Basic fibroblast growth factor is an extracellular matrix component required for supporting the proliferation of vascular endothelial cells and the differentiation of PC12 cells.

Vascular endothelial cells (ECs) seeded sparsely on extracellular matrix (ECM) will proliferate in the absence of exogenous basic fibroblast growth factor (bFGF). This ECM will also stimulate neurite outgrowth in PC12 cells in the absence of exogenous growth factors. We have previously shown that bFGF is found in subendothelial ECM (Vlodavsky, I., J. Folkman, R. Sullivan, R. Fridman, R. Ishai-Michaeli, J. Sasse, and M. Klagsburn. 1987. Proc. Natl. Acad. Sci. USA. 84:2292-2296) and in basement membranes (Folkman, J., M. Klagsburn, J. Sasse, M. Wadzinski, D. Ingber, and I. Vlodavsky. 1988. Am. J. Pathol. 130:393-400). The actual requirement of ECM-associated bFGF for the growth of ECs and differentiation of PC12 cells was shown in two ways. First, polyclonal anti-bFGF antibodies added to subendothelial ECM inhibited both EC proliferation and PC12 neurite outgrowth. Secondly, PF-HR-9 cells, which do not synthesize bFGF and which produce an ECM not permissive for EC proliferation and PC12 neurite outgrowth, were transfected with bFGF cDNA. PF-HR-9 cells transfected with bFGF, but not with the dominant selectable marker SV2-neomycin, were found to express bFGF and to produce an ECM which did support both EC proliferation and PC12 differentiation. The ECM-mediated stimulatory effects were inhibited by anti-bFGF antibodies but not by anti-nerve growth factor antibodies or nonimmune rabbit IgG. These results indicate that bFGF associated with ECM is a required ECM component for ECM-mediated cell proliferation and differentiation.

Enhanced aggregation of human neutrophils by MnCl2 or DTT differentiates the roles of L-selectin and beta 2-integrins.

MnCl2 and dithiothreitol (DTT) enhance the adhesive functions of beta 2 -integrins. We have used these agents and flow cytometry to distinguish the contributions of beta 2-integrins and L-selectin to neutrophil aggregation. Although neither compound induced aggregation, they prolonged N-formyl-methionyl-leucyl-phenylalanine-induced aggregation and produced larger aggregates. Because activated polymorphonuclear granulocytes (PMN) shed L-selectin in the presence of MnCl2, but not DTT, we could evaluate the role of L-selectin in the early and late stages of aggregation. Blocking L-selectin sites with DREG200 Fab and/or beta 2-integrin sites with IB4 Fab indicated that aggregation under all conditions remained beta 2-integrin- and L-selectin-dependent. Disaggregation was integrin-dependent whether L-selectin was present or shed. The disaggregation kinetics suggested that integrin bonds turned over at a slower rate in MnCl2-treated cells. Enhanced aggregation due to DTT and MnCl2 required sustained energy output, suggesting intracellular rather than strictly conformational control. These results provide evidence that PMN aggregation, like leukocyte-endothelial cell adhesion, utilizes L-selectin to form intercellular contacts that are maintained through activated integrins.

Evidence for a third component in neutrophil aggregation: potential roles of O-linked glycoproteins as L-selectin counter-structures.

The homotypic aggregation of neutrophils requires the participation of L-selectin and the beta 2-integrins, but it has not been clear whether the two receptors recognize one another as counter-structures or whether other adhesion molecules are involved. We have examined aggregation of live neutrophils with target populations, manipulated to alter expression of adhesive epitopes, using flow cytometry. A target population depleted of both L-selectin and activatable beta 2-integrin displayed an ability to aggregate with live neutrophils, suggesting that these two molecules are not counter-structures. We also found that an O-sialoglycoprotease (GCP) from Pasteurella haemolytica is capable of inhibiting homotypic aggregation. Neutrophils treated with GCP lose O-glycosylated proteins but retain L-selectin and activatable beta 2-integrin. One or more of the GCP substrates appears to function in L-selectin-dependent binding but not in beta 2-integrin-dependent binding. Together the data suggest a mechanism of aggregation that is analogous to leukocyte-endothelial cell adhesion in which a low-affinity carbohydrate-dependent interaction precedes a high-affinity integrin-dependent adhesion.

Growth factor modulation of metastatic lung colonization.

