Alterations in protein glycosylation have been related to malignant transformation and tumour progression. We recently showed that low mRNA levels of Golgi alpha-mannosidase MAN1A1 correlate with poor prognosis in breast cancer patients. We analysed the role of MAN1A1 on a protein level using western blot analysis (n=105) and studied the impact of MAN1A1-related glycosylation on the prognostic relevance of adhesion molecules involved in breast cancer using microarray data (n=194). Functional consequences of mannosidase inhibition using the inhibitor kifunensine or MAN1A1 silencing were investigated in breast cancer cells in vitro. Patients with low/moderate MAN1A1 expression in tumours showed significantly shorter disease-free intervals than those with high MAN1A1 levels (P=0.005). Moreover, low MAN1A1 expression correlated significantly with nodal status, grading and brain metastasis. At an mRNA level, membrane proteins ALCAM and CD24 were only significantly prognostic in tumours with high MAN1A1 expression. In vitro, reduced MAN1A1 expression or mannosidase inhibition led to a significantly increased adhesion of breast cancer cells to endothelial cells. Our study demonstrates the prognostic role of MAN1A1 in breast cancer by affecting the adhesive properties of tumour cells and the strong influence of this glycosylation enzyme on the prognostic impact of some adhesion proteins.
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