Heterogenous Nuclear Ribonucleoprotein L Regulates The Selective Expression Of Glucocorticoid Receptor Translational Isoforms In HL-60 Cells

Abstract

Selective glucocorticoid receptor (GR) translational isoforms, i.e. the GR-D isoforms, mediate glucocorticoid protection of neutrophils from spontaneous apoptosis. HL-60 cells, like neutrophils, have predominantly the GR-D isoform. We determined whether the translation factor heterogenous nuclear ribonucleoprotein L (hnRNPL) plays a role in selective expression of the GR isoforms in HL-60 cells. Knockdown using hnRNPL shRNA in HL-60 cells was performed using retroviral transduction. Empty vector was used as controls. Western blot analyses were used to determine the level of hnRNPL and GR isoforms. The expression of GR target genes in cells treated with vehicle or dexamethasone (DEX, 100 nM, 6h) were measured using realtime RT-PCR. Knockdown using hnRNPL shRNA reduced the level of hnRNPL to background level. After hnRNPL knockdown, the GR-D isoform in HL-60 cells decreased significantly and the GR-A isoform increased significantly. Reflecting the switch of the GR isoforms, GR function was altered. DEX increased the expression of IkappaB in control cells but not in cells expressing hnRNPL shRNA. In contrast, DEX increased the expression of GILZ in both control and shRNA expressing cells. In addition, TNF and retinoic acid both decreased the level of hnRNPL and switched the GR-D to the GR-A isoform. The translation factor hnRNPL regulates the selective expression of the GR-D isoforms in HL-60 cells. Selective expression of GR isoforms underlies gene-specific glucocorticoid responses in HL-60 cells.