Altered production and response to growth factors is often involved in neoplasia but little is known about their effect on the dissemination of tumors. Therefore, we have examined the effect of growth factors on metastatic lung colonization. Autocrine induction of the metastatic phenotype was demonstrated in NIH-3T3 cells transformed by a signal peptide-bFGF gene but not bFGF in the absence of the signal peptide. In addition, exogenous growth factor regulation of metastasis was demonstrated. Treatment of ras transformed C3H-10T 1/2 cells and ras or src transformed NIH-3T3 cells with bFGF prior to intravenous injection resulted in potent inhibition of metastatic potential. Stimulation of v-fms transformed cells by the natural fms-ligand, CSF-1, resulted in potent stimulation of metastatic behavior in freshly plated or refed cells, whereas following autocrine conditioning of the medium, the metastatic properties of these cells were sensitive to inhibitory effects of CSF-1. These observations indicate that specific growth factors can regulate the metastatic phenotype and, depending on the oncogenes responsible for cell transformation and autocrine conditioning, these effects can be either stimulatory or inhibitory.

The effect of retinoic acid on cyclic-AMP-binding proteins in mouse melanoma cells.

We have previously reported [(1980) J. Biol. Chem. 255, 5999-6002] that retinoic acid inhibited growth and increased cyclic-AMP-dependent protein kinase activity in mouse melanoma cells. A variant melanoma line having depressed levels of cyclic-AMP-dependent protein kinase was not growth-inhibited by retinoic acid. In this report we describe the effect of retinoic acid on cyclic AMP binding proteins in B16 mouse melanoma cells. Using the technique of photoaffinity labeling, we found three major proteins of Mr 49 000, 52 000, and 55 000 which were specifically labeled with 8-N3-[32P]AMP in both control and treated cells. Based upon their molecular weight, relative affinity for 8-N3-[32P]AMP and comigration with standards, we have designated the 49 000-Mr and 55 000-Mr species as RI and RII respectively. The position of the intermediate band (Mr 52 000) was not affected by pre-incubation with ATP or alkaline phosphatase, and two-dimensional gel analysis indicated that it had the same pI as RI. Retinoic acid increased the 8-N3-[32P]AMP labeling of RI within 24 h, reaching a maximal six fold increase by 48 h. These increases were limited to the 40 000 X g supernatant fraction and occurred prior to any growth inhibition. By using increasing concentrations of 8-N3-cAMP we were able to construct a saturation curve for RI binding. Calculation of apparent Kd values from these curves showed nearly identical affinities for RI binding of 8-N3-cAMP from control and retinoic-acid-treated cells. Therefore we conclude that retinoic acid is increasing the amount of RI rather than altering its properties. Corroboration of these results was obtained by DEAE-cellulose chromatography. Peak I (corresponding to type I protein kinase) from retinoid-treated cells was increased about six fold in binding activity.

Characterization of tumors produced by signal peptide-basic fibroblast growth factor-transformed cells.

Basic fibroblast growth factor (bFGF) is found in a variety of cells and tissues. We have previously shown that bFGF is a transforming growth factor, but only when fused to a signal peptide (sp-bFGF). Cells expressing the native bFGF are tumorigenic in nude mice only, where the tumors form at a low frequency and grow very slowly as compared to sp-bFGF tumors. The cells transformed by the sp-bFGF growth factor gene cause rapidly growing tumors within 10 days in 100% of syngeneic and nude mice. In nude mice, the tumors are highly vascularized, while the vascularization in immunocompetent syngeneic mice is not as prominent. The syngeneic mice have a characteristic humoral immune response to sp-bFGF tumors, which differs from that mounted against ras-induced tumors. The ability of bFGF to induce tumorigenicity is significant in view of the recent discoveries of three new oncogenes: hst, int-2, and an oncogene from a human colon cancer. In addition to homology with FGF, the proteins encoded by these oncogenes all have a potential signal peptide at the protein's amino terminus, suggesting a mode of action analogous to that of our artificial signal peptide-bFGF (sp-bFGF) transforming growth factor model system.

Basic fibroblast growth factor fused to a signal peptide transforms cells.

