Aluminum ions induce DNA synthesis but not cell proliferation in human fibroblasts in vitro

The effect in vitro of aluminum (Al) ions on DNA synthesis and human dermal fibroblast proliferation using [Al] concentrations from 1.85 to 74 μM and incubation periods of 1, 2, 3, 4, and 5 d was assessed. The lowest concentration of Al that exerted a slight positive, although not significant, effect on DNA synthesis was 1.85 μM, after d 3 or 5 of incubation. The stimulating action of Al was more evident and statistically significant from concentrations of 3.7 μM and 2 d exposure onward. This Al-induced effect on [³H] thymidine incorporation into DNA increased in a time-dependent manner as [Al] in the culture medium rose, provoking increments of up to 322% above the control at [Al] 74 μM and 5 d incubation. In contrast, Al salts moderately increased fibroblast division in a continuous manner only from 7.4 to 74 μM after 3 d of incubation. Although significant overall, the minimal and inconstant mitogenic activity of Al differs greatly from and is not parallel to DNA synthesis, which is not clearly related to exposure times or Al concentrations. Abnormalities in Al-induced cellular metabolic processes described herein and their influence on the cell cycle may constitute a toxicity mechanism for human tissues, leading to disease development. Further studies are required to determine whether these findings can be extrapolated to in vivo situations.     

In vitro synthesis of beta2-microglobulin by human fetal tissues.

Human fetal tissues were cultured in the presence of ¹⁴C-labeled amino acids and the culture fluids analyzed by radioimmunoelectrophoresis for the presence of radioactive β₂-microglobulin. Synthesis of the protein was demonstrated in all the tissues studied. Using the Ouchterlony method, β₂-microglobulin was also detected in culture media from serially transferred cell cultures of fetal tissues and established fetal cell strains.     

Interleukin-1 induced gene expression of neutrophil activating protein (interleukin-8) and monocyte chemotactic peptide in human synovial cells

We report here that human synovial cells stimulated by interleukin-1 alpha and interleukin-1 beta express mRNA for both IL-8 (neutrophil chemotactic peptide) and monocyte chemotactic protein. IL-1 stimulated synovial cells from both osteoarthritis and rheumatoid arthritis patients exhibited similar mRNA expression of interleukin-8 and monocyte chemotactic protein. A capacity to produce factors selectively chemotactic for neutrophils, lymphocytes and monocytes provides a mechanism whereby synovial cells can facilitate inflammatory arthritis.     

Glucocorticoids stimulate elastin production in differentiated bovine ligament fibroblasts but do not induce elastin synthesis in undifferentiated cells

Glucocorticoid treatment of fibroblasts from late gestation fetal bovine ligamentum nuchae resulted in a time- and dose-dependent selective increase in elastin production. Tropoelastin levels increased 2-3-fold in the presence of 10 nM dexamethasone while total protein synthesis and the rate of cell division decreased with glucocorticoid exposure. Two tropoelastin bands of molecular weights 64,500 and 61,000 were identified by immunoprecipitation and sodium dodecyl sulfate gradient-gel electrophoresis and both bands increased to an equal extent in the presence of dexamethasone. Undifferentiated cells from early-gestation animals did not synthesize elastin after hormone exposure, even though glucocorticoid receptors were demonstrated by nuclear-translocation experiments. These results indicate that glucocorticoids stimulate elastin production in elastin-producing ligament cells but do not induce elastin synthesis (differentiation) in undifferentiated cells.     

The biological activities of gro beta and IL-8 on human neutrophils are overlapping but not identical.

Gro beta and IL-8 are two members of the small induced secreted (SIS) cytokine family (C-X-C subgroup) with proinflammatory activities on neutrophils. In order to assess whether or not the interaction with their receptors results in similar biological actions, we compared the two cytokines in five different bioassays. Gro beta showed similar biological activities as IL-8 in tests of chemotaxis, induction of the respiratory burst, and induction of interleukin 6 (IL-6) production. However, for two other biological activities: augmentation of the expression of CD11b on the cell surface and rapid elevation of the intracellular calcium concentration, maximal effects required 100 times more gro beta than IL-8. Taken together, these results suggest that the stimulation of the IL-8 or gro beta receptor evokes three similar responses, but that only the activation of the IL-8 receptor and not that of gro beta results in elevated CD11b expression and calcium mobilization in human neutrophils.     

