Effect of glucocorticoid on epidermal growth factor receptor in human salivary gland adenocarcinoma cell line HSG

Abstract

Human salivary gland adenocarcinoma (HSG) cells treated with 10 −6 M triamcinolone acetonide for 48 h exhibited a 1.7- to 2.0-fold increase in [ 125I]human epidermal growth factor (hEGF) binding capacity as compared with untreated HSG cells. Scatchard analysis of [ 125I]EGF binding data revealed that the number of binding sites was 83 700 (± 29 200) receptors / cell in untreated cells and 160 500 (± 35 500) receptors / cell in treated cells. No substantial change in receptor affinity was detected. The dissociation constant of the EGF receptor was 0.78 (± 0.26) · 10 −9 M for untreated cells, whereas it was 0.93 (± 0.31) · 10 −9 M for treated cells. The triamcinolone acetonide-induced increase in [ 125I]EGF binding capacity was dose-dependent between 10 −9 and 10 −6 M, and maximal binding was observed at 10 −6 M. EGF receptors on HSG cells were affinity-labeled with [ 125I]EGF by use of the cross-linking reagent disuccinimidyl suberate (DSS). The cross-linked [ 125I]EGF was 3–4% of the total [ 125I]EGF bound to HSG cells. The affinity-labeled EGF receptor was detected as a specific 170 kDa band in the autoradiograph after SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Densitometric analysis revealed that triamcinolone acetonide amplified the intensity of this band 2.0-fold over that of the band of untreated cells. EGF receptor synthesis was also measured by immunoprecipitation of [ 3H]leucine-labeled EGF receptor protein with anti-hEGF receptor monoclonal antibody. Receptor synthesis was increased 1.7- to 1.8-fold when HSG cells were treated with 10 −8–10 −6 M triamcinolone acetonide for 48 h. When the immunoprecipitated, [ 35S]methionine-pulse-labeled EGF receptor was analyzed by SDS-PAGE and fluorography, the newly synthesized EGF receptor was detected at the position of 170 kDa; and treatment of HSG cells with triamcinolone acetonide resulted in a 2.0-fold amplification of this 170 kDa band. There was no significant difference in turnover rate of EGF receptor between treated and untreated HSG cells. These results demonstrate that the triamcinolone acetonide-induced increase in [ 125I]EGF binding capacity is due to the increased synthesis of EGF receptor protein in HSG cells.