ABSTRACT
EGF has been a representive growth factor for understanding the signal transduction that underlies the biological response of a number of growth factors. EGF plays an important role in the regulation of growth inhibition in the squamous cell carcinoma with over expressed EGF receptors, but the mechanism that determine sensitivity to the growth inhibition by EGF are not well understood. The KUMA3 parental cell line, derived from a squamous cell carcinoma of the human lower lip, was established and variant cell line derived from the parental cell line was acquired by treatment with high dose EGF (200 ng/mL) for 6 months. The KUMA3 parental cells treated with EGF showed marked scattering cells with prominent dendritic processes. On the other hand, EGF treated cells in the variant cell line showed a dense monolayer of ovoid cells similar to untreated cells. Therefore, it was conformed that the variant cell line was resistant to the growth inhibitory effect of EGF. To gain insight into the action mechanism of EGF in the KUMA3 parental and variant cell lines, Western blot analysis was examined to identify transregulation of EGF receptor. In the all parental cell lines treated with EGF, EGF receptor proteins were completely disappeared by lysosomal degradation. However, EGF receptor proteins were shown the periodic appearance according to the time course in the variant cell lines treated with EGF. In Western blot and immunocytochemical analyses, annexin II protein evenly distributed in the cytoplasm relocated to the plasma membrane at 9 hr exposure to EGF and was significantly decreased at 12 hr and 24 hr exposures to EGF in the variant cell line. However, annexin II protein relocated to the nuclear membrane at 9 hr exposure to EGF and was not any change in amount at 12 hr and 24 exposure to EGF in the parental cell line. In conclusion, this study suggests that the retention of colony formation pattern and cell morphology in the variant cell line treated with EGF might be owing to the heterologous desensitization of EGF receptor and exocytosis of annexin II.