Osteocalcin is incompletely spliced in non-osseous tissues

Molecular Aspects of Thyroid Calcification

In thyroid cancer, calcification is mainly present in classical papillary thyroid carcinoma (PTC) and in medullary thyroid carcinoma (MTC), despite being described in benign lesions and in other subtypes of thyroid carcinomas. Thyroid calcifications are classified according to their diameter and location. At ultrasonography, microcalcifications appear as hyperechoic spots ≤ 1 mm in diameter and can be named as stromal calcification, bone formation, or psammoma bodies (PBs), whereas calcifications > 1 mm are macrocalcifications. The mechanism of their formation is still poorly understood. Microcalcifications are generally accepted as a reliable indicator of malignancy as they mostly represent PBs. In order to progress in terms of the understanding of the mechanisms behind calcification occurring in thyroid tumors in general, and in PTC in particular, we decided to use histopathology as the basis of the possible cellular and molecular mechanisms of calcification formation in thyroid cancer. We explored the involvement of molecules such as runt-related transcription factor-2 (Runx-2), osteonectin/secreted protein acidic and rich in cysteine (SPARC), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteopontin (OPN) in the formation of calcification. The present review offers a novel insight into the mechanisms underlying the development of calcification in thyroid cancer.

Bone: Another potential target to treat, prevent and predict diabetes

Type 2 diabetes mellitus is now a worldwide health problem with increasing prevalence. Mounting efforts have been made to treat, prevent and predict this chronic disease. In recent years, increasing evidence from mice and clinical studies suggests that bone-derived molecules modulate glucose metabolism. This review aims to summarize our current understanding of the interplay between bone and glucose metabolism and to highlight potential new means of therapeutic intervention. The first molecule recognized as a link between bone and glucose metabolism is osteocalcin (OCN), which functions in its active form, that is, undercarboxylated OCN (ucOC). ucOC acts in promoting insulin expression and secretion, facilitating insulin sensitivity, and favouring glucose and fatty acid uptake and utilization. A second bone-derived molecule, lipocalin2, functions in suppressing appetite in mice through its action on the hypothalamus. Osteocytes, the most abundant cells in bone matrix, are suggested to act on the browning of white adipose tissue and energy expenditure through secretion of bone morphogenetic protein 7 and sclerostin. The involvement of bone resorption in glucose homeostasis has also been examined. However, there is evidence indicating the implication of the receptor activator of nuclear factor κ-B ligand, neuropeptide Y, and other known and unidentified bone-derived factors that function in glucose homeostasis. We summarize recent advances and the rationale for treating, preventing and predicting diabetes by skeleton intervention.

The Role of Osteocalcin and Alkaline Phosphatase Immunohistochemistry in Osteosarcoma Diagnosis

Background

The diagnosis of Osteosarcoma (OSA) is not always straightforward. OSA may resemble Other Primary Bone Tumours (OPBT). The diagnosis of osteosarcoma is sometimes difficult especially in a very small specimen. Immunohistochemistry is one of ancillary testing types that can help the diagnosis of many tumours. The aim of this study was to evaluate the validity of Osteocalcin (OCN) and Alkaline Phosphatase (ALP) immunohistochemistry in discriminating OSA from OPBT.

Method

This study included 50 selected human primary bone tumours, 25 cases of OSA and 25 cases of OPBT. Immunohistochemical evaluation of OCN and ALP was done for all cases. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy were calculated.

Result

The mean age of OSA and OPBT patients was 19.6 ± 13.6 and 40.0 ± 16.3 years, respectively. Osteocalcin was positive in 17/25 (68%) cases of OSA and 16/25 (64%) cases of OPBT (p = 0.061). Alkaline Phosphatase was positive in 24/25 (96%) cases of OSA and 5/25 (20%) cases of OPBT (p < 0.001). The sensitivity of OCN in OSA diagnosis was 68%, with specificity, PPV, NPV, and overall accuracy being 36%, 52%, 53%, and 52%, respectively. The sensitivity of ALP in OSA diagnosis was 96%, with specificity, PPV, NPV, and overall accuracy being 80%, 82.7%, 95.2%, and 88%, respectively.

Conclusion

ALP immunohistochemistry is useful in discriminating OSA from OPBT. ALP is superior to OCN in OSA diagnosis. OCN cannot be used to differentiate between OSA and OPBT.

An overview of osteocalcin progress

An increasing amount of data indicate that osteocalcin is an endocrine hormone which regulates energy metabolism, male fertility and brain development. However, the detailed functions and mechanism of osteocalcin are not well understood and conflicting results have been obtained from researchers worldwide. In the present review, we summarize the progress of osteocalcin studies over the past 40 years, focusing on the structure of carboxylated and undercarboxylated osteocalcin, new functions and putative receptors, the role of osteocalcin in bone remodeling, specific expression and regulation in osteoblasts, and new indices for clinical studies. The complexity of osteocalcin in completely, uncompletely and non-carboxylated forms may account for the discrepancies in its tertiary structure and clinical results. Moreover, the extensive expression of osteocalcin and its putative receptor GPRC6A imply that there are new physiological functions and mechanisms of action of osteocalcin to be explored. New discoveries related to osteocalcin function will assist its potential clinical application and physiological theory, but comprehensive investigations are required.

