CXCL4L1-fibstatin cooperation inhibits tumor angiogenesis, lymphangiogenesis and metastasis.

Anti-angiogenic and anti-lymphangiogenic drugs slow tumor progression and dissemination. However, an important difficulty is that a tumor reacts and compensates to obtain the blood supply needed for tumor growth and lymphatic vessels to escape to distant loci. Therefore, there is a growing consensus on the requirement of multiple anti-(lymph)angiogenic molecules to stop cell invasion efficiently. Here we studied the cooperation between endogenous anti-angiogenic molecules, endostatin and fibstatin, and a chemokine, the Platelet Factor-4 variant 1, CXCL4L1. Anti-angiogenic factors were co-expressed by IRES-based bicistronic vectors and their cooperation was analyzed either by local delivery following transduction of pancreatic adenocarcinoma cells with lentivectors, or by distant delivery resulting from intramuscular administration in vivo of adeno-associated virus derived vectors followed by tumor subcutaneous injection. In this study, fibstatin and CXCL4L1 cooperate to inhibit endothelial cell proliferation, migration and tubulogenesis in vitro. No synergistic effect was found for fibstatin-endostatin combination. Importantly, we demonstrated for the first time that fibstatin and CXCL4L1 not only inhibit in vivo angiogenesis, but also lymphangiogenesis and tumor spread to the lymph nodes, whereas no beneficial effect was found on tumor growth inhibition using molecule combinations compared to molecules alone. These data reveal the synergy of CXCL4L1 and fibstatin in inhibition of tumor angiogenesis, lymphangiogenesis and metastasis and highlight the potential of IRES-based vectors to develop anti-metastasis combined gene therapies.

Translation of CUG- but not AUG-initiated forms of human fibroblast growth factor 2 is activated in transformed and stressed cells.

Four isoforms of the human fibroblast growth factor 2 (FGF-2), with different intracellular localizations and distinct effects on cell phenotype, result from alternative initiations of translation at three CUG and one AUG start codons. We showed here by Western immunoblotting and immunoprecipitation that the CUG-initiated forms of FGF-2 were synthesized in transformed cells, whereas "normal" cells almost exclusively produced the AUG-initiated form. CUG-initiated FGF-2 was induced in primary skin fibroblasts in response to heat shock and oxidative stress. In transformed cells and in stressed fibroblasts, CUG expression was dependent on cis-elements within the 5' region of FGF-2 mRNA and was not correlated to mRNA level, indicating a translational regulation. UV cross-linking experiments revealed that CUG expression was linked to the binding of several cellular proteins to FGF-2 mRNA 5' region. Since translation of FGF-2 mRNA was previously shown to occur by internal ribosome entry, a nonclassical mechanism already described for picornaviruses, the cross-linking patterns of FGF-2 and picornavirus mRNAs were compared. Comigration of several proteins, including a p60, was observed. However, this p60 was shown to be different from the p57/PTB internal entry factor, suggesting a specificity towards FGF-2 mRNA. We report here a process of translational activation of the FGF-2 CUG-initiated forms in direct relation with trans-acting factors specific to transformed and stressed cells. These data favor a critical role of CUG-initiated FGF-2 in cell transformation and in the stress response.

Alternative initiation of translation determines cytoplasmic or nuclear localization of basic fibroblast growth factor.

Three forms of basic fibroblast growth factor (bFGF), initiated at an AUG (18 kDa) and two CUG (21 and 22.5 kDa) start codons, were produced following transfection of COS cells with human hepatoma bFGF cDNA. The subcellular localization of the different forms was investigated directly or by using chimeric genes constructed by fusion of the bFGF and chloramphenicol acetyltransferase open reading frames. The AUG-initiated proteins were cytoplasmic, while the CUG-initiated forms were nuclear. The signal sequence responsible for the nuclear localization of bFGF is contained within 37 amino acid residues between the second CUG and the AUG start codons. Alternative initiation of translation regulates the subcellular localization of bFGF and thus could modulate its role in cell growth and differentiation control.

cis-acting elements involved in the alternative translation initiation process of human basic fibroblast growth factor mRNA.

