RNA Expression Levels of (Co)Chaperone Molecules of the Glucocorticoid Receptor Are Not Related to In Vitro Prednisolone Resistance in Childhood ALL.

In vitro resistance to Glucocorticoids (GC) is an important adverse risk factor in the treatment of ALL. To induce apoptosis in ALL cells, GC have to bind to the GC receptor (hGR), which is tightly regulated by various (co)chaperone molecules. HSP70, ST13 and HSP40 facilitate hGR binding to HSP90 and HOP in an energy dependent fashion. This complex is stabilised by immunophillins FKBP 51, FKBP59, CYP40 and P23 and is necessary for the hGR to be able to bind GC. The ATPase BAG1 can function as negative regulator of HSP70, and may downregulate hGR activity. After the GC-hGR complex is formed, it is transported to the nucleus to regulate GC responsive genes. In this study, we tested the hypothesis that RNA expression levels of these (co) chaperone molecules are important determinants for in vitro prednisolone sensitivity in childhood ALL.

Methods: 20 children with leukemic cells in vitro sensitive to prednisolone (LC50<0.1μg/ml) were matched (according to age, immunophenotype and white blood cell count at diagnosis) each with an in vitro resistant patient (LC50 > 150 μg/ml). RNA expression levels of the different (co)chaperone molecules were measured by a quantitative real-time RT-PCR (Taqman) assay and standardised to endogenous GAPDH and RNAseP mRNA levels. In vitro resistance to prednisolone was measured by the MTT assay.

Results. The highest median expression levels, indicated as percentage of GAPDH levels were found for HSP90 (29%) and p23 (10%), whereas FKBP51 and ST13 were expressed at 2% and 1.6% respectively. HSP70 (0.1%), HSP40 (0.44%), HOP (0.2%), FKBP59 (0.4%), PPID (0.3%) and BAG-1 (0.4%) were expressed at relatively low levels. Using matched pair analysis, no significant differences were found for the expression levels of the various (co)chaperone molecules between in vitro sensitive and resistant patients. The ratio of different (co)chaperone molecules with opposing effect (HIP versus BAG-1, FKBP-51 versus FKBP-52, HSP-90 versus P23, and HSP-90 versus the functional GR-alpha receptor, positive and negative effect respectively) was not related to GC resistance as well.

Conclusion: Glucocorticoid resistance in childhood ALL can not be attributed to basal expression levels of the diverse (co)chaperone molecules involved in GC binding and transport of the GC-GR complex to the nucleus of the GR.