1α,25-Dihydroxyvitamin D3 antiproliferative actions involve vitamin D receptor-mediated activation of MAPK pathways and AP-1/p21waf1 upregulation in human osteosarcoma

Abstract

The molecular mechanisms underlying antiproliferative actions of the steroid 1α,25-dihydroxy vitamin D 3 (1,25D) in human osteosarcoma cells are known only partially. To better understand the signaling involved in 1,25D anti-tumorigenic properties in bone, we stably silenced vitamin D receptor (VDR) expression in the human osteosarcoma SaOS-2 cell line. We found that 1,25D treatment reduced cell proliferation by approximately 25% after 3 days only in SaOS-2 cells expressing native levels of VDR protein, and involved activation of MAPK/AP-1/p21 waf1 pathways. Both sustained (3 days) and transient (15 min) 1,25D treatment activated JNK and ERK1/2 MAPK signaling in a nongenomic VDR-dependent manner. However, only sustained exposure to hormone led to upregulation of p21 and subsequent genomic control of the cell cycle. Specific blockade of MEK1/MEK2 cascade upstream from ERK1/2 abrogated 1,25D activation of AP-1 and p21, and subsequent antiproliferative effects, even in the presence of a nuclear VDR. We conclude that 1,25D-induced inhibition of human osteosarcoma cell proliferation occurs via sustained activation of JNK and MEK1/MEK2 pathways downstream of nongenomic VDR signaling that leads to upregulation of a c-Jun/c-Fos (AP-1) complex, which in turn modulates p21 waf1 gene expression. Our results demonstrate a cross-talk between 1,25D/VDR nongenomic and genomic signaling at the level of MAP kinase activation that leads to reduction of cell proliferation in human osteosarcoma cells.

Vitamin D regulates tyrosine hydroxylase expression: N-cadherin a possible mediator

“…The response relationship is best described as an ''inverted U'' dose response. This dose and this doserelationship is entirely consistent with numerous previous studies examining the effects of this steroid in vitro (Kelly et al, 1985;Ryhanen et al, 1998;Toell et al, 2000;Chattopadhyay et al, 2003;Wu et al, 2007) .…”

The Active Form of Vitamin D Transcriptionally Represses Smad7 Signaling and Activates Extracellular Signal-regulated Kinase (ERK) to Inhibit the Differentiation of a Inflammatory T Helper Cell Subset and Suppress Experimental Autoimmune Encephalomyelitis

“…2 D 3 has been implicated in the modulation of MAPKs (ERK, p38, and JNK) by a nongenomic mechanism with rapid or late response, and it has been understood to be a cell-specific phenomenon (18 -20). Cell membrane and cytoplasmic localization of VDR has been shown to be vital for relaying the non-genomic functions of 1,25(OH) 2 D 3 in osteoblast, keratinocytes, and cancer cells (18,20,39,40). Although rapid responses of 1,25(OH) 2 D 3 were mainly executed by membrane VDR, it is cytoplasmic VDR that carries out late responses (18,40).…”

<b>1α,25(OH)</b><b>₂</b><b>D</b><b>₃</b><b> downregulates gene expression levels of muscle ubiquitin ligases MAFbx and MuRF1 in human </b><b>myotubes </b>

“…Therefore, it is possible that 1α,25(OH) 2 D 3 inhibits the expression REFERENCES mouse model in which colorectal cancer was induced by inflammation, dietary vitamin D 3 was reported to inhibit MAPK (p-P38 and p-JNK) activity and reduce the cancer incidence (26). On the other hand, 1α,25(OH) 2 D 3 combined with VDR non-genomically activates JNK and MAPK and thereby inhibits osteosarcoma proliferation (45). These findings suggest that 1α,25(OH) 2 D 3 , like skeletal muscle cytokines, regulates metabolism by acting as a promoter or inhibitor depending on the conditions in vivo.…”