Four forms of basic fibroblast growth factor (bFGF) are synthesized from the same mRNA, resulting from alternative initiations of translation at three CUG start codons and one AUG start codon. The CUG- and AUG-initiated forms have distinct intracellular localizations and can modify cell phenotypes differently, indicating that control of the alternative expression of the different forms of bFGF has an important impact on the cell. In this study, we investigated the roles of the mRNA 5' untranslated region and the alternatively translated region located between the CUG and AUG codons in the regulation of alternative translation of the different forms of bFGF. Deletions and site-directed mutagenesis were carried out in bFGF mRNA leader, and translation was studied in vitro and in vivo. The results enabled us to identify five cis-acting RNA elements (two in the 5' untranslated region and three in the alternatively translated region) involved in the regulation of either global or alternative initiation of translation. Each of these elements had a specific effect on the level of synthesis of the different forms of bFGF. Furthermore, we showed that the 5' untranslated region regulatory elements had different effects on bFGF translation, depending on the translation system used. These results suggest that bFGF translation is modulated by cis-acting elements corresponding to secondary or tertiary RNA structures, which could be the targets of cell-specific trans-acting factors.

Two independent internal ribosome entry sites are involved in translation initiation of vascular endothelial growth factor mRNA.

The mRNA of vascular endothelial growth factor (VEGF), the major angiogenic growth factor, contains an unusually long (1,038 nucleotides) and structured 5' untranslated region (UTR). According to the classical translation initiation model of ribosome scanning, such a 5' UTR is expected to be a strong translation inhibitor. In vitro and bicistronic strategies were used to show that the VEGF mRNA translation was cap independent and occurred by an internal ribosome entry process. For the first time, we demonstrate that two independent internal ribosome entry sites (IRESs) are present in this 5' UTR. IRES A is located within the 300 nucleotides upstream from the AUG start codon. RNA secondary structure prediction and site-directed mutagenesis allowed the identification of a 49-nucleotide structural domain (D4) essential to IRES A activity. UV cross-linking experiments revealed that IRES A activity was correlated with binding of a 100-kDa protein to the D4 domain. IRES B is located in the first half of the 5' UTR. An element between nucleotides 379 and 483 is required for its activity. Immunoprecipitation experiments demonstrated that a main IRES B-bound protein was the polypyrimidine tract binding protein (PTB), a well-known regulator of picornavirus IRESs. However, we showed that binding of the PTB on IRES B does not seem to be correlated with its activity. Evidence is provided of an original cumulative effect of two IRESs, probably controlled by different factors, to promote an efficient initiation of translation at the same AUG codon.

Alternative translation of human fibroblast growth factor 2 mRNA occurs by internal entry of ribosomes.

Alternative initiations of translation of the human fibroblast growth factor 2 (FGF-2) mRNA, at three CUG start codons and one AUG start codon, result in the synthesis of four isoforms of FGF-2. This process has important consequences on the fate of FGF-2: the CUG-initiated products are nuclear and their constitutive expression is able to induce cell immortalization, whereas the AUG-initiated product, mostly cytoplasmic, can generate cell transformation. Thus, the different isoforms probably have distinct targets in the cell. We show here that translation initiation of the FGF-2 mRNA breaks the rule of the cap-dependent ribosome scanning mechanism. First, translation of the FGF-2 mRNA was shown to be cap independent in vitro. This cap-independent translation required a sequence located between nucleotides (nt) 192 and 256 from the 5' end of the 318-nt-long 5' untranslated region. Second, expression of bicistronic vectors in COS-7 cells indicated that the FGF-2 mRNA is translated through a process of internal ribosome entry mediated by the mRNA leader sequence. By introducing additional AUG codons into the RNA leader sequence, we localized an internal ribosome entry site to between nt 154 and 318 of the 5' untranslated region, just upstream of the first CUG. The presence of an internal ribosome entry site in the FGF-2 mRNA suggests that the process of internal translation initiation, by controlling the expression of a growth factor, could have a crucial role in the control of cell proliferation and differentiation.

