Down-regulation of epidermal growth factor receptor induced by estrogens and phytoestrogens promotes the differentiation of U2OS human osteosarcoma cells

Single-Cell RNA Sequencing Pro-angiogenic Macrophage Profiles Reveal Novel Prognostic Biomarkers and Therapeutic Targets for Osteosarcoma

Osteosarcoma (OS) is a malignant bone tumor that most commonly occurs in children and adolescents. OS patients have a poor prognosis, and 5-year survival rates have rarely improved significantly over the past few decades. OS prognosis may be related to the infiltration of tumor-associated macrophages (TAMs). However, the role of proangiogenic macrophages, a subtype of TAMs, in OS prognosis has not been reported. In this study, seven subtypes of TAMs were identified from single-cell RNA sequencing (scRNA-seq) data that we propose defining as proangiogenic TAMs (Angio-TAMs), interferon-primed TAMs (IFN-TAMs), inflammatory cytokine-enriched TAMs (Inflam-TAMs), immune regulatory TAMs (Reg-TAMs), lipid-associated TAMs (LA-TAMs), and resident-tissue macrophages like TAMs (RTM-TAMs) (containing two subcellular types). In the survival analysis of each macrophage subtype, it was found that patients with Angio-TAMs had the most significant difference in survival. Eight genes associated with Angio-TAMs were obtained by differential expression analysis, and these genes were built into a prognostic model using the LASSO algorithm. Clinical OS case samples were categorized into high-risk and low-risk subgroups using median risk scores. In comparison to the low-risk subgroup, the survival time of the high-risk subgroup was much shorter. Additional studies on immune cell infiltration and immune checkpoint molecule expression in the two risk subgroups were carried out. In immunotherapy response prediction, the Angio-TAM-associated gene risk signature was found to be negatively correlated with immune checkpoint responses. In addition, the associated enriched GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways were mainly involved in the malignant progression of tumors. As suggested by these findings, the Angio-TAM gene risk signature may be an underlying prognostic biomarker and novel therapeutic target for OS patients.Kindly check and confirm whether the ESM file is correctly identifiedWe have checked this file and confirmed that it can be correctly identified.

Multi-Anticancer Activities of Phytoestrogens in Human Osteosarcoma

Phytoestrogens are plant-derived bioactive compounds with estrogen-like properties. Their potential health benefits, especially in cancer prevention and treatment, have been a subject of considerable research in the past decade. Phytoestrogens exert their effects, at least in part, through interactions with estrogen receptors (ERs), mimicking or inhibiting the actions of natural estrogens. Recently, there has been growing interest in exploring the impact of phytoestrogens on osteosarcoma (OS), a type of bone malignancy that primarily affects children and young adults and is currently presenting limited treatment options. Considering the critical role of the estrogen/ERs axis in bone development and growth, the modulation of ERs has emerged as a highly promising approach in the treatment of OS. This review provides an extensive overview of current literature on the effects of phytoestrogens on human OS models. It delves into the multiple mechanisms through which these molecules regulate the cell cycle, apoptosis, and key pathways implicated in the growth and progression of OS, including ER signaling. Moreover, potential interactions between phytoestrogens and conventional chemotherapy agents commonly used in OS treatment will be examined. Understanding the impact of these compounds in OS holds great promise for developing novel therapeutic approaches that can augment current OS treatment modalities.

Potential of natural products in osteosarcoma treatment: Focus on molecular mechanisms

