Pan-cancer analysis of altered glycosyltransferases confers poor clinical outcomes

Glycosylation is a post-translational modification (PTM) process that attaches carbohydrates to proteins and lipids. Protein glycosylation can be N-linked or O-linked depending on adding sugars onto the side chains of Asn or Ser/Thr residues, respectively. PTM comprises glycan-modifying enzymes glycosyltransferases (GTs) and glycosidases.

O-glycan truncation, N-glycan branching, sialylation, and fucosylation are the most well-known cancer-associated glycosylations. The glycan-modifying enzymes stimulate various malignant behaviors of tumors, such as tumor proliferation, invasion, epithelial-mesenchymal transition, metastasis, angiogenesis, immune modulation, and cell-matrix interactions (1, 2). Over 200 glycosyltransferases regulate glycosylation. An unbiased global approach must be used to identify glycogenes in cancer. In this study, Yin et al. (3)(2022) investigated the fascinating examination of glycosyltransferases in pan-cancer using bioinformatics investigation from CCLE, TCGA, single-cell RNA sequencing datasets and proteogenomic assets across various cancer types.

The study by Yin et al. (3) uncovered mutations of GTs across 33 types of cancer. Also, the study has interestingly discovered that the top three mutated GTs are ALG13 (11.6%) in uterine corpus endometrial carcinoma (UCEC), FUT9 (10.6%), GALNT13 (10.6%) in skin cutaneous melanoma (SKCM), and UGGT2 (>5%) in colon adenocarcinoma (COAD). The survival analysis of patients with UGGT2 mutations in COAD was linked to worse clinical outcomes, whereas ALG13 mutations in UCEC were linked with better survival. This finding indicates that GTs mutations play a vital role in the patients’ overall survival. Yin et al. (3) further analyzed the drug sensitivity study from CCLE databases which revealed that the UGGT2 mutation was resistant to EGFR inhibitors (Erlotinib and Lapatinib) in colon cancer cell lines, and ALG13 mutation was sensitive to Panobinostat and Sorafenib in endometrial cancer cell lines (Figure 1A). These findings imply that identifying GTs mutations will pave the way for better cancer treatment.

Figure 1: Genetic alteration and clinical significance of glycosyltransferases pan-cancer.

A) Identification of GTs mutations across 33 types of cancer. The top 3 mutated GTs are ALG13 (11.6%) in UCEC and FUT9 (10.6%), GALNT13 (10.6%) in SKCM, and UGGT2 (>5%) in COAD. The survival analysis revealed poor survival with UGGT2 mutation in COAD and better survival with ALG13 mutation in UCEC. The colon cell lines with UGGT2 mutation showed resistance to EGFR inhibitors, and the endometrial cancer cell lines with ALG13 mutation are sensitive to HDAC inhibitors. B) ALG3, B3GALT2, and ST6GALNAC3 displayed consistent expression alterations across 16 cancers; this could cause tumor progression. Aberrant expression of GALNT14, B3GNT3 in LUAD, and downregulation of GYS2 in LIHC lead to poor clinical outcomes in the patient.

The extended study by Yin et al. showed expressional changes in GTs in 16 tumors; among them, three GTs (ALG3, B3GALT2, and ST6GALNAC3) displayed consistent alterations across 16 cancers. Interestingly, upregulation of ALG3 and downregulation of B3GALT2 and ST6GALNAC3 were found across cancer types. The functional analysis of these three GTs indicates that the changes in expression and biological effects are functionally similar across different types of cancer. These findings also suggest that biological function influences tumorigenesis in all types of 16 cancers. Furthermore, the expression of GTs is tightly associated with patients’ prognoses. The reduced expression of GYS2 conveyed a poor prognosis in liver hepatocellular carcinoma (LIHC). The aberrant expression of B3GNT3 and GALNT14 were related to overall survival in lung adenocarcinoma (LUAD) (Figure 1B).

In addition, the study by Yin et al. demonstrated the correlation between GTs and tumor microenvironment (TME) in cancer. The expression of MFNG is positively correlated to activated CD8+ T cells in LUAD and SKCM. The high infiltration of active CD8+ T cells indicates a favorable prognosis, indicating that activating these cells in the TME has a therapeutic advantage. The single-cell RNA sequencing dataset revealed that MFNG was expressed in CX3CR1+ cytotoxic T cells ((4, 5). Identifying the association between MFNG and CD8+ T cells will lead to a better prognosis in LAUD and SKCM (Figure 2A). In the proteogenomic study, Yin et al. (3) identified and validated that GALNT4, MGAT5, and UGGT2, were substantially correlated with proliferation. The interaction between the TME components and GTs is significantly associated with angiogenesis, EMT, hypoxia, and stromal cells in LIHC. Patients with high MGAT5 and UGGT2 expression had shorter overall survival according to the protein expression study by tissue microarrays (TMAs) (N154). Moreover, the inhibition effect of the GTs (GALNT4, MGAT5, and UGGT2) downregulates migration and proliferation in LIHC cell lines. These findings imply that GALNT4, MGAT5, and UGGT2 expression and TME factors lead to a worse prognosis in LIHC patients.

Figure 2: The role of glycosyltransferases in the tumor microenvironment, tumorigenesis, and metastasis in cancers.

