Characterization of lamins A and C expression during differentiation of HL-60 cells towards monocytes/macrophages in vitro.

Abstract

The inducible human promyelocytic cell line HL-60 is known to express a limited complement of intermediate filament proteins (IFPs). In the undifferentiated state these cells express B-type nuclear lamins, but lack lamins A and C and the cytoplasmic IFP vimentin (Paulin-Levasseur et al., 1988). In the present study, the HL-60 cell system was used to determine whether expression of lamins A and C was associated with the differentiated phenotype. HL-60 were treated with two different inducers of monocyte/macrophage differentiation: vitamin $\rm D\sb3$ and TPA. A detailed kinetic analysis of lamins A and C protein expression throughout the differentiation period was made using immunofluorescence microscopy (IFM). The expression of vimentin, the monocyte marker 63D3 and transferrin receptor (TR) were assessed in like manner. HL-60 proliferation was monitored by cell counts, $\sp3$H-thymidineincorporation and cell cycle analysis. Induction of HL-60 cell differentiation by vitamin $\rm D\sb3$ did not lead to expression of either lamins A/C or vimentin. Treatment with TPA, on the other hand, resulted in expression of these proteins in the vast majority of cells within 24 hours. Examination of marker expression and proliferation confirmed that both vitamin $\rm D\sb3$ and TPA induced differentiation in the treated cells. However, exposure to the vitamin resulted in cells which were monocyte-like, while TPA treatment gave rise to cells that more closely resembled macrophages. Lamins A/C expression was clearly not associated with growth arrest in the vitamin $\rm D\sb3$-treated cells, and was found to follow inhibition of replication in TPA-treated populations. It was determined that lamins A/C expression was not coincident with expression of the differentiated phenotype. These results suggested that lamins A/C expression was a post-differentiation event in the HL-60 cell system. (Abstract shortened by UMI.)