Activation of the insulin-like growth factor binding protein-5 promoter by parathyroid hormone in osteosarcoma cells requires activation of an activated protein-2 element

Abstract

We have previously shown that parathyroid hormone (PTH) stimulates the expression of insulin-like growth factor binding protein-5 (IGFBP-5) transcript levels in the osteosarcoma cell-line, UMR106-01 cells. In the present study we examined the molecular basis for the PTH induction of IGFBP-5 mRNA in these cells. PTH had no effect on the half-life of the IGFBP-5 transcript but did stimulate the transactivation of the proximal 889 base pairs of the rat IGFBP 58 flanking region in a luciferase fusion construct, suggesting that PTH stimulates transcript levels through transcriptional mechanisms. Progressive 58 deletions to -59 base pairs of the proximal promoter region had no effect on PTH induction of transactivation, indicating that an element existed within the first -59 base pairs upstream of the transcription start site that was responsive to PTH. Within the -59 base pairs there are CCAAT/enhancer binding protein (C/EBP), E-box, nuclear factor-1 (NF-1) and activator protein-2 (AP-2) elements. Mutation of the C/EBP, E-box or NF-1 elements had no effect on the ability of PTH to induce the transactivation of the IGFBP-5 promoter. Mutation of the AP-2 element resulted in a 40% reduction of PTH-stimulated luciferase activity. When three tandem repeats of the AP-2 consensus sequence were fused to a luciferase reporter, PTH stimulated a 25% increase in reporter activity. Electrophoretic mobility shift assays using UMR106-01 cell nuclear extracts showed that PTH caused a prominent shifted band in a probe spanning the region containing all four elements. The shifted band was almost completely absent when the probe contained a mutated AP-2 element. These results suggest that the AP-2 element functions in the PTH induction of IGFBP-5 gene expression.

Functional roles and clinical values of insulin-like growth factor-binding protein-5 in different types of cancers

“…Erclik et al [129] showed that parathyroid hormone (PTH) induced IGFBP5 protein expression in UMR106-01 osteosarcoma cells and found that activation of cyclic AMP, protein lipase Cα, and protein kinase Cδ increased IGFBP5 mRNA level[129]. They also found that PTH mediates the activation of IGFBP5 gene transcription in osteoblast cells[130]. Also, Akt was phosphorylated through IGFIR phosphorylation, which was induced by IGFBP5[131].…”

Contrasting bone effects of temporary versus permanent IGFBP administration in rodents

“…IGFBP-5 is abundantly expressed by osteoblasts and an important role of IGFBP-5 for bone growth can be presumed due to the presence of a bone morphogenetic protein-7-responsive element and a parathyroid hormone responsive region [30] in the rat or human IGFBP-5 promoter, respectively. In fact, systemic administration of rhIGFBP-5 with or without IGF-I resulted in increased serum concentrations of alkaline phosphatase or osteocalcin in mice [31].…”

Insulin Like Growth Factor-I: A Critical Mediator of the Skeletal Response to Parathyroid Hormone

“…BPs 1 and 6 have received less study in bone. PTH stimulation of BP-5 expression has been observed [78], but this has not been reported for other BPs.…”