Osteosarcoma is the most frequent type of bone cancer found in children and adolescents, and commonly arises in the metaphyseal region of tubular long bones. Standard therapeutic approaches, such as surgery, chemotherapy, and radiation therapy, are used in the management of osteosarcoma. In recent years, the mortality rate of osteosarcoma has decreased due to advances in treatment methods. Today, the scientific community is investigating the use of different naturally derived active principles against various types of cancer. Natural bioactive compounds can function against cancer cells in two ways. Firstly they can act as classical cytotoxic compounds by non-specifically affecting macromolecules, such as DNA, enzymes, and microtubules, which are also expressed in normal proliferating cells, but to a greater extent by cancer cells. Secondly, they can act against oncogenic signal transduction pathways, many of which are activated in cancer cells. Some bioactive plant-derived agents are gaining increasing attention because of their anti-cancer properties. Moreover, some naturally-derived compounds can significantly promote the effectiveness of standard chemotherapy drugs, and in certain cases are able to ameliorate drug-induced adverse effects caused by chemotherapy. In the present review we summarize the effects of various naturally-occurring bioactive compounds against osteosarcoma.

Investigation of inhibition effect of daidzein on osteosarcoma cells based on experimental validation and systematic pharmacology analysis

Objective

This study aims to explore the effect of daidzein, which is a natural isoflavone compound mainly extracted from soybeans, on osteosarcoma and the potential molecular mechanism.

Material and Methods

143B and U2OS osteosarcoma cells were treated with gradient concentrations of daidzein, and MTT assay was used to determine the cell proliferation capacity and IC₅₀. Hoechst 33342 staining and Annexin V-FITC/PI detection were used to determine apoptosis. Cell cycle was analyzed by flow cytometry, and migration ability were detected by transwell assays and scratch wound assay. An osteosarcoma xenograft mice model was applied to investigate the effect of daidzein on osteosarcoma in vivo. Systematic pharmacology and molecular modeling analysis were applied to predict the target of daidzein to osteosarcoma, and the target Src was verified by western blotting. We also observed the effect of daidzein on cell proliferation and apoptosis of Src-overexpressing osteosarcoma cells.

Results

In vitro, daidzein significantly inhibited 143B and U2OS osteosarcoma cell proliferation and migration, and induced cell cycle arrest. In vivo, daidzein exerts antitumor effects in osteosarcoma xenograft mice. After systematic screening and analysis, Src-MAPK signaling pathway was predicted as the highest-ranked pathway. Western blot demonstrated that daidzein inhibited phosphorylation of the Src-ERK pathway in osteosarcoma cells. Also, overexpression of Src could partially reverse the inhibitory effects of daidzein on osteosarcoma cell proliferation.

Conclusion

Daidzein exerts an antitumor effect on osteosarcoma, and the mechanism may be through the Src-ERK pathway.

β-Arrestin 1 in Thyrotropin Receptor Signaling in Bone: Studies in Osteoblast-Like Cells

A direct action of thyrotropin (TSH, thyroid-stimulating hormone) on bone precursors in humans is controversial. Studies in rodent models have provided conflicting findings. We used cells derived from a moderately differentiated osteosarcoma stably overexpressing human TSH receptors (TSHRs) as a model of osteoblast precursors (U2OS-TSHR cells) to investigate TSHR-mediated effects in bone differentiation in human cells. We review our findings that (1) TSHR couples to several different G proteins to induce upregulation of genes associated with osteoblast activity-interleukin 11 (IL-11), osteopontin (OPN), and alkaline phosphatase (ALPL) and that the kinetics of the induction and the G protein-mediated signaling pathways involved were different for these genes; (2) TSH can stimulate β-arrestin-mediated signal transduction and that β-arrestin 1 in part mediates TSH-induced pre-osteoblast differentiation; and (3) TSHR/insulin-like growth factor 1 (IGF1) receptor (IGF1R) synergistically increased OPN secretion by TSH and IGF1 and that this crosstalk was mediated by physical association of these receptors in a signaling complex that uses β-arrestin 1 as a scaffold. These findings were complemented using a novel β-arrestin 1-biased agonist of TSHR. We conclude that TSHR can signal via several transduction pathways leading to differentiation of this model system of human pre-osteoblast cells and, therefore, that TSH can directly regulate these bone cells.

