Ciliary neurotrophic factor constitutively expressed in the nervous system of transgenic mice protects embryonic dorsal root ganglion neurons from apoptosis

Ciliary neurotrophic factor (CNTF) is a potent survival factor for several neuronal populations. It is expressed postnatally by Schwann cells in the peripheral nervous system and by some glial and neuronal cells in the central nervous system. We used the promoter of the neurofilament light chain gene to produce transgenic mice that express CNTF in neurons from the beginning of neuronal differentiation. These transgenic animals may represent a suitable model to identify neuronal cell types responsive to CNTF in vivo and to study the mechanism of action of this neurotrophic factor. We show that dorsal root ganglion neurons of transgenic mice expressing CNTF in neurons are protected from apoptosis during embryonic development: 40% of these cells undergo apoptosis between embryonic day 12.5 and postnatal day 5 in transgenic mice whereas 60% do so in control animals. However, protection from apoptosis does not result in an increase in the total number of neurons at the end of development. We discuss our results with regard to CNTF potentialities in vivo and the significance of programmed cell death during development.

Specific expression in brain and liver driven by the hemopexin promoter in transgenic mice

Transgenic mice harboring the human hemopexin promoter sequences linked to the lacZ reporter gene were generated and analyzed for temporal and spatial distribution of beta-galactosidase. Upstream sequences spanning from -1800, -700 and -500 bp to the transcription start point direct regulated beta-galactosidase expression specifically to the liver and to the brain of transgenic mice. These results suggest that the 500 bp DNA fragment flanking the 5'end of the human hemopexin gene contains the cis-acting elements required for tissue and developmental stage-specific expression in vivo and provide evidence for a new extrahepatic site of expression of the hemopexin gene.

Analysis of regulatory regions of the ciliary neutrophic factor gene in transgenic mice

In order to study the regulatory regions of the human ciliary neurotrophic factor (CNTF) gene we made constructs containing sequences upstream and downstream of CNTF coding regions and the lacZ gene and analysed their expression in transgenic mice. We show that 240 bp upstream of the translation start codon are sufficient for the transcription of the lacZ gene. A further 4 kb upstream sequence is required for the expression of the transgene in Schwann cells. These two upstream regions together with a 2 kb downstream fragment drive high level of expression of the lacZ gene in the sciatic nerve. Our results indicate that these three fragments contain regulatory regions able to mimic the CNTF expression pattern in the mouse peripheral nervous system.

p125FAK tyrosine phosphorylation and focal adhesion assembly: studies with phosphotyrosine phosphatase inhibitors

p125FAK is a major tyrosine kinase phosphorylated in response to integrin-dependent adhesion. In this study we use vanadate and phenylarsine oxide (PAO), known inhibitors of phosphotyrosine phosphatases (PTPases), as a tool to artificially modulate p125FAK phosphorylation in human endothelial and in Chinese hamster ovary cells. Vanadate treatment strongly upregulates in a dose-dependent manner the level of tyrosine phosphorylation of several proteins in adherent cells. PAO induces a more restricted profile of tyrosine-phosphorylated proteins, increasing primarily a broad band of 120-140 kDa. Maximal stimulation of p125FAK tyrosine phosphorylation is reached at 10 microM PAO. In contrast, in vanadate-treated cells the p125FAK tyrosine phosphorylation shows a biphasic curve, being increased at high doses of vanadate (100 microM) and downregulated at low doses (25 microM). Immunofluorescence analysis of cells treated with PTPase inhibitors showed a direct correlation between the level of p125FAK tyrosine phosphorylation and the assembly of focal adhesions and actin stress fibers. Downregulation of p125FAK tyrosine phosphorylation is observed by treating cells with cytochalasin D (CD), a drug known to rapidly disrupt the actin cytoskeleton. When PTPase inhibitors are added in combination to CD, the level of tyrosine phosphorylation of p125FAK remains high and focal adhesions and actin stress fibers are preserved from the CD-mediated disruption. Based on these data we suggest that assembly of actin cytoskeleton plays an important role in inhibiting PTPases involved in p125FAK tyrosine phosphorylation.

DNA neosynthesis in Auerbach plexus ganglia isolated from the rat hypertrophic gut: an electrophoretic analysis

We analysed using electrophoresis the total genomic DNA extracted from isolated Auerbach plexus ganglia of the hypertrophic duodenum upstream from a partial experimental stenosis. Results indicated the presence of two extra-bands migrating below the high molecular weight DNA. suggesting that DNA amplification is the basic mechanism of the DNA neosynthesis previously observed in myenteric neurons.

