First results about ProAKAP4 concentration in stallion semen after cryopreservation in two different freezing media

The quality of fresh or thawed sperm in stallions has been generally determined by the viability and total and progressive motility of the sperm. Today, the expression of ProAKAP4, a protein present in the flagellum of spermatozoa, appears to be an innovative and relevant functional marker to assess semen quality and male fertility. This study aims to compare the concentration of ProAKAP4 in the semen from 5 stallions frozen with two different extenders immediately after thawing (T0) and 4 h post-thawing (T4). Viability, total and progressive motility were measured in parallel. Significant differences for sperm viability and total motility were observed between the two extenders, as was the concentration of ProAKAP4 both at T0 and T4. At T4, all quality parameters and ProAKAP4 content significantly decreased compared to T0, but with a considerably slower decrease in one extender than the other. These preliminary results suggest that measuring the concentration of ProAKAP4 is a promising tool for the comparison of different extenders and the selection of the optimal freezing medium for each stallion ejaculate.

145 ProAKAP4 concentrations in semen as a predictive tool of bull fertility: A preliminary study

Recently, ProAKAP4 has been described as a pertinent indicator of sperm quality in humans, pigs, and stallions. In knockout mouse models lacking AKAP4 expression, the male mice were infertile. As high proAKAP4 levels were significantly correlated with a lower proportion of abortions in intrauterine insemination settings in human reproduction, proAKAP4 could be considered a pertinent new sperm parameter for assessing embryo quality. Our main goal was to assess the proAKAP4 concentrations in Holstein bull semen for comparison with the motility sperm parameters and fertility outcomes in post-thawed conditions. Straws issued from 52 ejaculates from 13 bulls, retrospectively identified with known nonreturn rates (NRR) as a fertility indicator, were provided by Evolution XY. Expression of ProAKAP4 and AKAP4 was assessed using enzyme-linked immunosorbent assay, western blotting, flow cytometry, and microscopy methods. Using the Bull 4MID kit (4BioDx), striking variations in proAKAP4 concentrations were observed independently of the classic sperm parameters that were measured using computer-assisted semen analysis. A mean proAKAP4 concentration of 44.42ng per 10 million spermatozoa was obtained through all our series. Interestingly, the variations in proAKAP4 concentrations were positively correlated with progressive motility and with the linearity coefficient parameter. Furthermore, the post-thawed concentrations of proAKAP4 were significantly higher in bulls with a higher NRR in a field study of more than 190 000 AI. We then demonstrated for the first time a correlation between the semen concentration of proAKAP4 and NRR (P=0.05) in bulls. Threshold values of proAKAP4 were then determined, with good values being between 25 and 60ngmL−1. Below 25ngmL−1, the sperm were of poor quality. The proportion of functional spermatozoa (i.e. spermatozoa expressing proAKAP4 in ejaculates) was assessed using flow cytometry. We observed that the cell debris and dead spermatozoa were never immunolabeled with proAKAP4 antibodies. On testis tissue sections, proAKAP4 was expressed only from the spermatids stages up to the ejaculated spermatozoa, being influenced by external factors and reflecting good spermatogenesis. Our preliminary study highlighted the pertinence of proAKAP4 in assessing sperm quality in bulls. It could be interesting to further analyse the effect of proAKAP4 level of expression on capacitation and IVF. As high levels of proAKAP4 were significantly correlated with fertility rates and with progressive motility, proAKAP4 could be proposed as a predictive marker of bull fertility and could be further investigated to evaluate the quality of invitro-produced embryos.

Endocan or endothelial cell specific molecule-1 (ESM-1): a potential novel endothelial cell marker and a new target for cancer therapy

