Submitted February 6, 2008
Accepted June 11, 2008
Requirement of TLR2-mediated signalling for the induction of IL-15 gene expression in human monocytic cells by HSV-1
Rasheed Ahmad, Souad El Bassam, Paulo Cordeiro, and Jose Menezes*
Ste-Justine Hospital Research Center and Department of Microbiology & Immunology, University of Montreal, Montreal, Quebec, Canada
* Corresponding author; email: jose.menezes{at}recherche-ste-justine.qc.ca.
Exposure of human monocytic cells to HSV-1 results in immediate upregulation of IL-15 gene expression. However, the receptor involved in this induction is not known. Here, we provide evidence that this induction depends on TLR2-mediated signalling pathway. Through the use of small interfering RNAs (siRNA), we demonstrate that HSV-1-induced upregulation of IL-15 gene expression in monocytic THP1 cells requires the presence of the adaptors MyD88, IRAK1 and TRAF6. Interestingly, TIRAP/Mal, an adaptor molecule specifically recruited to TLR2 and TLR4, was also required for maximal upregulation of IL-15. This response was completely abrogated by anti-TLR2, but not anti-TLR4, blocking mAbs in both primary monocytes and THP1 cells. Furthermore, THP1 cells rendered defective in TLR2 expression by disrupting the expression of Sp1, a major transcription factor involved in TLR2 promoter activity, were unable to upregulate IL-15 gene expression in response to HSV-1. In addition, HSV-1-induced NF-
B activation was significantly reduced following neutralization of TLR2 and the adaptor proteins. Altogether, these results obtained using both genetic and pharmacological approaches, unequivocally show that HSV-1 induces TLR2-dependent activation of IL-15 gene expression, which requires the recruitment of both MyD88 and TIRAP/Mal and the activation of IRAK1 and TRAF6 leading to NF-B translocation to the nucleus.
