Characterization of differentiation-inducer-resistant HL-60 cells

Area of Science:

• Cell Biology
• Molecular Biology
• Cancer Research

Background:

• The human promyelocytic leukemia cell line HL-60 is a model for studying granulocytic and monocytic differentiation.
• Understanding the mechanisms of drug resistance in cancer cells is crucial for developing effective therapies.
• Granulocytic differentiation can be induced by agents such as retinoic acid (RA) and dimethylsulfoxide (DMSO).

Purpose of the Study:

• To generate and characterize HL-60 sub-lines resistant to multiple inducers of granulocytic differentiation.
• To investigate the cross-resistance patterns and underlying genetic alterations in these resistant cell lines.
• To determine if differentiation pathways for granulocytes and monocytes are mechanistically distinct.

Main Methods:

• Step-wise selection of HL-60 cells for growth and differentiation resistance to RA, DMSO, and 6-thioguanine (6TG).
• Quantification of resistance by comparing drug concentrations required for 50% differentiation in resistant sub-lines versus wild-type cells.
• Karyotypic analysis, including assessment of double minute chromosomes and c-myc oncogene amplification.

Main Results:

• Generated RA-resistant, DMSO-resistant, and 6TG-resistant HL-60 sub-lines with varying degrees of resistance and cross-resistance.
• No cross-resistance was observed with monocyte/macrophage inducers (sodium butyrate, TPA) or with other agents like BUdR and oubain.
• RA-resistant and 6TG-resistant sub-lines exhibited numerous double minute chromosomes, indicative of gene amplification, while c-myc amplification showed minimal change.

Conclusions:

• The neutrophilic granulocytic and monocytic/macrophagic differentiation programs in HL-60 cells are mechanistically separable.
• Multiple agent-specific and common quantitative alterations contribute to resistance against granulocytic differentiation.
• Genetic defects underlying differentiation resistance may involve amplification of genes other than c-myc.