Ciliary neurotrophic factor-induced gene expression in human neuroblastoma cell lines

We have analyzed the response of the human neuroblastoma cell lines SK-N-SH (clone SY5Y) and SK-N-BE to the ciliary neurotrophic factor CNTF. In both cell lines CNTF induced the expression of the mRNA for two transcription factors, c-fos and NGF1A. The induction was rapid and transient reaching a maximum between 30 and 60 min after exposure to CNTF and subsequently declining. The level of induction of both c-fos and NGF1A mRNAs was much higher in SK-N-BE neuroblastoma cells compared to the SY5Y. Both cells express comparable levels of the transcript for the CNTF receptor-alpha. This mRNA was down regulated after 5 days of CNTF stimulation in both cell lines. CNTF also induced increased levels of the transcript for the growth cone associated protein GAP43 in SK-N-BE, but not in SY5Y cells. Induction followed a slower kinetic compared to that observed for c-fos and NGF1A. In fact, the GAP43 mRNA levels increased during 2 days of exposure to CNTF. Morphological analysis of CNTF treated cells showed that SK-N-BE undergo significant differentiation in response to CNTF (increased number of cells with neurites and increased neurite length) while SY5Y did not show appreciable morphological differentiation. These data shows that CNTF may elicit different response in neuroblastoma cell lines.

Expression of beta 1B integrin isoform in CHO cells results in a dominant negative effect on cell adhesion and motility

The integrin subunit beta 1B, a beta 1 isoform with a unique sequence at the cytoplasmic domain, forms heterodimers with integrin alpha chains and binds fibronectin, but it does not localize to focal adhesion sites (Balzac, F., A. Belkin, V. Koteliansky, Y. Balabanow, F. Altruda, L. Silengo, and G. Tarone. 1993. J. Cell Biol. 121:171-178). Here we analyze the functional properties of human beta 1B by expressing it in hamster CHO cells. When stimulated by specific antibodies, beta 1B does not trigger tyrosine phosphorylation of a 125-kD cytosolic protein, an intracellular signalling pathway that is activated both by the endogenous hamster or the transfected human beta 1A. Moreover, expression of beta 1B results in reduced spreading on fibronectin and laminin, but not on vitronectin. Expression of beta 1B also results in severe reduction of cell motility in the Boyden chamber assay. Reduced cell spreading and motility could not be accounted for by preferential association of beta 1B with a given integrin alpha subunit. These data, together with our previous results, indicate that beta 1B interferes with beta 1A function when expressed in CHO cells resulting in a dominant negative effect on cell adhesion and migration.

Alpha v integrin subunit is predominantly located in nervous tissue and skeletal muscle during mouse development

Alpha v integrin subunit can dimerize with different beta subunits to form receptors for several matrix proteins. The function of these receptors in vivo is still largely unknown. We examined the localization of alpha v integrin during mouse development and showed that its distribution is dynamically regulated in the glia of the central nervous system and in skeletal muscle. Immunoreactivity in the neural tube was firstly localized at embryonic day 10.5 (E10.5) around cell bodies lining the lumen and along tiny fibres extending towards the outer margin. At E12.5 alpha v distribution follows the highly defined pattern of the radial glia: fascicles of immunoreactive fibres form parallel palisades, in particular along the hindbrain and the spinal cord. At E15.5, although with weaker intensity, alpha v was still detectable in radial glia fibres, and it codistributed with glial fibrillary acidic protein positive fascicles. After birth (P8) alpha v immunoreactivity in the brain and spinal cord decreased dramatically, but remained high in the radial glia of the cerebellum. In adult mice alpha v reactivity in the central nervous system disappeared. During myogenesis alpha v appears at E10.5 in myotomal cells and from E12.5 alpha v was evident in myoblasts and in myotubes. In the developing skeletal muscle of E15.5 embryos, immunoreactivity became more concentrated in the apical portion of the myotubes. In adult striated muscle the amount of alpha v subunit dramatically declined and immunostaining was no longer detectable. During development, alpha v was weakly evident in other sites including heart and endothelia of blood vessels, mesonephric tubula, smooth muscle of the digestive tract, and bronchia. Comparative analysis of the localization of alpha v, alpha 3, and alpha 5 integrin subunits indicated that alpha v has a unique and highly regulated distribution pattern. The distribution in the nervous system is consistent with a role of alpha v in neuron-glia interaction during the organization of the neuronal layers in the brain cortex and in the cerebellum. Moreover, alpha v is likely to be involved in the myotendinous junction during embryonic life, suggesting a dual functional role of this integrin in muscle and nervous tissue.

