Tyrosine kinase inhibition affects type 1 angiotensin II receptor internalization

Growth factor receptors activate tyrosine kinases and undergo endocytosis. Recent data suggest that tyrosine kinase inhibition can affect growth factor receptor internalization. The type 1 angiotensin II receptor (AT1R) which is a G-protein-coupled receptor, also activates tyrosine kinases and undergoes endocytosis. Thus, we examined whether tyrosine kinase inhibition affected AT1R internalization. To verify protein tyrosine phosphorylation, both LLCPKCl4 cells expressing rabbit AT1R (LLCPKAT1R) and cultured rat mesangial cells (MSC) were treated with angiotensin II (Ang II) [1-100 nM] then solubilized and immunoprecipitated with antiphosphotyrosine antisera. Immunoblots of these samples demonstrated that Ang II stimulated protein tyrosine phosphorylation in both cell types. Losartan [1 microM], an AT1R antagonist, inhibited Ang II-stimulated protein tyrosine phosphorylation. LLCPKAT1R cells displayed specific 125I-Ang II binding at apical (AP) and basolateral (BL) membranes, and both AP and BL AT1R activated tyrosine phosphorylation. LLCPKAT1R cells, incubated with genistein (Gen) [200 microM] or tyrphostin B-48 (TB-48) [50 microM], were assayed for acid-resistant specific 125I-Ang II binding, a measure of Ang II internalization. Both Gen (n = 7) and TB-48 (n = 3) inhibited AP 125I-Ang II internalization (80+/-7% inhibition; p<0.025 vs. control). Neither compound affected BL internalization. TB-1, a non-tyrosine kinase-inhibiting tyrphostin, did not affect AP 125I-Ang II endocytosis (n = 3), suggesting that the TB-48 effect was specific for tyrosine kinase inhibition. Incubating MSC with Gen (n = 5) or herbimycin A [150 ng/ml] (n = 4) also inhibited MSC 125I-Ang II internalization (82+/-11% inhibition; p<0.005 vs. control). Thus, tyrosine kinase inhibition prevented Ang II internalization in MSC and selectively decreased AP Ang II internalization in LLCPKAT1R cells suggesting that AP AT1R in LLCPKAT1R cells and MSC AT1R have similar endocytic phenotypes, and tyrosine kinase activity may play a role in AT1R internalization.

Ideas in theoretical biology. Origin of cancerous cells from tumours

With a previous paper (Niu & Wang, 1995), a general, hypothetical outline of the mechanism of carcinogenesis was proposed. With reference to the fact of starvation-induced hypermutation in micro-organisms, we propose that the hypoxia commonly seen in the cells at the centre of solid tumours might also result in hypermutation, and then p53-dependent programmed cell death. Like the apparently adaptive mutations in micro-organisms, only those genes (e.g. p53) that enable the cells to escape from apoptosis may be selected.

Inhibition of vascular endothelial cell morphogenesis in cultures by limbal epithelial cells

PURPOSE

To study the in vitro angiogenic activity of human conjunctival and limbal epithelial cells and conjunctival, limbal, and corneal fibroblasts in a three-cell-type coculture model.

METHODS

Human umbilical vein endothelial cells (EC) were cocultured with epithelial cells, fibroblasts, or epithelial cells and fibroblasts to test their effect on EC morphogenesis. Neutralizing antibodies to some known angiogenic factors were added to the culture to see whether the EC morphogenesis may be blocked by a particular antibody.

RESULTS

Conjunctival and limbal epithelial cells exhibited very little or no stimulatory effect on EC tube formation when examined in an EC- epithelial cell coculture system. In contrast, conjunctival, limbal, and corneal fibroblasts all promoted EC morphogenesis when examined under the same culture conditions. Fibroblast-induced EC morphogenesis was inhibited by addition of anti-vascular endothelial growth factor (VEGF) and/or anti-basic fibroblast growth factor (bFGF) antibodies to the culture medium. In the three-cell-type coculture system consisting of ECs, fibroblasts, and epithelial cells, limbal epithelial cells (but not conjunctival epithelial cells) exhibited a strong inhibitory effect on fibroblast-induced EC tube formation.