The beta2-microglobulin mRNA in human Daudi cells has a mutated initiation codon but is still inducible by interferon

The human Burkitt lymphoma cell line Daudi does not synthesize beta2-microglobulin (beta2m) and lacks the cell surface histocompatibility antigens. The cells, however, contain RNA hybridizing to a cloned human beta2m cDNA probe. cDNA from this Daudi beta2m RNA, was cloned and sequenced. By comparison with cDNA prepared from Ramos cells, which synthesized microglobulin, we determined the sequence of the 20 amino acid long leader peptide of pre-beta2m and show that in Daudi cells the initiator ATG has been mutated to ATC. Although Daudi beta2m RNA cannot be translated, interferon induces the beta2m RNA in Daudi cells as well as in normal human cells.     

Interferon-gamma is a strong modulator of NK susceptibility and expression of beta 2-microglobulin but not of transferrin receptors of K562 cells

The human cell line K562 was treated with human natural leukocyte interferon (IFN-alpha) and recombinant immune interferon (IFN-gamma). Cell cultures exposed to both types of IFNs displayed a reduced susceptibility to the cytotoxic activity of human PBL (NK activity). While this effect occurred preferentially at high doses of IFN-alpha, as little as 10 U/ml of IFN-gamma caused a marked decrease in susceptibility to NK-cell-mediated lysis. Using a monoclonal antibody against human beta2-microglobulin (beta2M) a low level of specific binding to K562 cells was detected. The binding increased after treatment with IFN-alpha (1.4-fold) and IFN-gamma (1.7-fold). The expression of transferrin receptors (TR) was not changed significantly. A hybrid cell line between K562 and a Burkitt's lymphoma-derived cell line displayed a similar pattern of response to IFN-alpha and IFN-gamma as did K562, when effects on NK susceptibility, beta2M expression, and TR expression were studied. The Burkitt's lymphoma line PUT showed no consistent changes in expression of beta2M and TR. These results demonstrate that IFN-gamma is highly efficient in modulating the NK susceptibility, and the expression of beta2M on K562. The presented data do not support a role for expression of TR as the only property that determines the degree of NK susceptibility, since there was no correlation between NK susceptibility and TR expression among the cell lines tested or when IFN-treated and untreated cells were compared.     

Expression and secretion of gro/MGSA by stimulated human endothelial cells.

Melanoma growth stimulatory activity factor (MGSA) is a polypeptide which was initially isolated from Hs294 human melanoma cells. Its sequence is identical to the deduced amino acid sequence of the human gro cDNA, isolated from a human tumor cell line. MGSA stimulates the proliferation of malignant melanoma cells, but its function for normal cells has not been defined. Here we report that human umbilical vein endothelial cells are capable of synthesizing and secreting MGSA. The expression and secretion of MGSA are strongly induced by factors often involved in inflammation such as IL-1, TNF, LPS and thrombin. The induction of MGSA mRNA is dose and time dependent and is independent of new protein synthesis. This stimulation could be mimicked by TPA, suggesting that the action could be mediated through activation of protein kinase C. Furthermore, addition of MGSA to the endothelial cell cultures induces gro/MGSA gene expression, implying that an autocrine mechanism exists. Our data suggest that the protein encoded by gro/MGSA mRNA may play a role in inflammation and exert its effects on endothelial cells in an autocrine fashion.     

Cytokine-induced gene expression of a neutrophil chemotactic factor/IL-8 in human hepatocytes

