Dual regulation of glucocorticoid-induced leucine zipper (GILZ) by the glucocorticoid receptor and the PI3-kinase/AKT pathways in multiple myeloma

Abstract

Glucocorticoids (GCs) are effective therapeutics commonly used in multiple myeloma (MM) treatment. Clarifying the pathway of GC-induced apoptosis is crucial to understanding the process of drug resistance and to the development of new targets for MM treatment. We have previously published results of a micro-array identifying glucocorticoid-induced leucine zipper (GILZ) as GC-regulated gene in MM.1S cells. Consistent with those results, GCs increased GILZ in MM cell lines and patient samples. Reducing the levels of GILZ with siRNA decreased GC-induced cell death suggesting GILZ may mediate GC-killing. We conducted a screen to identify other pathways that affect GILZ regulation and report that inhibitors of PI3-kinase/AKT enhanced GILZ expression in MM cell lines and clinical samples. The combination of dexamethasone (Dex) and LY294002, wortmannin, triciribine, or AKT inhibitor VIII dramatically up regulated GILZ levels and enhanced apoptosis. Addition of interleukin-6 (IL-6) or insulin-like growth factor (IGF1), both which activate the PI3-kinase/AKT pathway and inhibit GC killing, blocked up regulation of GILZ by GC and PI3-kinase/AKT inhibitors. In summary, these results identify GILZ as a mediator of GC killing, indicate a role of PI3-kinase/AKT in controlling GILZ regulation and suggest that the combination of PI3-kinase/AKT inhibitors and GCs may be a beneficial MM treatment.

The Role and Effects of Glucocorticoid-Induced Leucine Zipper in the Context of Inflammation Resolution

“…These results indicate that GILZ regulates T cell apoptosis and, similar to GC, induces apoptosis in resting T cells while protecting activated T lymphocytes. Inhibition of the PI3K/Akt pathway resulted in GILZ upregulation and increased apoptosis of multiple myeloma cells (46). Interestingly, GILZ acts as a Ras signal suppressor and decreases activation of ERK and Akt, leading to reduction of cell proliferation and transformation (47).…”

Role for MicroRNAs in Regulating Glucocorticoid Response and Resistance in Multiple Myeloma

“…Immunoblots were performed as described previously with these modifications [2]. Following treatment, 5×10 6 cells were harvested and washed with 1× phosphate-buffered saline (PBS) and lysed with 25 uL of Complete Lysis M (Roche) as described in the product manual.…”

“…For miRNA measurement, Taqman MicroRNA Assay Kit specific to miR-130b and RNU6B as a control (Applied Biosystems) is used for RT reaction and amplification. For measurement of GR-α and glucocorticoid-induced leucine zipper (GILZ), Taqman Gene Expression Assays were used as described previously [2]. …”

Glucocorticoids and Cancer

“…GC activation of the transcription factor GilZ has also been implicated in apoptosis. GilZ is regulated by GR in all known tissues, but, in contrast to other tissues, induces apoptosis in multiple myeloma [49]. …”