HOXB13 downregulates intracellular zinc and increases NF-κB signaling to promote prostate cancer metastasis

Characteristically, prostate cancer (PCa) cells exhibit marked decrease in intracellular zinc; however, the mechanism responsible is not clearly understood. HOXB13 is involved in PCa progression and is overexpressed in castration-resistant PCa. DNA microarray analysis of LNCaP Pca cells showed that ZnT zinc output transporters were strikingly upregulated among androgen-independent HOXB13 target genes. Furthermore, exogenous HOXB13 caused intracellular zinc concentrations to fall in PCa cells, stimulated NF-κB-mediated signaling by reducing inhibitor of NF-κB alpha (IκBα) and enhanced the nuclear translocation of RelA/p65. Human prostate tumors also exhibited strong inverse correlation between the protein expressions of HOXB13 and IκBα. Consequently, HOXB13 stimulated PCa cell invasion, and this was inhibited by the suppression of ZnT4. In addition, studies in a PC3 orthotopic mouse model of PCa metastasis showed that HOXB13 is a strong metastatic stimulator. Taken together, these results show that HOXB13 promotes PCa invasion and metastasis by decreasing intracellular zinc levels, thus stimulating NF-κB signals, and suggest that HOXB13 acts as a modulator of intracellular zinc levels that promotes the malignant characteristics of PCa.

Osteocalcin: skeletal and extra-skeletal effects

Osteocalcin (OC) is a non-collagenous, vitamin K-dependent protein secreted in the late stage of osteoblasts differentiation. The presence of the three residues of γ-carbossiglutamatic acid, specific of the active form of OC protein, allows the protein to bind calcium and consequently hydroxyapatite. The osteoblastic OC protein is encoded by the bone γ-carbossiglutamate gene whose transcription is principally regulated by the Runx2/Cbfa1 regulatory element and stimulated by vitamin D(3) through a steroid-responsive enhancer sequence. Even if data obtained in literature are controversial, the dual role of OC in bone can be presumed as follows: firstly, OC acts as a regulator of bone mineralization; secondly, OC regulates osteoblast and osteoclast activity. Recently the metabolic activity of OC, restricted to the un-carboxylated form has been demonstrated in osteoblast-specific knockout mice. This effect is mediated by the regulation of pancreatic β-cell proliferation and insulin secretion and adiponectin production by adipose tissue and leads to the regulation of glucose metabolism and fat mass. Nevertheless, clinical human studies only demonstrated the correlation between OC levels and factors related to energy metabolism. Thus further investigations in humans are required to demonstrate the role of OC in the regulation of human energy metabolism. Moreover, it is presumable that OC also acts on blood vessels by inducing angiogenesis and pathological mineralization. This review highlights the recent studies concerning skeletal and extra-skeletal effects of OC.

Vitamin D metabolism and effects on pluripotency genes and cell differentiation in testicular germ cell tumors in vitro and in vivo

Testicular germ cell tumors (TGCTs) are classified as either seminomas or nonseminomas. Both tumors originate from carcinoma in situ (CIS) cells, which are derived from transformed fetal gonocytes. CIS, seminoma, and the undifferentiated embryonal carcinoma (EC) retain an embryonic phenotype and express pluripotency factors (NANOG/OCT4). Vitamin D (VD) is metabolized in the testes, and here, we examined VD metabolism in TGCT differentiation and pluripotency regulation. We established that the VD receptor (VDR) and VD-metabolizing enzymes are expressed in human fetal germ cells, CIS, and invasive TGCTs. VD metabolism diminished markedly during the malignant transformation from CIS to EC but was reestablished in differentiated components of nonseminomas, distinguished by coexpression of mesodermal markers and loss of OCT4. Subsequent in vitro studies confirmed that 1,25(OH)(2)D(3) (active VD) downregulated NANOG and OCT4 through genomic VDR activation in EC-derived NTera2 cells and, to a lesser extent, in seminoma-derived TCam-2 cells, and up-regulated brachyury, SNAI1, osteocalcin, osteopontin, and fibroblast growth factor 23. To test for a possible therapeutic effect in vivo, NTera2 cells were xenografted into nude mice and treated with 1,25(OH)(2)D(3), which induced down-regulation of pluripotency factors but caused no significant reduction of tumor growth. During NTera2 tumor formation, down-regulation of VDR was observed, resulting in limited responsiveness to cholecalciferol and 1,25(OH)(2)D(3) treatment in vivo. These novel findings show that VD metabolism is involved in the mesodermal transition during differentiation of cancer cells with embryonic stem cell characteristics, which points to a function for VD during early embryonic development and possibly in the pathogenesis of TGCTs.

Transcriptional regulation of inducible nitric oxide synthase gene therapy: targeting early stage and advanced prostate cancer

BACKGROUND

Using the tumour type specific human osteocalcin (hOC) promoter, we have previously reported strong promoter activation in hormone independent prostate cancer cells in vitro. In the present study, we present a comparative study of the tissue specific promoter prostate specific membrane antigen (PSMA), and the tumour-type specific hOC promoter driving the inducible nitric oxide synthase (iNOS) transgene using both in vitro and in vivo models.

METHODS

In vitro cytotoxicity was assessed by clonogenic assay. Quantification of nitric oxide expression was determined by the Griess test. In vivo anti-tumour efficacy was determined by tumour growth delay following direct intra-tumoural injection of the constructs into PC3 xenografts. In addition, tumours were dissected post mortem and examined for morphological differences as well as changes in apoptotic protein expression.