Activation of GPER suppresses the malignancy of osteosarcoma cells via down regulation of IL-6 and IL-8

Estrogenic signals can regulate the progression of osteosarcoma (OS) via classic estrogen receptor α/β (ERα/β). G protein-coupled estrogen receptor (GPER) can mediate the non-genomic effects of estrogen and regulate the progression of various cancers. Our present study revealed that the expression of GPER in OS cells and tissues was lower than that in their corresponding controls. Activation of GPER via its specific agonist G-1 can decrease the proliferation, migration, and invasion of OS cells. By screening the expression of cytokines involved in the progression of OS, we found that activation of GPER can inhibit the expression of interleukin-6 (IL-6) and IL-8 in OS cells. Recombinant IL-6 (rIL-6) or rIL-8 can attenuate G-1 suppressed migration of OS cells. Mechanically, activation of GPER can rapidly decease the phosphorylation and nuclear translocation of NF-κB in OS cells. While over expression of p65 significantly attenuated G-1 induced down regulation of IL-6/IL-8. Further, G-1 can decrease the activation of p38-MAPK, which can further shorten the half-life of IL-8 mRNA. Collectively, we revealed that GPER can suppress the migration and invasion of OS cells via inhibition of IL-6 and IL-8. It suggested that GPER might be a potential therapy target for OS treatment.

Signal transduction growth factors: the effective governance of transcription and cellular adhesion in cancer invasion

Giulio Bizzozero classified the tissues concerning their capacity to self-renew during the adult life in labile, stable and permanent tissues. In 1940 Viktor Hamburger and Rita Levi Montalcini exposed the possibility to induce the growth of permanent cells thanks to a specific ligand Nerve Growth Factor (NGF). Stanley Cohen purified a protein the Epidermal Growth Factor (EGF), able to induce epidermis proliferation and to elicit precocious eye disclosure and teeth eruption, establishing the “inverse” relationships between the proliferation and differentiation. These two biological effects induced by EGF were according to EGFR signaling is involved in a large array of cellular functions such as proliferation, survival, adhesion, migration and differentiation. This review is focused on the key role of growth factors signaling and their downstream effectors in physiological and in pathological phenomena, the authors highlight the governance of Growth factors during the EMT in cancer invasion.

Discovery of a Positive Allosteric Modulator of the Thyrotropin Receptor: Potentiation of Thyrotropin-Mediated Preosteoblast Differentiation In Vitro

Recently, we showed that TSH-enhanced differentiation of a human preosteoblast-like cell model involved a β-arrestin 1 (β-Arr 1)-mediated pathway. To study this pathway in more detail, we sought to discover a small molecule ligand that was functionally selective toward human TSH receptor (TSHR) activation of β-Arr 1. High-throughput screening using a cell line stably expressing mutated TSHRs and mutated β-Arr 1 (DiscoverX1 cells) led to the discovery of agonists that stimulated translocation of β-Arr 1 to the TSHR, but did not activate G_s-mediated signaling pathways, i.e., cAMP production. D3-βArr (NCGC00379308) was selected. In DiscoverX1 cells, D3-βArr stimulated β-Arr 1 translocation with a 5.1-fold greater efficacy than TSH and therefore potentiated the effect of TSH in stimulating β-Arr 1 translocation. In human U2OS-TSHR cells expressing wild-type TSHRs, which is a model of human preosteoblast-like cells, TSH upregulated the osteoblast-specific genes osteopontin (OPN) and alkaline phosphatase (ALPL). D3-βArr alone had only a weak effect to upregulate these bone markers, but D3-βArr potentiated TSH-induced upregulation of ALPL and OPN mRNA levels 1.6-fold and 5.5-fold, respectively, at the maximum dose of ligands. Furthermore, the positive allosteric modulator effect of D3-βArr resulted in an increase of TSH-induced secretion of OPN protein. In summary, we have discovered the first small molecule positive allosteric modulator of TSHR. As D3-βArr potentiates the effect of TSH to enhance differentiation of a human preosteoblast in an in vitro model, it will allow a novel experimental approach for probing the role of TSH-induced β-Arr 1 signaling in osteoblast differentiation.

