Abstract
BackgroundThe eukaryotic translation initiation factor 5A1 (eIF5A1) is a highly conserved protein involved in many cellular processes including cell division, translation, apoptosis, and inflammation. Induction of apoptosis is the only function of eIF5A1 that is known to be independent of post-translational hypusine modification. In the present study, we investigated the involvement of mitogen- and stress-activated protein kinases during apoptosis of A549 lung cancer cells infected with adenovirus expressing eIF5A1 or a mutant of eIF5A1 that cannot be hypusinated (eIF5A1K50A).MethodsUsing adenoviral-mediated transfection of human A549 lung cancer cells to over-express eIF5A1 and eIF5A1K50A, the mechanism by which unhypusinated eIF5A1 induces apoptosis was investigated by Western blotting, flow cytometry, and use of MAPK and p53 inhibitors.ResultsPhosphorylation of ERK, p38 MAPK, and JNK was observed in response to adenovirus-mediated over-expression of eIF5A1 or eIF5A1K50A, along with phosphorylation and stabilization of the p53 tumor suppressor protein. Synthetic inhibitors of p38 and JNK kinase activity, but not inhibitors of ERK1/2 or p53 activity, significantly inhibited apoptosis induced by Ad-eIF5A1. Importantly, normal lung cells were more resistant to apoptosis induced by eIF5A1 and eIF5A1K50A than A549 lung cancer cells.ConclusionsCollectively these data indicate that p38 and JNK MAP kinase signaling are important for eIF5A1-induced cell death and that induction of apoptosis was not dependent on p53 activity.
Highlights
The eukaryotic translation initiation factor 5A1 is a highly conserved protein involved in many cellular processes including cell division, translation, apoptosis, and inflammation
Ad-eukaryotic translation initiation factor 5A1 (eIF5A1) and Ad-eIF5AK50A induce activation of Extracellular signalregulated kinase (ERK) kinase, p38 Mitogen-activated protein kinases (MAPK), and Jun NH2-terminal kinase (JNK) Previous studies have demonstrated that treatment with adenovirus eIF5A1 induces apoptosis in A549 lung carcinoma cells and improves duration of survival in mice bearing A549 xenograft tumors [14]
In order to explore the signaling pathways responsible for the antitumoral activity of eIF5A1, A549 cells were transduced with increasing amounts of adenovirus expressing eIF5A1 or a mutant of eIF5A1 that cannot be hypusinated, and analyzed by immunoblot for effects on MAPK/stress activated protein kinase (SAPK) signaling pathways
Summary
The eukaryotic translation initiation factor 5A1 (eIF5A1) is a highly conserved protein involved in many cellular processes including cell division, translation, apoptosis, and inflammation. We investigated the involvement of mitogen- and stress-activated protein kinases during apoptosis of A549 lung cancer cells infected with adenovirus expressing eIF5A1 or a mutant of eIF5A1 that cannot be hypusinated (eIF5A1K50A). The pro-apoptotic function of eIF5A1 appears to be the only activity of eIF5A1 that is independent of hypusine modification [13,15,16], and over-expression of eIF5A1 mutated at the hypusination site, lysine 50, induces apoptosis in a wide range of cancer cell types, including colon [13], cervical [15], and blood [16]. Suppression of eIF5A1 expression using RNA interference reduces activation of mitogen-activated protein kinases (MAPKs) [16,17] and can protect cells from apoptosis induced by cytotoxic drugs and cytokines [12,15,17]
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