Role of tyrosine phosphorylation in matrix-induced neurite outgrowth in human neuroblastoma cells

Adhesion of human neuroblastoma cells (SK-N-SH clone SY5Y) to laminin or collagen type IV promotes tyrosine phosphorylation of a group of proteins with molecular mass ranging from 100 to 130 kDa and of a protein of 180 kDa. The same pattern of tyrosine phosphorylation was observed when SY5Y cells were allowed to adhere to culture dishes coated with monoclonal antibodies directed to the integrin subunits expressed in the cells, alpha 1, alpha 3, and beta 1, indicating that these receptors are responsible for this signaling mechanism. Using specific antibodies we identified the focal adhesion kinase p125FAK as a component of the 100- to 130-kDa phosphoproteins. Treatment with genistein or herbimycin A, two specific tyrosine kinase inhibitors, greatly reduced the tyrosine phosphorylation of the 100- to 130- and the 180-kDa proteins in response to laminin or collagen IV. Concomitantly, neurite outgrowth on the matrix proteins was strongly inhibited. This effect was observed in two distinct neuroblastoma cell lines, SY5Y and SK-N-BE. Genistein and herbimycin A treatment did not affect cell viability nor cause retraction of preformed neurites. These data suggest that matrix-induced tyrosine phosphorylation events are involved in neurite extension.

Integrin-mediated signal transduction in human endothelial cells: analysis of tyrosine phosphorylation events

Adhesion of human umbilical endothelial cells to fibronectin resulted in increased tyrosine phosphorylation of a group of proteins with molecular mass ranging from 100 to 130 kDa and of a 70 kDa protein. This pattern of tyrosine phosphorylation was also observed when endothelial cells adhered to vitronectin, collagen IV, collagen I and laminin or to culture dishes coated with antibodies directed to either beta 1, alpha 3, alpha 5, alpha 6 or beta 3 integrin subunits. Increased phosphorylation of the 100-130 kDa proteins was detectable as early as 30 sec after adhesion, reached maximal level after 15 min, and remained high as long as the cells adhere to culture dishes. The 70 kDa protein was phosphorylated with a slower kinetics and its phosphorylation increased over a period of 3 h. Using specific monoclonal antibodies, the major component of the 100-130 kDa complex was identified as the focal adhesion tyrosine kinase p125FAK. The phosphorylation of the p125FAK was also observed by inducing beta 1 integrin clustering in non adherent HEC, indicating that this is a primary signalling event induced by integrins. Using tyrosine kinase inhibitors, we show a direct correlation between integrin-stimulated tyrosine kinases and assembly of focal adhesions and actin fibres.

The beta 1 integrin distal promoter is developmentally regulated in transgenic mice

Transgenic mice harbouring 5' flanking sequences of the human beta 1 integrin gene linked to the Escherichia coli lacZ gene have been generated to examine spatial and temporal distribution of the promoter activity during development. Our previous data showed that this regulatory region is composed by two promoters, called distal and proximal, located closely on the human genome. To determine the role of each promoter region during development we generated transgenic mice using these two sequences linked to the lacZ reporter gene. Their analysis shows that these two sequences, as determined by in vitro studies, have different efficiencies in promoting transcription. Actually mice carrying the proximal promoter region exhibit a weak lacZ expression resulting in an undetectable beta-galactosidase activity in both embryonic and adult tissues. On the other hand, transgenic mice carrying the distal promoter express beta-galactosidase at high efficiency during embryonic development. The pattern of transgene expression is consistent with the localization of beta 1 protein on mouse embryos evidenced by immunohistochemistry. Moreover the distal promoter is subjected to a temporal modulation since in adult transgenic mice lacZ expression decreases to a level detected only by RT-PCR analysis. We have determined a similar down-regulation analysing by Northern blot beta 1 mRNA in adult and embryonic organs such as heart and gut.