Genistein exerts growth inhibition on human osteosarcoma MG-63 cells via PPARγ pathway

The peroxisome proliferator-activated receptor γ (PPARγ) is emerging as an important regulator in various metabolic processes of cancer. Genistein, as a major isoflavonoid isolated from dietary soybean, possesses a wide variety of biological activities, particularly, in cancer prevention. However, the mechanisms by which genistein elicits its growth inhibiting effects in osteosarcoma (OS) MG-63 cells have not been extensively elucidated. MG-63 cells were treated for 2 days with various concentrations of genistein and/or GW9662 (a selective antagonist of PPARγ). The effect of different drugs on cell viability was determined by Cell Counting Kit-8 (CCK-8). The assay of cell proliferation was performed using 5-ethynyl-2'-deoxyuridine (EdU). The changes of apoptosis and cell cycle progression were detected by flow cytometry experiments. The protein expression of PPARγ pathway (PPARγ, PTEN, BCL-2, Survivin, P21WAF1/CIP1 and Cyclin B1) was determined by western blot analysis. The expression of PPARγ and PTEN mRNA was detected by real-time quantitative RT-PCR analysis. We report that genistein caused OS cell growth inhibition. We found that the PPARγ expression in OS cells increased after genistein treatment. Further studies on the mechanisms of genistein revealed a series of cell growth changes related to the PPARγ pathway; while cell cycle changes can be reversed by GW9662. Genistein plays an important role in preventing OS cell growth, which can impede the OS cell cycle as a non-toxic activator of PPARγ, providing novel insights into the mechanisms of the therapeutic activities of genistein.

Coleusin factor, a novel anticancer diterpenoid, inhibits osteosarcoma growth by inducing bone morphogenetic protein-2-dependent differentiation

Coleusin factor is a diterpenoid compound isolated from the root of a tropical plant, Coleus forskohlii. Although Coleusin factor has been reported to suppress proliferation of and induce apoptosis in several types of cancer cells, the effects of Coleusin factor on osteosarcoma and the underlying mechanism are still not fully understood. In this study, we show that Coleusin factor treatment potently inhibits the growth of osteosarcoma cells associated with G(1) cell-cycle arrest. Interestingly, apoptosis and cell death are not induced. Instead, Coleusin factor causes osteosarcoma cells to exhibit typical properties of differentiated osteoblasts, including a morphologic alteration resembling osteoblasts, the expression of osteoblast differentiation markers, elevated alkaline phosphatase activity, and increased cellular mineralization. Coleusin factor treatment significantly increases the expression of bone morphogenetic protein-2 (BMP-2), a crucial osteogenic regulator, and runt-related transcription factor 2 (RUNX2), one of the key transcription factors of the BMP pathway. When BMP-2 signaling is blocked, Coleusin factor fails to inhibit cell proliferation and to induce osteoblast differentiation. Thus, upregulation of BMP-2 autocrine is critical for Coleusin factor to induce osteoblast differentiation and exert its anticancer effects on osteosarcoma. Importantly, administration of Coleusin factor inhibits the growth of osteosarcoma xenografted in nude mice without systemic or immunologic toxicity. Osteosarcoma is a highly aggressive cancer marked by the loss of normal differentiation. Coleusin factor represents a new type of BMP-2 inducer that restores differentiation in osteosarcoma cells. It may provide a promising therapeutic strategy against osteosarcoma with minimal side effects.