A new 34-kilodalton isoform of human fibroblast growth factor 2 is cap dependently synthesized by using a non-AUG start codon and behaves as a survival factor.

Four isoforms of human fibroblast growth factor 2 (FGF-2) result from alternative initiations of translation at three CUG start codons and one AUG start codon. Here we characterize a new 34-kDa FGF-2 isoform whose expression is initiated at a fifth initiation codon. This 34-kDa FGF-2 was identified in HeLa cells by using an N-terminal directed antibody. Its initiation codon was identified by site-directed mutagenesis as being a CUG codon located at 86 nucleotides (nt) from the FGF-2 mRNA 5' end. Both in vitro translation and COS-7 cell transfection using bicistronic RNAs demonstrated that the 34-kDa FGF-2 was exclusively expressed in a cap-dependent manner. This contrasted with the expression of the other FGF-2 isoforms of 18, 22, 22.5, and 24 kDa, which is controlled by an internal ribosome entry site (IRES). Strikingly, expression of the other FGF-2 isoforms became partly cap dependent in vitro in the presence of the 5,823-nt-long 3' untranslated region of FGF-2 mRNA. Thus, the FGF-2 mRNA can be translated both by cap-dependent and IRES-driven mechanisms, the balance between these two mechanisms modulating the ratio of the different FGF-2 isoforms. The function of the new FGF-2 was also investigated. We found that the 34-kDa FGF-2, in contrast to the other isoforms, permitted NIH 3T3 cell survival in low-serum conditions. A new arginine-rich nuclear localization sequence (NLS) in the N-terminal region of the 34-kDa FGF-2 was characterized and found to be similar to the NLS of human immunodeficiency virus type 1 Rev protein. These data suggest that the function of the 34-kDa FGF-2 is mediated by nuclear targets.

Determination of the functional domains involved in nucleolar targeting of nucleolin.

Nucleolin (713 aa), a major nucleolar protein, presents two structural domains: a N-terminus implicated in interaction with chromatin and a C-terminus containing four RNA-binding domains (RRMs) and a glycine/arginine-rich domain mainly involved in pre-rRNA packaging. Furthermore, nucleolin was shown to shuttle between cytoplasm and nucleolus. To get an insight on the nature of nuclear and nucleolar localization signals, a set of nucleolin deletion mutants in fusion with the prokaryotic chloramphenicol acetyltransferase (CAT) were constructed, and the resulting chimeric proteins were recognized by anti-CAT antibodies. First, a nuclear location signal bipartite and composed of two short basic stretches separated by eleven residues was characterized. Deletion of either motifs renders the protein cytoplasmic. Second, by deleting one or more domains implicated in nucleolin association either with DNA, RNA, or proteins, we demonstrated that nucleolar accumulation requires, in addition to the nuclear localization sequence, at least two of the five RRMs in presence or absence of N-terminus. However, in presence of only one RRM the N-terminus allowed a partial targeting of the chimeric protein to the nucleolus.

Role of fibroblast growth factor-2 isoforms in the effect of estradiol on endothelial cell migration and proliferation.

Both 17beta-estradiol (E2) and fibroblast growth factor-2 (FGF2) stimulate angiogenesis and endothelial cell migration and proliferation. The first goal of this study was to explore the potential link between this hormone and this growth factor. E2-stimulated angiogenesis in SC Matrigel plugs in Fgf2+/+ mice, but not in Fgf2-/- mice. Cell cultures from subcutaneous Matrigel plugs demonstrated that E2 increased both migration and proliferation in endothelial cells from Fgf2+/+ mice, but not from in Fgf2-/- mice. Several isoforms of fibroblast growth factor-2 (FGF2) are expressed: the low molecular weight 18-kDa protein (FGF2lmw) is secreted and activates tyrosine kinase receptors (FGFRs), whereas the high molecular weight (21 and 22 kDa) isoforms (FGF2hmw) remains intranuclear, but their role is mainly unknown. The second goal of this study was to explore the respective roles of FGF2 isoforms in the effects of E2. We thus generated mice deficient only in the FGF2lmw (Fgf2lmw-/-). E2 stimulated in vivo angiogenesis and in vitro migration in endothelial cells from Fgf2lmw-/- as it did in Fgf2+/+ mice. E2 increased FGF2hmw protein abundance in endothelial cell cultures from Fgf2+/+ and Fgf2lmw-/- mice. As shown using siRNA transfection, these effects were FGFR independent but involved FGF2-Interacting Factor, an intracellular FGF2hmw partner. This is the first report for a physiological role for the intracellular FGF2hmw found to mediate the effect of E2 on endothelial cell migration via an intracrine action.

