Biomedical subjects

G Mbalaviele

Publications and source records attributed to G Mbalaviele.

6 recordsLinked to original sources

PubMed1996

E-cadherin expression in human breast cancer cells suppresses the development of osteolytic bone metastases in an experimental metastasis model.

The molecular mechanisms by which human cancer cells spread to bone are largely unexplored. The process likely involves cell adhesion molecules (CAMs) that are responsible for homophilic and heterophilic cell-cell interactions. One relevant CAM may be the calcium-dependent transmembrane glycoprotein E-cadherin. To investigate the involvement of E-cadherin in breast cancer metastasis to bone, we used an in vivo model in which osteolytic bone metastases preferentially occur after injections of cancer cells directly into the arterial circulation through the left ventricle of the hearts of nude mice. We have found that E-cadherin-negative human breast cancer cells MDA-MB-231 (MDA-231) develop radiographically detectable multiple osteolytic bone metastases and cachexia in this model. However, MDA-231 breast cancer cells that were transfected with E-cadherin cDNA showed a dramatically impaired capacity to form osteolytic metastases and induce cachexia. Histological and histomorphometrical analyses of bones of mice bearing mock-transfected MDA-231 revealed aggressive metastatic tumor, whereas metastatic tumor burden was significantly decreased in the bones of mice bearing E-cadherin-expressing MDA-231. Nude mice bearing E-cadherin-transfected MDA-231 breast cancer cells survived longer than mice bearing mock-transfected MDA-231 breast cancer cells. Anchorage-dependent and -independent growth in culture and tumor enlargement in the mammary fat pad of nude mice were unchanged between mock-transfected and E-cadherin-expressing MDA-231, suggesting that these differences in metastatic behavior are not due to an impairment of cell growth and tumor-igenicity. Our results show the suppressive effects of E-cadherin expression on bone metastasis by circulating breast cancer cells and suggest that the modulation of expression of this CAM may reduce the destructive effects of breast cancer cells on bone.

Animals↗

PubMed1995

Short-term local injections of transforming growth factor-beta 1 decrease ovariectomy-stimulated osteoclastic resorption in vivo in rats.

Estrogen deficiency in rats is responsible for increased osteoclastic resorption and a subsequent rapid bone loss. TGF-beta, which is known to have acute effects on bone resorption in several in vitro models, has been shown to be secreted by osteoblastic cells in vitro in response to 17 beta-estradiol, but little is known about its in vivo effects on bone resorption. We therefore decided to investigate the short-term effect of TGF-beta 1 on bone resorption in ovariectomized rats. TGF-beta 1 (0.04-20 ng/injection), or vehicle, was injected daily directly into the bone marrow space, through a thin catheter implanted in the distal end of the right femur, during 4 consecutive days, starting 14 days after the ovariectomy. Bone histomorphometry was performed in the secondary spongiosa of the metaphysis of injected femurs and compared with vehicle-injected femurs of sham ovariectomized rats. Ovariectomy was associated with a marked increase in the resorption surface, a 2-fold increase in the number of osteoclasts, and no change in the number of TRAP-positive marrow cells distant from bone surfaces. Bone resorption was significantly lower in the TGF-beta 1-injected bones of ovariectomized rats, as compared with vehicle injected bones: the osteoclast surface and the number of osteoclasts were, respectively, 11.0 +/- 5.1% versus 20.8 +/- 1.3% and 287 +/- 41 versus 505 +/- 53, in bones injected with 0.2 ng of TGF-beta 1 as compared with vehicle-injected bones (mean +/- SE, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1995

Osteoclast formation from human cord blood mononuclear cells co-cultured with mice embryonic metatarsals in the presence of M-CSF.

Investigating the potentiality of cord monocytes to differentiate toward osteoclast-like cells (OCL) in vitro, we previously reported that in the presence of 1,25(OH)2 vitamin D3 (1,25-(OH)2D3), multinucleated-cells generated by cord monocyte cultures though displaying morphological features of OCL failed to resorb devitalized bones. We thus hypothesized that full differentiation of cord monocytes toward bone-resorbing cells may require the presence of factors released from and/or direct interactions with living osteogenic cells. In the present study, we tested these hypotheses using two culture systems supporting the development of bone-resorbing cells in the presence of bone matrix. First, cord mononuclear cells were co-cultured with murine fetal metatarsals depleted of osteoclast progenitor cells (stripped metatarsals) in the presence of 1,25-(OH)2D3. We found that cord mononuclear cells failed to differentiate toward OCL as indicated by the absence of the release of 45Ca previously incorporated in fetal bones and by the absence of formation of TRAP-positive (TRAP[+]) multinucleated cells which have invaded mineralized cartilage during the co-culture period. In the same model, we then investigated the effect of some soluble factors known as stimulators of osteoclast differentiation. Whereas exogenous rhIL6 and rhIL3 were ineffective in this assay, rhM-CSF consistently increased both the number of TRAP(+) multinucleated cells inside the mineralized cartilage and the release of 45Ca into the culture media. The effects of rhM-CSF were time-dependent reaching the maximum after 3 weeks of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The role of cadherin in the generation of multinucleated osteoclasts from mononuclear precursors in murine marrow.