RESULTS

PSMA/iNOS produced cytotoxicity in both androgen dependant and independent cell lines. Nitric oxide quantification confirmed that increased cytotoxicity was directly associated with nitric oxide production. Tumour growth delays were observed in all groups treated with the iNOS-expressing constructs ranging from 10.7 days for the hOC/iNOS single dose treatment group to a maximum of 52.2 days for the hOC/iNOS multiple dose group. Intra-tumoural assessment of iNOS and cleaved poly (ADP-ribose) polymerase protein expression demonstrated a significant up-regulation of both proteins, indicating cytotoxicity mediated through the intrinsic apoptotic pathway.

CONCLUSIONS

Highly significant tumour growth delay coupled with no detrimental side-effects were observed following treatment with the PSMA/iNOS and hOC/iNOS constructs. We consider that these findings provide a basis for the development of systemically delivered PSMA/iNOS or hOC/iNOS targeting early stage and advanced prostate cancer.

HOXB13 promotes androgen independent growth of LNCaP prostate cancer cells by the activation of E2F signaling

BACKGROUND

Androgen signaling plays a critical role in the development of prostate cancer and its progression. However, androgen-independent prostate cancer cells emerge after hormone ablation therapy, resulting in significant clinical problems. We have previously demonstrated that the HOXB13 homeodomain protein functions as a prostate cancer cell growth suppressor by inhibiting androgen-mediated signals. However, the role of the HOXB13 in androgen-independent growth of prostate cancer cells remains unexplained.

RESULTS

In this report, we first demonstrated that HOXB13 was highly overexpressed in hormone-refractory tumors compared to tumors without prostate-specific antigen after initial treatment. Functionally, in an androgen-free environment minimal induction of HOXB13 in LNCaP prostate cancer cells, to the level of the normal prostate, markedly promoted cell proliferation while suppression inhibited cell proliferation. The HOXB13-mediated cell growth promotion in the absence of androgen, appears to be mainly accomplished through the activation of RB-E2F signaling by inhibiting the expression of the p21waf tumor suppressor. Indeed, forced expression of HOXB13 dramatically decreased expression of p21waf; this inhibition largely affected HOXB13-mediated promotion of E2F signaling.

CONCLUSIONS

Taken together, the results of this study demonstrated the presence of a novel pathway that helps understand androgen-independent survival of prostate cancer cells. These findings suggest that upregulation of HOXB13 is associated with an additive growth advantage of prostate cancer cells in the absence of or low androgen concentrations, by the regulation of p21-mediated E2F signaling.

Differential CARM1 expression in prostate and colorectal cancers

Background

Coactivator-associated arginine methyltransferase 1 (CARM1) functions as a transcriptional coactivator of androgen receptor (AR)-mediated signaling. Correspondingly, overexpression of CARM1 has been associated with the development of prostate cancer (PCa) and its progression to androgen-independent PCa. In our preliminary study, however, the promoting effects of CARM1, with regard to androgen-stimulated AR target gene expression were minimal. These results suggested that the AR target gene expression associated with CARM1 may result primarily from non-hormone dependent activity. The goal of this study was to confirm the pattern of expression of CARM1 in human tumors and determine the mechanism of action in CARM1 overexpressed tumors.

Methods

Tissue microarray was used to determine the pattern of expression of CARM1 in human cancers by immunohistochemistry. CARM1 expression was also evaluated in prostate and colorectal surgical specimens and the clinical records of all cases were reviewed. In addition, a reporter transcription assay using the prostate-specific antigen (PSA) promoter was used to identify the signaling pathways involved in non-hormone-mediated signal activation associated with CARM1.

Results

The tissue microarray showed that CARM1 was particularly overexpressed in the colorectal cancers while CARM1 expression was not prevalent in the prostate and breast cancers. Further studies using surgical specimens demonstrated that CARM1 was highly overexpressed in 75% of colorectal cancers (49 out of 65) but not in the androgen-independent PCa. In addition, CARM1's coactivating effect on the entire PSA promoter was very limited in both androgen-dependent and androgen-independent PCa cells. These results suggest that there are other factors associated with CARM1 expression in PSA regulation. Indeed, CARM1 significantly regulated both p53 and NF-κB target gene transcription.

Conclusions

The results of this study suggest that, in addition to its role in activation of steroid receptors, CARM1 functions as a transcriptional modulator by altering the activity of many transcriptional factors, especially with regard to androgen independent PCa and colorectal cancers.

Changes in the mRNA expression of osteoblast-related genes in response to beta(3)-adrenergic agonist in UMR106 cells

Activation of adrenergic receptors (AR) was demonstrated to result in either bone gain or bone loss depending on the activated AR subtypes and concentrations of agonists used. While beta(2)-AR agonist was extensively investigated as an osteopenic agent, effects of beta(3)-AR activation on osteoblasts were still elusive. Rat osteoblast-like UMR106 cells were herein found to express several AR subtypes, including beta(3)-AR. After exposure to a low-dose beta(3)-AR agonist BRL37344 (10 nmol L(-1)), UMR106 cells downregulated the mRNA expression of transcription factors Runx2 and Dlx5, which are important for initiation of osteoblast differentiation. Low-dose BRL37344 also decreased the expression ratio of receptor activator of nuclear factor kappaB ligand (RANKL) over osteoprotegerin (OPG), suggesting the protective effect of beta(3)-AR agonist against bone resorption. Alkaline phosphatase expression was markedly decreased, whereas expressions of osteocalcin and osteopontin were increased by 100 nmol L(-1) BRL37344, indicating that beta(3)-AR activation could accelerate the transition of matrix maturation stage to mineralization stage. In conclusion, beta(3)-AR activation in rat osteoblasts induced alteration in the expression of osteoblast-related transcription factor genes as well as genes required for bone formation and resorption. The present results also suggest that, besides beta(2)-AR, beta(3)-AR is another AR subtype responsible for the sympathetic nervous system-induced bone remodeling.

Conditionally replicating adenovirus therapy utilizing bone sialoprotein promoter (Ad-BSP-E1a) in an in vivo study of treating androgen-independent intraosseous prostate cancer

BACKGROUND

Adenoviral based gene therapy has been used in clinical trials in control of advanced prostate cancer. In this study, a promising conditionally replicating adenovirus (CRAd) driven by a tissue specific bone sialoprotein promoter in controlling prostate cancer both in vitro and in vivo is demonstrated.

METHODS

C4-2B, an androgen-independent prostate cancer cell line, was treated with PBS, Ad-BSP-TK, or the Ad-BSP-E1a in vitro, and in subcutaneous and intraosseous xenographs. Cell proliferation, PSA level in condition medium, tumor volume, and/or serum PSA were followed.

RESULTS

The growth of C4-2B and the PSA production was dramatically suppressed by Ad-BSP-E1a at very low dosage (0.3 MOI) compared with PBS and Ad-BSP-TK treatment in vitro. In the subcutaneous model, the tumor volume was significantly lower statistically in the Ad-BSP-E1a treated group than the Ad-BSP-TK control group (P = 0.02). In the intraosseous model, the mice treated in the Ad-BSP-E1a treatment group demonstrated a significant lower PSA compared to that in the control group (P < 0.01) at week 8 and week 16 post-treatment.

CONCLUSIONS

The CRAd Ad-BSP-E1a revealed potential in treating prostate cancer in this model system. Using viral or none-viral mediated gene therapy to treat prostate carcinoma continues to be a potential avenue to treat afflicted men with prostate cancer.

Involvement of SMRT corepressor in transcriptional repression by the vitamin D receptor

To repress the expression of target genes, the unliganded nuclear receptor generally recruits the silencing mediator of retinoid and thyroid hormone receptor (SMRT)/nuclear receptor corepressor via its direct association with the conserved motif within bipartite nuclear receptor-interaction domains (IDs) of the corepressor. Here, we investigated the involvement of the SMRT corepressor in transcriptional repression by the unliganded vitamin D receptor (VDR). Using small interference RNA against SMRT in human embryonic kidney 293 cells, we demonstrated that SMRT is involved in the repression of the VDR-target genes, osteocalcin and vitamin D(3) 24-hydroxylase in vivo. Consistent with this, VDR and SMRT are recruited to the vitamin D response element of the endogenous osteocalcin promoter in the absence of 1alpha,25-(OH)(2)D(3) in chromatin immunoprecipitation assays. To address the involvement of the VDR-specific interaction of SMRT in this repression, we identified the molecular determinants of the interaction between VDR and SMRT. Interestingly, VDR specifically interacts with ID1 of the SMRT/nuclear receptor corepressor and that ID1 is required for their stable interaction. We also identified specific residues in the SMRT-ID1 that are required for VDR binding, using the one- plus two-hybrid system, a novel genetic selection method for specific missense mutations that disrupt protein-protein interactions. These mutational studies revealed that VDR interaction requires a wide range of the residues within and outside the extended helix motif of SMRT-ID1. Notably, SMRT mutants defective in the VDR interaction were also defective in the repression of endogenous VDR-target genes, indicating that the SMRT corepressor is directly involved in the VDR-mediated repression in vivo via an ID1-specific interaction with the VDR.

Runx2 is expressed in human glioma cells and mediates the expression of galectin-3

Runx2 is a member of the Runx family of transcription factors (Runx1-3) with a restricted expression pattern. It has so far been detected predominantly in skeletal tissues where, inter alia, it regulates the expression of the beta-galactoside-specific lectin galectin-3. Here we show that, in contrast to Runx3, Runx1 and Runx2 are expressed in a variety of human glioma cells. Runx2 expression pattern in these cells correlated completely with that of galectin-3, but not with that of other galectins. A similar correlation in the expression pattern of galectin-3 and Runx2 transcripts was detected in distinct types of 70 primary neural tumors, such as glioblastoma multiforme, but not in others, such as gangliocytomas. In glioma cells, Runx2 is directly involved in the regulation of galectin-3 expression, as shown by RNAi and transcription factor binding assays demonstrating that Runx2 interacts with a Runx2-binding motif present in the human galectin-3 promoter. Knockdown of Runx2 was thus accompanied by a reduction of both galectin-3 mRNA and protein levels by at least 50%, dependent on the glial tumor cell line tested. Reverse transcriptase-polymerase chain reaction analyses, aimed at finding other potential target genes of Runx2 in glial tumor cells, revealed the presence of bone sialoprotein, osteocalcin, osteopontin, and osteoprotegerin. However, their expression patterns only partially overlap with that of Runx2. These data suggest a functional contribution of Runx-2-regulated galectin-3 expression to glial tumor malignancy.

Expression and function of Cbfa-1/Runx2 in thyroid papillary carcinoma cells

CONTEXT

Development of calcifying foci is a common finding in human thyroid papillary carcinoma, but its mechanisms remain unknown.

OBJECTIVE

We therefore investigated whether osteocalcin and/or Cbfa-1 genes are expressed in malignant thyroid epithelial cells. We also studied the effects of Cbfa-1 on the expression of osteoblast-specific and thyrotropin receptor genes in thyrocytes.

RESULTS

The human thyroid papillary carcinoma cell line BHP18-21 expresses bone-type osteocalcin mRNA at higher levels than in MG63 osteosarcoma cells. Northern blot analysis and EMSA using nuclear extracts from BHP18-21 cells and FRTL-5 cells demonstrated that cells of thyroid epithelial origin expressed Cbfa-1/Runx2, the main transcription factor for the expression of osteocalcin. When we transfected pcDNA3.1-human Cbfa-1 into FRTL-5 cells, Cbfa-1 increased the gene expression of alkaline phosphatase, type I collagen, and osteocalcin but suppressed the expression of thyrotropin receptor. We then stained the calcified regions of human papillary thyroid carcinoma tissues with antiosteocalcin antibody and found that malignant cells, as well as follicular epithelial cells, were immunopositive for osteocalcin. Northern blot analysis revealed that the Cbfa-1/Runx2 gene was strongly expressed in tissues from four cases of surgically resected papillary carcinoma.

CONCLUSIONS

Thyrocytes share characteristics with osteoblasts. Cbfa-1 may play a role in calcification processes in human thyroid papillary carcinoma tissues.

Imatinib mesylate (IM)-induced growth inhibition is associated with production of spliced osteocalcin-mRNA in cell lines

It has been suggested that imatinib mesylate (IM) influences osteogenesis and bone turnover in treated patients. Here we show that the inhibitory effect of IM on cell multiplication is associated with an increased proportion of spliced osteocalcin (OCNs) in leukemia (HL-60) and osteosarcoma cells (MG-63, U-2 OS), despite a lower mRNA synthesis rate. In mouse osteoblastic MC3T3-E1 cells only OCNs is present, independently of treatment. As the stimulatory effect of IM on OCNs is also observed upon treatment with vitamin D, common regulatory processes may be considered.

Future innovations in treating advanced prostate cancer

Many novel techniques for the treatment of prostate cancer are being aggressively investigated because prostate cancer is prevalent in the population and the current treatments for advanced prostate cancer are woefully inadequate. Although the current treatment options prolong life, most patients will eventually experience local recurrence or develop advanced disease. A greater understanding of the molecular events underlying cancer has enabled investigators to explore gene therapy approaches that are targeted against these molecular events. This article discusses antiangiogenic therapy, immune based therapy, and gene therapy. Any of these experimental modalities could be developed to replace hormone ablation therapy which causes unpleasant side effects, decreases the quality of life of the patient, and only temporarily controls the disease.

Anti-tumor efficacy of a transcriptional replication-competent adenovirus, Ad-OC-E1a, for osteosarcoma pulmonary metastasis

BACKGROUND

Osteosarcoma (OSA) is the most frequent type of primary malignant bone tumor and is apt to occur in children and young adults. Pulmonary metastasis (OSPM) is the major reason for its fatal outcome. Osteocalcin (OC) is a major noncollagenous bone protein whose expression is limited almost exclusively to bone marrow and osteotropic tumors. OC is also known to express in cell lines with bone metastasis feathers. Gene therapy strategies with the OC promoter directing the replication of adenovirus in a tumor-specific manner are a potential modality for OSPM therapy.

METHODS

We detected OC mRNA expression by RNA in situ hybridization in OSA and OSPM samples from patients, and tested OC promoter transcriptional activity in OSA and non-OSA cell lines. Then we used a transcriptional replication-competent adenovirus, Ad-OC-E1a, to treat OSPM, and evaluated its tumor-specific replication and killing activities in vitro as well as anti-OSPM efficacy in vivo via systemic delivery.

RESULTS

OC mRNA was detected in all types of OSA tissues, including OSPM tissues. The transcriptional activity of the OC promoter was much higher in a OSPM cell line SAOS-2LM7 and primary OSA cell line MG63 than in non-OSA cell lines, including cell lines from breast cancer, colon cancer, and liver cancer. Ad-OC-E1a expressed E1a protein only in MG63 and SAOS-2LM7, which indicated that adenovirus E1a was under strict control by the OC promoter. Ad-OC-E1a demonstrated killing and viral replication activity close to wild-type adenovirus levels in MG63 and SAOS-2LM7, but the killing and viral replication activities were attenuated significantly in cells expressing low OC transcriptional activity. To test whether Ad-OC-E1a could be used to target human OSPM in vivo, SAOS-2LM7 pulmonary metastasis models in nude mice were induced and treated by tail-vein injection with Ad-OC-E1a. Compared to tumor nodules in the lung in groups treated with PBS or control virus, the quantity of metastasized tumor nodules decreased significantly. Adenovirus-infected cells were stained immunohistochemically only inside and around the OSPM nodules but spared normal lung tissue and other organs.

CONCLUSIONS

These data demonstrated that OC promoter could direct adenovirus replication by controlling the E1a gene to target human OSPM in a tumor-specific manner, providing an efficient tool to develop a feasible therapeutic modality for OSPM.

Expression and functional significance of osteocalcin splicing in disease progression of hematological malignancies

The aim of this study was to investigate the expression of osteocalcin (OCN) splicing variants in hematological malignancies. We analysed bone marrow obtained from two patients with chronic myeloid leukemia (CML), seven patients with other myeloproliferative diseases (MPD) and four patients with acute myeloid leukemia (AML). RT-PCR analyses were performed in order to assess and quantify spliced (OCNs) and unspliced (OCNu) mRNA, the associated transcription factors (AML1 and AML3) as well as c-KIT which is a marker for activated stem cells. Our data indicate that OCNs mRNA and OCN protein is expressed in c-KIT positive neoplastic stem cells in hematological malignancies.