Cell transformation results in the loss of the density-dependent translational regulation of the expression of fibroblast growth factor 2 isoforms.

Alternative initiation of translation at three CUG and one AUG start codons leads to the synthesis of four isoforms of fibroblast growth factor 2 (FGF-2) that have distinct intracellular localizations and affect the cell phenotype differently. We show here that the expression of FGF-2 CUG-initiated isoforms decreases in a cell-density-dependent manner in normal human skin fibroblasts (HSFs) concomitantly with the FGF-2 mRNA level. In contrast, CUG-initiated FGF-2 expression is constitutive in SK-HEP-1 cells and in HSFs transformed with SV40 large T antigen. Cell transfection using a plasmid containing the FGF-2 mRNA leader fused to chloramphenicol acetyl transferase demonstrated that up-regulation of the CUG codons depends on cis-elements located in this leader. Furthermore, UV cross-linking experiments revealed a correlation between CUG codons utilization and the binding of several proteins to the mRNA leader. On the basis of the presence of an internal ribosome entry site (IRES) in the FGF-2 mRNA, we used bicistronic vectors to transfect normal and transformed cells. The density-dependent regulation in normal HSFs was cap-dependent, whereas the constitutive CUG-initiated FGF-2 expression in transformed cells occurred essentially by an IRES-dependent mechanism. Unexpectedly, the use of the AUG start codon occurred exclusively by internal entry, which suggests the presence of a second independent IRES in the FGF-2 mRNA that would be constitutive. A study of the eIF-4E levels and of the 4E-BP1 phosphorylation state at increasing cell densities showed a decrease of the eIF-4E level, concomitant with 4E-BP1 dephosphorylation in normal cells but not in transformed cells. These data point out a complex mechanism for the regulation of FGF-2 isoforms expression involving both the cap-dependent and the cap-independent initiation of translation and favor a positive role of CUG-initiated FGF-2 in cellular proliferation and transformation.

Inhibition of fibroblast growth factor 2 expression by antisense RNA induced a loss of the transformed phenotype in a human hepatoma cell line.

Fibroblast growth factor 2 (FGF-2 or basic FGF) is associated with the cell-transformed phenotype. To clarify the function of FGF-2 in the malignancy of tumor cells, we designed experiments to express antisense RNA in a hepatoma cell line. Using FGF-2 mRNA, alternative initiations of translation at one AUG and three CUG start codons led to the synthesis of four isoforms. SK-Hep1 cells, which naturally produce the four FGF-2 proteins, were stably transfected with expression vectors that generate antisense RNAs targeted against different sites of human FGF-2 mRNA. A variable decrease of all of the isoforms of FGF-2 synthesis was observed compared with the control: the strongest inhibition was obtained with the smaller antisense targeted against AUG codon. Our results clearly demonstrated that inhibition of FGF-2 expression led to a loss of anchorage independence in soft agar. This effect was not reversed by adding exogenous FGF-2, indicating that an intracrine process of FGF-2 probably is involved in the phenotypic changes of SK-Hep1 cells. Furthermore, the inhibition of FGF-2 synthesis was correlated with a loss of tumorigenicity in nude mice. These results clearly argue for a key role of endogenous FGF-2 in transformation and tumorigenesis of the hepatoma cell line used in this study.

