Parallel study on protein O-GlcNAcylation in prostate cancer cell with a sensitive microarray biochip

Androgen-repressed lncRNA LINC01126 drives castration-resistant prostate cancer by regulating the switch between O-GlcNAcylation and phosphorylation of androgen receptor

BACKGROUND

Prostate cancer (PCa) initially shows satisfactory response to therapies targeting the androgen receptor (AR). However, progression to a castration-resistant stage indicates poor prognosis in PCa patients. AR signalling still plays a central role in most castration-resistant prostate cancers (CRPC). Therefore, unveiling the mechanisms of AR reactivation under androgen-deprived conditions is imperative to discover novel therapeutic targets for CRPC.

METHODS

Using an integrative analysis of the transcriptomics of three independent PCa cohorts and a published landscape of AR-regulated long non-coding RNA (lncRNA), lncRNA LINC01126 was selected as a candidate gene that could drive CRPC progression for further study. Quantitative reverse transcription polymerase chain reaction, in situ hybridisation (ISH) and fluorescent ISH were performed to detect LINC01126 in PCa tissues and cells. The functional role and mechanism of LINC01126 were further investigated using in vitro and in vivo gain and loss of function assays.

RESULTS

LINC01126, identified as an AR-repressed lncRNA, was significantly upregulated after AR-targeted therapies. In addition, we found that LINC01126 was upregulated in CRPC and was associated with poor prognosis. We also proved that LINC01126 stabilised AR protein and enhanced AR nuclear translocation and transactivation by promoting the transition from O-GlcNAcylation at threonine 80 to phosphorylation at serine 81 (S81) within the AR protein. Mechanism analysis revealed that LINC01126 facilitates the interaction of CDK9 with AR and impedes the binding of O-linked N-acetylglucosamine (O-GlcNAc) transferase to AR. Consequently, LINC01126 expression was sufficient to activate AR signalling without androgen. LINC01126 overexpression increased, whereas LINC01126 knockdown decreased castration resistance traits in PCa cells in vitro and in vivo. Furthermore, our data showed that LINC01126-targeting antisense oligonucleotides (ASO) substantially inhibited CRPC cells in vitro.

CONCLUSIONS

Our research expands the functions of AR-regulated lncRNA in sustaining androgen-independent AR activity and promoting CRPC progression and reveals that LINC01126 may be a new therapeutic target for PCa.

O-GlcNAcylation in cancer development and immunotherapy

O-linked β-D-N-acetylglucosamine (O-GlcNAc), as a posttranslational modification (PTM), is a reversible reaction that attaches β-N-GlcNAc to Ser/Thr residues on specific proteins by O-GlcNAc transferase (OGT). O-GlcNAcase (OGA) removes the O-GlcNAc from O-GlcNAcylated proteins. O-GlcNAcylation regulates numerous cellular processes, including signal transduction, the cell cycle, metabolism, and energy homeostasis. Dysregulation of O-GlcNAcylation contributes to the development of various diseases, including cancers. Accumulating evidence has revealed that higher expression levels of OGT and hyper-O-GlcNAcylation are detected in many cancer types and governs glucose metabolism, proliferation, metastasis, invasion, angiogenesis, migration and drug resistance. In this review, we describe the biological functions and molecular mechanisms of OGT- or O-GlcNAcylation-mediated tumorigenesis. Moreover, we discuss the potential role of O-GlcNAcylation in tumor immunotherapy. Furthermore, we highlight that compounds can target O-GlcNAcylation by regulating OGT to suppress oncogenesis. Taken together, targeting protein O-GlcNAcylation might be a promising strategy for the treatment of human malignancies.

In Situ Imaging of O-Linked β-N-Acetylglucosamine Using On-Tissue Hydrolysis and MALDI Mass Spectrometry

Post-translational O-glycosylation of proteins via the addition of N-acetylglucosamine (O-GlcNAc) is a regulator of many aspects of cellular physiology. Processes driven by perturbed dynamics of O-GlcNAcylation modification have been implicated in cancer development. Variability in O-GlcNAcylation is emerging as a metabolic biomarker of many cancers. Here, we evaluate the use of MALDI-mass spectrometry imaging (MSI) to visualize the location of O-GlcNAcylated proteins in tissue sections by mapping GlcNAc that has been released by the enzymatic hydrolysis of glycoproteins using an O-GlcNAc hydrolase. We use this strategy to monitor O-GlcNAc within hepatic VX2 tumor tissue. We show that increased O-GlcNAc is found within both viable tumor and tumor margin regions, implicating GlcNAc in tumor progression.

The Differential Antitumor Activity of 5-Aza-2'-deoxycytidine in Prostate Cancer DU145, 22RV1, and LNCaP Cells

DNA methylation is a DNA methyltransferase-mediated epigenetic modification affecting gene expression. This process is involved in the initiation and development of malignant disease. 5-Aza-2'-deoxycytidine (5-Aza), a classic DNA methyltransferase inhibitor, possesses antitumor proliferation activity. However, whether 5-Aza induces cytotoxicity in solid tumors warrants further investigated. In this study, human prostate cancer (CaP) cells were treated with 5-Aza and subjected to cell viability and cytotoxicity analysis. Reverse transcription-polymerase chain reaction and methylation-specific polymerase chain reaction assay were utilized to test the gene expression and methylation status of the p53 and p21 gene promoters. The results showed that 5-Aza differentially inhibited spontaneous proliferation, arrested the cell cycle at S phase in DU145, at G1 phase in 22RV1 and LNCaP cells, and G2 phase in normal RWPE-1 cells, as well as induced the expression of phospho-H2A.X and tumor suppressive mammary serine protease inhibitor (maspin) in all three types of CaP cells. 5-Aza also increased p53 and p21 transcription through promoter demethylation, and decreased the expression of oncogene c-Myc in 22RV1 and LNCaP cells. Western blotting analysis showed that the poly (ADP-ribose) polymerase cleavage was detected in DU145 and 22RV1 cells. Moreover, there were no significant changes in p53, p21 and c-Myc expression in DU145 cells following treatment with 5-Aza. Thus, in responsible for its apoptotic induction and DNA damage, the mechanism of the antitumor activities of 5-Aza may involve in an increase of tumor suppressive maspin, upregulation of wild type p53-mediated p21 expression and a decrease of oncogene c-Myc level in 22RV1 and LNCaP cells, and enhancing the tumor suppressive maspin expression in DU145 cells. These results enriched our understanding of the multifaceted antitumor activity of 5-Aza, and provided the expression basis of biomarkers for its possible clinical application in prostate cancer.