Activation of the PI3K/Akt pathway early during vaccinia and cowpox virus infections is required for both host survival and viral replication.
Viral manipulation of the transduction pathways associated with key cellular functions such as actin remodeling, microtubule stabilization, and survival may favor a productive viral infection. Here we show that consistent with the vaccinia virus (VACV) and cowpox virus (CPXV) requirement for cytoskeleton alterations early during the infection cycle, PBK/Akt was phosphorylated at S473 [Akt(S473-P)], a modification associated with the mammalian target of rapamycin complex 2 (mTORC2), which was paralleled by phosphorylation at T308 [Akt(T308-P)] by PI3K/PDK1, which is required for host survival. Notably, while VACV stimulated Akt(S473-P/T308-P) at early (1 h postinfection [p.i.]) and late (24 h p.i.) times during the infective cycle, CPXV stimulated Akt at early times only. Pharmacological and genetic inhibition of PI3K (LY294002) or Akt (Akt-X and a dominant-negative form of Akt-K179M) resulted in a significant decline in virus yield (from 80% to >/=90%). This decline was secondary to the inhibition of late viral gene expression, which in turn led to an arrest of virion morphogenesis at the immature-virion stage of the viral growth cycle. Furthermore, the cleavage of both caspase-3 and poly(ADP-ribose) polymerase and terminal deoxynucleotidyl transferase-mediated deoxyuridine nick end labeling assays confirmed that permissive, spontaneously immortalized cells such as A31 cells and mouse embryonic fibroblasts (MEFs) underwent apoptosis upon orthopoxvirus infection plus LY294002 treatment. Thus, in A31 cells and MEFs, early viral receptor-mediated signals transmitted via the PI3K/Akt pathway are required and precede the expression of viral antiapoptotic genes. Additionally, the inhibition of these signals resulted in the apoptosis of the infected cells and a significant decline in viral titers.
Soares
Jamária A P
JA
Grupo de Transdução de Sinal, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil.
Leite
Flávia G G
FG
Andrade
Luciana G
LG
Torres
Alice A
AA
De Sousa
Lirlândia P
LP
Barcelos
Lucíola S
LS
Teixeira
Mauro M
MM
Ferreira
Paulo C P
PC
Kroon
Erna G
EG
Souto-Padrón
Thaís
T
Bonjardim
Cláudio A
CA
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D015605:Cowpox / Q000378:metabolism; D015608:Cowpox virus / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015967:Gene Expression Regulation, Viral; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D014615:Vaccinia / Q000378:metabolism; D014616:Vaccinia virus / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication
D002867:Chromones; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D011065:Poly(ADP-ribose) Polymerases; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D053148:Caspase 3