Cellular expression, trafficking, and function of two isoforms of human ULBP5/RAET1G

Eagle, R.A., Flack, G., Warford, A., Martínez-Borra, J., Jafferji, I., Traherne, J.A., Ohashi, M., Boyle, L.H., Barrow, A.D., Caillat-Zucman, S., Young, N.T. and Trowsdale, J. 2009. Cellular expression, trafficking, and function of two isoforms of human ULBP5/RAET1G. PLoS ONE. 4 (2), p. e4503.

TitleCellular expression, trafficking, and function of two isoforms of human ULBP5/RAET1G
AuthorsEagle, R.A., Flack, G., Warford, A., Martínez-Borra, J., Jafferji, I., Traherne, J.A., Ohashi, M., Boyle, L.H., Barrow, A.D., Caillat-Zucman, S., Young, N.T. and Trowsdale, J.
Abstract

Background

The activating immunoreceptor NKG2D is expressed on Natural Killer (NK) cells and subsets of T cells. NKG2D contributes to anti-tumour and anti-viral immune responses in vitro and in vivo. The ligands for NKG2D in humans are diverse proteins of the MIC and ULBP/RAET families that are upregulated on the surface of virally infected cells and tumours. Two splicing variants of ULBP5/RAET1G have been cloned previously, but not extensively characterised.

Methodology/Principal Findings

We pursue a number of approaches to characterise the expression, trafficking, and function of the two isoforms of ULBP5/RAET1G. We show that both transcripts are frequently expressed in cell lines derived from epithelial cancers, and in primary breast cancers. The full-length transcript, RAET1G1, is predicted to encode a molecule with transmembrane and cytoplasmic domains that are unique amongst NKG2D ligands. Using specific anti-RAET1G1 antiserum to stain tissue microarrays we show that RAET1G1 expression is highly restricted in normal tissues. RAET1G1 was expressed at a low level in normal gastrointestinal epithelial cells in a similar pattern to MICA. Both RAET1G1 and MICA showed increased expression in the gut of patients with celiac disease. In contrast to healthy tissues the RAET1G1 antiserum stained a wide variety or different primary tumour sections. Both endogenously expressed and transfected RAET1G1 was mainly found inside the cell, with a minority of the protein reaching the cell surface. Conversely the truncated splicing variant of RAET1G2 was shown to encode a soluble molecule that could be secreted from cells. Secreted RAET1G2 was shown to downregulate NKG2D receptor expression on NK cells and hence may represent a novel tumour immune evasion strategy.

Conclusions/Significance

We demonstrate that the expression patterns of ULBP5RAET1G are very similar to the well-characterised NKG2D ligand, MICA. However the two isoforms of ULBP5/RAET1G have very different cellular localisations that are likely to reflect unique functionality.

JournalPLoS ONE
Journal citation4 (2), p. e4503
ISSN1932-6203
Year2009
PublisherPublic Library of Science
Digital Object Identifier (DOI)doi:10.1371/journal.pone.0004503
Publication dates
Published2009

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