“MARCO” “POLO”: HOW RAINBOW TROUT CELLS FIND BACTERIA USING A CLASS A SCAVENGER RECEPTOR
Sarah Poynter, University of Waterloo
Sarah J Poynter1, Andrea Monjo2, Gabriella Micheli3, Stephanie J DeWitte-Orr23*
1. Department of Biology, University of Waterloo, 200 University Ave W, Waterloo, ON
2. Department of Biology, Wilfrid Laurier University, 75 University Ave W, Waterloo, ON
3. Department of Health Sciences, Wilfrid Laurier University, 75 University Ave W, Waterloo, ON
*Corresponding author. Address: Wilfrid Laurier University, 75 University Ave W, Waterloo, ON N2L 3C5. Tel.: 519-884-0710 ext. 4317
E-mail address: sdewitteorr@wlu.ca
Class A scavenger receptors (SR-As) are a family of surface-expressed receptors who bind a wide range of polyanionic ligands including bacterial components and nucleic acids. These receptors play a role in a variety of cellular functions, including innate immunity. Macrophage receptor with collagenous structure (MARCO) is a SR-A family member that has been studied in mammals largely for its role in binding bacteria. To date there is little information about MARCO specifically and SR-As in general in fish, and which SR-As bind to bacteria remains largely unknown. In the present study two novel rainbow trout (rt)MARCO transcript variants have been identified; the deduced amino acid sequences have been analyzed for conserved domains and similarity to existing sequences. When overexpressed in CHSE-214, a Chinook salmon cell line that lacks functional scavenger receptors, GFP-tagged rainbow trout rtMARCO- 1 and rtMARCO-2 were able to bind gram-positive, and gram-negative bacteria of both mammalian and aquatic sources. In mammals the scavenger receptor cysteine-rich (SRCR) domain is necessary for binding bacterial ligands, this was also in the case in rainbow trout, when the rtMARCO proteins were mutated to remove the SRCR the bacteria binding capability of both variants was lost. rtMARCO-1 and rtMARCO-2 did not show any binding to the yeast cell wall component zymosan or to double-stranded (ds)RNA. This is the first time rainbow trout MARCO sequences have been identified and the first in-depth study exploring their ligand binding profile. This study provides novel insight into the role of rainbow trout MARCO in innate immunity.