CONCLUSIONS

The proangiogenic activity of ocular surface fibroblasts is probably mediated through a paracrine mechanism by VEGF and bFGF. Limbal epithelial cells, but not conjunctival epithelial cells, inhibit fibroblast-stimulated angiogenesis.

Tuberculin purified protein derivative up-regulates the telomerase activity of peripheral blood mononuclear cells from patients with pulmonary tuberculosis

Telomerase activity was detectable in cells of tuberculous pleural effusions at high percentage. To investigate the possible role of telomerase in the immune function, we examined the proliferating state and the expression of telomerase activity in peripheral blood mononuclear cells (PBMC) from 13 patients with pulmonary tuberculosis (TB) and 13 healthy volunteers in response to tuberculin purified protein derivative (PPD) challenge. Exposure of cells to phytohemagglutinin (PHA) significantly promoted PBMC proliferation during a 6 day-period in both TB patient and healthy volunteer groups. PPD treatment also significantly promoted PBMC proliferation during a 6 day-period in TB patient group, but had no significant effect in healthy volunteer group. During the same period, telomerase activity was detected in every PHA- and PPD-treated samples of the TB patient group. However, the telomerase activity was not detected in PPD-treated samples from healthy donors and all the untreated samples. Our results indicate that the telomerase activity in PBMC could be induced by PPD stimulation in TB patients. Telomerase activity may thus play a permissive role in cell division and clonal expansion of the immune cells in response to TB.

The identification of myriocin-binding proteins

BACKGROUND

Myriocin is a natural product that potently induces apoptosis of a murine cytotoxic T lymphocyte cell line (CTLL-2) and inhibits a serine palmitoyltransferase (SPT) activity that has been detected in cell extracts and is thought to initiate sphingolipid biosynthesis. Because SPT has never been biochemically purified and a comprehensive appraisal of myriocin-binding proteins has not been conducted, we isolated specific targets using myriocin-based affinity chromatography.

RESULTS

Myriocin derivatives were synthesized and evaluated using CTLL-2 proliferation and SPT activity assays. Guided by these results, affinity chromatography matrices were prepared and two specific myriocin-binding proteins were isolated from CTLL-2 lysates. Analyses of these polypeptides establish conclusively that they are murine LCB1 and LCB2, mammalian homologs of two yeast proteins that have been genetically linked to sphingolipid biosynthesis.

CONCLUSION

The ability of myriocin-containing matrices to bind factors that have SPT activity and the exclusive isolation of LCB1 and LCB2 as myriocin-binding proteins demonstrates that the two proteins are directly responsible for SPT activity and that myriocin acts directly upon these polypeptides.

Pseudosparing of the endplate: a potential pitfall in using MR imaging to diagnose infectious spondylitis

OBJECTIVE

The objective of this study was to describe a potential pitfall in using MR imaging to diagnose infectious spondylitis called "pseudosparing" of the endplate, in which the diseased endplate appears to be better defined than a healthy endplate.

CONCLUSION

Poor definition of the endplate is a classic radiographic finding in infectious spondylitis; on MR imaging, however, increased conspicuity, or "pseudosparing," was common in our study. Pseudosparing occurs when the normal chemical shift artifact seen in healthy endplates is lost as a result of infiltration of the bone marrow by a pathologic process.

Transfection of an active cytochrome P450 arachidonic acid epoxygenase indicates that 14,15-epoxyeicosatrienoic acid functions as an intracellular second messenger in response to epidermal growth factor