β-Arrestin-1 mediates thyrotropin-enhanced osteoblast differentiation

Thyrotropin (TSH) activation of the TSH receptor (TSHR), a 7-transmembrane-spanning receptor (7TMR), may have osteoprotective properties by direct effects on bone. TSHR activation by TSH phosphorylates protein kinases AKT1, p38α, and ERK1/2 in some cells. We found TSH-induced phosphorylation of these kinases in 2 cell lines engineered to express TSHRs, human embryonic kidney HEK-TSHR cells and human osteoblastic U2OS-TSHR cells. In U2OS-TSHR cells, TSH up-regulated pAKT1 (7.1±0.5-fold), p38α (2.9±0.4-fold), and pERK1/2 (3.1±0.2-fold), whereas small molecule TSHR agonist C2 had no or little effect on pAKT1 (1.8±0.08-fold), p38α (1.2±0.09-fold), and pERK1/2 (1.6±0.19-fold). Furthermore, TSH increased expression of osteoblast marker genes ALPL (8.2±4.6-fold), RANKL (21±5.9-fold), and osteopontin (OPN; 17±5.3-fold), whereas C2 had little effect (ALPL, 1.7±0.5-fold; RANKL, 1.3±0.6-fold; and OPN, 2.2±0.7-fold). β-Arrestin-1 and -2 can mediate activatory signals by 7TMRs. TSH stimulated translocation of β-arrestin-1 and -2 to TSHR, whereas C2 failed to translocate either β-arrestin. Down-regulation of β-arrestin-1 by siRNA inhibited TSH-stimulated phosphorylation of ERK1/2, p38α, and AKT1, whereas down-regulation of β-arrestin-2 increased phosphorylation of AKT1 in both cell types and of ERK1/2 in HEK-TSHR cells. Knockdown of β-arrestin-1 inhibited TSH-stimulated up-regulation of mRNAs for OPN by 87 ± 1.7% and RANKL by 73 ± 2.4%, and OPN secretion by 74 ± 10%. We conclude that TSH enhances osteoblast differentiation in U2OS cells that is, in part, caused by activatory signals mediated by β-arrestin-1.

Inverse regulation of EGFR/HER1 and HER2-4 in normal and malignant human breast tissue

Cross-talk between the estrogen and the EGFR/HER signalling pathways has been suggested as a potential cause of resistance to endocrine therapy in breast cancer. Here, we determined HER1-4 receptor and neuregulin-1 (NRG1) ligand mRNA expression levels in breast cancers and corresponding normal breast tissue from patients previously characterized for plasma and tissue estrogen levels. In tumours from postmenopausal women harbouring normal HER2 gene copy numbers, we found HER2 and HER4, but HER3 levels in particular, to be elevated (2.48, 1.30 and 22.27 –fold respectively; P<0.01 for each) compared to normal tissue. Interestingly, HER3 as well as HER4 were higher among ER+ as compared to ER- tumours (P=0.004 and P=0.024, respectively). HER2 and HER3 expression levels correlated positively with ER mRNA (ESR1) expression levels (r=0.525, P=0.044; r=0.707, P=0.003, respectively). In contrast, EGFR/HER1 was downregulated in tumour compared to normal tissue (0.13-fold, P<0.001). In addition, EGFR/HER1 correlated negatively to intra-tumour (r=-0.633, P=0.001) as well as normal tissue (r=-0.556, P=0.006) and plasma estradiol levels (r=-0.625, P=0.002), suggesting an inverse regulation between estradiol and EGFR/HER1 levels. In ER+ tumours from postmenopausal women, NRG1 levels correlated positively with EGFR/HER1 (r=0.606, P=0.002) and negatively to ESR1 (r=-0.769, P=0.003) and E2 levels (r=-0.542, P=0.020). Our results indicate influence of estradiol on the expression of multiple components of the HER system in tumours not amplified for HER2, adding further support to the hypothesis that cross-talk between these systems may be of importance to breast cancer growth in vivo.

