A novel function for lysyl oxidase in pluripotent mesenchymal cell proliferation and relevance to inflammation-associated osteopenia.

Lysyl oxidase is a multifunctional enzyme required for collagen biosynthesis. Various growth factors regulate lysyl oxidase during osteoblast differentiation, subject to modulation by cytokines such as TNF-α in inflammatory osteopenic disorders including diabetic bone disease. Canonical Wnt signaling promotes osteoblast development. Here we investigated the effect of Wnt3a and TNF-α on lysyl oxidase expression in pluripotent C3H10T1/2 cells, bone marrow stromal cells, and committed osteoblasts. Lysyl oxidase was up-regulated by a transcriptional mechanism 3-fold in C3H10T1/2 cells, and 2.5-fold in bone marrow stromal cells. A putative functional TCF/LEF element was identified in the lysyl oxidase promoter. Interestingly, lysyl oxidase was not up-regulated in committed primary rat calvarial- or MC3T3-E1 osteoblasts. TNF-α down-regulated lysyl oxidase both in Wnt3a-treated and in non-treated C3H10T1/2 cells by a post-transcriptional mechanism mediated by miR203. Non-differentiated cells do not produce a collagen matrix; thus, a novel biological role for lysyl oxidase in pluripotent cells was investigated. Lysyl oxidase shRNAs effectively silenced lysyl oxidase expression, and suppressed the growth of C3H10T1/2 cells by 50%, and blocked osteoblast differentiation. We propose that interference with lysyl oxidase expression under excess inflammatory conditions such as those that occur in diabetes, osteoporosis, or rheumatoid arthritis can result in a diminished pool of pluripotent cells which ultimately contributes to osteopenia.

Collagen advanced glycation inhibits its Discoidin Domain Receptor 2 (DDR2)-mediated induction of lysyl oxidase in osteoblasts.

Diabetes increases the risk of bone fracture. Organic and inorganic bone extracellular matrix components determine bone strength. Previous studies indicate that in diabetes, glycation of collagen causes abnormal arrangements of collagen molecules and fragile bones. Diabetic bone fragility is additionally attributed to reduced levels of lysyl oxidase enzyme-dependent collagen cross-links. The mechanism underlying the presence of lower enzymatic collagen cross-links in diabetic bone has not been directly investigated. Here we determine in primary osteoblast cultures the regulation of lysyl oxidase protein by type I collagen and collagen modified by carboxymethylation (CML-collagen), a form of advanced glycation endproducts. Data indicate that non-glycated collagen up-regulates lysyl oxidase levels both in primary non-differentiated and in differentiating mouse and rat osteoblast cultures, while CML-collagen fails to regulate lysyl oxidase in these cells. Collagen binding to Discoidin Domain Receptor-2 (DDR2) mediates lysyl oxidase increases, determined in DDR2 shRNA knockdown studies. DDR2 binding and activation were disrupted by collagen glycation, pointing to a mechanism for the diminished levels of lysyl oxidase and consequently low lysyl oxidase-derived cross-links in diabetic bone. Our studies indicate that collagen-integrin interactions may not play a major role in up-regulating lysyl oxidase. Furthermore, non-collagenous ligands for the receptor for advanced glycation end products (RAGE) failed to alter lysyl oxidase levels. Taken together with published studies a new understanding emerges in which diabetes- and age-dependent inhibition of normal collagen-stimulated DDR2- and integrin-signaling, and independent advanced glycation-stimulated RAGE-signaling, each contributes to different aspects of diabetic osteopenia.

Requirement for active glycogen synthase kinase-3ß in TGF-ß1 upregulation of connective tissue growth factor (CCN2/CTGF) levels in human gingival fibroblasts.

Connective tissue growth factor (CCN2/CTGF) mediates transforming growth factor-ß (TGF-ß)-induced fibrosis. Drug-induced gingival overgrowth is tissue specific. Here the role of the phosphoinositol 3-kinase (PI3K) pathway in mediating TGF-ß1-stimulated CCN2/CTGF expression in primary human adult gingival fibroblasts and human adult lung fibroblasts was compared. Data indicate that PI3K inhibitors attenuate upregulation of TGF-ß1-induced CCN2/CTGF expression in human gingival fibroblasts independent of reducing JNK MAP kinase activation. Pharmacologic inhibitors and small interfering (si)RNA-mediated knockdown studies indicate that calcium-dependent isoforms and an atypical isoform of protein kinase C (PKC-δ) do not mediate TGF-ß1-stimulated CCN2/CTGF expression in gingival fibroblasts. As glycogen synthase kinase-3ß (GSK-3ß) can undergo phosphorylation by the PI3K/pathway, the effects of GSK-3ß inhibitor kenpaullone and siRNA knockdown were investigated. Data in gingival fibroblasts indicate that kenpaullone attenuates TGF-ß1-mediated CCN2/CTGF expression. Activation of the Wnt canonical pathways with Wnt3a, which inhibits GSK-3ß, similarly inhibits TGF-ß1-stimulated CCN2/CTGF expression. In contrast, inhibition of GSK-3ß by Wnt3a does not inhibit, but modestly stimulates, CCN2/CTGF levels in primary human adult lung fibroblasts and is ß-catenin dependent, consistent with previous studies performed in other cell models. These data identify a novel pathway in gingival fibroblasts in which inhibition of GSK-3ß attenuates CCN2/CTGF expression. In adult lung fibroblasts inhibition of GSK-3ß modestly stimulates TGF-ß1-regulated CCN2/CTGF expression. These studies have potential clinical relevance to the tissue specificity of drug-induced gingival overgrowth.

Transdifferentiation of glioblastoma stem-like cells into mural cells drives vasculogenic mimicry in glioblastomas.

