Overexpression of regucalcin blocks the migration, invasion, and bone metastatic activity of human prostate cancer cells: Crosstalk between cancer cells and bone cells

Bone metastases of prostate cancer: Molecular mechanisms, targeted diagnosis and targeted therapy (Review)

Prostate cancer (PCa) is second only to lung cancer in terms of death among men worldwide. Advanced PCa frequently results in bone metastases, which occur in ~90% of patients and frequently result in severe skeleton‑related events. Currently, the treatment for this disease is limited to alleviating its clinical symptoms and cannot provide a complete cure. Therefore, the development of novel treatment strategies is particularly important. In recent years, numerous novel strategies for the diagnosis and treatment of PCa have emerged, resulting in good clinical efficacy. For example, strategies targeting prostate specific membrane antigen, poly ADP‑ribose polymerase and programmed cell death protein 1 have been applied to PCa‑induced bone metastasis, and have shown initial efficacy and great potential. Therefore, understanding the molecular mechanisms underlying the formation of bone metastases in patients with PCa is of importance for the effective management of this disease. The purpose of the present review is to comprehensively outline the roles of protein‑coding genes and non‑coding RNAs in the development of bone metastases of PCa to elucidate their significance in the management of PCa. The aim is to offer clinicians and researchers a comprehensive understanding of this topic.

Extracellular Regucalcin: A Potent Suppressor in the Cancer Cell Microenvironment

The regucalcin gene is located on the X chromosome, comprising seven exons and six introns. This gene and protein are expressed in various tissues and cells and is predominantly expressed in human liver, kidney, and adrenal tissues. Regucalcin gene expression is enhanced via a mechanism mediated by several signaling molecules and transcription factors. Regucalcin plays a multifunctional role in cellular regulation in maintaining cell homeostasis. In addition, regucalcin has been implicated in several metabolic disorders and diseases. In particular, regucalcin plays a role as a novel suppressor in several types of cancer patients. Increased expression of regucalcin suppresses the growth of human cancer cells, suggesting its pivotal role in suppressing tumor development. The survival time of cancer patients is prolonged with increased expression of regucalcin in the tumor tissues. The adhesion, migration, invasion, and bone metastatic activity of cancer cells are blocked by the overexpression of regucalcin, promoting dormancy in cancer patients. Interestingly, regucalcin is also found in human serum, suggesting its character as a novel biomarker in various diseases. This extracellular regucalcin has been shown to suppress human cancer cells' growth and bone metastatic activity. Thus, extracellular regucalcin may play a vital role as a suppressor of human cancer activity. Alteration of the serum regucalcin levels in physiological and pathophysiological conditions may influence the activity of cancer cells in the microenvironment. This review will discuss the potential role of extracellular regucalcin in cancer cell activity as a critical suppressor in the cancer microenvironment.

Downregulated Regucalcin Expression Induces a Cancer-like Phenotype in Non-Neoplastic Prostate Cells and Augments the Aggressiveness of Prostate Cancer Cells: Interplay with the G Protein-Coupled Oestrogen Receptor?

BACKGROUND/OBJECTIVES

Regucalcin (RGN) is a calcium-binding protein and an oestrogen target gene, which has been shown to play essential roles beyond calcium homeostasis. Decreased RGN expression was identified in several cancers, including prostate cancer (PCa). However, it is unknown if the loss of RGN is a cause or a consequence of malignancy. Also, it needs confirmation if RGN oestrogenic regulation occurs through the G-protein-coupled oestrogen receptor (GPER). This study investigates how RGN knockdown affects prostate cell fate and metabolism and highlights the GPER/RGN interplay in PCa.

METHODS

Bioinformatic analysis assessed the relationship between RGN expression levels and patients' outcomes. RGN knockdown (siRNA) was performed in non-neoplastic prostate and castration-resistant PCa. Wild-type and RGN knockdown PCa cells were treated with the GPER agonist G1. Viability (MTT), proliferation (Ki-67 immunocytochemistry), apoptosis (caspase-3-like activity) and migration (Transwell assays) were evaluated. Spectrophotometric analysis was used to determine glucose consumption, lactate production and lactate dehydrogenase activity. Lipid content was assessed using the Oil Red assay.

RESULTS/CONCLUSIONS

Bioinformatic analysis showed that the loss of RGN correlates with the development of metastatic PCa and poor survival outcomes. RGN knockdown induced a cancer-like phenotype in PNT1A cells, indicated by increased cell viability and proliferation and reduced apoptosis. In DU145 PCa cells, RGN knockdown augmented migration and enhanced the glycolytic profile, which indicates increased aggressiveness, in line with patients' data. GPER activation modulated RGN expression in PCa cells and RGN knockdown in DU145 cells influenced GPER actions, which highlighted an interplay between these molecular players with relevance for their potential use as biomarkers or therapeutic targets.