The liver participates in inflammation via the elaboration of acute phase proteins from hepatocytes in response to IL-1, TNF-alpha, and IL-6/INF-beta 2/hepatocyte-stimulating factor. In addition, some inflammatory states of the liver are characterized by leukocyte infiltrates. Here we demonstrate that human hepatocyte lines are capable of expressing mRNA and biologic activity for a neutrophil chemotactic factor (NCF)/IL-8 in response to the inflammatory mediators IL-1 alpha, IL-1 beta, and TNF. Two human hepatoma cell lines (SK-Hep and Hep-G2) displayed a time- and dose-dependent increase in steady state levels of NCF/IL-8 mRNA and secretion of chemotactic activity in response to TNF and IL-1. Neutralizing antibody to NCF/IL-8 inhibited hepatocyte-derived chemotactic activity by 88%. In contrast to IL-1 and TNF, hepatocytes did not respond to LPS or IL-6 within the time and dose parameters used above. Although the expression of NCF/IL-8 mRNA (1.8 kb) was first detectable between 1 and 2 h poststimulation, significant chemotactic bioactivity was not observed until about 4 h. Heat-inactivated (100 degrees C, 30 min) cytokine failed to induced NCF/IL-8 mRNA synthesis, and cotreatment of cells with cytokine and cycloheximide super-induced NCF/IL-8 mRNA while inhibiting production of bioactivity. Thus, NCF/IL-8 expression is a primary induction phenomenon. Our data demonstrate the stimulus specific induction of NCF/IL-8 in hepatocytes and suggest that cytokine cell-to-cell communication circuits may be important in neutrophil-mediated inflammatory processes in the liver.     

Compactin and simvastatin, but not pravastatin, induce bone morphogenetic protein-2 in human osteosarcoma cells

Bone morphogenetic protein (BMP)-2, a member of the BMP family, plays an important role in osteoblast differentiation and bone formation. To discover small molecules that induce BMP-2, a luciferase reporter vector containing the 5'-flanking promoter region of the human BMP-2 gene was constructed and transfected into human osteosarcoma (HOS) cells. By the screening of an in-house natural product library with stably transfected HOS cells, a fungal metabolite, compactin, known as an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was isolated. The stimulation of the promoter activity by compactin seemed to be specific for BMP-2 gene in HOS cells, since it had little effect on BMP-4 or SV40 promoter activity and the stimulation was not observed in Chinese hamster ovary (CHO) cells. RT-PCR analysis and alkaline phosphatase assay revealed that compactin induced an increase in the expression of BMP-2 mRNA and protein. Like compactin, simvastatin also activated the BMP-2 promoter, whereas pravastatin did not. The statin-mediated activation of BMP-2 promoter was completely inhibited by the downstream metabolite of HMG-CoA reductase, mevalonate, indicating that the activation was a result of the inhibition of the enzyme. These results suggest that statins, if they are selectively targeted to bone, have beneficial effects in the treatment of osteoporosis or bone fracture.     

Loss of the zymogen granule protein syncollin affects pancreatic protein synthesis and transport but not secretion

Syncollin is a small protein that is abundantly expressed in pancreatic acinar cells and that is tightly associated with the lumenal side of the zymogen granule membrane. To shed light on the hitherto unknown function of syncollin, we have generated syncollin-deficient mice. The mice are viable and show a normal pancreatic morphology as well as normal release kinetics in response to secretagogue stimulation. Although syncollin is highly enriched in zymogen granules, no change was found in the overall protein content and in the levels of chymotrypsin, trypsin, and amylase. However, syncollin-deficient mice reacted to caerulein hyperstimulation with a more severe pancreatitis. Furthermore, the rates of both protein synthesis and intracellular transport of secretory proteins were reduced. We conclude that syncollin plays a role in maturation and/or concentration of zymogens in zymogen granules.     

Fluvastatin and lovastatin but not pravastatin induce neuroglial differentiation in human mesenchymal stem cells

Recent studies have shown that statins, the most potent inhibitors of 3-hydroxy-2-methylglutaryl coenzyme A (HMG-CoA) reductase, stimulate bone formation in vitro and in rodents by activating the expression of bone morphogenetic protein-2 (BMP-2), one of the most critical osteoblast differentiation-inducing factors. However, the effect of statins on mesenchymal stem cells (MSCs) is yet to be reported. The purpose of this study is to investigate the influence of fluvastatin, lovastatin, and pravastatin, three commonly prescribed lipid-lowering agents, on the proliferation and differentiation of human MSCs. To our surprise, even though fluvastatin and lovastatin effectively suppressed the growth of human MSCs, a neuroglia rather than osteoblast-like morphology was observed after treatment. Interestingly, such morphological change was inhibited by the co-addition of geranylgeranyl pyrophosphate (GGPP). Immunofluorescence staining with antibodies against neuron-, astrocyte-, as well as oligodendrocyte-specific markers confirmed the neuroglial identity of the differentiated cells. However, BMP-2 is unlikely to play a positive role in neuroglial differentiation of MSCs since its expression was down-regulated in fluvastatin-treated cells. Taken together, our results suggest that fluvastatin and lovastatin induce neuroglial differentiation of human MSCs and that these cholesterol-lowering agents might be used in conjunction with MSC transplantation in the future for treating neurological disorders and injuries.     