Morphological and biological modifications induced in a rat pancreatic acinar cancer cell line (AR4-2J) by unscheduled expression of basic fibroblast growth factors.

The role of the different basic fibroblast growth factor (bFGF) forms on the regulation of pancreatic acinar cancer cells was analyzed on the rat cell line AR4-2J. This cell line expresses bFGF receptors but does not produce bFGF. AR4-2J cells were retrovirally transfected with the wild type or with point-mutated bFGF complementary DNAs in order to obtain the expression of all the bFGF forms (clone A4), or of that of the M(r) 22,500 form (clone A3), or of that of the M(r) 18,000 form (clone A5). Each clone was less tumorigenic in nude mice than AR4-2J cells. In culture, only the coexpression of all the bFGF forms modified cell morphology (fibroblast-like) and secretory enzyme synthesis (about a 20-fold decrease of amylase and lipase). Cells expressing the high molecular weight bFGF (A3 and A4) were able to grow in serum-free medium. As for AR4-2J, exogenously added bFGF still exerted mitogenic effects on the bFGF-producing cells. These results suggest that pancreatic acinar cancer cells may respond to endogenous bFGF; furthermore, they seem very sensitive to the coexpression of the different bFGF forms which is often described in cancer cells.

Radioresistance induced by the high molecular forms of the basic fibroblast growth factor is associated with an increased G2 delay and a hyperphosphorylation of p34CDC2 in HeLa cells.

The basic fibroblast growth factor-(bFGF) mediated signal transduction pathway has been implicated in cellular resistance to ionizing radiation. bFGF is synthesized from the same mRNA in four isoforms resulting from alternative initiations of translation at three CUG start codons (24, 21.5, and 21 kDa) and one AUG start codon (18 kDa). We analyzed the implication of high- and low-molecular forms of bFGF in radioresistance acquisition. For this, we transfected HeLa cells with retroviral vector containing either the CUG-initiated 24-kDa molecular form (HeLa 3A cells), the AUG-initiated 18-kDa molecular bFGF form (HeLa 5A cells), or the vector alone (HeLa PINA cells). A significantly increased radioresistance was obtained only in HeLa 3A cells (Dq = 810 +/- 24 cGy) compared with wild-type cells (Dq = 253 +/- 49 cGy) or HeLa PINA cells (Dq = 256 +/- 29 cGy; P < 0.001). This radioprotective effect was independent of an inhibition of radiation-induced apoptosis but related to an increased G2 duration after irradiation and to an hyperphosphorylation of p34cdc2 kinase. Knowledge of the high-molecular bFGF form-induced radioresistance pathway could offer novel targets for decreasing the radioresistance phenotype of tumors expressing high amounts of bFGF, such as glioblastoma.

p53 directs conformational change and translation initiation blockade of human fibroblast growth factor 2 mRNA.

Tumour suppressor p53 has been shown to inhibit fibroblast growth factor 2 expression post-transcriptionally in cultured cells. Here we have investigated the mechanism responsible for this post-transcriptional blockade. Deletion mutagenesis of the FGF-2 mRNA leader revealed the requirement of at least four RNA cis-acting elements to mediate the inhibitory effect of p53 in SK-Hep-1 transfected cells, suggesting the involvement of RNA secondary or tertiary structures. Recombinant wild-type, but not Ala(143) mutant p53, was able to specifically repress FGF-2 mRNA translation in rabbit reticulocyte lysate, in a dose dependent manner. Sucrose gradient experiments showed that p53 blocks translation initiation by preventing 80S ribosome formation on an mRNA bearing the FGF-2 mRNA leader sequence. Interaction of wild-type and mutant p53 with different RNAs showed no significant correlation between p53 RNA binding activity and its translational inhibiting effect. However, by checking the accessibility of the FGF-2 mRNA leader to complementary oligonucleotide probes, we showed that the binding to RNA of wild-type, but not mutant p53, induced RNA conformational changes that might be responsible for the translational blockade. This strongly suggests that p53 represses FGF-2 mRNA translation by a direct mechanism involving its nucleic acid unwinding-annealing activity.