Basic fibroblast growth factor (bFGF) is a potent growth and angiogenic factor that is found in abundance in tissues such as brain, hypothalamus, kidney and cartilage. Despite this copious production of bFGF, most of these tissues are not undergoing either active growth or angiogenesis, suggesting that bFGF activity must be regulated so as to prevent autostimulation of cell growth. In cultured cells, bFGF is associated mainly with cells and basement membranes and is not released into the medium. Prevention of release could be a mechanism for regulation of bFGF activity and may be a consequence of the apparent absence of a secretory-signal sequence in the bFGF protein. Here we investigate whether this regulation can be overridden through the forced secretion of bFGF. Such secretion might provide the bFGF access to its receptor and in turn lead to autocrine transformation of the cell. We report that bFGF, as specified by a recombinant plasmid, is itself unable to induce such transformation, but acquires this ability after fusion with a secretory-signal sequence. The resulting transformants undergo unusual morphological alteration and display tumorigenicity.

Purification of 18- and 22-kDa forms of basic fibroblast growth factor from rat cells transformed by the ras oncogene.

Normal Rat-1 fibroblasts and Rat-1 cells transformed by the H-ras oncogene (Rat-1-EJ) were analyzed for cell-associated growth factor activity. The two cell lines grew at the same rate, but at any given stage of growth the Rat-1-EJ cells synthesized two to four times more cell-associated growth factor activity than did the Rat-1 cells. For each cell line, the level of cell-associated growth factor activity was five to eight times greater at confluent densities compared to sparse densities. Heparin affinity chromatography and Western blot analysis demonstrated that the cell-associated growth factor was basic fibroblast growth factor (bFGF). The bFGF synthesized by the Rat-1-EJ cells appeared in two molecular mass forms, about 40% as an 18-kDa form which comigrated with recombinant bFGF and about 60% as a higher molecular mass doublet of about 22 kDa. The two forms of bFGF were biologically active and could be separated on a Mono S cation exchange column. Separation and purification to homogeneity of both the 18-kDa bFGF and the 22-kDa bFGF doublet were achieved by a combination of CM-Sepharose cation exchange, heparin affinity-fast performance liquid chromatography, and C4 reverse phase high performance liquid chromatography.

Cyclic adenosine monophosphate-mediated induction of F9 teratocarcinoma differentiation in the absence of retinoic acid.

F9 teratocarcinoma stem cells differentiate into parietal endoderm-like cells when given retinoic acid (RA) and dibutyryl cyclic adenosine monophosphate (DB-cAMP). It is generally accepted that the stem cells are resistant to the action of cAMP alone and need to be primed by RA in order to respond to cAMP. In this report, we demonstrate that F9 stem cells differentiate into parietal endoderm-like cells in the absence of exogenous RA when treated with cholera toxin and 1-methyl,3-isobutyl xanthine (CT/MIX) or 8-bromo-cAMP/MIX (8B2-cAMP/MIX). Cells treated with CT/MIX or 8B2-cAMP/MIX were morphologically similar to parietal endoderm-like cells, produced high amounts of plasminogen activator, and synthesized both type IV collagen and laminin mRNA. Conversely, markers made in abundance by stem cells such as stage-specific embryonic antigen (SSEA-1) and an mRNA species of 6.8 kb (pST6-135) were markedly reduced in CT/MIX-treated cells. To prove that cAMP alone could induce differentiation Lipidex-1000, a hydrophobic gel, was used to remove 80-90% of the endogenous serum retinoids. F9 cells grown in this retinoid-depleted serum and treated with 8B2-cAMP/MIX differentiated to parietal endoderm-like cells as shown by both dramatic changes in morphology and induction of type IV collagen mRNA. Our results indicate that the differentiation of F9 to parietal endoderm-like cells can be induced by increased intracellular cAMP and is not strictly dependent on the addition of RA.

Enzyme destruction by a protease contaminant in bacitracin.

Bacitracin, as purchased from biochemical supply companies, is a mixture of more than 30 different substances. The major antibiotic isoforms A and B account for about 60% of the mixture. A newly identified impurity in some, but not all, of the bacitracin lots is a powerful subtilisin-type protease capable of cleaving many proteins including protein disulfide isomerase (PDI), myosin, and a variety of artificial substrates Thus, it is important for investigators who use bacitracin as a protease or other enzyme inhibitor to determine if the bacitracin they are using is contaminated with a protease enzyme. If it is present, they may have to reinterpret their results and retest with an enzyme-free bacitracin reagent.

Sulfhydryl regulation of L-selectin shedding: phenylarsine oxide promotes activation-independent L-selectin shedding from leukocytes.