Endocan, previously called endothelial cell specific molecule-1, is a soluble proteoglycan of 50 kDa, constituted of a mature polypeptide of 165 amino acids and a single dermatan sulphate chain covalently linked to the serine residue at position 137. This dermatan sulphate proteoglycan, which is expressed by the vascular endothelium, has been found freely circulating in the bloodstream of healthy subjects. Experimental evidence is accumulating that implicates endocan as a key player in the regulation of major processes such as cell adhesion, in inflammatory disorders and tumor progression. Inflammatory cytokines such as TNF-alpha, and pro-angiogenic growth factors such as VEGF, FGF-2 and HGF/SF, strongly increased the expression, synthesis or the secretion of endocan by human endothelial cells. Endocan is clearly overexpressed in human tumors, with elevated serum levels being observed in late-stage lung cancer patients, as measured by enzyme-linked immunoassay, and with its overexpression in experimental tumors being evident by immunohistochemistry. Recently, the mRNA levels of endocan have also been recognized as being one of the most significant molecular signatures of a bad prognosis in several types of cancer including lung cancer. Overexpression of this dermatan sulphate proteoglycan has also been shown to be directly involved in tumor progression as observed in mouse models of human tumor xenografts. Collectively, these results suggest that endocan could be a biomarker for both inflammatory disorders and tumor progression as well as a validated therapeutic target in cancer. On the basis of the recent successes of immunotherapeutic approaches in cancer, the preclinical data on endocan suggests that an antibody raised against the protein core of endocan could be a promising cancer therapy.

Hepatocyte growth factor/scatter factor and its interaction with heparan sulphate and dermatan sulphate

Hepatocyte growth factor (HGF)/scatter factor (SF) is a unique growth factor, in that it binds both heparan sulphate (HS) and dermatan sulphate (DS). The sequences in HS and DS that specifically interact with and modulate HGF/SF activity have not yet been fully identified. Ascidian DS, which uniquely possesses O-sulphation at C-6 (and not C-4) of its N -acetylgalactosamine unit, was analysed for HGF/SF-binding activity in the biosensor. The kinetic analysis revealed a strong, biologically relevant interaction with an equilibrium dissociation constant ( K (d)) of approx. 1 nM. An Erk activation assay also demonstrated stimulation of the MAP kinase pathway downstream of the Met receptor following addition of both HGF/SF and ascidian DS to the glycosaminoglycan-deficient CHO-745 mutant cell line. Furthermore, the activation of Met and the MAP kinase pathway by HGF/SF and ascidian DS leads to a cellular response in the form of migration.

Endocan is a novel chondroitin sulfate/dermatan sulfate proteoglycan that promotes hepatocyte growth factor/scatter factor mitogenic activity

Proteoglycans that modulate the activities of growth factors, chemokines, and coagulation factors regulate in turn the vascular endothelium with respect to processes such as inflammation, hemostasis, and angiogenesis. Endothelial cell-specific molecule-1 is mainly expressed by endothelial cells and regulated by pro-inflammatory cytokines (Lassalle, P., Molet, S., Janin, A., Heyden, J. V., Tavernier, J., Fiers, W., Devos, R., and Tonnel, A. B. (1996) J. Biol. Chem. 271, 20458-20464). We demonstrate that this molecule is secreted as a soluble dermatan sulfate (DS) proteoglycan. This proteoglycan represents the major form either secreted by cell lines or circulating in the human bloodstream. Because this proteoglycan is specifically secreted by endothelial cells, we propose to name it endocan. The glycosaminoglycan component of endocan consists of a single DS chain covalently attached to serine 137. Endocan dose-dependently increased the hepatocyte growth factor/scatter factor (HGF/SF)-mediated proliferation of human embryonic kidney cells, whereas the nonglycanated form of endocan did not. Moreover, DS chains purified from endocan mimicked the endocan-mediated increase of cell proliferation in the presence of HGF/SF. Overall, our results demonstrate that endocan is a novel soluble dermatan sulfate proteoglycan produced by endothelial cells. Endocan regulates HGF/SF-mediated mitogenic activity and may support the function of HGF/SF not only in embryogenesis and tissue repair after injury but also in tumor progression.