Tumour suppressor p53 inhibits human fibroblast growth factor 2 expression by a post-transcriptional mechanism.

Fibroblast growth factor-2 (FGF-2) is a powerful mitogen and angiogenic factor whose expression is strongly regulated at the translational level. The constitutive upregulation of FGF-2 isoforms in transformed cells prompted us to investigate the post-transcriptional effects of a tumour suppressor, p53, on FGF-2 expression. We show here in human primary skin fibroblasts that the cell density-dependent variation of FGF-2 mRNA translatability was inversely correlated with endogenous p53 expression. Transient cell transfection revealed an inhibitory effect of wild-type p53 on the expression of chimeric FGF--CAT proteins. RNAse mapping experiments ruled out any effect of p53 on FGF--CAT mRNA accumulation, suggesting a translational inhibition. This inhibition was mediated by the FGF-2 mRNA leader, but not by vascular endothelial growth factor or platelet derived growth factor mRNA leaders. Neither p53-like protein p73, nor p21/waf had any inhibitory activity. Furthermore a set of hot spot mutants of p53 bearing mutations in the DNA binding domain had no post-transcriptional inhibitory effect. In contrast a p53 mutant of the transactivating domain was still able to block FGF--CAT expression, indicating that the post-transcriptional activity of p53 described here was independent of the trans-activation of target genes. Such data reveal a novel mechanism by which p53 efficiently blocks the expression of a major proliferating, anti-apoptotic and angiogenic gene.

Antiproliferative effect of phorbol esters on MCF-7 human breast adenocarcinoma cells: relationship with enhanced expression of transforming growth-factor-beta 1.

In human breast carcinoma MCF-7 cells, phorbol diesters inhibit proliferation and induce cell maturation. We have recently reported that exogenous TGF-beta 1 reverses the resistance of a breast adenocarcinoma MCF-7 subline (MCF-7:RPh-4) to these phorbol ester effects. Here, we investigated the involvement of TGF-beta 1 in the PKC-mediated inhibition of breast-cancer cell proliferation. Parental MCF-7-conditioned medium contained a 20-fold higher transforming activity on NRK-49F fibroblasts than the TPA-resistant subline. TPA increased TGF-beta activity in MCF-7 conditioned medium. MCF-7 cells also expressed more TGF-beta 1 mRNA than the resistant subline. TPA induced a dose-dependent increase in TGF-beta 1 mRNA levels that paralleled the inhibitory effect on MCF-7 proliferation. The lower level of TGF-beta mRNA expression in TPA resistant subline was not modified after addition of TPA, but was significantly increased in the presence of exogenous TGF-beta 1. These data argue in favor of a role of endogenous TGF-beta 1 in the maturation process induced by protein kinase C activation.

New vascular endothelial growth factor isoform generated by internal ribosome entry site-driven CUG translation initiation.

We recently demonstrated that the very long 5'-untranslated region (5'-UTR) of the vascular endothelial growth factor (VEGF) mRNA contains two independent internal ribosome entry sites (IRES A and B). In the human sequence, four potential CUG translation initiation codons are located in between these IRES and are in frame with the classical AUG start codon. By in vitro translation and COS-7 cell transfections, we demonstrate that a high mol wt VEGF isoform [called large VEGF (L-VEGF)] is generated by an alternative translation initiation process, which occurs at the first of these CUG codons. Using a bicistronic strategy, we show that the upstream IRES B controls the translation initiation of L-VEGF. This isoform is 206 amino acids longer than the classical AUG-initiated form. With a specific antibody raised against this NH2 extension, we show that the L-VEGF is present in different mouse tissues or in transfected COS-7 cells. We also demonstrate that L-VEGF is cleaved into two fragments: a 23-kDa NH2-specific fragment and a fragment with an apparent size similar to that of the classical AUG-initiated form. This cleavage requires the integrity of a hydrophobic sequence located in the central part of the L-VEGF molecule. This sequence actually plays the role of signal peptide in the classical AUG-initiated form. The AUG-initiated form and the COOH cleavage product of the L-VEGF are both secreted. In contrast, the large isoform and its NH2 fragment present an intracellular localization. These data unravel a further level of complexity in the regulation of VEGF expression.

