 mRNA expression, and its hypermethylation was related to a poorer PCa prognosis. SLC16A5 acted as an important factor for PCa diagnosis, with an AUC of 0.9038 (95% CI: 0.8597-0.9479; p < .0001). Besides, the aberrant SLC16A5 expression revealed close correlations with multiple immune cells. Overall, these results indicate that decreased SLC16A5 expression might be a potential biomarker for determining prognosis and immune infiltration in PCa. The positive SLC16A5 modulation might be a promising therapeutic target for PCa.

Reactive oxygen species in cancer: Current findings and future directions

Reactive oxygen species (ROS), a class of highly bioactive molecules, have been widely studied in various types of cancers. ROS are considered to be normal byproducts of numerous cellular processes. Typically, cancer cells exhibit higher basal levels of ROS compared with normal cells as a result of an imbalance between oxidants and antioxidants. ROS have a dual role in cell metabolism: At low to moderate levels, ROS act as signal transducers to activate cell proliferation, migration, invasion, and angiogenesis. In contrast, high levels of ROS cause damage to proteins, nucleic acids, lipids, membranes, and organelles, leading to cell death. Extensive studies have revealed that anticancer therapies that manipulate ROS levels, including immunotherapies, show promising in vitro as well as in vivo results. In this review, we summarize molecular mechanisms and oncogenic functions that modulate ROS levels and are useful for the development of cancer therapeutic strategies. This review also provides insights into the future development of effective agents that regulate the redox system for cancer treatment.

Six-transmembrane epithelial antigen of the prostate 1 accelerates cell proliferation by targeting c-Myc in liver cancer cells

Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) has emerged as an ideal target in cancer therapeutics. However, the functions of STEAP1 in liver cancer remain unexplored. The current study aimed to characterize the biological roles of STEAP1 in liver cancer. STEAP1 expression was upregulated in tumor tissues, and high STEAP1 expression was associated with poor clinical outcomes in patients with liver cancer, according to several publicly available datasets. STEAP1 silencing using small interfering RNA inhibited cell proliferation and was accompanied by G₁ arrest induced by the suppression of cyclin D1 and the promotion of p27. STEAP1 silencing suppressed c-Myc expression, which was identified as a component in STEAP1 signal transduction by mining publicly available datasets and was then confirmed by PCR array. In conclusion, the knockdown of STEAP1 in liver cancer cell lines led to inhibition of cell proliferation involving G₁ arrest by suppressing c-Myc. The present study provides a preclinical concept for STEAP1 as a druggable target in liver cancer.

Regulatory Roles of Six-Transmembrane Epithelial Antigen of the Prostate Family Members in the Occurrence and Development of Malignant Tumors

The human six-transmembrane epithelial antigen of the prostate (STEAP) proteins, which include STEAP1-4 and atypical STEAP1B, contain six transmembrane domains and are located in the cell membrane. STEAPs are considered archaeal metal oxidoreductases, based on their heme groups and F420H2:NADP+ oxidoreductase (FNO)-like structures, and play an important role in cell metal metabolism. Interestingly, STEAPs not only participate in biological processes, such as molecular transport, cell cycling, immune response, and intracellular and extracellular activities, but also are closely related to the occurrence and development of several diseases, especially malignant tumors. Up to now, the expression patterns of STEAPs have been found to be diverse in different types of tumors, with controversial participation in different aspects of malignancy, such as cell proliferation, migration, invasion, apoptosis, and therapeutic resistance. It is clinically important to explore the potential roles of STEAPs as new immunotherapeutic targets for the treatment of different malignant tumors. Therefore, this review focuses on the molecular mechanism and function of STEAPs in the occurrence and development of different cancers in order to understand the role of STEAPs in cancer and provide a new theoretical basis for the treatment of diverse cancers.

Six-transmembrane epithelial antigen of the prostate 1 expression promotes ovarian cancer metastasis by aiding progression of epithelial-to-mesenchymal transition

Ovarian cancer is a severe malignant tumour of the female genital organs. Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) expression is correlated with the occurrence and progression of multiple cancers. Here, we assessed STEAP1 expression in ovarian cancer and explored the relationship between STEAP1 and ovarian cancer progression. We used immunohistochemistry and public databases to test STEAP1 expression in normal human ovarian tissues, benign ovarian tumours, and ovarian cancer. The expression of STEAP1 and epithelial-to-mesenchymal transition (EMT)-related genes was analysed using immunocytochemistry, quantitative reverse transcription polymerase chain reaction, and western blotting in ovarian cancer cell lines. Lentivirus was used to knockdown and overexpress STEAP1. Invasion, migration, growth, clonogenicity, and apoptosis were assessed using transwell assay, growth curve, plate clone formation assay, and flow cytometry. We used a tumour xenograft to verify the relationship between STEAP1 and in vivo ovarian cancer cell growth. Matrix metalloproteinase-2 (MMP2) and matrix metalloproteinase-9 (MMP9) activities were examined using Matrix metalloproteinase zymography assay. STEAP1 was highly expressed in the human ovarian cancer tissues and a highly invasive ovarian cancer cell line. Overexpression of STEAP1 was related to poor prognosis in ovarian cancer patients. Down-regulation of STEAP1 suppressed the invasion, migration, proliferation, clonogenicity, EMT progression in human ovarian cancer cells and xenograft tumour growth in vivo, but it enhanced apoptosis. In human ovarian cancer, the STEAP1 gene is highly expressed, and its function is correlated with human ovarian cancer cell metastasis and growth. STEAP1 may be a possible target for suppressing ovarian cancer metastasis.