Hepatocyte growth factor/scatter factor stimulates migration of rat mammary fibroblasts through both mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt pathways

Hepatocyte growth factor/scatter factor (HGF/SF) is considered to be a mesenchymal-derived factor that acts via a dual system receptor, consisting of the MET receptor and proteoglycans present on adjacent epithelial cells. Surprisingly, HGS/SF stimulated the migration of rat mammary (Rama) 27 fibroblasts, although it failed to stimulate their proliferation. HGF/SF stimulated a transient activation of mitogen-activated protein kinases p44 and p42 (p42/44(MAPK)), with a maximum level of dual phosphorylation of p42/44(MAPK) occurring 10-15 min after the addition of the growth factor, which was followed by a rapid decrease to near basal levels after 20 min. Interestingly, a second phase of p42/44(MAPK) dual phosphorylation was observed at later times (3 h to 10 h). PD098059, a specific inhibitor of MEK-1, prevented the dual phosphorylation of p42/44(MAPK) and also the phosphorylation of p90(RSK) (ribosomal subunit S6 kinase), which mirrored the kinetics of p42/44(MAPK) phosphorylation. Moreover, PD098059 prevented the HGF/SF-induced migration of Rama 27 cells. HGF/SF also induced an early increase in the phosphorylation of protein kinase B/Akt. Akt phosphorylation was elevated 15 min after the addition of HGF/SF and then declined to basal levels by 30 min. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PtdIns3K), prevented the increase in Akt phosphorylation and abolished HGF/SF-induced migration of fibroblasts. PD098059 also inhibited the stimulation of Akt phosphorylation by HGF/SF and wortmannin similarly inhibited the stimulation of p42/44(MAPK) dual phosphorylation. These results suggest that HGF/SF-induced motility depends on both the transient dual phosphorylation of p42/44(MAPK) and the activation of PtdIns3K in Rama 27 fibroblasts and that these pathways are mutually dependent.

Proteoglycans: pericellular and cell surface multireceptors that integrate external stimuli in the mammary gland

Proteoglycans consist of a core protein and an associated glycosaminoglycan (GAG) chain of heparan sulfate, chondroitin sulfate, dermatan sulfate or keratan sulfate, which are attached to a serine residue. The core proteins of cell surface proteoglycans may be transmembrane, e.g., syndecan, or GPI-anchored, e.g., glypican. Many different cell surface and matrix proteoglycan core proteins are expressed in the mammary gland and in mammary cells in culture. The level of expression of these core proteins, the structure of their GAG chains, and their degradation are regulated by many of the effectors that control the development and function of the mammary gland. Regulatory proteins of the mammary gland that bind GAG include many growth factors and morphogens (fibroblast growth factors, hepatocyte growth factor/scatter factor, members of the midkine family, wnts), matrix proteins (collagen, fibronectin, and laminin), enzymes (lipoprotein lipase) and microbial surface proteins. Structural diversity within GAG chains ensures that each protein-GAG interaction is as specific as necessary and a number of sequences of saccharides that recognize individual proteins have been elucidated. The GAG-protein interactions serve to regulate the signal output of growth factor receptor tyrosine kinase and hence cell fate as well as the storage and diffusion of extracellular protein effectors. In addition, GAGs clearly coordinate stromal and epithelial development, and they are active participants in mediating cell-cell and cell-matrix interactions. Since a single proteoglycan, even if it carries a single GAG chain, can bind multiple proteins, proteoglycans are also likely to act as multireceptors which promote the integration of cellular signals.

Impact of Bcl-2 and Ha-ras on keratinocytes in organotypic culture

In this study, the role of specific molecular alterations associated with multistep skin carcinogenesis was assessed using in vitro organotypic cultures of the spontaneously immortalized, nontumorigenic HaCaT keratinocyte cell line. HaCaT vector control clones and clones expressing bcl-2, activated Ha-ras, or both genes were generated. Clones were induced to stratify and differentiate by culturing on dermal equivalents for 2 wk at the air-medium interface. In parental and vector control HaCaT rafts the expression and distribution of cytokeratin K1, K14, involucrin, proliferating cell nuclear antigen, and p21cip1/waf1 were assessed using immunohistochemistry and immunoblotting and were similar to normal epidermis. Apoptosis was also examined using the TUNEL technique. HaCaT-bcl-2 rafts were similar to control rafts but exhibited lower spontaneous rates of apoptosis and a moderate increase in the rate of proliferation. Differentiation was significantly inhibited in HaCaT-ras organotypic cultures and was associated with high rates of proliferation and lower rates of spontaneous apoptosis. Additionally, HaCaT-ras rafts exhibited significantly higher rates of apoptosis following ultraviolet irradiation compared with vector control or HaCaT-bcl-2 rafts. Bcl-2 was able to largely restore normal differentiation, proliferation, and apoptosis in HaCaT-ras/bcl-2 organotypic cultures. Bcl-2 also abrogated apoptosis induction following ultraviolet irradiation in HaCaT-ras/bcl-2 organotypic cultures. Organotypic keratinocyte culture represents a valuable in vitro system to evaluate the impact of individual molecular genetic alterations on the coordinate regulation of cell proliferation, differentiation, and cell death.