A common feature of most isolated cell systems is low or undetectable levels of bioactive cytochrome P450. We therefore developed stable transfectants of the renal epithelial cell line, LLCPKcl4, that expressed an active regio- and enantioselective arachidonic acid (AA) epoxygenase. Site-specific mutagenesis was used to convert bacterial P450 BM-3 into an active regio- and stereoselective 14S,15R-epoxygenase (F87V BM-3). In clones expressing F87V BM-3 (F87V BM-3 cells), exogenous AA induced significant 14S,15R-epoxyeicosatrienoic acid (EET) production (241. 82 ng/10(8) cells, >97% of total EETs), whereas no detectable EETs were seen in cells transfected with vector alone. In F87V BM-3 cells, AA stimulated [3H]thymidine incorporation and increased cell proliferation, which was blocked by the tyrosine kinase inhibitor, genistein, by the phosphatidylinositol 3 (PI-3) kinase inhibitors, wortmannin and LY294002, and by the mitogen-activated protein kinase kinase inhibitor, PD98059. AA also induced tyrosine phosphorylation of extracellular signal-regulated kinase (ERK) and PI-3 kinase that was inhibited by the cytochrome P450 BM-3 inhibitor, 17-ODYA. Epidermal growth factor (EGF) increased EET production in F87V BM-3 cells, which was completely abolished by pretreatment with either 17-ODYA or the phospholipase A2 (PLA2) inhibitor, quinacrine. Compared with vector-transfected cells, F87 BM-3 transfected cells demonstrated marked increases in both the extent and sensitivity of DNA synthesis in response to EGF. These changes occurred in the absence of significant differences in EGF receptor expression. As seen with exogenous AA, EGF increased ERK tyrosine phosphorylation to a significantly greater extent in F87V BM-3 cells than in vector-transfected cells. Furthermore, in these control cells, neither 17-ODYA nor quinacrine inhibited EGF-induced ERK tyrosine phosphorylation. On the other hand, in F87V BM-3 cells, both inhibitors reduced ERK tyrosine phosphorylation to levels indistinguishable from that seen in cells transfected with vector alone. These studies provide the first unequivocal evidence for a role for the AA epoxygenase pathway and endogenous EET synthesis in EGF-mediated signaling and mitogenesis and provide compelling evidence for the PLA2-AA-EET pathway as an important intracellular-signaling pathway in cells expressing high levels of cytochrome P450 epoxygenase.

Immunolocalization of high-density lipoproteins in arterial walls of rats

The inverse correlation between serum high-density lipoprotein (HDL) levels and coronary heart disease in humans suggests that HDL has a protective effect against the development of atherosclerosis. However, there is a lack of data concerning its distribution across the arterial wall. In order to detect this lipoprotein, we performed immunogold labeling on ultrathin sections of L.R. White embedded rat arterial tissue. Electron microscopic examination revealed that HDL was localized in the cytoplasm of the endothelial cells and the smooth muscle cells, but not in the nucleus or other organelles. The HDL was also present in the subendothelial space, the extracellular matrix as well as the intercellular clefts between the endothelial cells. Quantitative study revealed that rats on a high cholesterol diet for one month have more immunogold labeling (P < 0.05) in the subendothelial space, the smooth muscle cells and the extracellular matrix as compared to rats on a normal diet. After 12 months of normal diet, the intracellular labeling was significantly increased (P < 0.05) in the endothelial cells and the smooth muscle cells as compared to 1 month on the normal diet. The increase was greater (P < 0.05) for the high-cholesterol diet than for the normal diet treatment.

Once-a-month treatment with a combination of mifepristone and the prostaglandin analogue misoprostol

In this two centre study, the efficacy of 200 mg mifepristone orally followed 48 h later by 0.4 mg misoprostol orally for menstrual regulation was investigated. The dose of mifepristone was taken the day before the expected day of menstruation. Each volunteer was planned to participate for up to 6 months. A plasma beta human chorionic gonadotrophin (HCG) was measured on the day of mifepristone intake. The study was disrupted prematurely due to low efficacy. In 125 treatment cycles the overall pregnancy rate was 17.6% (22 pregnancies) and the rate of continuing pregnancies (failure) was 4.0%. Eight women discontinued the study due to bleeding irregularities which were seen in 15 cycles (12%). These effects on bleeding pattern made the timing of treatment day difficult. Late luteal phase treatment with a combination of mifepristone and misoprostol is not adequately effective for menstrual regulation.

Bifid ribs observed in the third and the fourth ribs

Three cases of bifid ribs were found in two cadavers during routine dissections at the Iwate Medical University School of Dentistry. All of the cases were found in the third or the fourth rib. The distal parts of the osseous rib bifurcated with an angle of 60 degrees and both of the branches had their own costal cartilage. The costal cartilage fused again to form the trunk which was connected to the sternum. The space between the two branches was filled with presumably normal intercostal muscles. Blood supply was maintained by a small branch from the interthoracic artery to the upper branches. However, the intercostal nerves did not branch toward the upper branch but only ran along the lower margins of the lower branches of the bifid ribs.

