Control of cell differentiation during proliferation — II. Myeloid differentiation and cell cycle arrest of HL-60 promyelocytes preceded by nuclear structural changes

Abstract

The time-dependent dynamics of nuclear structure, cell cycle transit and arrest, and cellular differentiation were studied using the human promyelocytic leukemia cell line HL-60. Myeloid differentiation of HL-60 cells was induced by 10 −1 M β, all trans, retinoic acid (RA). During exponential growth the cells had G1, S, G2 and M durations of 9, 11, 0.5 and 0.5 h respectively. Significant growth arrest in the G1/0 phase of the cell cycle was apparent after 48 h of RA exposure or after two division cycles. Thereafter, cells arrested in G1/0 with wide dispersion in times of arrest which extended over several cell cycle generation times. The kinetics of phenotypic differentiation, detected by phorbol myristate acetate inducible superoxide production, paralleled those of G1/0 growth arrest with similar lag and dispersion. These kinetics are consistent with a model hypothesizing the existence of an S-phase differentiation control (DC) point regulating both terminal proliferation and differentiation. Before any cell differentiation or termination of cell proliferation occurred, the nuclei of RA-treated cells underwent a structural change detected by narrow-angle light scatter measured with flow cytometry. Narrow-angle light scatter was transiently reduced, reaching a nadir at 24–48 h and returning to control values at 96 h. This change was independent of cell cycle phase or total nuclear protein content. It was associated with a morphological change of the nuclear membrane from a smooth to dimpled or pitted structure. These findings focus attention on the potential significance of nuclear structural reorganization as an early event during cell differentiation.