Expression of beta 1 integrin complexes on the surface of unfertilized mouse oocyte

Integrins are a family of cell surface receptors that mediate cell-cell and cell-matrix interactions in a variety of different cellular systems. Here we show that unfertilized mouse oocytes express beta 1 class integrins both at mRNA and protein levels. Using the reverse transcription polymerase chain reaction and oligonucleotide primers based on the DNA sequence of mouse integrins, the RNA transcripts for the beta 1, alpha 5 and alpha 6 subunits were detected in unfertilized oocytes. The expression of the mRNAs is paralleled by the expression of the corresponding proteins, in fact, the alpha 5/beta 1 and the alpha 6/beta 1 complexes can be immunoprecipitated with specific antibodies form 125I-surface-labeled oocytes. Using subunit-specific antibodies we also demonstrate the presence of the alpha 3/beta 1 at the oocyte surface but alpha 1, alpha 2, alpha 4 or alpha V subunits were not detectable. Since the mouse alpha 3 DNA sequence is not available, we have not tested for the corresponding transcript. Integrin subunits alpha 6 and beta 1 were differently distributed on the oocyte surface, as visualized by immunofluorescence staining and by immunoelectron microscopy. alpha 6 antigen was mainly confined to the microvillous area of the oocyte surface, while beta 1 was more homogeneously distributed over the whole oolemma. These data demonstrate for the first time the expression of three beta 1 integrin complexes in unfertilized mouse oocytes. Such proteins may have a role in sperm-egg interaction or during very early steps of embryogenesis.

Expression and functional analysis of a cytoplasmic domain variant of the beta 1 integrin subunit

We have previously described a variant form of the integrin beta 1 subunit (beta 1B)1 characterized by an altered sequence at the cytoplasmic domain. Using polyclonal antibodies to a synthetic peptide corresponding to the unique sequence of the beta 1B, we analyzed the expression of this molecule in human tissues and cultured cells. Western blot analysis showed that the beta 1B is expressed in skin and liver and, in lower amounts, in skeletal and cardiac muscles. The protein was not detectable in brain, kidney, and smooth muscle. In vitro cultured keratinocytes and hepatoma cells are positive, but fibroblasts, endothelial cells, and smooth muscle cells are negative. An astrocytoma cell line derived from immortalized fetal astrocytes was found to express beta 1B. In these cells beta 1B represent integral of 30% of the beta 1 and form heterodimers with alpha 1 and alpha 5 subunits. To investigate the functional properties of beta 1B, the full-length cDNA coding for this molecule was transfected into CHO cells. Stable transfectants were selected and the beta 1B was identified by a mAb that discriminate between the transfected human protein and the endogenous hamster beta 1A. Immunoprecipitation experiments indicated that the beta 1B was exported at the cell surface in association with the endogenous hamster alpha subunits. The alpha 5/beta 1B complex bound to a fibronectin-affinity matrix and was specifically released by RGD-containing peptides. Thus beta 1B and beta 1A are similar as far as the alpha/beta association and fibronectin binding are concerned. The two proteins differ, however, in their subcellular localization. Immunofluorescence studies indicated, in fact, that beta 1B, in contrast to beta 1A, does not localize in focal adhesions. The restricted tissue distribution and the distinct subcellular localization, suggest that beta 1B has unique functional properties.

Human beta 1-integrin gene expression is regulated by two promoter regions

We report the cloning of two full-length cDNAs coding for the human beta 1-integrin which diverge from each other for their 5'-untranslated sequences. Characterization of a genomic clone containing these two sequences showed that they are contiguous, spaced by 261 nucleotides, and both followed by donor splice sites. Analysis by primer extension and transient transfection in a human osteogenic sarcoma cell line (MG-63) demonstrated the existence of two independent promoters for transcription initiation. The two promoter regions are very G+C-rich, and lack both a TATA box and a CAAT box. Northern blot analysis showed that transcripts starting from the distal promoter (with respect to the first coding exon) are at least 20-fold more abundant than transcripts originating from the proximal one. The levels of both transcripts increase after transforming growth factor-beta 1 induction, however, mRNAs originating from the proximal promoter increase at an higher extent. Reverse transcriptase/polymerase chain reaction analysis performed on different human tissues and cell lines revealed that, while the distal promoter is ubiquitously active, the proximal promoter is not. These findings suggest a possible complex pattern for regulation of the human beta 1-integrin gene expression.

