Protein-pattern changes and morphological effects due to methionine starvation or treatment with 5-azacytidine of the phorbol-ester-sensitive cell lines HL-60, CCL-119, and U-937.

Methionine starvation causes changes in the protein pattern of HL-60 promyelocytic leukemia cells as observed by two-dimensional electrophoresis. One group of proteins is apparently modified, appearing in new positions. A further series of proteins, including several principal nuclear polypeptides, is substantially diminished. The morphology of a fraction of the cells in the culture changes concomitantly, with condensation and fragmentation of the nucleus and eventual remolding of the cell to a "grape-cluster" appearance. Similar effects are produced by a DNA methylation inhibitor, 5-azacytidine, but not by various other toxic agents tested. A defect in DNA methylation, either by depletion of S-adenosyl-L-methionine (the methyl donor) or by inactivation of the relevant enzyme, may be responsible. The T-lymphoblastoid line CCL-119 and the histiocytic lymphoma line U-937 also show these effects, but most fibroblast, epithelial, and lymphoblastoid lines do not. These changes can be largely prevented in each of the three susceptible lines by prior treatment with the tumor promoter, phorbol myristate acetate (PMA), an agent known to cause differentiation in at least two of the lines. The results thus suggest interesting relationships between methionine metabolism, protein and structural changes in the cell nucleus, and PMA-induced cell differentiation.