A critical step in bone resorption is the fusion of mononuclear osteoclast precursors to form multinucleated osteoclasts. However, little is known of the molecular mechanisms that are responsible for this important process. Since the expression of proteins in the cadherin family of homophilic calcium-dependent cell adhesion molecules is involved in the fusion process for certain other cells, we examined their role in osteoclast formation. Immunohistochemical examination of human and mouse bone using monoclonal antibodies to human and mouse E-cadherin clearly demonstrated positive staining in osteoclasts. N- and P-cadherin were not detected. In cultures of murine marrow mononuclear cells in which osteoclasts form by cell fusion, E-cadherin expression determined by Western blotting reached the highest levels as fusion was taking place. Expression of E-cadherin gene fragment was also detected in the marrow cultures by polymerase chain reaction. To study the functional role of E-cadherin expression in osteoclastic differentiation, neutralizing monoclonal antibodies were examined for their effects on osteoclast formation. The antibodies decreased the number of tartrate-resistant acid phosphatase (a marker of murine osteoclast)-positive multinucleated cell (TRAP-positive MNC) by inhibiting the fusion of mononuclear osteoclast precursors, but not proliferation of these cells or their attachment to plastic dish surfaces. This inhibitory effect was reversible. Furthermore, synthetic peptides containing the cell adhesion recognition sequence of cadherins also decreased TRAP-positive MNC formation. The antibodies and peptides inhibited not only osteoclast formation but also bone resorption. Antibodies to other types of cadherins and control rat IgG had no effects in these culture systems. Our findings suggest that E-cadherin expression may be involved in fusion (differentiation) of hemopoietic osteoclast precursors into mature multinucleated osteoclasts.

Amino Acid Sequence↗

PubMed1992

Transforming growth factor-beta enhances calcitonin-induced cyclic AMP production and the number of calcitonin receptors in long-term cultures of human umbilical cord blood monocytes in the presence of 1,25-dihydroxycholecalciferol.

Transforming growth factor-beta (TGF-beta) is a multifunctional polypeptide, abundant in bone, that regulates both proliferation and differentiation of a wide variety of cells, but its role in osteoclast differentiation remains controversial. We have recently shown that long-term cultures of human cord blood monocytes, in the presence of 1,25 dihydroxycholecalciferol (1,25-(OH)2D3), give rise to cells that express two markers of the osteoclast phenotype, namely, the vitronectin receptor (VNR) and the calcitonin receptor (CTR). TGF-beta enhanced the proportion of cells expressing the VNR. In the present study, we investigated the effect of TGF-beta on the expression of CTR in cord blood monocytes cultured during 3 weeks in the presence of 1,25-(OH)2D3. When added within the first 2 weeks of culture, TGF-beta (500 pg/ml) significantly decreased the cell protein content. TGF-beta alone did not stimulate basal cAMP production. The 10 nM-sCT-stimulated cAMP production was enhanced by increasing TGF-beta concentrations from 50 pg/ml to 1,000 pg/ml: for 500 pg/ml TGF-beta, it was 294 +/- 28% vs. 140 +/- 25% for control cultures (p less than 0.01). The sCT dose-response curves showed a higher cAMP production from 10(-9) M to 10(-7) M of sCT in the presence of 500 pg/ml TGF-beta than in control cultures. The increase was 325 +/- 36% in the presence of TGF-beta and 195 +/- 13% in the absence of TGF-beta, for 10(-7) M sCT (p less than 0.01). This effect of TGF-beta on cAMP production was not observed either when it was added to monocyte cultures the last day or 2 hours before the end of the culture or in MCF7, a human breast cancer cell line that expresses CTR. [125I]-sCT binding studies performed on confluent cells showed similar Kd in control and TGF-beta-treated cells. By contrast, the CTR number was significantly increased in the presence of TGF-beta: 6.1 +/- 2 x 10(4) receptors per cell in control cultures and 28.8 +/- 8.1 x 10(4) receptors per cell in TGF-beta-treated cultures (p less than 0.05). It is thus suggested that TGF-beta increases the number of CTR of these cells that have other features of preosteoclasts. The role of this cytokine on the process of osteoclast differentiation and in bone resorption is thus emphasized.

Autoradiography↗

PubMed1991

Human umbilical cord blood monocytes express calcitonin receptors in culture in the presence of 1,25 dihydroxyvitamin D.

Calcitonin (CT) is a potent inhibitor of bone resorption and there are abundant CT receptors on mature osteoclasts. The relationship between osteoclast precursors and monocyte lineage is far from clear. We recently showed that human cord monocytes in culture, by contrast to adult monocytes, develop some features of osteoclast precursors. We therefore assessed the presence of CT receptors on monocytes. We could not demonstrate any CT receptors on adult monocytes. By contrast, we observed in cultured cord monocytes increased cAMP production in presence of CT. This cAMP response was observed after a 2-week culture and only in the presence of 10(-9) M 1,25-dihydroxyvitamin D. After a 3-week culture, CT 10(-9) to 10(-6) M increased cAMP production dose dependently from 10(-9) M; however the curve was shallower than the one observed in a control CT receptor positive tumoral cell line, MCF7. 125I sCT bound specifically to cord monocytes cultured during 3 weeks; apparent dissociation constant (Kd) was 3.3 +/- 2.2 10(-10) M and average receptor number was 5.1 +/- 0.4 10(4)/cell. On autoradiography all the cells, whether mono or multinucleated, were labeled with 125sCT. One or 2-h exposure to salmon CT did not induce cell contraction. In conclusion, CT receptors can be induced on newborn cord monocytes in the presence of 1,25-dihydroxyvitamin D. This observation shows that osteoclasts and fetal monocytes share a common membrane determinant.

Calcitonin↗