The rat cytomegalovirus R33-encoded G protein-coupled receptor signals in a constitutive fashion.
The rat cytomegalovirus (RCMV) R33 gene is conserved among all betaherpesviruses and encodes a protein (pR33) that shows sequence similarity with chemokine-binding G protein-coupled receptors (GPCRs). Previously, the physiological significance of the R33 gene was demonstrated by the finding that an RCMV strain with R33 deleted is severely attenuated in vivo and is unable to either enter or replicate in the salivary glands of infected rats. Here, we report that RCMV pR33 is expressed as a functional GPCR that signals in an agonist-independent manner in both COS-7 and Rat2 cells. Transient expression of pR33 in COS-7 cells results in constitutive activation of phospholipase C (PLC) due to coupling to G proteins of the G(q) class. Interestingly, PLC activation is partially inhibited by cotransfection with G(alpha)-transducin subunits, which indicates the involvement of G(betagamma) as well as Galpha subunits in pR33-mediated signaling. Surprisingly, PLC activation is also partially inhibited by addition of pertussis toxin (PTX), suggesting that pR33 activates not only G(q) but also G(i/0) proteins. The constitutive activation of G(i/0) proteins by pR33 is further demonstrated by the PTX-sensitive decrease of CRE-mediated transcription and the PTX-sensitive increase of both NF-kappaB- and SRE-mediated transcription. In contrast to its homolog of human herpesvirus 6B (pU12), pR33 does not bind RANTES.
Gruijthuijsen
Yvonne K
YK
Department of Medical Microbiology, Cardiovascular Research Institute Maastricht, University of Maastricht, 6202 AZ Maastricht, The Netherlands.
Casarosa
Paola
P
Kaptein
Suzanne J F
SJ
Broers
Jos L V
JL
Leurs
Rob
R
Bruggeman
Cathrien A
CA
Smit
Martine J
MJ
Vink
Cornelis
C
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D018946:Chemokine CCL5 / Q000378:metabolism; D002522:Chlorocebus aethiops; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019204:GTP-Binding Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018146:Muromegalovirus / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D018946:Chemokine CCL5; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D008164:Luminescent Proteins; D016328:NF-kappa B; D011956:Receptors, Cell Surface; C066670:UL33 protein, Human herpesvirus 1; D014759:Viral Envelope Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins