Alpha 6 integrin is up-regulated in step increments accompanying neoplastic transformation and tumorigenic conversion of human fibroblasts

Integrins are a family of transmembrane glycoproteins that serve as cell-cell and cell-substratum adhesion molecules and help regulate cellular differentiation and proliferation. In malignant cells, which exhibit abnormal differentiation and growth properties, the expression of an altered integrin repertoire could therefore be expected. From a tumorigenic human fibrosarcoma cell line we isolated a unique complementary DNA corresponding to the alpha 6 integrin subunit. Northern blot analysis using this complementary DNA as probe indicated that alpha 6 integrin mRNA was abundantly expressed in all neoplastically transformed fibroblast cell lines but not in normal diploid fibroblasts. In addition to its potential as a marker for the neoplastic transformation of human fibroblasts, the alpha 6 integrin mRNA was also found to be consistently expressed at higher levels in tumorigenic fibroblasts than in immortalized but nontumorigenic fibroblasts. This differential expression of alpha 6 integrin was reflected at the cell surface protein level using cytofluorometric analysis with specific monoclonal antibody. In contrast, the levels of cell surface expression of other integrins were unchanged (such as alpha 3 and beta 1) or down-regulated (such as alpha 5) when transformed cells were compared with normal fibroblasts. The incremental up-regulation of alpha 6 integrin was selective and paralleled the progression of normal cells to immortalized cells and finally to tumorigenic cells. This elevated alpha 6 subunit associated with the beta 1 subunit to form a heterodimer receptor for laminin. Since fibrosarcoma cell invasion of basement membrane has been shown to involve alpha 6 beta 1 integrin, then the induction or up-regulation of alpha 6 expression is an important step in tumor progression and evolution to the invasive phenotype in fibrosarcoma.

Inhibition by the serotonin1A agonist, 8-hydroxy-2- (di-n-propylamino)tetralin, of antidromically identified paraventricular nucleus neurons in the rat

Experiments were performed using urethane-anesthetized rats to delineate the role of serotonin (5-hydroxytryptamine, 5-HT) receptors of the 5-HT1A subtype in the neural regulation of hypothalamo-pituitary-adrenocortical (HPA) secretion. The activity of single paraventricular nucleus (PVN) neurons antidromically identified as projecting to the median eminence was recorded following injection of the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Intraperitoneal administration of increasing doses of 8-OH-DPAT caused dose-dependent decreases in the spontaneous activity of all neurons tested. The data yielded an ED50 value of 0.19 mumol/kg for this effect. The decreases in PVN neuronal activity were accompanied by sustained decreases in mean arterial blood pressure, with an ED50 of 0.18 mumol/kg. These results provide evidence for an inhibitory role of 5-HT1A receptors in the regulation of PVN neuronal activity and support the suggestion that 5-HT may inhibit HPA secretory activity.

[Study on degradation of phenols in water]

The degradation of phenols in water and the effects of microbiolism, pH and dissolved oxygen (DO) on the degradation were investigated. The results showed that the degradation of phenols in water was mainly that of biochemistry, which depends on the existence of microbiolism. The most suitable pH for the degradation was 6 to 9, and no effects of DO on it were found. The accustomization of microbiolism with phenols would accelerate the degradation.

Lectin-like inhibition of immune complex receptor-mediated stimulation of neutrophils. Effects on cytosolic calcium release and superoxide production

