BACKGROUND: We previously showed the usefulness of a fused protein of human pancreatic ribonuclease1 (hRNase1) with human epidermal growth factor (hEGF) for molecular targeting of EGF receptor (EGFR)-overexpressing cells. In this study, the mechanisms underlying the inhibition of cell growth by RNase-EGF fused proteins was confirmed. MATERIALS AND METHODS: Des.1-7 hRNase1 was genetically fused to hEGF. The fused proteins were expressed and isolated from Escherichia coli. The internalization of hRNase1-hEGF was confirmed by confocal fluorescence microscopy. The growth-inhibitory effect of the fused proteins was evaluated by MTT assay. RESULTS: FITC-labelled hRNase1-hEGF was internalized into EGFR-overexpressing A431 cells. The internalization was not observed in A431 cells pre-treated with hEGF and EGFR-deficient H69 cells. The growth-inhibitory effect of des.1-7 hRNase1-hEGF against A431 cells was statistically significantly more pronounced than that of hRNase1-hEGF. CONCLUSION: RNase-EGF fused proteins are internalized through EGFR and inhibit cell growth by exerting their ribonucleolytic activity in the cytosol.
BACKGROUND: We previously showed the usefulness of a fused protein of humanpancreatic ribonuclease1 (hRNase1) with humanepidermal growth factor (hEGF) for molecular targeting of EGF receptor (EGFR)-overexpressing cells. In this study, the mechanisms underlying the inhibition of cell growth by RNase-EGF fused proteins was confirmed. MATERIALS AND METHODS: Des.1-7 hRNase1 was genetically fused to hEGF. The fused proteins were expressed and isolated from Escherichia coli. The internalization of hRNase1-hEGF was confirmed by confocal fluorescence microscopy. The growth-inhibitory effect of the fused proteins was evaluated by MTT assay. RESULTS:FITC-labelled hRNase1-hEGF was internalized into EGFR-overexpressing A431 cells. The internalization was not observed in A431 cells pre-treated with hEGF and EGFR-deficient H69 cells. The growth-inhibitory effect of des.1-7 hRNase1-hEGF against A431 cells was statistically significantly more pronounced than that of hRNase1-hEGF. CONCLUSION: RNase-EGF fused proteins are internalized through EGFR and inhibit cell growth by exerting their ribonucleolytic activity in the cytosol.