Bax gene disruption alters the epidermal response to ultraviolet irradiation and in vivo induced skin carcinogenesis

Bcl-2 family member proteins are differentially expressed in skin and in non-melanoma skin cancer (NMSC). To elucidate the contribution of bcl-2 and bax proteins to epidermal differentiation and skin carcinogenesis, we investigated keratinocyte proliferation, differentiation and tumourigenesis in bcl-2(-/-) and bax(-/-) mice. The rate and pattern of proliferation and spontaneous cell death in the bcl-2(-/-) and bax(-/-) mice were not different from control mice. The epidermis of bcl-2(-/-) and bax(-/-) expressed sightly higher levels of cytokeratin 1 and loricrin compared to control littermates. The apoptotic response to ultraviolet-induced genotoxic stress was assessed by quantitating TUNEL positive cells. Bax(-/-) keratinocytes showed a significant resistance to UV-induced cell death compared to control mice. The life-span of bcl-2(-/-) mice precluded an assessment of bcl-2 gene disruption on in vivo tumourigenesis. A significant increase in tumour incidence was observed in bax(-/-) mice compared to control mice in two-step chemical carcinogenesis studies. These findings suggest that bcl-2 and bax gene products may be important determinants of normal keratinocyte differentiation and response to genotoxic stress in vivo, and indicate that bax may provide a tumour suppressor effect during skin carcinogenesis.

Heparan sulphate. Regulation of growth factors in the mammary gland

Heparan sulphate (HS) is a linear glycosaminoglycan found ubiquitously on the surface and in the pericellular matrix of metazoan cells that is covalently attached to core proteins to form HS proteoglycans. HS interacts specifically with a large number (> 100) of extracellular regulatory proteins, many of which are key players in mammary development and function. HS thus acts a receptor, in which capacity it regulates the bioavailability, localisation and activity of these regulatory proteins.

Fibroblast growth factor-2 stimulation of p42/44MAPK phosphorylation and IkappaB degradation is regulated by heparan sulfate/heparin in rat mammary fibroblasts

Fibroblast growth factor-2 (FGF-2) interacts with a dual receptor system consisting of tyrosine kinase receptors and heparan sulfate proteoglycans (HSPGs). In rat mammary fibroblasts, FGF-2 stimulated DNA synthesis and induced a sustained phosphorylation of p42/44(MAPK) and of its downstream target, p90(RSK). Moreover, FGF-2 also stimulated the transient degradation of IkappaBalpha and IkappaBbeta. PD098059, a specific inhibitor of p42/44(MAPK) phosphorylation, inhibited FGF-2-stimulated DNA synthesis, phosphorylation of p42/44(MAPK) and p90(RSK), and degradation of IkappaBbeta. In contrast, in chlorate-treated and hence sulfated glycosaminoglycan-deficient cells, FGF-2 was unable to stimulate DNA synthesis. However, FGF-2 was able to trigger a transient phosphorylation of both p42/44(MAPK) and p90(RSK), which peaked at 15 min and returned to control levels at 30 min. In these sulfated glycosaminoglycan-deficient cells, no degradation of IkappaBalpha and IkappaBbeta was observed after FGF-2 addition. However, in chlorate-treated cells, the addition of heparin or purified HSPGs simultaneously with FGF-2 restored DNA synthesis, the sustained phosphorylation of p42/44(MAPK) and p90(RSK), and the degradation of IkappaBalpha and IkappaBbeta. These results suggest that the HSPG receptor for FGF-2 not only influences the outcome of FGF-2 signaling, e.g. cell proliferation, but importantly regulates the immediate-early signals generated by this growth factor.