Puerarin stimulates proliferation and differentiation and protects against cell death in human osteoblastic MG-63 cells via ER-dependent MEK/ERK and PI3K/Akt activation

Puerarin, the main isoflavone glycoside found in the Chinese herb radix of Pueraria lobata (Willd.) Ohwi, has received increasing attention because of its possible role in the prevention of osteoporosis. Previously, we showed that puerarin could inhibit the bone absorption of osteoclasts and promote long bone growth in fetal mouse in vitro. Further study confirmed that puerarin stimulated proliferation and differentiation of osteoblasts in rat. However, the mechanisms underlying its actions on human bone cells have not been well defined. Here we show that puerarin increases proliferation and differentiation and opposes cisplatin-induced apoptosis in human osteoblastic MG-63 cells containing two estrogen receptor (ER) isoforms. Puerarin promotes proliferation by altering cell cycle distribution whereas puerarin-mediated survival may be associated with up-regulation of Bcl-xL expression. Treatment with the ER antagonist ICI 182,780 abolishes the above actions of puerarin on osteoblast-derived cells. Using small interfering double-stranded RNA technology, we further demonstrate that the effects of puerarin on proliferation, differentiation and survival are mediated by both ERα and ERβ. Moreover, we also demonstrate that puerarin functions at least partially through activation of MEK/ERK and PI3K/Akt signaling. This agent also shows much weaker effect on breast epithelial cell growth than that of estrogen. Therefore, puerarin will be a promising agent that prevents or retards osteoporosis.

Dual programmed cell death pathways induced by p53 transactivation overcome resistance to oncolytic adenovirus in human osteosarcoma cells

Tumor suppressor p53 is a multifunctional transcription factor that regulates diverse cell fates, including apoptosis and autophagy in tumor biology. p53 overexpression enhances the antitumor activity of oncolytic adenoviruses; however, the molecular mechanism of this occurrence remains unclear. We previously developed a tumor-specific replication-competent oncolytic adenovirus, OBP-301, that kills human osteosarcoma cells, but some human osteosarcoma cells were OBP-301-resistant. In this study, we investigated the antitumor activity of a p53-expressing oncolytic adenovirus, OBP-702, and the molecular mechanism of the p53-mediated cell death pathway in OBP-301-resistant human osteosarcoma cells. The cytopathic activity of OBP-702 was examined in OBP-301-sensitive (U2OS and HOS) and OBP-301-resistant (SaOS-2 and MNNG/HOS) human osteosarcoma cells. The molecular mechanism in the OBP-702-mediated induction of two cell death pathways, apoptosis and autophagy, was investigated in OBP-301-resistant osteosarcoma cells. The antitumor effect of OBP-702 was further assessed using an orthotopic OBP-301-resistant MNNG/HOS osteosarcoma xenograft tumor model. OBP-702 suppressed the viability of OBP-301-sensitive and -resistant osteosarcoma cells more efficiently than OBP-301 or a replication-deficient p53-expressing adenovirus (Ad-p53). OBP-702 induced more profound apoptosis and autophagy when compared with OBP-301 or Ad-p53. E1A-mediated miR-93/106b upregulation induced p21 suppression, leading to p53-mediated apoptosis and autophagy in OBP-702-infected cells. p53 overexpression enhanced adenovirus-mediated autophagy through activation of damage-regulated autophagy modulator (DRAM). Moreover, OBP-702 suppressed tumor growth in an orthotopic OBP-301-resistant MNNG/HOS xenograft tumor model. These results suggest that OBP-702-mediated p53 transactivation is a promising antitumor strategy to induce dual apoptotic and autophagic cell death pathways via regulation of miRNA and DRAM in human osteosarcoma cells.

The cannabinoid receptor inverse agonist AM251 regulates the expression of the EGF receptor and its ligands via destabilization of oestrogen-related receptor α protein

BACKGROUND AND PURPOSE

AM251 is an inverse agonist of the cannabinoid 1 receptor (CB(1)R) that can exert 'off-target' effects in vitro and in CB(1)R knock-out mice. AM251 is also potent at modulating tumour cell growth, suggesting that growth factor-mediated oncogenic signalling could be regulated by AM251. Since dysregulation of the EGF receptor has been associated with carcinogenesis, we examined AM251 regulation of EGF receptor (EGFR) expression and function.