HOXB13 is downregulated in colorectal cancer to confer TCF4-mediated transactivation

Mutations in the Wnt signalling cascade are believed to cause aberrant proliferation of colorectal cells through T-cell factor-4 (TCF4) and its downstream growth-modulating factors. HOXB13 is exclusively expressed in prostate and colorectum. In prostate cancers, HOXB13 negatively regulates β-catenin/TCF4-mediated transactivation and subsequently inhibits cell growth. To study the role of HOXB13 in colorectal tumorigenesis, we evaluated the expression of HOXB13 in 53 colorectal tumours originated from the distal left colon to rectum with their matching normal tissues using quantitative RT–PCR analysis. Expression of HOXB13 is either lost or diminished in 26 out of 42 valid tumours (62%), while expression of TCF4 RNA is not correlated with HOXB13 expression. TCF4 promoter analysis showed that HOXB13 does not regulate TCF4 at the transcriptional level. However, HOXB13 downregulated the expression of TCF4 and its target gene, c-myc, at the protein level and consequently inhibited β-catenin/TCF-mediated signalling. Functionally, forced expression of HOXB13 drove colorectal cancer (CRC) cells into growth suppression. This is the first description of the downregulation of HOXB13 in CRC and its mechanism of action is mediated through the regulation of TCF4 protein stability. Our results suggest that loss of HOXB13 may be an important event for colorectal cell transformation, considering that over 90% of colorectal tumours retain mutations in the APC/β-catenin pathway.

Gene Therapy for Prostate Cancer by Controlling Adenovirus E1a and E4 Gene Expression with PSES Enhancer

PSES is a chimeric enhancer containing enhancer elements from prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) genes that are prevalently expressed in androgen-independent prostate cancers. PSES shows strong activity equivalent to cytomegalovirus (CMV) promoter, specifically in PSA/PSMA-positive prostate cancer cells, the major cell types in prostate cancer in the absence of androgen. We developed a recombinant adenovirus (AdE4PSESE1a) by placing adenoviral E1a and E4 genes under the control of the bidirectional enhancer PSES and enhanced green fluorescent protein gene for the purpose of intratumoral virus tracking under the control of CMV promoter. Because of PSES being very weak in nonprostatic cells, including HEK293 and HER911 that are frequently used to produce recombinant adenovirus, AdE4PSESE1a can only be produced in the HER911E4 cell line which expresses both E1 and E4 genes. AdE4PSESE1a showed similar viral replication and tumor cell killing activities to wild-type adenovirus in PSA/PSMA-positive prostate cancer cells. The viral replication and tumor cell killing activities were dramatically attenuated in PSA/PSMA-negative cells. To test whether AdE4PSESE1a could be used to target prostate tumors in vivo, CWR22rv s.c. tumors were induced in nude mice and treated with AdE4PSESE1a via intratumoral and tail vein injection. Compared to tumors treated with control virus, the growth of CWR22rv tumors was dramatically inhibited by AdE4PSESE1a via tail vein injection or intratumoral injection. These data show that adenoviral replication can be tightly controlled in a novel fashion by controlling adenoviral E1a and E4 genes simultaneously with a single enhancer.

HOXB13 induces growth suppression of prostate cancer cells as a repressor of hormone-activated androgen receptor signaling

Androgen receptor (AR) signals play a decisive role in regulating the growth and differentiation of both normal and cancerous prostate cells by triggering the regulation of target genes, in a process in which AR cofactors have critical functions. Because of the highly prostate-specific expression pattern of HOXB13, we studied the role of this homeodomain protein in prostate cells. Expression of HOXB13 was limited to AR-expressing prostate cells. Reporter transcription assay demonstrated that HOXB13 significantly suppressed hormone-mediated AR activity in a dose-responsive manner, and suppression was specific to AR with which HOXB13 physically interacts. Overexpression of HOXB13 further down-regulated the androgen-stimulated expression of prostate-specific antigen, and suppression of endogenous HOXB13 stimulated transactivation of AR. Functionally, HOXB13 suppressed growth of LNCaP prostate cancer cells, which could be counteracted by additional hormone-activated AR. On the other hand, the growth-suppressive function of HOXB13 in AR-negative CV-1 cells was not affected by AR. These results suggest that HOXB13 functions as an AR repressor to modulate the complex AR signaling and subsequent growth regulation of prostate cancer cells. In addition to the loss of HOXB13 expression, maintaining AR may be an important step for prostate cancer cells to tolerate the suppressor function of HOXB13. Altogether, our data present a novel mechanism for the HOXB13-mediated repression of AR signaling, which can be interpreted to a growth-suppressive event.

HOXB13 homeodomain protein suppresses the growth of prostate cancer cells by the negative regulation of T-cell factor 4

In prostate gland, HOXB13 is highly expressed from the embryonic stages to adulthood. However, the function of HOXB13 in normal cell growth and tumorigenesis is not yet known. We investigated the role of HOXB13 and mechanism by which it functions in HOXB13-negative cells. Expression of HOXB13 was forced in HOXB13-negative PC3 prostate cancer cells using a liposome-mediated gene transfer approach. Compared with the control clones, HOXB13-expressing PC3 cells exhibited significant inhibition of in vitro and in vivo cell growth with G1 cell cycle arrest mediated by the suppression of cyclin D1 expression. Because cyclin D1 is mainly regulated by beta-catenin/T-cell factor (TCF), TCF-4 response element was used in a reporter gene transcription assay, demonstrating that HOXB13 significantly inhibits TCF-4-mediated transcriptional activity in both prostate and nonprostate cells. This inhibition occurred in a dose-responsive manner and was specific to TCF-4 response element. Western blot analysis demonstrated that HOXB13 down-regulates the expression of TCF-4 and its responsive genes, c-myc and cyclin D1. HOXB13 also suppressed the activity of natural c-myc promoter. This study suggests that HOXB13, a transcription factor, functions as a cell growth suppressor by negatively regulating the expression of TCF-4, which eventually provides negative signals for cell proliferation. This observation will provide valuable insight into the molecular basis of prostate tumorigenesis.

Release of Intact and Fragmented Osteocalcin Molecules from Bone Matrix during Bone Resorption in Vitro

Osteocalcin detected from serum samples is considered a specific marker of osteoblast activity and bone formation rate. However, osteocalcin embedded in bone matrix must also be released during bone resorption. To understand the contribution of each type of bone cell in circulating osteocalcin levels, we used immunoassays detecting different molecular forms of osteocalcin to monitor bone resorption in vitro. Osteoclasts were obtained from rat long bones and cultured on bovine bone slices using osteocalcin-depleted fetal bovine serum. In addition, human osteoclasts differentiated from peripheral blood mononuclear cells were used. Both rat and human osteoclasts released osteocalcin from bovine bone into medium. The amount of osteocalcin increased in the presence of parathyroid hormone, a stimulator of resorption, and decreased in the presence of bafilomycin A1, an inhibitor of resorption. The amount of osteocalcin in the medium correlated with a well characterized marker of bone resorption, the C-terminal telopeptide of type I collagen (r > 0.9, p < 0.0001). The heterogeneity of released osteocalcin was determined using reverse phase high performance liquid chromatography, and several molecular forms of osteocalcin, including intact molecule, were identified in the culture medium. In conclusion, osteocalcin is released from the bone matrix during bone resorption as intact molecules and fragments. In addition to the conventional use as a marker of bone formation, osteocalcin can be used as a marker of bone resorption in vitro. Furthermore, bone matrix-derived osteocalcin may contribute to circulating osteocalcin levels, suggesting that serum osteocalcin should be considered as a marker of bone turnover rather than bone formation.

Osteogenic Cells Derived From Embryonic Stem Cells Produced Bone Nodules in Three-Dimensional Scaffolds

An approach for 3D bone tissue generation from embryonic stem (ES) cells was investigated. The ES cells were induced to differentiate into osteogenic precursors, capable of proliferating and subsequently differentiating into bone-forming cells. The differentiated cells and the seeded scaffolds were characterized using von Kossa and Alizarin Red staining, electron microscopy, and RT-PCR analysis. The results demonstrated that ES-derived bone-forming cells attached to and colonized the biocompatible and biodegradable scaffolds. Furthermore, these cells produced bone nodules when grown for 3-4 weeks in mineralization medium containing ascorbic acid and beta-glycerophosphate both in tissue culture plates and in scaffolds. The differentiated cells also expressed osteospecific markers when grown both in the culture plates and in 3D scaffolds. Osteogenic cells expressed alkaline phosphatase, osteocalcin, and osteopontin, but not an ES cell-specific marker, oct-4. These findings suggest that ES cell can be used for in vitro tissue engineering and cultivation of graftable skeletal structures.

New targets for therapy in prostate cancer: modulation of stromal-epithelial interactions

Changes in genomic and phenotypic expression of progressing prostate tumors and their stroma occur in a dynamic fashion based on bidirectional signaling from stromal-epithelial interactions. These interactions may underlie the ability of prostate cancer cells to survive and proliferate in the prostate and bone. By investigating the phenotypic and genotypic changes of stromal cells adjacent to cancer cells and the reciprocal changes of cancer cells, novel molecular markers may be developed to diagnose cancer earlier before pathologic appearance of cancer cells at the primary site. Attacking epithelial and stromal elements together is a unique approach to both localized and metastatic prostate cancer therapy. Co-targeting both tumor cells and stroma requires identifying a reliable tumor and tissue-specific cis-DNA element, such as osteocalcin (OC) promoter. OC expression is elevated in prostate tumor cells and in prostate and bone stromal cells interdigitating with both localized and metastatic prostate epithelium. We have previously designed an adenovirus-based therapeutic gene vehicle and demonstrated that a replication-competent adenoviral vector (Ad vector) is highly efficient in blocking the growth of cancer cells in culture, including cells without androgen receptor as well as cells that do or do not make prostate-specific antigen. In vivo, intravenous administration of an Ad-OC vector was effective against preexisting human prostate cancer subcutaneous and bone xenografts. The addition of vitamin D(3) enhanced further viral replication at target sites. Co-targeting tumor cells and stroma using systemic Ad vector is a viable and promising option for treatment of both localized and metastatic prostate cancer.

