Modulation of Osteopontin Post-translational State by 1,25-(OH)2-Vitamin D3

Abstract

Osteopontin (OPN) 1 is a non-collagenous, glycosylated phosphoprotein originally found in bone matrix (1, 2), but now known to be expressed in many tissues including kidney, hypertrophic chondrocytes, placenta, T-lymphocytes, macrophages, secretory epithelia and ganglia of the inner ear, and smooth muscle of the vascular system (3, 4). OPN is also found in biological fluids such as milk (5), urine (6), and plasma (7), and it displays elevated expression in many transformed cells (8). OPN is highly acidic with approximately 25% of the amino acid composition aspartate and glutamate and significant numbers of phosphoserine and phosphothreonine (1, 2). The amino acid sequence contains a conserved Gly-Arg-Gly-Asp-Ser (GRGDS) sequence (2, 3). As a result, OPN binds effectively to the ␣ V ␤ 3 integrin (9), as well as to the ␣ V ␤ 5 and ␣ V ␤ 1 integrins (10). OPN also contains a thrombin cleavage site located near the middle of the molecule. Both peptides produced by thrombin cleavage are capable of supporting integrin-mediated cell attachment (11). Potential roles for OPN function through the ␣ V ␤ 3 integrin were proposed (12). OPN can promote attachment of various cell types and can initiate signal transduction through integrin-associated kinases. Other proposed roles for OPN include chemotaxis (13, 14), inhibition of nitric oxide synthase expression (15), activation of pp60 c-src (16), hydroxyapatite binding (17), and Ca 2ϩ binding (18). Hormone regulation plays an important role in OPN production. Our laboratory has examined the effect of the seco-steroid hormone 1,25-dihydroxyvitamin D 3 (1,25-(OH) 2 D 3 ) on OPN expression and secretion. After uptake of 1,25-(OH) 2 D 3 into a cell, the hormone binds to the vitamin D receptor (VDR), translocates to the nucleus, dimerizes preferentially with the retinoid X receptor, then binds to the vitamin D response element (VDRE) located in the promoter region of 1,25-(OH) 2 D 3 -responsive genes (19). In the case of OPN, this results in increased transcription as seen by higher OPN mRNA steady state levels at 24 -48 h (20) and, eventually, higher secreted protein levels (21). The OPN gene in rat is regulated by the additive action of two VDREs (3), which respond to both 1,25-(OH) 2 D 3 and to bioactive analogs of 1,25-(OH) 2 D 3 that bind to nuclear receptors (20).1,25-(OH) 2 D 3 regulation also occurs through rapid plasma membrane-initiated responses, which have been well studied in osteoblasts. We previously reported the 1,25-(OH) 2 D 3 regulation of L-type voltage-sensitive calcium channels (VSCC) in ROS 17/2.8 osteosarcoma cells (22,23 activates other osteoblast signaling pathways that are independent of transcription such as a rapid increase in phospholipase C activity (24), activation of protein kinase C (25), and regulation of whole cell chloride currents (26).In this publication, we report the effect of 1,25-(OH) 2 D 3 on osteoblast-like ROS 17/2.8 cells at a time period between the classic genomic response and the rapid membrane-associated responses. Examination of O...

Integrins and Extracellular Matrix Proteins at the Maternal-Fetal Interface in Domestic Animals

“…As noted above, increases in OPN transcription may also be induced by IL-l, TGFß1, FGF, TNF·, IFNÁ, estrogen, progesterone and 1,25-dihydroxy vitamin D3 [Craig and Denhardt, 1991;Mukherjee et al, 1995;Tuo et al, 1996b;Rittling and Novick, 1997;Safran et al, 1998;Omigbodun et al, 1997;Johnson et al, 2000]. As IL-1, TGFß1, FGF, type I and II interferons, and conceptus estrogen are all temporally upregulated in association with maternal recognition of pregnancy [Bazer, 1992;Gupta et al, 1996Gupta et al, , 1997Gupta et al, , 1998aLefevre et al, 1990Lefevre et al, , 1998], the contributions of paracrine factors to the presence of OPN protein in histotroph requires further study.…”

“…While OPN was originally isolated from bone [Franzen and Heinegard, 1985], it has since been found to be widely expressed in epithelia and in secretions of many tissues including the gastrointestinal tract, kidney, and reproductive tissues including breast, testes, oviduct, uterus, trophoblast and placenta [Brown et al, 1992;McKee et al, 1995;Fazlea-206 Cells Tissues Organs 2002;172:202-217 Burghardt/Johnson/Jaeger/Ka/Garlow/ Spencer/Bazer bas et al , 1997;Cancel et al, 1999;Gabler et al, 1999;Nomura et al, 1999] as well as leukocytes, smooth muscle cells, and tumor cells [Denhart and Guo, 1993]. Increases in transcription of the OPN gene may be induced by interleukin-1· and ß (IL-1), transforming growth factor beta-1 (TGFß1), fibroblast growth factor (FGF), tumor necrosis factor alpha (TNF·), interferon gamma (IFNÁ), estrogen, progesterone and 1,25-dihydroxy vitamin D3 [Craig and Denhardt, 1991;Mukherjee et al, 1995;Rittling and Novick, 1997;Safran et al, 1998;Omigbodun et al, 1997].…”

Post-translational Modifications of SIBLING Proteins and Their Roles in Osteogenesis and Dentinogenesis

“…Notably, different forms of OPN that vary in their phosphorylation have been reported in transformed osteogenic cells Safran et al, 1998a). The level of phosphorylation of OPN was shown to be modulated by 1,25-dihydroxyvitamin D3 in a non-transcriptional mechanism (Safran et al, 1998a). The addition of this hormone to cultures of ROS17/2.8 cells lowers the level of OPN phosphorylation prior to transcriptional up-regulation by 1,25-dihydroxyvitamin D3.…”

Cell Type-specific Post-translational Modifications of Mouse Osteopontin Are Associated with Different Adhesive Properties

“…Likewise, differentiating rat osteoblasts produce two forms of OPN as seen on SDS-polyacrylamide gels; a 55-kDa form that contains little phosphorylation and a highly phosphorylated 44-kDa form (30). The extent of phosphorylation of OPN in osteoblast and epidermal cells is responsive to hormonal influences such as 1,25-dihydroxyvitamin D 3 (31,32), and oncogene-transfected Rat-1 cells switch from the synthesis of sialylated to non-sialylated OPN upon phorbol ester treatment (33).…”