Calcium-dependent upregulation of E4BP4 expression correlates with glucocorticoid-evoked apoptosis of human leukemic CEM cells

Abstract

Glucocorticoid (GC)-evoked apoptosis of T-lymphoid cells is preceded by increases in the intracellular Ca 2+ concentration ([Ca 2+ ] i ), which may contribute to apoptosis. This report demonstrates that GC-mediated upregulation of the bZIP transcriptional repressor gene, E4BP4, is dependent on [Ca 2+ ] i levels, and correlates with GC-evoked apoptosis of GC-sensitive CEM-C7-14 cells. Calcium chelators EGTA and BAPTA reduced [Ca 2+ ] i levels and protected CEM-C7-14 cells from Dex-evoked E4BP4 upregulation as well as apoptosis. In the GC-resistant sister clone, CEM-C1-15, Dex treatment did not induce [Ca 2+ ] i levels, E4BP4 expression or apoptosis, however, the calcium ionophore A23187 restored Dex-evoked E4BP4 upregulation and apoptosis. CEM-C7-14 cells were more sensitive to GC-independent increases in [Ca 2+ ] i levels by thapsigargin, and a corresponding increase in E4BP4 expression and cell death, compared to CEM-C1-15 cells, suggesting a direct correlation between [Ca 2+ ] i levels, E4BP4 expression, and apoptosis.

Negative Regulation of the Osteoblast Function in Multiple Myeloma through the Repressor Gene E4BP4 Activated by Malignant Plasma Cells

“…E4BP4 was inhibited by dexamethasone because its 2 -DDCt value was the lowest (0.185). These results corroborated the PTHrP specificity in inducing E4BP4, whereas its suppression by dexamethasone was contrary to previous data in T lymphoblasts (17). The defective E4BP4 induction by dickkopf1 (2 -DDCt = 0.890) is in line with the independence of this osteoblast inhibitor from the PTH-1-R pathway.…”

“…E4BP4 is also inducible by IL-3 and glucocorticoids in B and T cells, respectively (16,17). With the purpose of exploring their effect on osteoblasts, we stimulated them with IL-3 and dexamethasone and measured the expression of E4BP4 and morphogenetic factors.…”

“…E4BP4, a repressor gene induced in osteoblasts through the type 1 parathyroid hormone receptor (PTH-1-R; ref. 15), by IL-3 in murine pro-B cells (16) and by glucocorticoids in human T lymphoblasts (17), was overexpressed. Hyperactivity of E4BP4 in myeloma-conditioned osteoblasts definitely inhibited the cyclooxygenase-2 (COX-2) pathway that regulates the expression of both Runx2 and Osterix (18).…”

New Frontiers for the NFIL3 bZIP Transcription Factor in Cancer, Metabolism and Beyond

“…The glucocorticoid receptor (GR) is normally regulated by a negative feedback mechanism upon activation; the GR mRNA and protein are down-regulated after GC addition 3 . However, in certain GC treated murine leukemic T cell lines, GR activation is not attenuated leading to glucocorticoid induced cell death 3,72,73 . The Nfil3 gene is induced under these conditions and is thought to be part of the mechanism that activates apoptosis.…”

Correlation of glucocorticoid-mediated E4BP4 upregulation with altered expression of pro- and anti-apoptotic genes in CEM human lymphoblastic leukemia cells

“…We have established a crucial relationship between GC-dependent upregulation of E4BP4 and sensitivity to GC-evoked apoptosis in the human leukemic CEM cell culture model [5]. E4BP4 (or NFIL3) is a bZIP transcription factor with a role in anti-inflammatory response, circadian oscillation, apoptosis regulation, and immune cell development [6- 8].…”