Alpha 6.beta 1 integrin (laminin receptor) is down-regulated by tumor necrosis factor alpha and interleukin-1 beta in human endothelial cells

Endothelial cells from human umbilical vein (HEC) express several distinct integrin complexes that mediate the interaction with the basal membrane components. In this paper we show that treatment with tumor necrosis factor alpha (TNF alpha) down-regulates the expression of the laminin receptor alpha 6.beta 1 integrin in cultured HEC. After 48 h of treatment with TNF alpha, the level of expression of the alpha 6.beta 1 complex reached 20% of the control value. The down-regulation of the alpha 6.beta 1 integrin is caused by a decreased expression of the alpha 6 subunit, whereas the synthesis of the beta 1 subunit remains constant. Northern blot analysis shows that the decreased level of alpha 6 subunit synthesis is caused by down-regulation of alpha 6 mRNA in TNF alpha-treated HEC. TNF alpha treatment does not alter the expression of alpha 2, alpha 3, and alpha 5 integrins, also present on endothelial cell surface, thus showing that this cytokine has a selective action on distinct integrin complexes. Down-regulation of alpha 6.beta 1 correlates with pronounced reduction in adhesion of TNF alpha-treated HEC to laminin, but not to fibronectin-coated culture dishes. In addition to TNF alpha, interleukin-1 beta also decreases the expression of the alpha 6.beta 1 integrin and reduces adhesion to laminin, thus suggesting that this regulation plays an important role in inflammation.

A recombinant human 'mini'-hexokinase is catalytically active and regulated by hexose 6-phosphates

Mammalian hexokinase type I is a 100 kDa enzyme that has been considered to be evolved from an ancestral 50 kDa yeast-type hexokinase, insensitive to product inhibition, by gene duplication and fusion. According to this model, and based on many experimental data, the catalytic site is associated with the C-terminal half of the enzyme, although an allosteric site for the binding of glucose 6-phosphate could be present on the N-terminal half of the molecule. We have isolated a cDNA clone of hexokinase from a lambda gt11 human placenta library comprising 2658 bp, containing a single open reading frame of 1893 nucleotides, which encodes a truncate form of hexokinase starting from asparagine-287 to the terminal serine-917. This clone was further digested with restriction enzyme NcoI to obtain almost only the C-terminal half of human hexokinase starting from methionine-455 to the terminal amino acid and was overexpressed in active form in Escherichia coli and purified by ion-exchange h.p.l.c. The overexpressed 'mini'-hexokinase was found not only to catalyse glucose phosphorylation, but also to be inhibited by glucose 6-phosphate and other mono- and bis-phosphate sugars exactly like the complete mammalian enzyme. These results suggest that the C-terminal half of human hexokinase, in addition to the catalytic site, also contains the regulatory site and that the evolutionary relationship between the hexokinases should be reconsidered by including the appearance of a regulatory site before the gene duplication.

Mapping of human hexokinase 1 gene to 10q11----qter

Two partial-length cDNAs encoding the type 1 human hexokinase (ATP:D-hexose 6-phosphotransferase) were isolated from a placenta cDNA library using a 50-bp oligonucleotide synthesized according to the known sequence of human HK1. Using the larger (1.8 kb) cDNA insert as a probe and a panel of human-hamster somatic cell hybrids, we were able to assign the HK1 gene to the long arm of chromosome 10.

Electrophoretic analysis of neuronal genomic DNA from hypertrophic spinal ganglia during lizard tail regeneration

Cytoplasmic and nuclear hypertrophy in neurons from the last 3 pairs of sensory ganglia left in situ cranially to the plane of amputation occurs during lizard tail regeneration. Cytophotometry after Feulgen staining demonstrated the presence of some neurons, from hypertrophic ganglia, whose quantity of DNA exceeded the diploid level (hyperdiploid neurons). In the present work agarose gel electrophoresis of total genomic DNA extracted from hypertrophic ganglia showed one or two bands migrating below the high molecular weight DNA, pointing to a selective amplification of discrete DNA segments.

