O-GlcNAcylation is a dynamic PTM of nuclear and cytoplasmic proteins, regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase, which catalyze the addition and removal of O-GlcNAc, respectively. This modification is associated with glucose metabolism, which plays important roles in many diseases including cancer. Although emerging evidence reveals that some tumor-associated proteins are O-GlcNAc modified, the total O-GlcNAcylation in cancer is still largely unexplored. Here, we demonstrate that O-GlcNAcylation was increased in primary breast malignant tumors, not in benign tumors and that this augmentation was associated with increased expression of OGT level. Using 2D O-GlcNAc immnoblotting and LC-MS/MS analysis, we successfully identified 29 proteins, with seven being uniquely O-GlcNAcylated or associated with O-GlcNAcylation in cancer. Of these identified proteins, some were related to the Warburg effect, including metabolic enzymes, proteins involved in stress responses and biosynthesis. In addition, proteins associated with RNA metabolism, gene expression, and cytoskeleton were highly O-GlcNAcylated or associated with O-GlcNAcylation. Moreover, OGT knockdown showed that decreasing O-GlcNAcylation was related to inhibition of the anchorage-independent growth in vitro. These data indicate that aberrant protein O-GlcNAcylation is associated with breast cancer. Abnormal modification of these O-GlcNAc-modified proteins might be one of the vital malignant characteristics of cancer.

O-GlcNAcylation is a post-translational modification of serine and threonine residues which is dynamically regulated by 2 enzymes; O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) that catalyze the addition and removal of a single N-acetylglucosamine (GlcNAc) molecule, respectively. This modification is thought to be a nutrient sensor in highly proliferating cells via the hexosamine biosynthesis pathway, a minor branch of glycolysis. Although emerging evidence suggests that O-GlcNAc modification is associated with many types of cancer, identification of O-GlcNAc-modified proteins and their role in cancer remain unexplored. In the present study, we demonstrated that O-GlcNAcylation is increased in primary colorectal cancer tissues, and that this augmentation is associated with an increased expression of OGT levels. Using 2-dimensional O-GlcNAc immunoblotting and LC-MS/MS analysis, 16 proteins were successfully identified and 8 proteins showed an increase in O-GlcNAcylation, including cytokeratin 18, heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1), hnRNP H, annexin A2, annexin A7, laminin-binding protein, α-tubulin and protein DJ-1. Among these identified proteins, annexin A2 was further confirmed to show overexpression of O-GlcNAc in all cancer samples. The results, therefore, indicate that aberrant O-GlcNAcylation of proteins is associated with colorectal cancer and that identification of O-GlcNAc-modified proteins may provide novel biomarkers of cancer.

Increasing glucose consumption is thought to provide an evolutionary advantage to cancer cells. Alteration of glucose metabolism in cancer influences various important metabolic pathways including the hexosamine biosynthesis pathway (HBP), a relatively minor branch of glycolysis. Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), an end product of HBP, is a sugar substrate used for classical glycosylation and O-GlcNAcylation, a post-translational protein modification implicated in a wide range of effects on cellular functions. Emerging evidence reveals that certain cellular proteins are abnormally O-GlcNAc modified in many kinds of cancers, indicating O-GlcNAcylation is associated with malignancy. Since O-GlcNAc rapidly on and off modifies in a similar time scale as in phosphorylation and these modifications may occur on proteins at either on the same or adjacent sites, it suggests that both modifications can work to regulate the cellular signaling pathways. This review describes the metabolic shifts related to the HBP, which are commonly found in most cancers. It also describes O-GlcNAc modified proteins identified in primary breast and colorectal cancer, as well as in the related cancer cell lines. Moreover, we also discuss the potential use of aberrant O-GlcNAcylated proteins as novel biomarkers of cancer.