Evaluation of the Prognostic Value of STEAP1 in Lung Adenocarcinoma and Insights Into Its Potential Molecular Pathways via Bioinformatic Analysis

Background

Upregulation of the six-transmembrane epithelial antigen of prostate-1 (STEAP1) is closely associated with prognosis of numerous malignant cancers. However, its role in lung adenocarcinoma (LUAD), the most common type of lung cancer, remains unknown. This study aimed to investigate the role of STEAP1 in the occurrence and progression of LUAD and the potential mechanisms underlying its regulatory effects.

Methods

STEAP1 mRNA and protein expression were analyzed in 40 LUAD patients via real-time PCR and western blotting, respectively. We accessed the clinical data of 522 LUAD patients from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) to investigate the expression and prognostic role of STEAP1 in LUAD. Further, we performed gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and gene set enrichment analysis (GSEA) to elucidate the potential mechanism underlying the role of STEAP1 in LUAD. The protein-protein interaction (PPI) network of STEAP1 was analyzed using the Search Tool for the Retrieval of Interacting Genes (STRING) database, and hub genes with significant positive and negative associations with STEAP1 were identified and their role in LUAD prognosis was predicted.

Results

STEAP1 was significantly upregulated in LUAD patients and associated with LUAD prognosis. Further, TCGA data indicated that STEAP1 upregulation is correlated with the clinical prognosis of LUAD. GO and KEGG analysis revealed that the genes co-expressed with STEAP1 were primarily involved in cell division, DNA replication, cell cycle, apoptosis, cytokine signaling, NF-kB signaling, and TNF signaling. GSEA revealed that homologous recombination, p53 signaling pathway, cell cycle, DNA replication, apoptosis, and toll-like receptor signaling were highly enriched upon STEAP1 upregulation. Gene Expression Profiling Interactive Analysis (GEPIA) analysis revealed that the top 10 hub genes associated with STEAP1 expression were also associated with the LUAD prognosis.

Conclusion

STEAP1 upregulation potentially influences the occurrence and progression of LUAD and its co-expressed genes via regulation of homologous recombination, p53 signaling, cell cycle, DNA replication, and apoptosis. STEAP1 is a potential prognostic biomarker for LUAD.

STEAP2 is down-regulated in breast cancer tissue and suppresses PI3K/AKT signaling and breast cancer cell invasion in vitro and in vivo

The six-transmembrane epithelial antigen of prostate 2 (STEAP2) protein was identified in advanced prostate cancer, and is highly over-expressed in various types of cancer. This study aimed to investigate the prognostic value and the function of STEAP2 in breast cancer. STEAP2 mRNA and protein expressions in breast normal and cancer tissues, breast cancer cell lines (MCF-7, BT-549, BT-474, MDA-MB-361, HCC1937, and MDA-MB-468) and normal mammary epithelial cell lines (HBL-100 and MCF-10A) were evaluated by immunohistochemistry, real time RT-qPCR and western blotting. The expression of STEAP2 in breast cancer tissues and its value of evaluating the prognosis of breast cancer patients was validated in the Public Databases (Oncomine and Kaplan-Meier plotter database). Lentiviral vectors with STEAP2 cDNA and shRNA were constructed and used to infect breast cancer cell lines and normal mammary epithelial cell line to investigate the effects of STEAP2 up- and down- regulation on the biological behavior of breast cells. The low expression of STEAP2 was detected in breast cancer tissues, which was associated with malignant phenotype and poor prognosis of breast cancer. The public databases analyses were consistent with our findings. STEAP2 up-regulation hindered cellular proliferation, invasion and metastasis abilities by inhibiting EMT process and suppressing PI3K/AKT/mTOR signaling pathway. On the other hand, STEAP2 down-regulation could promote cell proliferation and invasion by inducing EMT and activating the PI3K/AKT/mTOR signaling pathway. Collectively, STEAP2 acted as an anti-oncogene in breast cancer development, which suggested a new research objective for the future studies.