The L-selectin adhesion molecule mediates leukocyte recruitment to inflammatory sites and lymphocyte trafficking through the peripheral lymph nodes. In response to leukocyte activation, L-selectin is proteolytically released from the cell surface, disabling leukocytes from the subsequent L-selectin-dependent interactions. We have found that L-selectin shedding is sensitive to sulfhydryl chemistry; it is promoted by thiol-oxidizing or -blocking reagents and inhibited by reducing reagents. Phenylarsine oxide (PAO), a trivalent arsenical that interacts with vicinal dithiols, is most potent in inducing rapid shedding of L-selectin from isolated neutrophils, eosinophils, and lymphocytes as well as from neutrophils in whole blood. PAO does not cause cell activation, nor does it interfere with integrin function or alter the expression of several other cell surface molecules at the low concentrations that induce L-selectin shedding. PAO is not required to enter the cell to induce L-selectin shedding. TAPI-2 ((N-(D,L-[2-(hydroxyaminocarbonyl)-methyl]-4-methylpentanoyl)-L-3-(tert-butyl)-alanyl-l -alanine, 2-aminoethyl amide), which has previously been shown to inhibit the activation-dependent L-selectin shedding, is also capable of inhibiting PAO-induced L-selectin shedding. We hypothesize that PAO-induced L-selectin shedding involves a regulatory molecule, such as protein disulfide isomerase (PDI), an enzyme that plays a role in the formation and rearrangement of disulfide bonds, contains PAO-binding, vicinal dithiol-active sites, and is expressed on the neutrophil surface. Cell surface expression of PDI, L-selectin shedding induced by PDI-blocking Abs and by bacitracin, a known inhibitor of PDI activity, and direct binding of PDI to PAO, provide supporting evidence for this hypothesis.

Hydroxamate-based metalloprotease inhibitor blocks shedding of L-selectin adhesion molecule from leukocytes: functional consequences for neutrophil aggregation.

L-selectin is an adhesion molecule that mediates the recruitment of neutrophils to inflammatory sites and initiates the migration of lymphocytes into the peripheral lymph nodes. In response to cell activation, L-selectin is shed from the cell surface, and altered levels of functional soluble L-selectin are detected in the plasma of patients suffering from numerous inflammatory diseases as well as AIDS. The mechanism that regulates L-selectin shedding is poorly understood. Here we show that a hydroxamate-based metalloprotease inhibitor, N-(D,L-[2-(hydroxyaminocarbonyl)- methyl]-4-methylpentano)-L-3-(tert-butyl)-alanyl-L-alanine, 2-aminoethyl amide, which blocks leukocyte TNF, TNF receptor, and IL-6 receptor release, also inhibits L-selectin shedding from neutrophils, eosinophils, and lymphocytes. Moreover, we show that such inhibition of L-selectin shedding profoundly affects neutrophil aggregation and permits reaggregation in the presence of a heterologous stimulus.

A human DNA segment with properties of the gene that predisposes to retinoblastoma and osteosarcoma.

The genomes of various tumour cells contain mutant oncogenes that act dominantly, in that their effects can be observed when they are introduced into non-malignant cells. There is evidence for another class of oncogenes, in which tumour-predisposing mutations are recessive to wild-type alleles. Retinoblastoma is a prototype biological model for the study of such recessive oncogenes. This malignant tumour, which arises in the eyes of children, can be explained as the result of two distinct genetic changes, each causing loss of function of one of the two homologous copies at a single genetic locus, Rb, assigned to the q14 band of human chromosome 13. Mutations affecting this locus may be inherited from a parent, may arise during gametogenesis or may occur somatically. Those who inherit a mutant allele at this locus have a high incidence of non-ocular, second tumours, almost half of which are osteosarcomas believed to be caused by the same mutation. Here we describe the isolation of a complementary DNA segment that detects a chromosomal segment having the properties of the gene at this locus. The gene is expressed in many tumour types, but no RNA transcript has been found in retinoblastomas and osteosarcomas. The cDNA fragment detects a locus spanning at least 70 kilobases (kb) in human chromosome band 13q14, all or part of which is frequently deleted in retinoblastomas and osteosarcomas.

Identification and molecular cloning of a novel mouse mucosal mast cell serine protease.

