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Infection and Immunity, November 2005, p. 7133-7141, Vol. 73, No. 11
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.11.7133-7141.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Gene Silencing and Overexpression of Porcine Peptidoglycan Recognition Protein Long Isoforms: Involvement in ß-Defensin-1 Expression

Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas 66506

Received 6 February 2005/ Returned for modification 7 March 2005/ Accepted 25 July 2005

Peptidoglycan recognition proteins (PGRPs) are a group of newly identified proteins with emerging functions in mammalian innate immunity. Here we report the identification and characterization of two long isoforms of porcine PGRP. Their complete cDNA sequences encode predicted peptides of 252 and 598 residues and are named pPGRP-L1 and pPGRP-L2, respectively. These porcine isoforms share identical PGRP domains at their C terminus, which are highly conserved with human and mouse orthologs. pPGRP-L1 is expressed constitutively in several tissues, including bone marrow, intestine, liver, spleen, kidney, and skin. pPGRP-L2 is highly expressed in the duodenum and liver, and expression in intestinal tissues is increased by Salmonella infection. In intestinal cells, expression of both pPGRP-L1 and pPGRP-L2 is increased by bacterial infection. Recombinant pPGRP-L1 and pPGRP-L2 have N-acetylmuramoyl-L-alanine amidase activity. Loss-of-function and gain-of-function experiments indicate that these two pPGRPs are involved in expression of the antimicrobial peptide ß-defensin-1. Silencing of pPGRP-L2 in intestinal cells challenged with Listeria monocytogenes results in downregulation of ß-defensin-1. Conversely, overexpression of pPGRP-L1 or pPGRP-L2 dramatically upregulates expression of ß-defensin-1. Collectively, these findings suggest that porcine PGRPs are involved in antimicrobial peptide expression.

Editor: J. F. Urban, Jr.

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