Stimulation of DNA synthesis and cell proliferation of human mammary myoepithelial-like cells by hepatocyte growth factor/scatter factor depends on heparan sulfate proteoglycans and sustained phosphorylation of mitogen-activated protein kinases p42/44

Hepatocyte growth factor/scatter factor (HGF/SF) is a heparan/dermatan sulfate-binding growth factor produced by stromal cells that acts as a paracrine effector on neighboring epithelia. HGF/SF stimulated DNA synthesis in human mammary (Huma) 109 myoepithelial-like cells grown on collagen I and fibronectin substrata but not when grown on plastic. Dual phosphorylation of mitogen-activated protein kinases (p42/44(MAPK)) was required for this stimulation of DNA synthesis. In Huma 109 cells cultured on plastic, HGF/SF stimulated a transient phosphorylation of p42/44(MAPK), which reached a maximum at 10 min after addition of the growth factor and returned to near basal levels after 20 min. In contrast, the phosphorylation of p42/44(MAPK) stimulated by HGF/SF in cells cultured on collagen I or fibronectin was sustained over 45 min. In Huma 109 cells deficient in sulfated glycosaminoglycans, HGF/SF failed to stimulate p42/44(MAPK) phosphorylation or DNA synthesis on any substratum, even when soluble heparan sulfate proteoglycans purified from the cells or from the culture medium were added. However, HGF/SF stimulated DNA synthesis and a sustained phosphorylation of p42/44(MAPK) in sulfated glycosaminoglycan-deficient Huma 109 cells plated on a substratum of medium HSPGs but not cell HSPGs. The HGF/SF-induced proliferation is thus highly dependent on heparan sulfate proteoglycans in myoepithelial-like cells.

Altered expression of bcl-2 family member proteins in nonmelanoma skin cancer

BACKGROUND

Differentiation, proliferation, and cell death are coordinated tightly within the epidermis. Alterations within keratinocytes that disrupt these processes are believed to contribute to the development of nonmelanoma skin cancers (NMSC). In the current study the authors examined the expression of selected members of the bcl-2 gene family in the skin and in case-matched samples of NMSC.

METHODS

Immunohistochemistry was performed on tissue sections using antibodies against bcl-2, bcl-x, bax, and bak. Case-matched frozen nonneoplastic skin samples and tumor tissues were used for Western blot analysis.

RESULTS

In normal epidermis, bcl-2 oncoprotein is expressed in keratinocytes of the basal layer but is down-regulated in suprabasal layers. The proapoptotic bax protein is expressed at low levels in basal keratinocytes and is up-regulated in suprabasal layers. The bcl-x and bak proteins both are expressed in the basal and spinous strata but are down-regulated in the granular cell layer. Both bcl-2 and bax were diffusely cytosolic whereas bcl-x and bak exhibited a distinct perinuclear distribution. Squamous cell carcinomas (SCC) were negative for bcl-2 whereas bcl-2 increased 5.5-fold in basal cell carcinomas (BCC). The distribution of bcl-x and bax proteins within BCC and SCC overlapped and were associated with squamous differentiation. Bax protein was increased twofold to threefold in NMSC. An increase in bak protein also was observed in SCC. However, bak was diffusely cytosolic within BCC in contrast to the perinuclear distribution in nonneoplastic keratinocytes.

CONCLUSIONS

These findings suggest that altered expression of bcl-2 family members may play a role in the pathogenesis of NMSC.

Nerve growth factor is mitogenic for cancerous but not normal human breast epithelial cells

We show here that nerve growth factor (NGF), the archetypal neurotrophic factor, is able to stimulate the proliferation of breast cancer cells (MCF-7 and MDA-MB-231 cell lines), although it is unable to stimulate growth of normal breast epithelial cells (NBEC). This stimulation induced cells in the G0 phase to reenter the cell cycle, as well as shortening cell cycle duration. Immunoblotting experiments revealed that both the two cancer cell lines and the NBEC express high affinity (p140(trk)) and low affinity (p75) NGF receptors. Inhibition of the NGF growth-promoting effect by the drugs K-252a and PD98059 indicated that activation of Trk-tyrosine kinase activity and the mitogen-activated protein kinase cascade are necessary to obtain the mitogenic effect. Activation of mitogen-activated protein kinase can be detected in breast cancer cells after 10 min of NGF stimulation, whereas no change was detected in NBEC. These results demonstrate that NGF is a mitogenic factor for human breast cancer cells and that it might constitute a new regulator of breast tumor growth.