A novel 28,000 Mr serine protease, designated mouse mast cell protease-2 (MMCP-2), that is stored in the secretory granules of Kirsten sarcoma virus-immortalized mouse mast cells (KiSV-MC) has been identified and its NH2-terminal amino acid sequence has been determined. Analysis of a 953-base pair cDNA that encodes MMCP-2 revealed that this serine protease is a basically charged protein, possessing the histidine-aspartic acid-serine charge relay system that is characteristic of other serine proteases. DNA blot analysis using the full-length MMCP-2 cDNA indicated the existence of a family of highly related serine protease genes in the mouse genome. When the same DNA blot was probed with the 149-base pair KpnI----3' fragment of the cDNA, the probe hybridized to a single DNA fragment, thereby demonstrating that this 3' fragment could be used as a gene-specific probe. The presence of high levels of the MMCP-2 mRNA transcript in the intestines of nematode-infected mice, and its absence in mouse bone marrow-derived mast cells and peritoneal cavity-derived connective tissue mast cells, suggest that this member of the mouse mast cell protease family is preferentially expressed late in the differentiation of mucosal mast cells.

Endothelial cells synthesize basic fibroblast growth factor and transforming growth factor beta.

Endothelial cells, including human umbilical vein endothelial cells (HUVEC), bovine aortic endothelial cells (BAEC), and bovine capillary endothelial cells (BCEC) in culture synthesize basic fibroblast growth factor (bFGF) and transforming growth factor type beta (TGF-beta). Basic FGF was cell-associated and synthesis was demonstrated by (i) the presence of bFGF mRNA species, (ii) binding to heparin-Sepharose and elution at 1.5 M NaCl, (iii) cross-reactivity with anti-bFGF antibodies when analyzed by electrophoretic blotting, and (iv) biological activity. Basic FGF was found in cell lysates at 2.3 ng/10(6) cells in HUVEC, 2.0 ng/10(6) cells in BCEC, and 13 ng/10(6) cells in BAEC. TGF-beta was secreted into media, and synthesis was demonstrated by (i) presence of TGF-beta mRNA species, (ii) cross-reactivity with anti-TGF-beta antibodies when analyzed by immunoprecipitation, (iii) competitive binding with authentic human platelet-derived TGF-beta that was blocked by TGF-beta specific blocking antibodies, and (iv) inhibition of [3H]TdR incorporation in CCl-64 cells. TGF-beta was secreted in an inactive form and required acid activation for detection. HUVEC synthesized 2.0 ng TGF-beta/10(6) cells per 12 hr; BCEC, 3.5 ng; and BAEC, 3.5 ng. HUVEC proliferation was not affected by treatment with exogenous TGF-beta, while BCEC proliferation was decreased by treatment with TGF-beta. Vascular endothelium is thus a source for these two potent multifunctional regulatory molecules, both of which may affect the growth of endothelium and neighboring fibroblasts, smooth muscle cells and white blood cells. The activation or release of these factors by endothelium may be a precipitating event in important cellular processes such as wound healing, organogenesis, and angiogenesis.

P-selectin glycoprotein ligand-1 (PSGL-1) is a ligand for L-selectin in neutrophil aggregation.

In inflammation, activated neutrophils adhere to endothelial cells and aggregate with one another. While beta 2-integrin and L-selectin are essential for aggregation, their ligands remain to be identified. We have previously shown that L-selectin mediates a carbohydrate-dependent interaction in aggregation (Simon et al: J Immunol 149:2765, 1992; Rochon et al: J Immunol 152:1385, 1994). We have suggested that the L-selectin counter-structure is a mucinlike protein and proposed that aggregation occurs through a two-step process involving L-selectin, beta 2-integrin, and their distinct counter-structures (Bennett et al: J Leuk Biol 58:510, 1995). A candidate ligand for L-selectin is P-selectin glycoprotein ligand-1 (PSGL-1), a mucinlike protein on neutrophils that binds P-and E-selectin. Using flow cytometry we show that the number and size of neutrophil aggregates is reduced with Fab fragments of PL1, an anti-PSGL-1 monoclonal antibody that blocks the interaction between P-selectin and PSGL-1 (Moore et al: J Cell Biol 128:661, 1995). In addition, monoclonal antibodies to L-selectin and PSGL-1 were used simultaneously to modulate the availability of these adhesion molecules on individual cell populations. The inhibition of aggregation by these antibodies is consistent with L-selectin and PSGL-1 being counter-structures. We suggest that L-selectin and PSGL-1 support a collisional cell-cell interaction that represents the first step in neutrophil aggregation.