MODIFICATIONS OF CELLULAR THIOLS DURING GROWTH AND SQUAMOUS DIFFERENTIATION OF CULTURED HUMAN BRONCHIAL EPITHELIAL-CELLS

Thiol modifications during growth and differentiation of cultured norm al human bronchial epithelial cells was studied by analysis of their c ontent and redox state of low-molecular-weight thiols and protein thio ls. Subculture of the cells with trypsin decreased the cellular conten t of the major low-molecular-weight thiol, i.e., reduced glutathione, although the glutathione content had returned to levels comparable to those before subculture already after 4 h in conjunction with cell att achment. During subsequent culture, increases in the cellular contents of glutathione, total cysteine equivalents, and total protein thiols occurred. These modifications in the amounts and redox balance of thio ls were transient and preceded the major growth phase. Exposure of cel ls at clonal density to either diethylmaleate, a thiol-depleting agent , or buthionine sulfoximine, an inhibitor of glutathione synthesis, de creased the proliferative ability of the cells as demonstrated by a ma rkedly decreased colony forming efficiency. Moreover, in mass cultures exposed to buthionine sulfoximine, a marked depletion of the glutathi one content was again accompanied by inhibition of growth. Exposure of the cells to agents known to induce growth arrest and terminal squamo us differentiation, i.e., fetal bovine serum, Ca2+, or transforming gr owth factor-beta 1, resulted in increased levels of reduced glutathion e. No consistent alteration in the contents of the other thiols was no ted. Overall, the results demonstrate consistent variations in the amo unts and redox state of cellular thiols, particularly reduced glutathi one, supporting a role of thiols in regulation of growth and squamous differentiation of human bronchial epithelial cells. (C) 1994 Academic Press, Inc.