Recent evidence has shown that glioblastoma stem-like cells (GSCs) can transdifferentiate into endothelial cells and vascular-like tumor cells. The latter pattern of vascularization indicates an alternative microvascular circulation known as vasculogenic mimicry (VM). However, it remains to be clarified how the GSC-driven VM makes a significant contribution to tumor vasculature. Here, we investigated 11 cases of glioblastomas and found that most of them consisted of blood-perfused vascular channels that coexpress mural cell markers smooth muscle α-actin and platelet-derived growth factor receptor ß, epidermal growth factor receptor, and vascular endothelial growth factor receptor 2 (Flk-1), but not CD31 or VE-cadherin. This microvasculature coexisted with endothelial cell-associated vessels. GSCs derived from patients with glioblastomas developed vigorous mural cell-associated vascular channels but few endothelial cell vessels in orthotopic animal models. Suppression of Flk-1 activity and gene expression abrogated GSC transdifferentiation and vascularization in vitro, and inhibited VM in animal models. This study establishes mural-like tumor cells differentiated from GSCs as a significant contributor to microvasculature of glioblastoma and points to Flk-1 as a potential target for therapeutic intervention that could complement current anti-angiogenic treatment.

A Matrigel-based tube formation assay to assess the vasculogenic activity of tumor cells.

Over the past several decades, a tube formation assay using growth factor-reduced Matrigel has been typically employed to demonstrate the angiogenic activity of vascular endothelial cells in vitro. However, recently growing evidence has shown that this assay is not limited to test vascular behavior for endothelial cells. Instead, it also has been used to test the ability of a number of tumor cells to develop a vascular phenotype. This capability was consistent with their vasculogenic behavior identified in xenotransplanted animals, a process known as vasculogenic mimicry (VM). There is a multitude of evidence demonstrating that tumor cell-mediated VM plays a vital role in the tumor development, independent of endothelial cell angiogenesis. For example, tumor cells were found to participate in the blood perfused, vascular channel formation in tissue samples from melanoma and glioblastoma patients. Here, we described this tubular network assay as a useful tool in evaluation of vasculogenic activity of tumor cells. We found that some tumor cell lines such as melanoma B16F1 cells, glioblastoma U87 cells, and breast cancer MDA-MB-435 cells are able to form vascular tubules; but some do not such as colon cancer HCT116 cells. Furthermore, this vascular phenotype is dependent on cell numbers plated on the Matrigel. Therefore, this assay may serve as powerful utility to screen the vascular potential of a variety of cell types including vascular cells, tumor cells as well as other cells.

Role of YKL-40 in the angiogenesis, radioresistance, and progression of glioblastoma.

Glioblastoma is one of the most fatal cancers, characterized by a strong vascularized phenotype. YKL-40, a secreted glycoprotein, is overexpressed in patients with glioblastomas and has potential as a novel tumor biomarker. The molecular mechanisms of YKL-40 in glioblastoma development, however, are poorly understood. Here, we aimed to elucidate the role YKL-40 plays in the regulation of VEGF expression, tumor angiogenesis, and radioresistance. YKL-40 up-regulated VEGF expression in glioblastoma cell line U87, and both YKL-40 and VEGF synergistically promote endothelial cell angiogenesis. Interestingly, long term inhibition of VEGF up-regulated YKL-40. YKL-40 induced coordination of membrane receptor syndecan-1 and integrin αvß5, and triggered a signaling cascade through FAK(397) to ERK-1 and ERK-2, leading to elevated VEGF and enhanced angiogenesis. In addition, γ-irradiation of U87 cells increased YKL-40 expression that protects cell death through AKT activation and also enhances endothelial cell angiogenesis. Blockade of YKL-40 activity or expression decreased tumor growth, angiogenesis, and metastasis in xenografted animals. Immunohistochemical analysis of human glioblastomas revealed a correlation between YKL-40, VEGF, and patient survival. These findings have shed light on the mechanisms by which YKL-40 promotes tumor angiogenesis and malignancy, and thus provide a therapeutic target for tumor treatment.

A YKL-40-neutralizing antibody blocks tumor angiogenesis and progression: a potential therapeutic agent in cancers.

Accumulating evidence has indicated that expression levels of YKL-40, a secreted glycoprotein, were elevated in multiple advanced human cancers. Recently, we have identified an angiogenic role of YKL-40 in cancer development. However, blockade of the function of YKL-40, which implicates therapeutic value, has not been explored yet. Our current study sought to establish a monoclonal anti-YKL-40 antibody as a neutralizing antibody for the purpose of blocking tumor angiogenesis and metastasis. A mouse monoclonal anti-YKL-40 antibody (mAY) exhibited specific binding with recombinant YKL-40 and with YKL-40 secreted from osteoblastoma cells MG-63 and brain tumor cells U87. In the functional analysis, we found that mAY inhibited tube formation of microvascular endothelial cells in Matrigel induced by conditioned medium of MG-63 and U87 cells, as well as recombinant YKL-40. mAY also abolished YKL-40-induced activation of the membrane receptor VEGF receptor 2 (Flk-1/KDR) and intracellular signaling mitogen-activated protein (MAP) kinase extracellular signal-regulated kinase (Erk) 1 and Erk 2. In addition, mAY enhanced cell death response of U87 line to γ-irradiation through decreased expression of pAKT and AKT and accordingly, abrogated angiogenesis induced by the conditioned medium of U87 cells in which YKL-40 levels were elevated by treatment with γ-irradiation. Furthermore, treatment of xenografted tumor mice with mAY restrained tumor growth, angiogenesis, and progression. Taken together, this study has shown the therapeutic use for the mAY in treatment of tumor angiogenesis and metastasis.