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Osteosarcoma is a common malignant bone tumor in children and adolescents. The current 5-year survival rate is ~60% and that seems to be reaching a plateau. In order to improve treatment outcomes of osteosarcoma, a better understanding of tumorigenesis and underlying molecular mechanisms is required for searching out possible new treatment targets. This study aimed to identify the potential proteins involving the pathogenesis of osteosarcoma using a proteomics approach. Proteins extracted from primary cell culture of osteosarcoma (n=7) and osteoblasts of cancellous bone (n=7) were studied. Using 2-DE based proteomics and LC-MS/MS analysis, we successfully determined seven differentially expressed protein spots. Four upregulated proteins and three downregulated proteins were observed in this study in which KH-type splicing regulatory protein (KSRP) was selected for further exploration. KSRP was significantly upregulated in osteosarcoma cells compared to osteoblasts using western blot assay. In addition, immunohistochemistry demonstrated that KSRP was also highly expressed in osteosarcoma tissue of independent cases from the experimental group. More importantly, KSRP silencing of osteosarcoma cell lines significantly decreased cell proliferation, migration ability, as well as implantation and growth ability in chick chorioallantoic membrane assay. Taken together, these findings demonstrate, that KSRP plays important roles in regulatory controls of osteosarcoma pathogenesis and serves as a potentially therapeutic target of osteosarcoma.

O-GlcNAcylation is a dynamic post-translational modification that has extensive crosstalk with phosphorylation either at the same or adjacent sites of various proteins. We have previously reported that O-GlcNAcylation level was increased in primary breast and colorectal cancer, but the interplay of the two modifications remains unclear. Therefore, we explored crosstalk of the modifications by RNA interference against O-GlcNAc transferase (OGT) in colorectal cancer cells. Two-dimensional immunoblotting and mass spectrometric analysis showed that the levels of O-GlcNAc and serine phosphorylation of many proteins including serine hydroxymethyltransferase, cytokeratin-8, pyruvate kinase M2 (PKM2), heterogeneous nuclear ribonucleoprotein L, and lamin-B1, were reduced in siOGT cells compared to siScramble cells. In HT29 cells, immunoprecipitated PKM2 revealed decreased O-GlcNAc and serine phosphorylation levels after siOGT knockdown, but increased levels after treatment with Thiamet-G, an inhibitor of O-GlcNAcase (OGA). In addition, when global O-GlcNAcylation was enhanced by treating cells with Thiamet-G, PKM2 expression level was upregulated, but PKM2-specific activity was decreased. On the other hand, in OGT knockdown cells, PKM2 expression level was downregulated, but PKM2-specific activity was increased. Moreover, the metastatic colorectal cancer cells, SW620, had more O-GlcNAc-PKM2 and showed lower PKM2-specific activity compared to the non-metastatic colorectal cancer SW480 cells. These results suggested roles of O-GlcNAcylation in modulating serine phosphorylation, as well as in regulating PKM2 activity and expression. Interfering levels of O-GlcNAcylation of PKM2 may be a novel target in controlling cancer metabolism and tumorigenesis of colorectal cancer.

Background This study identifies the overall survival status of lung cancer patients with bone metastasis and metastasis patterns. Poor prognostic factors were identified to develop a scoring system for estimating survival period after bone metastasis. Methods A retrospective cohort analysis was performed at Chiang Mai University for the period January 1, 2006 and December 31, 2013. Time-to-event analysis was performed to estimate survival rate. The primary end point was death related to lung cancer. Univariate and multivariate analysis of the prognostic variables was done using the Cox's regression model. The score was derived from the corresponding estimated regression coefficients of significantly poor prognostic factors. Results A total of 505 lung cancer with bone metastasis patients were analyzed. Four hundred two cases (79.6%) were concurrent diagnosis and 103 (20.4%) were subsequent diagnosis. The median survival time of lung cancer after bone metastasis 148 days. Male gender and ECOG 3–4 were significant poor prognostic factors for lung cancer after bone metastasis, with hazard ratios of 1.42 (95% CI 1.17–1.73), and 1.30 (95% CI 1.06–1.60), respectively. Prognosis score was determined using the binary term present/not-present for those factors. The curve from prognostic score summations of 2, 1 and 0 presented a good discrimination of survival expectancy, showing an expected median survival time of approximately 109, 146, and 225 days, respectively. Conclusions Prognostic score is a clinically simple and easy method for estimating life expectancy and for guiding interventions in bone metastasis of lung cancer.