FIF [fibroblast growth factor-2 (FGF-2)-interacting-factor], a nuclear putatively antiapoptotic factor, interacts specifically with FGF-2.

Numerous evidence indicates that some of the activities of fibroblast growth factor 2 (FGF-2) depend on an intracrine mode of action. Recently, we showed that three high molecular mass (HMM) nuclear forms of FGF-2 are part of a 320-kDa protein complex while the cytoplasmic AUG-initiated form is included in a 130-kDa complex. Consequently, the characterization of FGF endogenous targets has become crucial to allow the elucidation of their endogenous activities. Through the screening of GAL4-based yeast two-hybrid expression libraries, we have isolated a gene encoding a nuclear protein of 55 kDa, FIF (FGF-2-interacting-factor), which interacts specifically with FGF-2 but not with FGF-1, FGF-3, or FGF-6. In this system, FIF interacts equally well with the NH2-extended 24-kDa FGF form as with the 18-kDa form, indicating that the FIF-binding motif is located in the last 155 amino acids of FGF-2. Nevertheless, coimmunoprecipitation experiments showed an exclusive association with HMM FGF-2. The predicted protein contains a canonical leucine zipper domain and three overlapping hydrophobic heptad repeats. The region spanning these repeats is, together with a region located in the N-terminal part of the FIF protein, implicated in the binding to FGF-2. In contrast to the full-length FIF protein, several deletion constructs were able to transactivate a lac-Z reporter gene. Furthermore, the COOH-terminal part, but not the full-length FIF protein, has previously been shown to exhibit antiapoptotic properties. Thus we discuss the possibility that these activities could reflect a physiological function of FIF through its interaction with FGF-2.

Regulation of the src homology 2 domain-containing protein tyrosine phosphatase PTP1C by glucocorticoids in rat pancreatic AR42J cells.

The effect of glucocorticoids, known to induce inhibition of growth and differentiation of pancreatic cells, has been examined on the tyrosine phosphatase containing two src homology 2 domains, PTP1C, in rat pancreatic cancer AR42J cells. Immunoblotting analysis revealed that PTP1C protein was present in AR42J cells as two PTP1C species of 66 and 31 kilodaltons (kDa), the 31-kDa species representing a proteolytic product of the larger form. Dexamethasone increased the level of the two PTP1C species by 2 to 3 times. Nearly 80% of the PTP1C molecules were found in the particulate fraction in control cells and dexamethasone did not change the distribution of PTP1C. The increase of PTP1C protein was also detected by immunohistochemical analysis. Dexamethasone increased the tyrosine phosphatase activity of immunoprecipitated PTP1C. In addition, dexamethasone raised the level of expression of PTP1C messenger RNA in a time- and dose-dependent manner in relation with its effect on cell growth and differentiation. This effect was selective, the messenger RNA levels of the other tyrosine phosphatase containing two src homology 2 domains (SH2), PTP1D, and that of the cytosolic PTP1 being not affected. This is the first report of glucocorticoid increase of PTP1C expression, suggesting that PTP1C may be involved in the glucocorticoid-mediated pancreatic cell differentiation.

Cloning of the hexA mismatch-repair gene of Streptococcus pneumoniae and identification of the product.

The hexA mismatch repair gene of Streptococcus pneumoniae has been cloned into multicopy plasmid vectors. The cloned hexA gene is expressed as judged from its ability to complement various chromosomal hexA- alleles. Its direction of transcription was defined and the functional limits were localized by original methods relying on homology-dependent integration of nonautonomous chimeric plasmids carrying chromosomal inserts into the chromosome. Comparison of the proteins encoded by recombinant plasmids and by restriction fragments allowed us to identify an Mr 94 000 protein as the probable product of the hexA gene.