We have tested the role of lectin-like interactions, with particular emphasis on CR3, in insoluble immune complex (IC)-mediated activation of human polymorphonuclear leukocytes (PMN). The ability of IC to trigger intracellular Ca2+ release and O2- production by normal PMN, saccharide-treated cells, and CR3-deficient PMN (leukocyte adhesion deficiency, LAD, patients) were tested. When indo-1-labeled normal PMN were stimulated with IC in Ca(2+)-free buffer, intracellular Ca2+ rose from approximately 100 nM to approximately 230 nM. However, when LAD PMN were tested, a small rise in intracellular Ca2+ was observed. Because previous studies have shown that certain saccharides inhibit CR3-Fc gamma RIII co-capping, we tested a panel of saccharides to determine their ability to influence IC-mediated intracellular Ca2+ release. When normal PMN were exposed to 0.15 M N-acetyl-D-glucosamine (NADG), D-mannose, or alpha-methyl-mannoside, the Ca2+ response to IC was significantly reduced. However, addition of 0.15 M glucose, raffinose, sucrose, galactose, fructose, or sorbitol did not significantly affect the Ca2+ response, suggesting that the response was specific for certain saccharides. To test the physiologic consequences of these Ca2+ signals, we have examined the ability of saccharides to influence O2- production by normal PMN and the ability of LAD PMN to produce O2- upon triggering by IC. Normal PMN stimulated with IC generated 4.3 +/- 1.7 nmol/10(6) cells/30 min of O2-. In contrast, O2- production was inhibited by 0 to 20% by glucose, galactose, sucrose, sorbitol, fructose, and raffinose and > or = 50% by NADG and mannose. LAD PMN, which display diminished Ca2+ signals, were found to produce O2- at 47 +/- 6% of control levels. NADG and mannose dose-response studies indicated that they cooperatively block O2-.

Lectin-like inhibition of immune complex receptor-mediated stimulation of neutrophils. Effects on cytosolic calcium release and superoxide production

We have tested the role of lectin-like interactions, with particular emphasis on CR3, in insoluble immune complex (IC)-mediated activation of human polymorphonuclear leukocytes (PMN). The ability of IC to trigger intracellular Ca2+ release and O2- production by normal PMN, saccharide-treated cells, and CR3-deficient PMN (leukocyte adhesion deficiency, LAD, patients) were tested. When indo-1-labeled normal PMN were stimulated with IC in Ca(2+)-free buffer, intracellular Ca2+ rose from approximately 100 nM to approximately 230 nM. However, when LAD PMN were tested, a small rise in intracellular Ca2+ was observed. Because previous studies have shown that certain saccharides inhibit CR3-Fc gamma RIII co-capping, we tested a panel of saccharides to determine their ability to influence IC-mediated intracellular Ca2+ release. When normal PMN were exposed to 0.15 M N-acetyl-D-glucosamine (NADG), D-mannose, or alpha-methyl-mannoside, the Ca2+ response to IC was significantly reduced. However, addition of 0.15 M glucose, raffinose, sucrose, galactose, fructose, or sorbitol did not significantly affect the Ca2+ response, suggesting that the response was specific for certain saccharides. To test the physiologic consequences of these Ca2+ signals, we have examined the ability of saccharides to influence O2- production by normal PMN and the ability of LAD PMN to produce O2- upon triggering by IC. Normal PMN stimulated with IC generated 4.3 +/- 1.7 nmol/10(6) cells/30 min of O2-. In contrast, O2- production was inhibited by 0 to 20% by glucose, galactose, sucrose, sorbitol, fructose, and raffinose and > or = 50% by NADG and mannose. LAD PMN, which display diminished Ca2+ signals, were found to produce O2- at 47 +/- 6% of control levels. NADG and mannose dose-response studies indicated that they cooperatively block O2-.

Ribonuclease III cleavage of a bacteriophage T7 processing signal. Divalent cation specificity, and specific anion effects

