Zoledronic acid decreases mRNA six-transmembrane epithelial antigen of prostate protein expression in prostate cancer cells

Overexpression of goat STEAP4 promotes the differentiation of subcutaneous adipocytes

Objective: The focus of this study was the six-transmembrane epithelial antigen of the prostate 4 (STEAP4) gene, on the basis of the cloned goat STEAP4 gene sequence. Its molecular and expression characteristics were analyzed, and its influence on the differentiation of goat subcutaneous adipocytes was explored through overexpression. Method: Reverse-transcription PCR (RT-PCR) was used to clone the goat STEAP4 sequence, and online tools were used to analyze the molecular characteristic. Real-time quantitative PCR (qPCR) was used to detect the expression level of STEAP4 in goat tissues and subcutaneous adipocyte differentiation. Liposome transfection, BODIPY, Oil Red O staining, and qPCR were used to explore the effect of overexpression of STEAP4 on adipocyte differentiation. Results: The cloned goat STEAP4 gene sequence was 1388 bp, and the complete coding sequence (CDS) region was 1197 bp, which encoded a total of 398 amino acids. Compared with the predicted sequence (XM_005679300.3), there were three base mutations in the CDS region of goat STEAP4, A188G, T281C, and A507G. Among them, A507G changed the amino acid at position 170 from Ile to Val. Analysis of the physical and chemical properties of the protein showed that STEAP4 was a stable hydrophilic basic protein. STEAP4 gene expression level was highest in goat liver tissue ( P < 0.01 ), followed by lung and back subcutaneous adipose tissue. STEAP4 showed different expression levels in goat subcutaneous adipocytes at different times during the induction of differentiation. The expression in the late stage of differentiation was higher than that before differentiation and lowest at 12 h ( P < 0.01 ). Overexpression of STEAP4 promoted the accumulation of intracellular lipid droplets; C/EBP β (CCAAT enhancer binding protein) was extremely significantly up-regulated ( P < 0.01 ), and aP2 (fatty acid binding protein) was significantly up-regulated ( P < 0.05 ). Conclusion: Overexpression of STEAP4 could promote the differentiation of goat subcutaneous preadipocytes. This study lays the foundation for an in-depth study of the role of STEAP4 in goat lipid deposition.

Six-transmembrane epithelial antigen of the prostate 1 is associated with tumor invasion and migration in endometrial carcinomas

Six-transmembrane epithelial antigen of the prostate 1 (STEAP1), a member of the STEAP family, is a general tumor antigen. However, no information has been available to date regarding the function of STEAP1 in the progression of endometrial carcinoma. In this study, we used in vitro and in vivo strategies to prove that STEAP1 plays an important role in the progression of endometrial carcinoma. Immunohistochemistry, immunocytochemistry, quantitative reverse transcription polymerase chain reaction (RT-qPCR), and Western blot analysis were used to detect the expression of STEAP1 in normal endometrial cells and endometrial cancer cell lines. The progression of the cell cycle, plate clone formation assay, and transwell migration and invasion assays were performed to examine the effects of STEAP1 on cell proliferation, clonogenicity, migration, and their invasive capacity. In addition, we confirmed that STEAP1 was tightly correlated with the development of tumor in vivo. The relationship between epithelial to mesenchymal transition (EMT) and STEAP1 expression was evaluated by RT-qPCR and Western blot analysis. Matrix metalloproteinase (MMP) zymography assay was used to detect the activities of MMP2 and MMP9. STEAP1 was restrictively expressed in endometrial carcinoma and downregulation of the STEAP1 gene increased proliferation and clonogenicity, as well as promoted cell migration, invasion, and the progress of EMT. STEAP1 is downregulated in endometrial carcinoma and can restrict migration and invasion of endometrial carcinoma cells. Overall, STEAP1 may be an ideal target for tumor therapy and diagnosis in the future.

