The androgen receptor controls expression of the cancer-associated sTn antigen and cell adhesion through induction of ST6GalNAc1 in prostate cancer

Abstract

Patterns of glycosylation are important in cancer, but the molecular mechanisms that drive changes are often poorly understood. The androgen receptor drives prostate cancer (PCa) development and progression to lethal metastatic castration-resistant disease. Here we used RNA-Seq coupled with bioinformatic analyses of androgen-receptor (AR) binding sites and clinical PCa expression array data to identify ST6GalNAc1 as a direct and rapidly activated target gene of the AR in PCa cells. ST6GalNAc1 encodes a sialytransferase that catalyses formation of the cancer-associated sialyl-Tn antigen (sTn), which we find is also induced by androgen exposure. Androgens induce expression of a novel splice variant of the ST6GalNAc1 protein in PCa cells. This splice variant encodes a shorter protein isoform that is still fully functional as a sialyltransferase and able to induce expression of the sTn-antigen. Surprisingly, given its high expression in tumours, stable expression of ST6GalNAc1 in PCa cells reduced formation of stable tumours in mice, reduced cell adhesion and induced a switch towards a more mesenchymal-like cell phenotype in vitro. ST6GalNAc1 has a dynamic expression pattern in clinical datasets, being significantly up-regulated in primary prostate carcinoma but relatively down-regulated in established metastatic tissue. ST6GalNAc1 is frequently upregulated concurrently with another important glycosylation enzyme GCNT1 previously associated with prostate cancer progression and implicated in Sialyl Lewis X antigen synthesis. Together our data establishes an androgen-dependent mechanism for sTn antigen expression in PCa, and are consistent with a general role for the androgen receptor in driving important coordinate changes to the glycoproteome during PCa progression.

Glycosylation is a global target for androgen control in prostate cancer cells

“…Induction of ST6GalNAc1 was found to promote a more mesenchymal cell phenotype in prostate cancer cells and to inhibit the formation of stable tumour masses in mouse models. Further analysis of prostate cancer tissue showed that although ST6GalNAc1 is increased in primary tumours, expression is dramatically downregulated in metastatic disease, indicating that ST6GalNAc1 may have a transient role in prostate cancer progression (Munkley et al 2015c). Our analysis of the prostate cancer transcriptome also identified the core 2 branching enzyme GCNT1 as an AR target gene in prostate cancer patients .…”

“…Increased expression of sialylated glycans creates negative charges and can inhibit the cell adhesion through electrostatic repulsion (Munkley & Elliott 2016b). We found previously that in prostate cancer cells, the androgen receptor controls the expression of the cancer-associated sTn antigen and cell adhesion through induction of ST6GalNAc1 (Munkley et al 2015c) (Fig. 3).…”

“…As GALNT7 initiates O-glycosylation, upregulation of this enzyme could be linked to a range of changes to O-glycans in prostate cancer cells. We also identified the sialyltransferase ST6GalNAc1 as being directly regulated by androgens in prostate cancer cells (Munkley et al 2015c. ST6GalNAc1 adds sialic acid to the Tn antigen to produce the cancer-associated onco-foetal sialyl-Tn (sTn) antigen, which is linked to poor prognosis in numerous cancer types (Munkley 2016).…”

“…O-glycan biosynthesis ST6GALNAC1 Sialylation of O-glycans to produce the cancer-associated sTn antigen (Munkley 2016) Associated with poor prognosis in numerous cancer types (Munkley 2016). Promotes tumourigenicity and metastasis in breast and gastric cancer cells (Julien et al 2006, Ozaki et al 2012 ST6GALNAC1 shown to synthesise sTn and reduce cell adhesion in prostate cancer cells (Munkley et al 2015c, Munkley & Elliott 2016b. sTn antigen expressed in high grade prostate tumours (Myers et al 1994, Genega et al 2000.…”

“…sTn antigen expressed in high grade prostate tumours (Myers et al 1994, Genega et al 2000. Androgen regulated in prostate cancer cells (Munkley et al 2015c) GALNT7…”