Polarised secretion of cytokines in primary human microvascular endothelial cells is not dependent on N-linked glycosylation

Human microvascular endothelial cells (HMVEC) grow in monolayers on Transwell filters and restrict permeability between the apical and basolateral media. We show that these cell monolayers are capable of sorting labelled endogenous proteins, including chemokines, growth factors and cytokines, to either the apical or basolateral media. IL-8 and GMCSF were secreted predominantly into the apical medium, whereas MIC-1 was secreted into the basolateral medium. This polarity did not correlate with glycosylation, as IL-8 and MIC-1 are both N-glycosylated, but were sorted to opposite sides of the cell. IL-6 is not glycosylated and did not display significant polarity in secretion. Similarly, the polarity of secretion of endogenous glycoproteins was not related to their glycosylation.