Modifications of cellular thiols during growth and squamous differentiation of cultured human bronchial epithelial...

Thiol modifications during growth and differentiation of cultured normal human bronchial epithelial cells was studied by analysis of their content and redox state of low-molecular-weight thiols and protein thiols. Subculture of the cells with trypsin decreased the cellular content 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 attachment. 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 thiols were transient and preceded the major growth phase. Exposure of cells at clonal density to either diethylmaleate, a thiol-depleting agent, or buthionine sulfoximine, an inhibitor of glutathione synthesis, decreased the proliferative ability of the cells as demonstrated by a markedly decreased colony forming efficiency. Moreover, in mass cultures exposed to buthionine sulfoximine, a marked depletion of the glutathione content was again accompanied by inhibition of growth. Exposure of the cells to agents known to induce growth arrest and terminal squamous differentiation, i.e., fetal bovine serum, Ca2+, or transforming growth factor-beta 1, resulted in increased levels of reduced glutathione. No consistent alteration in the contents of the other thiols was noted. Overall, the results demonstrate consistent variations in the amounts and redox state of cellular thiols, particularly reduced glutathione, supporting a role of thiols in regulation of growth and squamous differentiation of human bronchial epithelial cells.