Adenoviral vector saturates Akt pro-survival signaling and blocks insulin-mediated rescue of tumor necrosis-factor-induced apoptosis.
Recombinant adenoviruses are used extensively as delivery vectors in clinical gene therapy and in molecular biology, but little is known about how the viral carrier itself contributes to cellular responses. Here we show that infection with an E1/E3-deleted adenoviral vector (Adv) sensitizes human epithelial cells to tumor necrosis factor (TNF)-induced apoptosis. To explore the mechanism of Adv-mediated sensitization, we measured activity time courses for three protein kinases (MK2, IKK and JNK1) centrally involved in the TNF-receptor signaling network, as well as two kinases (Akt and ERK) activated by growth factors. Both the pro-apoptotic signal MK2 and the anti-apoptotic signal Akt were upregulated when Adv-infected cells were stimulated with TNF, and MK2 and Akt each contributed significantly to TNF-induced cell fate. Surprisingly, further activation of Akt in Adv-infected cells via insulin treatment did not significantly reduce apoptosis or MK2 activity. We show that the ineffectiveness of insulin-mediated anti-apoptotic signaling through Akt is due to saturation of Akt-effector substrate phosphorylation in Adv-infected cells. Normalizing Akt signaling relative to its Adv-induced baseline activity identified a global dose-response curve that relates Akt signaling to cellular survival. Thus, the background Akt activity induced by Adv limits the transmission of anti-apoptotic signals in response to further cytokine or growth-factor stimulation. The phenotypic and intracellular synergy between Adv and TNF may have implications for interpreting cellular responses in gene-therapy and laboratory applications.
Miller-Jensen
Kathryn
K
Biotechnology Process Engineering Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Janes
Kevin A
KA
Wong
Yun-Ling
YL
Griffith
Linda G
LG
Lauffenburger
Douglas A
DA
D000256:Adenoviridae / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects; D005822:Genetic Vectors / Q000378:metabolism*; D019073:HT29 Cells; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
D007328:Insulin; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D051057:Proto-Oncogene Proteins c-akt