Knockdown of STEAP1 inhibits cell growth and induces apoptosis in LNCaP prostate cancer cells counteracting the effect of androgens

Six transmembrane epithelial antigen of the prostate 1 (STEAP1) is overexpressed in numerous types of tumors, especially in prostate cancer. STEAP1 is located in the plasma membrane of epithelial cells and may play an important role in inter- and intracellular communication. Several studies suggest STEAP1 as a potential biomarker and an immunotherapeutic target for prostate cancer. However, the role of STEAP1 in cell proliferation and apoptosis remains unclear. Therefore, the role of STEAP1 in prostate cancer cells proliferation and apoptosis was determined by inducing STEAP1 gene knockdown in LNCaP cells. In addition, the effect of DHT on the proliferation of LNCaP cells knocked down for STEAP1 gene was evaluated. Our results demonstrated that silencing the STEAP1 gene reduces LNCaP cell viability and proliferation, while inducing apoptosis. In addition, we showed that the cellular and molecular effects of STEAP1 gene knockdown may be independent of DHT treatment, and blocking STEAP1 may reveal to be an appropriate strategy to activate apoptosis in cancer cells, as well as to prevent the proliferative and anti-apoptotic effects of DHT in prostate cancer.

Six transmembrane epithelial antigen of the prostate 1 is down-regulated by sex hormones in prostate cells

BACKGROUND

STEAP1 is over-expressed in several types of tumors, especially prostate cancer, where it is localized in the plasma membrane of epithelial cells, at cell-cell junctions. Its role in prostate carcinogenesis and its regulation in prostate cells remain unknown. Therefore, we propose to study the effect of sex hormones in the regulation of STEAP1 expression in prostate cells in vitro and in vivo.

METHODS

LNCaP prostate cells were incubated with fetal bovine serum (FBS), charcoal-stripped FBS (CS-FBS), 5α-dihydrotestosterone (DHT), and 17β-estradiol (E2 ) for different periods of stimulation. In addition, adult male Wistar rats were castrated and treated with DHT and E2 . The levels of STEAP1 in response to treatments were analyzed by real-time PCR, Western blot, and immunohistochemistry.

RESULTS

The treatment of LNCaP cells with DHT or E2 induces a down-regulation of STEAP1 expression, while incubation with CS-FBS has the opposite effect. Experiments using inhibitors of androgen and estrogen receptor (AR and ER) showed that down-regulation of STEAP1 is AR-dependent, but ER-independent. However, the mediation of six transmembrane epithelial antigen of the prostate 1 (STEAP1) expression by AR seems to be dependent of de novo protein synthesis. In vivo studies showed that castrated rats express higher levels of STEAP1 protein when compared to intact rats, an effect reversed by DHT or E2 replacement.

CONCLUSIONS

STEAP1 is down-regulated by DHT and E2 in LNCaP cells and in rat prostate.

The STEAP protein family: versatile oxidoreductases and targets for cancer immunotherapy with overlapping and distinct cellular functions

The human six-transmembrane epithelial antigen of the prostate (STEAP) protein family contains at least five homologous members. The necessity of multiple homologous STEAP proteins is still unclear, but their peculiar and tissue-specific expression suggests that they are assigned to distinct functional tasks. This concept is supported by the fact that especially STEAP1, and to a lesser extent STEAP2 and -4, are highly over-expressed in many different cancer entities, while being only minimally expressed in a few normal tissues. Despite their very similar domain organisation, STEAP3 seems to act as a potent metalloreductase essential for physiological iron uptake and turnover, while in particular STEAP4 appears to be rather involved in responses to nutrients and inflammatory stress, fatty acid and glucose metabolism. Moreover, individual STEAP proteins possess overlapping functions important for growth and survival of cancer cells. Due to their membrane-bound localisation and their high expression in many different cancers such as prostate, breast and bladder carcinoma as well as Ewing's sarcoma, STEAP proteins have been recognised and utilised as promising targets for cell- and antibody-based immunotherapy. This review summarises our present knowledge of the individual members of the human STEAP family and highlights the functional differences between them.