The marine factor 3,5-dihydroxy-4-methoxybenzyl alcohol prevents TNF-α-mediated impairment of mineralization in mouse osteoblastic MC3T3-E1 cells: Impact of macrophage activation

The phenolic antioxidant 3,5-dihydroxy-4-methoxybenzyl alcohol (DHMBA), found in the Pacific oyster Crassostrea gigas, is a superior peroxyl radical scavenger compared to other materials, including Trolox. DHMBA may play an important role in the prevention of health disorders. This study elucidates whether DHMBA prevents the impairment of mineralization of mouse osteoblastic MC3T3-E1 cells under inflammatory conditions by using mouse macrophage RAW264.7 cells in vitro. Culturing with DHMBA (1-100 μM) did not affect the proliferation and death of MC3T3-E1 cells. DHMBA stimulated osteoblastic mineralization. DHMBA blocked the decrease in mineralization of MC3T3-E1 cells caused by culture with the inflammatory cytokine TNF-α. DHMBA inhibited the production of TNF-α by stimulation with lipopolysaccharide (LPS) in RAW264.7 cells. The growth of MC3T3-E1 cells was suppressed by coculture with macrophages under LPS stimulation through the crosstalk of both cells. Interestingly, the growth of MC3T3-E1 cells was suppressed by culturing with the conditioned medium obtained by culturing macrophages with LPS. The effect of the conditioned medium was blocked by the presence of DHMBA or Bay 11-7082, an inhibitor of the TNF-α pathway. The blocking effect of DHMBA was not further enhanced in the presence of Bay 11-7082. Mechanistically, DHMBA was found to decrease the levels of NF-κB p65 and the activity of NF-κB reporter expression in MC3T3-E1 cells. DHMBA was shown to prevent the impairment of osteoblastic mineralization via TNF-α signaling involved in macrophage activation in the bone marrow microenvironment. This study may provide a novel strategy for the therapy of osteoblastic impairment.

Regucalcin Is a Potential Regulator in Human Cancer: Aiming to Expand into Cancer Therapy

Regucalcin, a calcium-binding protein lacking the EF-hand motif, was initially discovered in 1978. Its name is indicative of its function in calcium signaling regulation. The rgn gene encodes for regucalcin and is situated on the X chromosome in both humans and vertebrates. Regucalcin regulates pivotal enzymes involved in signal transduction and has an inhibitory function, which includes protein kinases, protein phosphatases, cysteinyl protease, nitric oxide dynthetase, aminoacyl-transfer ribonucleic acid (tRNA) synthetase, and protein synthesis. This cytoplasmic protein is transported to the nucleus where it regulates deoxyribonucleic acid and RNA synthesis as well as gene expression. Overexpression of regucalcin inhibits proliferation in both normal and cancer cells in vitro, independent of apoptosis. During liver regeneration in vivo, endogenous regucalcin suppresses cell growth when overexpressed. Regucalcin mRNA and protein expressions are significantly downregulated in tumor tissues of patients with various types of cancers. Patients exhibiting upregulated regucalcin in tumor tissue have shown prolonged survival. The decrease of regucalcin expression is linked to the advancement of cancer. Overexpression of regucalcin carries the potential for preventing and treating carcinogenesis. Additionally, extracellular regucalcin has displayed control over various types of human cancer cells. Regucalcin may hold a prominent role as a regulatory factor in cancer development. Supplying the regucalcin gene could prove to be a valuable asset in cancer treatment. The therapeutic value of regucalcin suggests its potential significance in treating cancer patients. This review delves into the most recent research on the regulatory role of regucalcin in human cancer development, providing a novel approach for treatment.

The inflammatory macrophages repress the growth of bone metastatic human prostate cancer cells via TNF-α and IL-6 signaling: Involvement of cell signaling regulator regucalcin

Macrophages in the cancer microenvironments may play a regulatory role in the progression and metastasis of prostate cancer cells. However, the crosstalk between macrophages and prostate cancer cells is poorly understood. This study elucidates whether inflammatory macrophages regulate the proliferation and death of human prostate cancer cells in vitro. The RAW264.7 mouse macrophages were cocultured with PC-3 or DU-145 wild-type cells by using a Transwell chamber in vitro. RAW264.7 cells were cocultured with PC-3 or DU-145 cells in the presence of lipopolysaccharide (LPS). This coculturing blocked the proliferation and accelerated the death of cancer cells. Interestingly, cancer cell proliferation was repressed and death was promoted by the addition of the conditioned medium obtained from RAW264.7 cells treated with LPS. Culturing with LPS mostly augmented the production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the culture medium of RAW264.7 cells. The effects of the conditioned medium on the proliferation and death of PC-3 or DU-145 cells were blocked by NF-κB or STAT3 signaling inhibitors. Moreover, the effects of the conditioned medium on the proliferation and death of prostate cancer cells were not expressed in regucalcin-overexpressing cancer cells that diminish the levels of NF-κB p65 and STAT3. Culturing with extracellular TNF-α, IL-6, or regucalcin triggered inhibition of the proliferation of PC-3 wild-type cells. The levels of regucalcin in PC-3 cells were elevated by TNF-α or IL-6 stimulation. This study demonstrates that inflammatory macrophages triggered the loss of prostate cancer cells via the signaling process of NF-κB, STAT3, or regucalcin.