Escherichia coli ribonuclease III, purified to homogeneity from an overexpressing bacterial strain, exhibits a high catalytic efficiency and thermostable processing activity in vitro. The RNase III-catalyzed cleavage of a 47 nucleotide substrate (R1.1 RNA), based on the bacteriophage T7 R1.1 processing signal, follows substrate saturation kinetics, with a Km of 0.26 microM, and kcat of 7.7 min.-1 (37 degrees C, in buffer containing 250 mM potassium glutamate and 10 mM MgCl2). Mn2+ and Co2+ can support the enzymatic cleavage of the R1.1 RNA canonical site, and both metal ions exhibit concentration dependences similar to that of Mg2+. Mn2+ and Co2+ in addition promote enzymatic cleavage of a secondary site in R1.1 RNA, which is proposed to result from the altered hydrolytic activity of the metalloenzyme (RNase III 'star' activity), exhibiting a broadened cleavage specificity. Neither Ca2+ nor Zn2+ support RNase III processing, and Zn2+ moreover inhibits the Mg(2+)-dependent enzymatic reaction without blocking substrate binding. RNase III does not require monovalent salt for processing activity; however, the in vitro reactivity pattern is influenced by the monovalent salt concentration, as well as type of anion. First, R1.1 RNA secondary site cleavage increases as the salt concentration is lowered, perhaps reflecting enhanced enzyme binding to substrate. Second, the substitution of glutamate anion for chloride anion extends the salt concentration range within which efficient processing occurs. Third, fluoride anion inhibits RNase III-catalyzed cleavage, by a mechanism which does not involve inhibition of substrate binding.

Increased levels of p21ras-GTP and enhanced DNA synthesis accompany elevated tyrosyl phosphorylation of GAP-associated proteins, p190 and p62, in c-src overexpressors

While examining the role of pp60c-src in cellular proliferation, we found that overexpression of c-src in C3H10T1/2 murine fibroblasts results in an augmented mitogenic response to epidermal growth factor (EGF) [Luttrell, D.K., Luttrell, L.M. & Parsons, S.J. (1988). Mol. Cell. Biol., 8, 497-501; Wilson, L.K., Luttrell, D.K., Parsons, S.J. (1989). Mol. Cell. Biol., 9, 1536-1544] and enhanced tyrosyl phosphorylation of specific cellular proteins [Wilson, L.K. & Parsons, S.J. (1990). 5, 1471-1480]. Here we identify two of these proteins as the GAP (GTPase-activating protein of p21ras)-associated proteins, p190 and p62. Evidence is presented to support the notion that, in 10T1/2 fibroblasts, p190 is a preferred substrate of pp60c-src, while p62 is preferentially phosphorylated by the EGF receptor. First, the phosphotyrosine content of p190 in quiescent cells is three- to fivefold higher in c-src overexpressors than in control cells and is not altered by growth factor treatment. In contrast, tyrosyl phosphorylation of p62 is undetectable in quiescent cells and transiently observable upon EGF addition. Second, the phosphotyrosine content of p190 in cells overexpressing defective pp60c-src is reduced in comparison with wild-type (wt) c-src overexpressors, while that of p62 is significantly less affected. Further studies revealed that tyrosyl phosphorylation of p190 and p62 is not required for GAP complex formation, as equal amounts of p190 and p62 proteins could be detected in GAP complexes from wt and variant c-src overexpressors both before and after EGF stimulation. However, analysis of GTP-bound p21ras revealed higher basal and EGF-stimulated levels in c-src overexpressors than in control cells. Taken together, these results suggest that one mechanism by which pp60c-src may contribute to early events in the EGF-induced mitogenic pathway in 10T1/2 fibroblasts is by increasing the level of GAP-associated p190 and p62 tyrosyl phosphorylation, which in turn results in higher levels of p21ras-GTP.

Effects of estrogen and epidermal growth factor on prolactin and Pit-1 mRNA in GH3 cells

The effects of epidermal growth factor (EGF) and 17 beta-estradiol (E2) on the expression of prolactin (PRL), the transcription factor Pit-1/GHF-1 (Pit-1), and on dopamine D2 receptor mRNA in GH3 cells were analyzed by immunocytochemistry, in situ hybridization, and Northern analysis in a defined serum-free cell culture medium. Radioimmunoassay was used to determine PRL secretion. Both EGF and E2 stimulated PRL mRNA and PRL secretion, although the effects of EGF were more rapid than those of E2. Pit-1 mRNA levels were not significantly changed in spite of the 2- to 8-fold increases in PRL mRNA levels and significant increases in PRL secretion. Analysis of dopamine D2 receptor mRNA by in situ hybridization and Northern hybridization detected expression of dopamine receptor in GH3 cells, but the receptor mRNA levels were not modified by EGF or E2 treatment in complete serum or in serum-free media. These observations suggest that EGF and E2 modulate PRL mRNA levels and PRL secretion significantly in vitro, while the mRNA levels of Pit-1 do not change significantly in GH3 cells cultured in a defined culture medium.

