EGF activates an inducible survival response via the RAS-> Erk-1/2 pathway to counteract interferon-α-mediated apoptosis in epidermoid cancer cells

Abstract

The mechanisms of tumor cell resistance to interferon-a (IFNa) are at present mostly unsolved. We have previously demonstrated that IFNa induces apoptosis on epidermoid cancer cells and EGF antagonizes this effect. We have also found that IFNa-induced apoptosis depends upon activation of the NH 2 -terminal Jun kinase-1 (Jnk-1) and p 38 mitogenactivated protein kinase, and that these effects are also antagonized by EGF. At the same time, IFNa increases the expression and function of the epidermal growth factor receptor (EGF-R). Here we report that the apoptosis induced by IFNa occurs together with activation of caspases 3, 6 and 8 and that EGF also antagonizes this effect. On the basis of these results, we have hypothesized that the increased EGF-R expression and function could represent an inducible survival response that might protect tumor cells from apoptosis caused by IFNa via extracellular signal regulated kinase 1 and 2 (Erk-1/2) cascades. We have found an increased activity of Ras and Raf-1 in IFNa-treated cells. Moreover, IFNa induces a 50% increase of the phosphorylated isoforms and enzymatic activity of Erk-1/2. We have also demonstrated that the inhibition of Ras activity induced by the transfection of the dominant negative Ras plasmid RASN17 and the inhibition of Mek-1 with PD098059 strongly potentiates the apoptosis induced by IFNa. Moreover, the selective inhibition of this pathway abrogates the counteracting effect of EGF on the IFNa-induced apoptosis. All these findings suggest that epidermoid tumor cells counteract the IFNa-induced apoptosis through a survival pathway that involves the hyperactivation of the EGF-dependent Ras->Erk signalling. The selective targeting of this pathway appears to be a promising approach in order to enhance the antitumor activity of IFNa.

Citrinin induces apoptosis via a mitochondria-dependent pathway and inhibition of survival signals in embryonic stem cells, and causes developmental injury in blastocysts

“…Survival signalling processes protect against apoptosis induced by specific stimuli [19,21]. Our group and others have demonstrated that some apoptotic stimuli inhibit the Ras → ERK survival signal pathway by decreasing the protein levels of various survival components [21,32].…”

“…In addition, the Ras-regulated ERK activation signal transduction pathway, which includes Raf-1 and MEK, is involved in both proliferation and anti-apoptosis [18]. Ras → ERK-mediated survival signalling has been shown to protect human epidermoid cancer KB cells from various apoptotic inducers [19][20][21]. Together, these previous results suggest that HSP90/multichaperone complex-mediated regulation of apoptotic or survival signal pathway kinases is an efficient mechanism for regulating cell death and survival at the protein level.…”

C-Raf antagonizes apoptosis induced by IFN-α in human lung cancer cells by phosphorylation and increase of the intracellular content of elongation factor 1A

“…We have previously reported that IFNa activates an anti-apoptotic pathway mediated by an EGF-ras-C-RafMek signal transduction pathway. 19 Therefore, it was analyzed if this pathway was responsible for the phosphorylation of eEF-1A. H1355 cells, exposed or not to IFNa, were immunoprecipitated with anti-eEF-1A or anti-C-Raf antibody and blotted with anti-C-Raf or anti-eEF-1A antibody, respectively.…”

“…It was found that IFNa increased the phosphorylation of both serine and threonine residues in eEF-1A. Because in the same experimental model, IFNa induces an increase in the level and activity of epidermal growth factor receptor (EGF-R) and of the Ras-C-Raf-Mek1-Erk-1/2 signalling pathway that has a prominent role in anti-apoptotic effects, 19 it was evaluated if the phosphorylation of eEF-1A could be mediated by C-Raf. It was found that eEF-1A indeed interacts with CRaf and these effects could be potentiated by IFNa.…”

“…18 Moreover, in these cells IFNa triggers an important survival mechanism mediated by an epidermal growth factor (EGF)-Ras-mitogen activated protein kinase-dependent cascade. 19 The specific inhibition of this pathway potentiates the apoptosis induced by IFNa in epidermoid cancer cell lines. [20][21][22] However, the mechanisms by which this signal transduction pathway antagonizes the pro-apoptotic effects of IFNa are presently unknown.…”