Kaposi's sarcoma-associated herpesvirus induces the phosphatidylinositol 3-kinase-PKC-zeta-MEK-ERK signaling pathway in target cells early during infection: implications for infectivity.
Human herpesvirus 8 (HHV-8) is implicated in the pathogenesis of Kaposi's sarcoma. HHV-8 envelope glycoprotein B (gB) possesses the RGD motif known to interact with integrin molecules, and HHV-8 infectivity was inhibited by RGD peptides, by antibodies against alpha3 and beta1 integrins, and by soluble alpha3beta1 integrin (S. M. Akula, N. P. Pramod, F.-Z. Wang, and B. Chandran, Cell 108:407-419, 2002). Anti-gB antibodies immunoprecipitated the virus alpha3 and beta1 complexes, and virus-binding studies suggest a role for alpha3beta1 in HHV-8 entry. HHV-8 infection induced the integrin-mediated activation of focal adhesion kinase (FAK), implicating a role for integrin and the associated signaling pathways in HHV-8 entry into the target cells. Immediately after infection, target cells exhibited morphological changes and cytoskeletal rearrangements, suggesting the induction of signal pathways. As early as 5 min postinfection, HHV-8 activated the MEK-ERK1/2 pathway. The focal adhesion components phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase C-zeta (PKC-zeta) were recruited as upstream mediators of the HHV-8-induced ERK pathway. Anti-HHV-8 gB-neutralizing antibodies and soluble alpha3beta1 integrin inhibited the virus-induced signaling pathways. Early kinetics of the cellular signaling pathway and its activation by UV-inactivated HHV-8 suggest a role for virus binding and/or entry but not viral gene expression in this induction. Studies with human alpha3 integrin-transfected Chinese hamster ovary cells and FAK-negative mouse DU3 cells suggest that the alpha3beta1 integrin and FAK play roles in the HHV-8 mediated signal induction. Inhibitors specific for PI 3-kinase, PKC-zeta, MEK, and ERK significantly reduced the virus infectivity without affecting virus binding to the target cells. Examination of viral DNA entry suggests a role for PI 3-kinase in HHV-8 entry into the target cells and a role for PKC-zeta, MEK, and ERK at a post-viral entry stage of infection. These findings implicate a critical role for integrin-associated mitogenic signaling in HHV-8's infection of target cells and suggest that, by orchestrating the signal cascade, HHV-8 may create an appropriate intracellular environment to facilitate the infection.
Naranatt
Pramod P
PP
Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City 66160, USA.
Akula
Shaw M
SM
Zien
Christopher A
CA
Krishnan
Harinivas H
HH
Chandran
Bala
B
D000199:Actins / Q000378:metabolism; D001483:Base Sequence; D001704:Biopolymers / Q000378:metabolism; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019288:Herpesvirus 8, Human / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000378:metabolism*; D014774:Virulence; D000099221:Protein Kinase C zeta
D000199:Actins; D001704:Biopolymers; D017931:DNA Primers; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D000099221:Protein Kinase C zeta