The role of integrin adhesion receptors in gingival wound healing

Integrins, a family of cell adhesion receptors, play an important part in wound healing. These complex macromolecules are defined, and their roles explored.

Isolation of multiple mouse cDNAs with coding homology to Saccharomyces cerevisiae CDC25: identification of a region related to Bcr, Vav, Dbl and CDC24

In Saccharomyces cerevisiae, the product of the CDC25 gene is an essential Ras activator that appears to function by stimulating guanine nucleotide exchange on Ras. Using the ability of a mouse cDNA expression library to complement yeast cells lacking functional CDC25, Martegani et al. have identified a 1.7 kb partial cDNA from a gene, designated CDC25Mm, with homology to CDC25. We have now screened a mouse brain cDNA library to identify full-length clones of CDC25Mm. This cloning has led to the isolation of six distinct full-length cDNAs, each of which appear to be derived from the CDC25Mm gene, since their 3' 2 kb appear to be identical and to encode the same 661 C-terminal amino acids. Three cDNAs are predicted to encode protein products of 666 or 667 amino acids. The other three cDNAs encode products that are 836, 1120 and 1260 amino acids, respectively. A 241 amino acid region near the N-terminus of the two largest products was found to have homology to a domain shared by Bcr, Vav, Dbl and CDC24. Polyclonal antibodies raised to a peptide encoded by all the cDNAs have identified at least two protein products in NIH3T3 fibroblasts. Their apparent molecular weights are 75 and 95 kDa, which correspond closely to those predicted to be encoded, respectively, by the two shorter classes of cDNAs. In NIH3T3, the 95 kDa form is much more abundant than the 75 kDa form, while PC-12 pheochromocytoma cells contain relatively high levels of the 75 kDa form. We conclude that CDC25Mm is a complex gene whose protein products are regulated in a tissue-specific manner.

Biochemistry of the renal V-ATPase

In most eukaryotic cells, vacuolar H(+)-ATPases (V-ATPases) are present primarily or exclusively in intracellular membrane compartments, functioning in the acidification of the endocytic and secretory vacuolar apparatus necessary for constitutive cell function. V-ATPases also participate in renal hydrogen ion secretion in both the proximal and distal nephron, residing at high concentrations on the plasma membrane, where they are regulated physiologically to maintain the acid-base balance of the organism. Recent experiments have begun to reveal how the kidney controls transcellular proton transport while still maintaining acidification of intracellular compartments. Control may occur by recruitment of proton pumps to or away from the plasma membrane. The proton-transporting plasma membrane of intercalated cells is a specialized apparatus that translocates the enzyme between an intracellular membrane pool and the plasma membrane in response to physiological stimuli. Regulation may also occur by changes in the kinetics of the V-ATPase. V-ATPases are a family of structurally similar enzymes which differ in the composition of specific subunits. Cytosolic regulatory enzymes present in renal cells may preferentially affect V-ATPases in selective membrane compartments.