Epoxyeicosatrienoic acids and their sulfonimide derivatives stimulate tyrosine phosphorylation and induce mitogenesis in renal epithelial cells

In our present studies utilizing a well characterized proximal tubule cell line, LLCPKcl4, we determined that all four EET regioisomers (5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET) stimulated [3H]thymidine incorporation, with 14,15-EET being the most potent. In contrast, no mitogenic effects were seen with arachidonic acid, other cP450 arachidonate metabolites (12R-hydroxyeicosatetraenoic acid (12R-HETE), 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), or 20-HETE), or lipoxygenase metabolites (5S-HETE, leukotriene B4, or lipoxin A4). We found that their metabolically more stable sulfonimide (SI) analogs (11,12-EET-SI and 14,15-EET-SI) were also potent mitogens. In addition 14,15-EET-SI also increased cell proliferation as well as expression of both c-fos and egr-1 mRNA. The protein kinase C and A inhibitors, H-7 and H-8, or the cyclooxygenase inhibitor, indomethacin, had no effect upon 14, 15-EET-induced [3H]thymidine incorporation, but the selective tyrosine kinase inhibitor, genistein, significantly inhibited it. Immunoprecipitation and immunoblotting demonstrated increased tyrosine phosphorylation of PI3-kinase and epidermal growth factor receptor (EGFR) within 1 min of EET administration. EETs also stimulated association of PI3-kinase with EGFR. PI3-kinase inhibitors, wortmannin and LY 294002, markedly inhibited 14, 15-EET-SI-stimulated [3H]thymidine incorporation. In addition, 14, 15-EET-SI administration stimulated tyrosine phosphorylation of src homologous and collagen-like protein (SHC) and association of SHC with both growth factor receptor-binding protein (GRB2) and EGFR. Mitogen-activated protein kinase was also activated within 5 min. Pretreatment of the cells with the mitogen-activated protein kinase kinase inhibitor, PD98059, inhibited the 14,15-EET-SI-stimulated [3H]thymidine incorporation. Moreover, immunoblotting indicated that 14,15-EET stimulated tyrosine phosphorylation of the specific pp60(c-src) substrate p120 and c-Src association with EGFR. 14, 15-EET increased src kinase activity within 1 min. Our data indicate that EETs are potent mitogens for renal epithelial cells, and the mitogenic effects of the EETs are mediated, at least in part, by the activation of Src kinase and initiation of a tyrosine kinase phosphorylation cascade.

Oxidized LDL promotes vascular endothelial cell pinocytosis via a prooxidation mechanism

Human low density lipoprotein (LDL) is prepared in the presence of antioxidants and is oxidized to different levels (measured by thiobarbituric acid reactive substance) with copper ion. The effects of unoxidized LDL and oxidized LDL (ox-LDL) on stress fiber formation, cell membrane ruffling, and pinocytosis (measured by [14C]sucrose uptake) in cultured human umbilical cord vein endothelial cells (EC) are compared. We show that at a concentration range of 100 to 200 microg cholesterol/ml, both unoxidized LDL and ox-LDL promote EC elongation and stress fiber formation, but the effect by the latter is more prominent when compared at the same dose range. In addition, ox-LDL also induces EC membrane ruffling and promotes pinocytosis. These effects are positively correlated with the extent of LDL oxidation and depend on the dose of ox-LDL. Ox-LDL-promoted membrane ruffling and pinocytosis are effectively blocked by brief preexposure of the cells to antioxidants. In contrast, stress fiber formation is not affected by antioxidant pretreatment. Although unoxidized LDL also promotes [14C]sucrose uptake, it is less potent than ox-LDL and significantly higher concentrations are required to produce a detectable effect. Unlike ox-LDL, unoxidized LDL-enhanced pinocytosis is not accompanied by the appearance of membrane ruffling; therefore, they may act via different mechanisms. Elevated pinocytosis may increase transcytotic activity of the endothelium, leading to an increased influx of plasma components such as LDL into the subendothelial space.

A regression analysis estimating the number of drug-using arrestees in 185 US cities

OBJECTIVES

This study sought to provide population-based estimates of drug-using arrestees in the 185 largest US cities.

METHODS

A prevalence model for drug-using arrestees was developed by relating selected social indicators (from 1990 census data) and drug use rates (from Drug Use Forecasting program data) via logistic regression analysis.