Notch signaling and ERK activation are important for the osteomimetic properties of prostate cancer bone metastatic cell lines

Prostate cancer bone metastases are characterized by their ability to induce osteoblastic lesions and local bone formation. It has been suggested that bone metastatic prostate cancer cells are osteomimetic and capable of expressing genes and proteins typically expressed by osteoblasts. The ability of preosteoblasts to differentiate and express osteoblastic genes depends on several pathways, including Notch and MAPK. Here we show that notch1 expression is increased 4-5 times in C4-2B and MDA PCa 2b cells (osteoblastic skeletal prostate metastatic cancer cell lines) when compared with nonskeletal metastatic cell lines (LNCaP and DU145). Notch1 ligand, dll1, is expressed only in C4-2B cells. Immunohistochemical studies demonstrate that Notch1 is present in both human clinical samples from prostate cancer bone metastases and the C4-2B cell line. To determine whether prostate cancer bone metastases respond to osteogenic induction similar to osteoblasts, C4-2B cells were cultured in osteogenic medium that promotes mineralization. C4-2B cells mineralize and express HES-1 (a downstream target of Notch), an effect that is completely inhibited by L-685,458, a Notch activity inhibitor. Furthermore, osteogenic induction increases ERK activation, runx2 expression, and nuclear localization, independent of Notch signaling. Finally, we show that Notch and ERK activation are essential for Runx2 DNA binding activity and osteocalcin gene expression in C4-2B cells in response to osteogenic induction. These studies demonstrate that prostate cancer bone metastatic cell lines acquire osteoblastic properties through independent activation of ERK and Notch signaling; presumably, both pathways are activated in the bone microenvironment.

Prostate cancer expression of runt-domain transcription factor Runx2, a key regulator of osteoblast differentiation and function

BACKGROUND

Prostate cancer (CaP) bone metastases express numerous proteins associated with bone cells. Specific transcription factors, including Runx2, regulate the expression of many bone-related factors in osteoblasts. Expression of these transcription factors in CaP may be linked to the ability of CaP bone metastases to influence bone remodeling.

METHODS

CaP tissues and cell lines were analyzed for expression of Runx2 mRNA by RT-PCR and in situ hybridization, and protein by immunohistochemistry, Western blotting, and electrophoretic mobility shift assays (EMSA).

RESULTS

Runx2 mRNA and protein were detected in CaP tissues and cell lines. A specific Runx2: OSE2 complex could be formed with PC-3 nuclear extracts.

CONCLUSIONS

Expression of Runx2 in CaP may be the molecular switch that is associated with expression of various bone-specific factors in CaP. In turn, expression of these factors can influence bone remodeling and possibly play a role in the growth and survival of CaP in bone.

Comprehensive microarray analysis of bone morphogenetic protein 2-induced osteoblast differentiation resulting in the identification of novel markers for bone development

Osteoblasts are cells responsible for matrix deposition during bone development and although temporal expression of many genes has been related to osteoblast differentiation, a complete description of osteoblast-specific gene regulation will lead to a better understanding of osteoblast function. In this study, microarray technology was used to analyze gene expression on a broad scale during osteoblast differentiation. Expression analysis of 9596 sequences revealed 342 genes and expressed sequence tags (ESTs) to be modulated differentially during a time course experiment in which murine C2C12 mesenchymal progenitor cells were induced to differentiate into mature osteoblasts by treatment with bone morphogenetic protein 2 (BMP-2). By means of hierarchical clustering, these genes were grouped by similarities in their expression profiles, resulting in subsets of early, intermediate, and late response genes, which are representative of the distinct stages of osteoblast differentiation. To identify new bone markers, the bone specificity of the late response genes was determined by comparing BMP-induced expression in C2C12 and MC3T3 osteoblasts with that in NIH3T3 fibroblasts. This resulted in the identification of nine novel genes and ESTs that were induced specifically in osteoblasts, in addition to the well-known markers ALP and osteocalcin. For at least one of these novel genes, Wnt inhibitory factor 1, and two of the ESTs, expression in developing bone was verified in vivo by in situ hybridization of E16.5 mouse embryos. In conclusion, by a combination of in vitro and in vivo screening approaches, a set of new genes related to osteoblast differentiation and skeletal development has been identified.

Regulation of human osteocalcin promoter in hormone-independent human prostate cancer cells

Osteocalcin (OC) is a small (6 kDa) polypeptide whose expression was thought to be limited to mature osteoblasts. The discovery of OC expression in prostate cancer specimens led us to study the regulation of OC gene in androgen-independent metastatic human prostate PC3 cells. An 800-bp human OC (hOC) promoter-luciferase construct exhibited strong basal and vitamin D-induced activity in OC-positive human prostate and osteosarcoma cell lines. Through deletion analysis of the hOC promoter, the functional hierarchy of the cis-acting elements, OSE1, OSE2, and AP-1/VDRE, was established in PC3 cells (OSE1 > AP-1/VDRE > OSE2). By juxtaposing dimers of these 3 cis-elements, we produced a minimal hOC promoter capable of displaying high tissue specific activity in prostate cancer cells. Our study demonstrated three groups of transcription factors, Runx2, JunD/Fra-2, and Sp1, responsible for the high hOC promoter activity in PC3 cells by binding to the OSE2, AP-1/VDRE, and OSE1 elements, respectively. Among the three groups of transcription factors, the expression levels of Runx2 and Fra-2 are higher in the OC-positive PC3 cells and osteoblasts, compared with the OC-negative LNCaP cells. Interestingly, unlike the mouse OC promoter, the OSE1 site in hOC promoter is regulated by members of Sp1 family instead of the osteoblast-specific factor Osf1. The molecular basis for androgen-independent prostate cancer cells behaving like mature osteoblasts may be explained by the interplay and coordination of these transcription factors under the tight regulation of autocrine and paracrine mediators.