Constitutive signaling of the human cytomegalovirus-encoded chemokine receptor US28.
Previously it was shown that the HHV-8-encoded chemokine receptor ORF74 shows considerable agonist-independent, constitutive activity giving rise to oncogenic transformation (Arvanitakis, L., Geras-Raaka, E., Varma, A., Gershengorn, M. C., and Cesarman, E. (1997) Nature 385, 347-350). In this study we report that a second viral-encoded chemokine receptor, the human cytomegalovirus-encoded US28, also efficiently signals in an agonist-independent manner. Transient expression of US28 in COS-7 cells leads to the constitutive activation of phospholipase C and NF-kappaB signaling via G(q/11) protein-dependent pathways. Whereas phospholipase C activation is mediated via Galpha(q/11) subunits, the activation of NF-kappaB strongly depends on betagamma subunits with a preference for the beta(2)gamma(1) dimer. The CC chemokines RANTES (regulated on activation, normal T cell expressed and secreted) and MCP-1 (monocyte chemotactic protein-1) act as neutral antagonists at US28, whereas the CX(3)C chemokine fractalkine acts as a partial inverse agonist with IC(50) values of 1-5 nm. Our data suggest that a high level of constitutive activity might be a more general characteristic of viral G protein-coupled receptors and that human cytomegalovirus might exploit this G protein-coupled receptor property to modulate the homeostasis of infected cells via the early gene product US28.
Casarosa
P
P
Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands.
Bakker
R A
RA
Verzijl
D
D
Navis
M
M
Timmerman
H
H
Leurs
R
R
Smit
M J
MJ
D000818:Animals; D019556:COS Cells; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D019743:Chemokines, CXC / Q000502:physiology; D002522:Chlorocebus aethiops; D003587:Cytomegalovirus / Q000235:genetics / Q000502:physiology*; D006023:Glycoproteins; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D016328:NF-kappa B / Q000378:metabolism; D019707:Receptors, Chemokine / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
C515538:CX3CL1 protein, human; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D019743:Chemokines, CXC; D006023:Glycoproteins; D007295:Inositol Phosphates; C113454:K8.1 protein, Human herpesvirus 8; D008565:Membrane Proteins; D016328:NF-kappa B; D019707:Receptors, Chemokine; D011994:Recombinant Proteins; C411191:US28 receptor, Cytomegalovirus; D014764:Viral Proteins; D010738:Type C Phospholipases; D020962:Heterotrimeric GTP-Binding Proteins