Up-regulation of the integrin alpha 1/beta 1 in human neuroblastoma cells differentiated by retinoic acid: correlation with increased neurite outgrowth response to laminin

Retinoic acid (RA) is known to induce differentiation of neuroblastoma cells in vitro. Here we show that treatment of two human neuroblastoma cell lines, SY5Y and IMR32, with RA resulted in a fivefold increase of the integrin alpha 1/beta 1 expression. The effect was selective because expression of the alpha 3/beta 1 integrin, also present in these cells, was not increased. The up-regulation of the alpha 1/beta 1 differentiated SY5Y cells correlated with increased neurite response to laminin. In fact, RA-treated SY5Y cells elongated neurites on laminin-coated substratum more efficiently compared with untreated cells or cells treated with nerve growth factor, insulin, or phorbol 12-myristate 13-acetate. These three agents induced partial morphological differentiation but did not increase alpha 1 integrin expression. Neurite extension in RA-treated cells was more efficient on laminin than on fibronectin or collagen type I and was inhibited with beta 1 integrin antibodies on all three substrates. Affinity chromatography experiments showed that alpha 1/beta 1 is the major laminin receptor in both untreated and RA-treated SY5Y cells. These data show that RA, a naturally occurring morphogen implicated in embryonic development, can selectively regulate the expression of integrin complexes in neuronal cells and suggest an important role of the alpha 1/beta 1 laminin receptor in the morphological differentiation of nerve cells.

Cloning and expression of a new human polypeptide which regulates protein phosphorylation in Escherichia coli

A 1,820 bp full-length clone encoding for a new human protein was isolated from a lambda gt11 placental cDNA library using anti-human hexokinase antibodies. The cDNA complete sequence includes a 12 bp 5' non-coding region, a single open reading frame encoding a protein of 55 KDa (HP-10) and a 177 bp non-coding with two putative polyadenylation signals upstream of 3' poly(A)tail. The deduced amino acid sequence reveals a sequence of 492 amino acids that contains a stretch of 7 glutamic acid from position 169 and one potential glycosylation site at position 274. Although antibodies against hexokinase recognize the fusion protein and antibodies against the fusion protein recognize hexokinase, HP-10 is not human hexokinase, by a number of criteria including the alignment of determined amino acid sequences. In searching for a possible functional role of HP-10 its cDNA was inserted into a procaryotic vector which allows the expression of the non-fused protein. Bacteria expressing the HP-10 encoded protein were isolated and found to have a dramatic increase in endogenous phosphorylated proteins. Since HP-10 does not have a protein kinase activity per se it should be considered a new regulatory phosphorylation protein which is active in E. coli.

Cloning and expression of human ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a survival factor for avian ciliary ganglion neurons and a variety of other neuronal cell types in vitro. We report here the cloning of the entire genomic sequence encoding human CNTF and its primary structure. Biologically active CNTF has been expressed in Chinese hamster ovary cells from a human genomic DNA clone. Human CNTF has no significant sequence similarity to any previously reported protein, although approximately 84% similarity exists compared with rat and rabbit CNTF. The lack of both an N-terminal signal sequence and consensus sequences for glycosylation or hydrophobic regions, and the fact that active CNTF is expressed but not released into the culture medium of transfected cells, argue in favour of human CNTF as a cytosolic protein. These data provide a basis for understanding the role of CNTF in nervous system physiology and pathology.

Differential distribution and modulation of expression of alpha 1/beta 1 integrin on human endothelial cells

In this paper we report that the integrin complex alpha 1/beta 1, a laminin/collagen receptor, is expressed on cultured foreskin microvascular endothelium, but is absent on endothelial cells from large vessels such as the aorta and umbilical and femoral veins. The restricted expression of integrin alpha 1/beta 1 to microvascular endothelium was also demonstrated in vivo, by immunohistochemical staining of human tissue sections. Alpha 1 specific antibodies reacted strongly with endothelial cells of small blood vessels and capillaries in several tissues, but not with endothelium of vein and arteries of umbilical cord. Expression of integrin alpha 1 can be induced in cultured umbilical vein endothelial cells by treatment with 5 ng/ml tumor necrosis factor alpha (TNF alpha). Induction of alpha 1 subunit expression also occurred after treatment of umbilical vein endothelium with 10(-5) M retinoic acid or with 10 nM PMA; Maximal induction of alpha 1 integrin was reached after 48 h of treatment and costimulation with TNF alpha and PMA resulted in a synergistic effect. The induction of alpha 1 integrin changed the adhesive properties of umbilical vein endothelial cells, by increasing the adhesiveness to collagen, laminin, and laminin fragment P1, while adhesion to fibronectin and laminin fragment E8 remained constant. The alpha 1 integrin is thus a marker of a specific population of endothelial cells and its expression confers distinctive properties of interaction with the underlying basal membrane.