Human keratin-1.bcl-2 transgenic mice aberrantly express keratin 6, exhibit reduced sensitivity to keratinocyte cell death induction, and are susceptible to skin tumor formation

Nonmelanoma skin cancers (NMSC) are among the most common malignancies in the world. Typically, these neoplasms grow slowly and are comparatively indolent in their clinical behavior. The most frequent molecular alterations implicated in the pathogenesis of these neoplasms involve genes known to be regulators of cell death including p53, Ha-ras and bcl-2. In order to evaluate the significance cell death deregulation during skin carcinogenesis, we generated a transgenic mouse model (HK1.bcl-2) using the human keratin 1 promoter to target the expression of a human bcl-2 minigene to the epidermis. Transgenic HK1.bcl-2 protein was expressed at high levels specifically in the epidermis extending from the stratum basale through the stratum granulosum. The epidermis of HK1.bcl-2 mice exhibited multifocal hyperplasia without associated hyperkeratosis and aberrant expression of keratin 6. The rate of proliferation was similar in HK1.bcl-2 and control epidermis although suprabasal BrdUrd incorporating cells were present only in HK1.bcl-2 skin. Keratinocytes from the HK1.bcl-2 mice were significantly more resistant to cell death induction by U.V.-B, DMBA, and TPA, compared to control keratinocytes. Furthermore, papillomas developed at a significantly greater frequency and shorter latency in the HK1.bcl-2 mice compared to control littermates following initiation with DMBA and promotion with TPA. Together these results support a role for bcl-2 in the pathogenesis of NMSC.

[Proteoglycans and breast cancer]

Proteoglycans (PG) are complex sulphated macromolecules composed of linear polysaccharide chains of glycosaminoglycans (GAG) covalently attached to a core protein. These GAG chains contain sulphate groups at various positions, giving them a high density of negative charges, and allowing them to interact with extracellular matrix molecules, including various growth factors. In the developing mammary gland, sulphated proteoglycans participate in morphogenesis and interact with extracellular matrix components in order to constitute a functional matrix. In breast pathogenesis, qualitative or quantitative changes in PG may have important consequences on cell proliferation and/or differentiation. Thus, several studies showed large variations in the nature and distribution of PG/GAG in breast cancer. Accumulation of chondroitin sulfate proteoglycans was described in the stromal compartment of mammary biopsy sections, and content in heparan sulfate proteoglycans, which were more specifically distributed in the epithelial compartment, increased with the level of malignancy and invasiveness of breast cancer tissues. Furthermore, heparan sulfate proteoglycans seem to be involved in control of the growth-promoting activity of numerous growth factors such as fibroblast growth factors also named Heparin-Binding Growth Factors (HBGF). The implication of PG in growth factor activity suggest that PG may have prognostic value in breast cancer. In future, structural studies into the specific HS-sequences involvement in growth factors binding could allow the development of new antiproliferative strategies.

Production of sulfated proteoglycans by human breast cancer cell lines: binding to fibroblast growth factor-2

