Adenovirus E4 open reading frame 4-induced apoptosis involves dysregulation of Src family kinases.
The adenoviral early region 4 open reading frame 4 (E4orf4) death factor induces p53-independent apoptosis in many cell types and appears to kill selectively transformed cells. Here we show that expression of E4orf4 in transformed epithelial cells results in early caspase-independent membrane blebbing, associated with changes in the organization of focal adhesions and actin cytoskeleton. Evidence that E4orf4 can associate with and modulate Src family kinase activity, inhibiting Src-dependent phosphorylation of focal adhesion kinase (FAK) and paxillin while increasing phosphorylation of cortactin and some other cellular proteins, is presented. Furthermore, E4orf4 dramatically inhibited the ability of FAK and c-src to cooperate in induction of tyrosine phosphorylation of cellular substrates, suggesting that E4orf4 can interfere with the formation of a signaling complex at focal adhesion sites. Consistent with a functional role for E4orf4-Src interaction, overexpression of activated c-src dramatically potentiated E4orf4-induced membrane blebbing and apoptosis, whereas kinase dead c-src constructs inhibited E4orf4 effects on cell morphology and death. Moreover treatment of E4orf4-expressing cells with PP2, a selective Src kinase inhibitor, led to inhibition of E4orf4-dependent membrane blebbing and later to a marked decrease in E4orf4-induced nuclear condensation. Taken together, these observations indicate that expression of adenovirus 2 E4orf4 can initiate caspase-independent extranuclear manifestations of apoptosis through a modulation of Src family kinases and that these are involved in signaling E4orf4-dependent apoptosis. This study also suggests that Src family kinases are likely to play a role in the cytoplasmic execution of apoptotic programs.
Lavoie
J N
JN
Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Québec, G1R 2J6, Canada. lavoie@crhdq.ulaval.ca
Champagne
C
C
Gingras
M C
MC
Robert
A
A
D000260:Adenoviruses, Human / Q000235:genetics*; D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure*; D002465:Cell Movement; D005353:Fibronectins; D006801:Humans; D007668:Kidney; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
C121517:E4orf4 protein, adenovirus; D005353:Fibronectins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D019061:src-Family Kinases; D020169:Caspases