EXPERIMENTAL APPROACH

The various biological functions of AM251 were measured in CB(1)R-negative human cancer cells. Pharmacological and genetic approaches were used to validate the data.

KEY RESULTS

The mRNA levels for EGFR and its associated ligands, including HB-EGF, were induced several fold in PANC-1 and HCT116 cells in response to AM251. This event was associated with enhanced expression of EGFR on the cell surface with concomitant increase in EGF-induced cellular responses in AM251-treated cells. Exposure to XCT790, a synthetic inverse agonist of the orphan nuclear oestrogen-related receptor α (ERRα), also induced EGFR and HB-EGF expression to the same extent as AM251, whereas pretreatment with the ERRα-selective agonist, biochanin A, blunted AM251 actions. AM251 promoted the degradation of ERRα protein without loss of the corresponding mRNA. Knock-down of ERRα by siRNA-based approach led to constitutive induction of EGFR and HB-EGF levels, and eliminated the biological responses of AM251 and XCT790. Finally, AM251 displaced diethylstilbestrol prebound to the ligand-binding domain of ERRα.

CONCLUSIONS AND IMPLICATIONS

AM251 up-regulates EGFR expression and signalling via a novel non-CB(1)R-mediated pathway involving destabilization of ERRα protein in selected cancer cell lines.

LC, a novel estrone-rhein hybrid compound, promotes proliferation and differentiation and protects against cell death in human osteoblastic MG-63 cells

Estrogen analogs are promising drugs for postmenopausal osteoporosis, but because of their possible side effects, estrogens which exert their estrogenic effects selectively on bone are desired. Based on our previous studies that rhein had high affinity for the bone mineral, we synthesized estrone-rhein hybrid compounds and confirmed that one of these hybrid compounds, LC, exhibited a selective profile in the bone and prevented bone loss but had no effect on endometrium growth in ovariectomized rats. However, the mechanisms underlying its actions on human bone cells have remained largely unknown. Here we show that LC increases proliferation and differentiation and opposes cisplatin-induced apoptosis in human osteoblastic MG-63 cells containing two estrogen receptor (ER) isoforms. LC promotes proliferation by altering cell cycle distribution whereas LC-mediated survival may be associated with up-regulation of X-linked inhibitor of apoptosis (XIAP) expression. Treatment with the ER antagonist ICI 182,780 abolishes the above actions of LC on osteoblast-derived cells. Using small interfering double-stranded RNAs technology, we further demonstrate that the effects of LC on proliferation and survival are mediated by both ERα and ERβ but those on differentiation primarily by ERα. Moreover, we demonstrate that LC may promote activation of the classic estrogen response element (ERE) pathway through increasing steroid receptor coactivator (SRC)-3 expression. Meanwhile, we find that regulation of osteoblastic proliferation and survival by LC involves Ras/MEK/ERK and PI3K/Akt signaling. Therefore, using rhein for conjugating compounds is a promising method of effectively targeting estrogens to the bone.

Therapeutic Implications of PPARgamma in Human Osteosarcoma

Osteosarcoma (OS) is the most common nonhematologic malignancy of bone in children and adults. Although dysregulation of tumor suppressor genes and oncogenes, such as Rb, p53, and the genes critical to cell cycle control, genetic stability, and apoptosis have been identified in OS, consensus genetic changes that lead to OS development are poorly understood. Disruption of the osteogenic differentiation pathway may be at least in part responsible for OS tumorigenesis. Current OS management involves chemotherapy and surgery. Peroxisome proliferator-activated receptor (PPAR) agonists and/or retinoids can inhibit OS proliferation and induce apoptosis and may inhibit OS growth by promoting osteoblastic terminal differentiation. Thus, safe and effective PPAR agonists and/or retinoid derivatives can be then used as adjuvant therapeutic drugs for OS therapy. Furthermore, these agents have the potential to be used as chemopreventive agents for the OS patients who undergo the resection of the primary bone tumors in order to prevent local recurrence and/or distal pulmonary metastasis.