ENHANCED EXPRESSION OF CALRETICULIN IN THE NUCLEUS OF RADIORESISTANT SQUAMOUS CARCINOMA-CELLS IN RESPONSE TO IONIZING-RADIATION

Ionizing radiation has been shown to modulate gene and protein express ion as well as cellular signal transduction pathways. However, the bio chemical and molecular mechanisms that underlie the cellular response to radiation are not fully understood. The effects of ionizing radiati on on the expression of nuclear proteins have now been investigated in radioresistant human head and neck squamous carcinoma cells (SQ-20B c ells) using the techniques of two-dimensional PAGE, silver staining, a nd computer-assisted quantitative analysis. Radiation (600 cGy) induce d the expression of 10 proteins and suppressed the expression of 5 pro teins in the nuclei of SQ-20B cells as detected 4 h after treatment. E lectroelution and NH2-terminal amino acid sequence analysis revealed t hat one of the radiation-induced proteins was the Ca2+-binding protein calreticulin. The expression of calreticulin was increased approximat ely 6-fold in the nuclei of irradiated SQ-20B cells. Calreticulin and the other proteins whose expression was affected by radiation may cont ribute to the radioresistance phenotype of SQ-20B cells.