The cellular distribution and nature of proteoglycans synthesised by human breast cancer cells in culture were studied. Proteoglycans were labelled with [35S] sulfate, purified, and characterised after ion-exchange chromatography followed by gel-filtration chromatography and treatment with glycosaminoglycan degrading enzymes. Proteoglycans were isolated from the culture medium and from cell layers of the hormono-dependent well-differentiated MCF-7 cell line, the hormono-independent poorly-differentiated MDA-MB-231 and the HBL-100 cell line which is derived from non malignant breast epithelium. HBL-100 and MDA-MB-231 cells produced larger amounts of proteoglycans which had a lower degree of sulfation than MCF-7 cells. Gel-filtration chromatography on Sepharose CL-6B indicated that HBL-100 and MDA-MB-231 cells accumulated cell surface heparan sulfate proteoglycans (HSPG), with a high apparent molecular weight (Kav 0.1). In contrast, the MCF-7 cell monolayers synthesised small sulfated macromolecules (Kav 0.4) which possessed mostly chondroitin sulfate chains. Moreover, considerable differences in the nature of the sulfated proteoglycans released into the culture medium of these breast epithelial cell lines were observed. MCF-7 cells released into the culture medium HSPG as the main proteoglycan component while MDA-MB-231 and HBL-100 cells released mainly chondroitin sulfate proteoglycans. In these three cell lines, medium-released sulfated macromolecules have a higher hydrodynamic size than cell-associated ones. Proteoglycans purified by ion-exchange chromatography were tested for their ability to bind 125I FGF-2. We demonstrated that HBL-100 and MDA-MB-231 cells bind more FGF-2 to their heparan sulfate proteoglycans than MCF-7 cells. Taken together, these results suggest that differences in proteoglycan synthesis of human breast epithelial cells could be responsible for differences in their proliferative and/or invasive properties.

Heparan sulfate proteoglycans play a dual role in regulating fibroblast growth factor-2 mitogenic activity in human breast cancer cells

The human breast cancer cell lines MCF-7 and MDA-MB-231 differ in their responsiveness to fibroblast growth factor-2 (FGF-2). This growth factor stimulates proliferation in well-differentiated MCF-7 cells, whereas the less well-differentiated MDA-MB-231 cells are insensitive to this molecule. To investigate the potential regulation of FGF-2 mitogenic activity by heparan sulfate proteoglycans (HSPG), we have treated human breast cancer cells by glycosaminoglycan degrading enzymes or a metabolic inhibitor of proteoglycan sulfation: sodium chlorate. The interaction between FGF-2 and proteoglycans was assayed by examining the binding of 125I-FGF-2 to breast cancer cell cultures as well as to cationic membranes loaded with HSPG. Using MCF-7 cells, we showed that heparinase treatment inhibited FGF-2 binding to HSPG and completely abolished FGF-2 induced growth; chlorate treatment of MCF-7 cells decreased FGF-2 binding to HSPG and cell responsiveness in a dose-dependent manner. This demonstrates a requirement of adequately sulfated HSPG for FGF-2 growth-promoting activity on MCF-7 cells. In highly invasive MDA-MB-231 cells which produce twice as much HSPG as MCF-7 cells and which are not normally responsive to exogenously added FGF-2, chlorate treatment decreased FGF-2 binding to HSPG and induced FGF-2 mitogenic effect. This chlorate effect was dose dependent and observed at concentrations of 10-30 mM; higher chlorate concentrations completely abolished the FGF-2 effect. This shows that the HSPG level of sulfation can also negatively regulate the biological activity of FGF-2. Taken together, these results demonstrate a crucial role for HSPG in both positive and negative control of FGF-2 mitogenic activity in breast cancer cell proliferation.

[Involvement of sulfated proteoglycans in the control of proliferation of MCF-7 breast cancer cells]

The MCF-7 breast cancer cells exhibit remarkable growth enhancement in response to basic fibroblast growth factor (FGF-2) stimulation in a dose dependent manner. To investigate the involvement of proteoglycans on control of FGF-2 induced proliferation, polysaccharide chains were degraded by specific enzymes. Our results showed that MCF-7 cells were unsensitive to FGF-2 after enzymatic degradation of heparin sulfate proteoglycans (HSPG) by heparinase. After metabolic inhibition of sulphation by sodium chloride, radiolabelled proteoglycans were purified and quantified by ion exchange chromatography. Sodium chlorate treatment reduced by 70% sulfation of proteoglycans. This decrease of sulphation totally inhibited FGF-2-mediated proliferation. The sulphated glycosaminoglycans which were critical in FGF-2-induced proliferation were strictly HSPG, as an addition of heparin in cell culture medium can restore FGF-2 mitogenic activity. In contrast, other glycosaminoglycans (chondroitin sulfate/hyaluronic acid) did not show any effect. These results provide clear evidence for the critical role of HSPG in FGF-2-induced proliferation on MCF-7 breast cancer cells.