NEU1 sialidase regulates the sialylation state of CD31 and disrupts CD31-driven capillary-like tube formation in human lung microvascular endothelia [Cell Biology]

February 18th, 2014 by Lee, C., Liu, A., Miranda-Ribera, A., Hyun, S. W., Lillehoj, E. P., Cross, A. S., Passaniti, A., Grimm, P. R., Kim, B.-Y., Welling, P. A., Madri, J. A., DeLisser, H. M., Goldblum, S. E.

The highly sialylated vascular endothelial surface undergoes changes in sialylation upon adopting the migratory/angiogenic phenotype. We recently established endothelial cell (EC) expression of NEU1 sialidase (Cross, AS et al; J Biol Chem 287:15966-15980, 2012). We asked whether NEU1 might regulate EC capillary-like tube formation on a Matrigel substrate. In human pulmonary microvascular EC (HPMEC)s, prior silencing of NEU1 did not alter tube formation. Infection of HPMECs with increasing MOIs of an adenovirus (Ad) encoding for catalytically-active wild-type (WT) NEU1 dose-dependently impaired tube formation whereas overexpression of either a catalytically-dead NEU1 mutant, NEU1-G68V, or another sialidase, NEU3, did not. NEU1 overexpression also diminished EC adhesion to the Matrigel substrate and restrained EC migration in a wounding assay. In HPMECs, the adhesion molecule, CD31, also known as platelet endothelial cell adhesion molecule (PECAM)-1, was sialylated via α2,6-linkages, as shown by Sambucus nigra agglutinin (SNA) lectin blotting. NEU1 overexpression increased CD31 binding to Arachis hypogaea or peanut agglutinin (PNA) lectin, indicating CD31 desialylation. In the postconfluent state, when CD31 ectodomains are homophilically engaged, NEU1 was recruited to and desialylated CD31. In postconfluent ECs, CD31 was desialylated compared with subconfluent cells, and prior NEU1 silencing completely protected against CD31 desialylation. Prior CD31 silencing and the use of CD31-null ECs each abrogated the NEU1 inhibitory effect on EC tube formation. Sialyltransferase (ST) 6 GAL-I overexpression increased α2,6-linked CD31 sialylation and dose-dependently counter-acted NEU1-mediated inhibition of EC tube formation. These combined data indicate that catalytically-active NEU1 inhibits in vitro angiogenesis through desialylation of its substrate, CD31.
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