B cells from subjects with CVI can be driven to Ig production in response to CD40 stimulation

The majority of patients with common variable immunodeficiency (CVI) have low to normal numbers of membrane Ig-bearing B cells; yet these cells fail to differentiate in vivo resulting in hypogammaglobulinemia. We have suggested that the differentiation failure of CVI B cells is related to a failure to respond appropriately to signals involved in terminal B cell differentiation as most CVI subjects' cells undergo activation and proliferation normally. Whether this failure relates to a direct "intrinsic" defect in the B cells or is secondary to a lack of appropriate T cell or other influences in vivo is uncertain. We have previously reported that the majority of patients with CVI have elevated circulating levels of IL-6. We now show that the IL-6 produced by these patients is functionally normal. Additionally, the display of IL-6 receptors on in vitro stimulated CVI B cells is normal. However, we found that the patients' cells do not make IgE in response to an IL-6/T-cell-dependent differentiation pathway employing exogenous interleukin-4 (IL-4). The failure to respond in the IL-6-dependent system could not be overcome by exogenous IL-6 or varying doses of IL-4. In contrast, when stimulated by CD40 plus IL-4 in a differentiation pathway that does not require IL-6, B cells from CVI patients were stimulated to produce IgE. These findings, along with our earlier data showing that 13-cis-retinoic acid can drive maturation in CVI patients, strengthen the concept that B cells in patients with CVI have the potential for terminal differentiation but do not appear to achieve this in vitro or in vivo through a polyclonal Ig differentiation pathway that employs IL-6 as one of its maturation signals.

The Drosophila spitz gene encodes a putative EGF-like growth factor involved in dorsal-ventral axis formation and neurogenesis

We describe the molecular characterization of the Drosophila gene spitz (spi), which encodes a putative 26-kD, EGF-like transmembrane protein that is structurally similar to TGF-alpha. Temporal and spatial expression patterns of spi transcripts indicate that spi is expressed throughout the embryo. Examination of mutant embryos reveals that spi is involved in a number of unrelated developmental choices, for example, dorsal-ventral axis formation, glial migration, sensory organ determination, and muscle development. We propose that spi may act as a ligand for cell-specific receptors, possibly rhomboid and/or the Drosophila EGF receptor homolog.

Mechanistic aspects of signaling through Ras in NIH 3T3 cells

Serum and growth factors can increase the proportion of Ras in the active guanosine triphosphate (GTP)-bound form. Growth factors might stimulate guanine nucleotide exchange or decrease the activity of the guanosine triphosphatase-activating proteins GAP and neurofibromin (NF1). In NIH 3T3 cells that overexpress the mutant Ras protein His116, which releases bound guanine nucleotide at a constitutively high rate and retains sensitivity to GAP and NF1, the proportion of GTP bound to the His116 protein was not altered by serum or platelet-derived growth factor. However, these mitogens increased the proportion of Ras in the GTP-bound form in cells that overexpressed control Ras proteins with a normal intrinsic rate of guanine nucleotide release. The amount of GTP-bound His116 or control Ras proteins was higher in cells at low density than in cells at high density, which have more GAP-like activity. The lower proportion of GTP-bound Ras in NIH 3T3 cells at high density may result from increased GAP-like activity. By contrast, serum and platelet-derived growth factors appear to stimulate guanine nucleotide exchange.

A cytosolic inhibitor of vacuolar H(+)-ATPases from mammalian kidney

Regulation of the vacuolar H(+)-ATPase in organellar and transepithelial acidification has been attributed to the effects of the proton electrochemical gradient across the membrane or to changes in the number of proton pumps. We now report the identification and purification of a protein from bovine kidney cytosol that inhibits both ATPase activity and proton translocating activity of vacuolar H(+)-ATPases. Its relative molecular weight (M(r)) is 6300, similar to that for protein inhibitors of the mitochondrial F0F1-ATPase. The newly identified cytosolic inhibitor protein may participate in the physiologic regulation of the vacuolar H(+)-ATPase by suppressing activity directly.