A) The cytotoxic T cells expressed the MFNG protein associated with activated CD8+ T cells, leading to a better prognosis in LUAD and SKCM. B) The loss of C1GALT1 increases aberrant glycosylation of O-linked Tn-antigens in CD44. The glycosylated CD44 aids stemness, tumor progression, and metastasis in pancreatic cancer cells. C) The p53^R175H mutation influences ST6GALNAC-I expression, which causes aberrant glycosylation of O-linked STn-antigens on MUC5AC. MUC5AC/STn stimulates migration, angiogenesis, and liver metastasis in lung cancer.

Supporting Yin et al. findings, a recent study provides evidence of the truncated glycans Tn and STn altered in pancreatic cancer (3). Frank et al. (6) revealed that C1GALT1 KO pancreatic cancer (PC) cells identified aberrant O-glycan truncation (Tn antigen) on CD44, which leads to enhanced CSC features, tumor progression, and metastasis (Figure 2B). Srikanth et al. (7) showed that O-glycosyltransferases GALNT3 and B3GNT3 expression regulate stemness via modification of sialyl lewis A (sLe^a) on CD44v6 in pancreatic cancer stem cells. Another in vivo study by Seema et al. (8) showed that the loss of C1galt1 promoted the development of aggressive PC and enhanced metastasis in KPC (Kras^G12D/+; Trp53^R172H/+; Pdx-1-Cre) mice. Knockout of C1GALT1 leads to increased tumorigenicity and truncation of O-glycosylation on MUC16 mucin in PC. Interestingly, the loss of C1GALT1 expression enhanced PC stemness, tumorigenic and metastatic potential. Another study suggests that human GTs are novel PC targets(1). The Sialyl-Tn antigen is highly expressed in various human carcinomas and is associated with aggressive carcinoma and poor prognosis (9). ST6GalNAc-I is an O-glycosyltransferase that catalyzes the addition of sialic acid to the initiating GalNAc residues forming sialyl Tn (STn) on glycoproteins. In lung cancer, Imayavaramban et al. (10) demonstrated that mutant p53^R175H mediates ST6GalNAc-I expression, leading to the sialyation of MUC5AC. GALNT3, GALNT5, and B3GNT3 GTs mRNA expression were downregulated in ST6GalNAc-I KO cells, whereas FUT9, COLGALT2, HAS3, and ST8Sia2 were upregulated in lung cancer cells. These exciting findings show that MUC5AC sialyation promotes angiogenesis, aggressive growth, and liver metastasis in LUAD.

In conclusion and perspective, glycan alteration is a major driver of tumor progression and metastasis, and glycan structure is uniquely expressed on tumor cells; they can serve as potential therapeutic targets. The pan-cancer analysis showed the molecular landscape and the clinical significance of GTs. Interestingly, this study identified the genetic alterations and highest mutation frequencies of GTs across 33 types of cancer. Furthermore, these findings revealed GT expression features, and their pathway interaction is linked to tumor progression in 16 different types of cancer. Overall, the pan-cancer analysis established a way to understand glycosylation dysregulation across cancer types. Furthermore, the study requires determining the common substrate and site-specific function of GTs, which will aid in the development of more useful prognostic, diagnostic, or treatment of cancers by targeting specific glycosylation with small-molecule inhibitors against GTs.

Abbreviations

ACC

Adrenocortical Carcinoma

BLCA

Bladder Urothelial Carcinoma

BRCA

Breast Invasive Carcinoma

CCLE

Cancer Cell Line Encyclopedia

CESC

Cervical Squamous Cell Carcinoma and Endocervical Adenocarcinoma

CHOL

Cholangio Carcinoma

COAD

Colon Adenocarcinoma

DLBC

Lymphoid Neoplasm Diffuse Large B-cell Lymphoma

EGFR

Epidermal growth factor receptor

EMT

Epithelial-mesenchymal transition

ESCA

Esophageal Carcinoma

GBM

Glioblastoma Multiforme

GBM

Glioblastoma

HNSC

Head and Neck Squamous Cell Carcinoma

KICH

Kidney Chromophobe

KIRC

Kidney Renal Clear Cell Carcinoma

KIRP

Kidney Renal Papillary Cell Carcinoma

LAML

Acute Myeloid Leukemia

LGG

Brain Lower Grade Glioma

LGG

Low-grade gliomas

LIHC

Liver Hepatocellular Carcinoma

LUAD

Lung Adenocarcinoma

LUSC

Lung Squamous Cell Carcinoma

MESO

Mesothelioma

OV

Ovarian Serous Cystadenocarcinoma

PAAD

Pancreatic Adenocarcinoma

PCPG

Pheochromocytoma and Paraganglioma

PDAC

Pancreatic ductal adenocarcinoma

PRAD

Prostate Adenocarcinoma

READ

Rectum Adenocarcinoma

SARC

Sarcoma

SKCM

Skin Cutaneous Melanoma

STAD

Stomach Adenocarcinoma

TCGA

The Cancer Genome Atlas

TGCT

Testicular Germ Cell Tumors

THCA

Thyroid Carcinoma

THYM

Thymoma

UCEC

Uterine Corpus Endometrial Carcinoma

UCS

Uterine Carcinosarcoma

UVM

Uveal Melanoma