Expression from the epidermal development element receptor (EGFR), a receptor tyrosine kinase connected with cell proliferation and success, is overactive in lots of tumors of epithelial source. of epithelial source, is connected with metastasis, poor prognosis, and level of resistance to chemotherapy (Nicholson et al., 2001), rendering it an ideal focus on for therapy. Multiple medical tests of using EGFR tyrosine kinase inhibitors in malignancy therapy have already been carried out, but blockage 718630-59-2 of tyrosine kinase activity only does not appear to reach optimum therapeutic efficacy. The 718630-59-2 overall response prices are between 10%C20% across a number of human being malignancies (Fukuoka et al., 2002; Kris et al., 2002; Cohen et al., 2003; Dancey and Freidlin, 2003). The manifestation degree of EGFR in malignancy tissues is usually correlated with prognosis, however, not with responsiveness, to EGFR tyrosine kinase inhibitor treatment 718630-59-2 (Arteaga, 2002), recommending that, impartial of its kinase activity, EGFR may donate to the development of malignancy. The existence of kinase-independent 718630-59-2 prosurvival function of EGFR is supported by several studies. To begin with, lack of kinase activity of EGFR will not produce similar phenotypes concerning lack of EGFR protein in vivo. EGFR knockout animals die immediately after birth (Miettinen et al., 1995), SLC2A4 but animals with severely compromised kinase mutant EGFR are completely viable and display only some epithelial defects (Luetteke et al., 1994). Second, EGFR without kinase activity was been shown to be in a position to stimulate DNA synthesis (Coker et al., 1994) and enhance cell survival (Ewald et al., 2003). Finally, inhibition from the kinase activity of EGFR by tyrosine kinase inhibitors often leads to decreased cell proliferation however, not cell death (Harari and Huang, 2004), whereas knocking down the EGFR receptor protein leads to cell death (Nagy et al., 2003). With this study, we investigated the mechanism of kinase-independent prosurvival function from the EGFR and discovered that, independent of its kinase activity, EGFR prevents cancer cells from autophagic cell death by maintaining the basal intracellular glucose level. SIGNIFICANCE Overexpression/activation of EGFR, which is often within tumors of epithelial origin, is connected with metastasis, poor prognosis, and resistance to chemotherapy. Multiple clinical trials using EGFR tyrosine kinase inhibitors in cancer therapy have already been conducted; however, blockage of tyrosine kinase activity alone will not appear to reach maximum therapeutic efficacy. We report here that EGFR, independent of its kinase activity, maintains the basal intracellular glucose level, thereby preventing cells 718630-59-2 from undergoing autophagic death. This function of EGFR may endow tumor cells with an elevated survival capacity even in the current presence of chemotherapeutic agents and tyrosine kinase inhibitors. Thus, the inhibition of the function and of the kinase activity of EGFR may both be essential for eradication of epithelial neoplasms. RESULTS Lack of Expression of EGFR, however, not Its Kinase Activity, Led to Autophagic Cell Death PC-3MM2 cells werecultured in minimum essentialmedium (MEM) containing physiological glucose content of 5.5 mM (Baltzan et al., 1962). As shown in Figure 1A, EGFR tyrosine kinase inhibitor, AEE788 (Traxler et al., 2004) (5.0 M), didn’t reduce the expression of EGFR but did completely inhibit its phosphorylation. On the other hand, the transfection from the cells with EGFR siRNA decreased the expression from the EGFR (Figure 1B). As shown in Figure 1C, unlike control cells, treatment of PC-3MM2 cells with AEE788 (5.0 M) for 3 days resulted in inhibition of cell proliferation, however, not to cell death. However, incubation of PC-3MM2 cells transfected with EGFR siRNA for 3 days in MEM led to cell death, as indicated by the current presence of sub-G1 cells. The usage of the commercial EGFR kinase inhibitor, AG1478 (data not shown), and various siRNA against EGFR produced similar results (Figure S1 available online). Open in another window Figure 1 Blocking the Kinase Activity of EGFR WILL NOT Result in Cell Death but Knocking Down EGFR with siRNA Does(A) PC3MM2 cells grown in MEM with 5.5 mM glucose were treated with AEE788 (5.0 M, with AEE788 readded every 24 hr) for 72 hr. Western blot analysis revealed that pEGFR was completely blocked by AEE788 weighed against the control. -actin served like a loading control (tEGFR, total EGFR). (B) Seventy-two hours later after cells were cultured in MEM with 5.5 mM glucose, tEGFR and pEGFR levels were both reduced by siRNA treatment weighed against the control that was transfected with siRNA vector-expressing scrambled sequences. -actin served like a loading control. (C) Compared.