Stimulation of procollagenase synthesis in human rheumatoid synovial fibroblasts by mononuclear cell factor/interleukin 1

In order to define mechanisms regulating the synthesis of procollagenase in human rheumatoid synovial fibroblasts, the proteins synthesized by cultured cells were labeled with [35S]methionine. Labeled medium proteins were analyzed by SDS-PAGE directly and after immunocomplexing with a specific antibody to human fibroblast collagenase. Labeling of both the predominant form of the enzyme (Mr approximately 55 000) as well as a minor species (Mr approximately 61 000) was increased following incubation with the monokine, mononuclear cell factor/interleukin 1. The approximately 61 kDa form of the procollagenase appears to be a glycosylated form of the approximately 55 kDa precursor based on binding to Con A-Sepharose and decrease in the approximately 61 kDa form after culture in the presence of tunicamycin. Thus, mononuclear cell factor, homologous with interleukin 1, partially purified from monocyte conditioned medium increased incorporation of [35S]methionine into several medium proteins, including those complexed by the anticollagenase antibody. In the presence of mononuclear cell factor/interleukin 1, labeling of the procollagenase was increased 12-14-fold over control cultures incubated with medium alone. Therefore, one of the mechanisms involved in increase of collagenase activity in the medium of cultured synovial fibroblasts in the presence of mononuclear cell factor/interleukin 1 is a stimulation of enzyme protein synthesis.     

Activated human Langerhans cells express mRNA for IL-1 alpha and IL-1 beta and produce these cytokines but do not secrete them.

Human Langerhans cells (LC) were isolated from epidermal cell preparations by panning with mouse anti-CD1 monoclonal antibody. RNA was prepared and probed for the presence of mRNAs for various cytokines using radiolabeled cDNAs. After stimulation with phorbol myristate acetate LC express RNA for interleukin 1 alpha (IL-1 alpha) and interleukin 1 beta (IL-1 beta) and produce proteins but do not secrete them at detectable levels. LC-associated IL-1, particularly IL-1 alpha, may play a role in antigen presentation. PMA did not induce IL-6 expression in LC. The addition of lipopolysaccharide, a muramyl dipeptide analog, ionomycin, IL-1 alpha, tumor necrosis factor-alpha, insulin-like growth factor-1 or IL-6 did not induce IL-1 mRNA in LC. UVB augmented IL-1 beta mRNA expression. Glucocorticoids did not detectably affect IL-1 alpha or IL-1 beta mRNA levels following PMA induction, however, staurosporin inhibited IL-1 beta mRNA synthesis. Thus the inducers and regulators of IL-1 formation in human LC and monocytes are not identical.     

Functional reconstitution of human FcRn in Madin-Darby canine kidney cells requires co-expressed human beta 2-microglobulin

The major histocompatibility complex class I-related neonatal Fc receptor, FcRn, assembles as a heterodimer consisting of a heavy chain and beta(2)-microglobulin (beta(2)m), which is essential for FcRn function. We observed that, in Madin-Darby canine kidney (MDCK) cells, the function of human FcRn in mediating the bidirectional transport of IgG was significantly increased upon co-expression of the human isoform of beta(2)m. In MDCK cells, the presence of human beta(2)m endowed upon human FcRn an enhanced ability to exit the endoplasmic reticulum and acquire mature carbohydrate side-chain modifications at steady state, a faster kinetics of maturation, and augmented localization at the cell surface as a mature glycoprotein able to bind IgG. Although human FcRn with immature carbohydrate side-chain modifications was capable of exhibiting pH-dependent binding of IgG, only human FcRn with mature carbohydrate side-chain modifications was detected on the cell surface. These results show that human FcRn travels to the cell surface via the normal secretory pathway and that the appropriate expression and function of human FcRn in MDCK cells depends upon the co-expression of human beta(2)m.