Distinct cell death pathways triggered by the adenovirus early region 4 ORF 4 protein

Abstract

In transformed cells, induction of apoptosis by adenovirus type 2 (Ad2) early region 4 ORF 4 (E4orf4) correlates with accumulation of E4orf4 in the cell membrane–cytoskeleton fraction. However, E4orf4 is largely expressed in nuclear regions before the onset of apoptosis. To determine the relative contribution of nuclear E4orf4 versus membrane-associated E4orf4 to cell death signaling, we engineered green fluorescent fusion proteins to target E4orf4 to specific cell compartments. The targeting of Ad2 E4orf4 to cell membranes through a CAAX-box or a myristylation consensus signal sufficed to mimic the fast Src-dependent apoptotic program induced by wild-type E4orf4. In marked contrast, the nuclear targeting of E4orf4 abolished the early induction of extranuclear apoptosis. However, nuclear E4orf4 still induced a delayed cell death response independent of Src-like activity and of E4orf4 tyrosine phosphorylation. The zVAD.fmk-inhibitable caspases were dispensable for execution of both cell death programs. Nevertheless, both pathways led to caspase activation in some cell types through the mitochondrial pathway. Finally, our data support a critical role for calpains upstream in the death effector pathway triggered by the Src-mediated cytoplasmic death signal. We conclude that Ad2 E4orf4 induces two distinct cell death responses, whose relative contributions to cell killing may be determined by the genetic background.

Cancer-selective therapy of the future: Apoptin and its mechanism of action

“…95,96 Unlike this, is the case with apoptin, where the nucleocytoplasmic shuttling of the protein is not affected by leptomycin B, an inhibitor of the CRM1 mediated nuclear export pathway. 97,98 E4orf4 gets phosphorylated at tyrosine residues Y26, Y42 and Y59 by src kinases, and this phosphorylation, and the interaction with the src kinases inhibits the nuclear import of the protein. The tyrosine phosphorylation of E4orf4 is correlated with the cell death induced by cytoplasmic E4orf4, as the mutation of these residues impairs the killing activity of E4orf4.…”

Galectin-1 induces nuclear translocation of endonuclease G in caspase- and cytochrome c-independent T cell death

“…As non-caspase proteases have also been implicated in cell death, 2,[19][20][21][22] we also examined the ability of several other protease inhibitors to inhibit galectin-1 cell death. We observed no reduction in galectin-1 induced PS exposure with calpain inhibitors I and II, serine protease inhibitors TPCK and TLCK, cathepsin inhibitors pepstatin and CA-074 Me, or the proteasome inhibitor lactacystin (data not shown).…”

Fusion protein of adenovirus E4orf4 and human epidermal growth factor inhibits tumor cell growth

“…As seen in previous reports, E4orf4 triggered distinct cell death pathways in different kinds of cells, such as caspase activation was shown in H1299 and 293T cells but not in other cell types. 7,8,24,25 In other words, the majority of cancer cells have their own complex genetic background and there is a specific signaling pathway to regulate cell proliferation and survival. Further investigations will be conducted to identify the EGFR-expression tumor that may be more sensitive to EGF-E4orf4 or suitable to accept the treatment by EGF-E4orf4.…”