Two unusual forms of human immunoglobulin E encoded by alternative RNA splicing of epsilon heavy chain membrane exons

We present evidence for RNA transcripts encoding two forms of human epsilon immunoglobulin (Ig) heavy chain that differ significantly from those of other isotypes. We previously demonstrated three human epsilon mRNA species, instead of the two, corresponding to membrane and secreted proteins, seen with other heavy chain transcripts. In human genomic DNA downstream of the C epsilon gene, we identified sequences homologous to the two putative murine exons M1 (encoding a hydrophobic, presumably transmembrane region) and M2 (encoding hydrophilic residues). To determine the structures of epsilon transcripts containing these sequences, we amplified epsilon-related RNAs with the reverse transcriptase polymerase chain reaction. RNA was examined from fresh human B cells stimulated to IgE production by interleukin 4 plus anti-CD40, as well as from the human IgE-producing line AF10. Instead of the single CH4-M1-M2 splice product predicted for murine membrane IgE, we found two other RNA species. One form has the structure CH4-M1'-M2, in which M1' includes the human sequence homologous to the murine M1 as well as a unique segment of 52 codons further upstream in the genomic sequence; this RNA species apparently encodes the IgE expressed on the membrane of IgE-producing lymphocytes. The other RNA has the structure CH4-M2', in which M2' is spliced in an alternative reading frame that includes an additional 109 codons downstream of the termination codon of the CH4-M1'-M2 form. Because the CH4-M2' mRNA form does not encode a hydrophobic segment, its translated product should be secreted. A secreted epsilon protein of approximately the size predicted for this form was identified by Western blotting. This novel IgE protein could play a significant and distinctive role in allergic disorders.

Mechanism of human keratinocyte migration on fibronectin: unique roles of RGD site and integrins

The migration of human keratinocytes over the wound bed plays an important role in the re-epithelialization of cutaneous wounds. Fibronectin, a large glycoprotein matrix component that is abundant within cutaneous wound beds, promotes keratinocyte migration. However, the mechanisms by which keratinocytes migrate over fibronectin are unknown. In this study, we sought to identify specific sites within the fibronectin molecule that induce keratinocyte locomotion and to characterize the cell surface receptors involved. The data show that the domain within the fibronectin molecule that induces human keratinocyte migration is the 120 kD cell-binding domain close to the carboxyl terminus. The 40 kD heparin-binding domain near the carboxyl terminus and the 45 kD gelatin-binding domain near the amino terminus did not promote keratinocyte migration. In addition, keratinocyte migration on both fibronectin and the 120 kD cell-binding domain was completely inhibited by the presence of GRGDSP peptide, suggesting that keratinocyte migration on fibronectin is mediated by recognizing the RGD sequence located within the cell-binding domain of fibronectin. Furthermore, keratinocytes were able to migrate directly on immobilized RGD substratum. Cell migration on fibronectin is mediated by the alpha 5 beta 1 integrin since antibodies blocking the alpha 5 and the beta 1 subunits completely inhibited keratinocyte migration on fibronectin. In addition, we demonstrate that human keratinocytes express alpha 5 beta 1 integrin in culture by flow cytometry.

Identification and partial purification of a cytosolic activator of vacuolar H(+)-ATPases from mammalian kidney

A factor that activates affinity-purified vacuolar H(+)-ATPase from bovine kidney microsomes was identified and partially purified from bovine kidney cytosol. The activator is a heat-stable, trypsin-sensitive acidic protein with a Mr by gel filtration of approximately 35,000. The activator increased the activity of renal microsomal and brush border H(+)-ATPase by over 60% but stimulated lysosomal H(+)-ATPase activity by only 28%; it had little or no activity against the remaining N-ethylmaleimide-insensitive ATPase in kidney microsomes and other transport ATPases. Stimulation of ATPase activity appeared to result from binding of the activator to the H(+)-ATPase. Activation was saturable, with a Hill coefficient of 1 at low protein concentrations. Both activator binding and stimulation of H(+)-ATPase activity were enhanced at pH values less than or equal to 6.5. The activator has selective effects on different H(+)-ATPases and is poised to activate the enzyme at low physiologic values of cytosolic pH; this newly identified cytosolic proteins may participate in the physiologic regulation of the vacuolar H(+)-ATPase.