RESULTS

It was estimated that in 1990, across the 185 cities, about 925,000 arrestees used cocaine, 317,000 used opiates, 213,000 used amphetamines, 389,000 were drug injectors, and 1,296,000 used an illicit drug.

CONCLUSIONS

This approach represents a cost-efficient method for prevalence estimation based on empirically demonstrable relationships between social indicators and drug use rates.

Differential effects of aneugens and clastogens on incidences of multinucleated cells and of micronucleate cells in Chinese hamster lung (V79) cell line in vitro

Two aneugens, vinblastine (0.025-0.4 microgram/ml) and colchicine (0.05-0.4 microgram/ml), and two clastogens, mitomycin C (0.05-0.4 microgram/ml) and cyclophosphamide (1-16 micrograms/ml) were applied respectively to the micronucleus test in Chinese hamster lung (V79) cells in vitro, and the frequency of multinucleated cells (Fmu) and that of micronucleate cells (Fmi) in each group were observed. The results showed that at relatively high concentrations, all four agents increased both Fmu and Fmi, but the ratios of Fmu to Fmi in groups of the two aneugens (average of 2.2, 2.8, respectively) were much (10-30 folds) higher than that in groups of the two clastogens (0.09, 0.20). The difference between aneugens and clastogens in the above ratio was much more remarkable than that in areas of micronuclei (only 1.6-2.5 folds for the latter). At relatively low concentrations, the two clastogens increased only Fmi (but not Fmu), while the two aneugens increased only Fmu (but not Fmi). This indicates that the induction of multinuclei by aneugens may be more sensitive than by clastogens, and the induction of micronuclei by clastogens may be more sensitive than by aneugens. So, it is possible for the ratio of Fmu to Fmi to become a simple and sensitive (though indirect) index for distinguishing aneugens from clastogens. Further studies with other mutagens and (or) other cell types will be needed to confirm the deduction. As no difference in frequency of polyploid cells was observed between control group and each treatment, the multinucleation does not seem related to endoreduplication of chromosomes.

Telomerase activity in pleural effusions: diagnostic significance

PURPOSE

To determine the diagnostic value of pleural fluid telomerase activity in distinguishing a malignant from a nonmalignant pleurol effusion in a cohort of patients undergoing thoracentesis.

PATIENTS AND METHODS

Using a polymerase chain reaction (PCR)-based assay, telomerase activity was examined in the pleural fluid cells obtained from 144 consecutive, unselected patients. According to the final diagnosis achieved, these patients were classified into three groups: group I consisted of 70 malignant pleural effusions diagnosed by either fluid cytology or pleural biopsy, group II consisted of 52 nonmalignant pleural effusions, and another 22 samples were categorized to be suspicious malignant pleural effusions (group III) due to inconclusive results in effusion cytology and percutaneous pleural biopsy, but were strongly suspicious in clinical settings.

RESULTS

The presence of telomerase activity was observed in 64 of 70 samples in group I (91.4%), three of 52 samples in group II (5.8%), and 20 of 22 samples in group III. All three nonmalignant, telomerase-positive pleural effusion samples in group II were obtained from patients with tuberculosis. As a diagnostic criterion for malignant pleural effusion in group I and group II patients, positive telomerase activity had a sensitivity of 91.4%, a specificity of 94.2%, and a positive and negative predictive value of 0.96 and 0.89, respectively.

CONCLUSION

Our results indicate that the detection of telomerase activity may be a useful adjunct to cytopathologic methods in the diagnosis of malignant pleural effusions.

Fibroblasts derived from tissue explants of dilantin-induced gingival hyperplasia and idiopathic gingival fibromatosis show distinct disparity in proliferative responsiveness to epidermal growth factor

Human gingival fibroblasts derived from tissue explants of two patients with dilantin-induced gingival hyperplasia (DGH) and one patient with idiopathic gingival fibromatosis (GF) were studied with respect to the effect of epidermal growth factor (EGF) on the proliferative characteristics of these cells. Immunohistochemical staining showed that there were more EGF receptor-positive cells among DGH fibroblasts than among either normal gingival fibroblasts (NG) or GF cells. Furthermore, EGF binding studies showed that, in spite of there being no disparity in binding affinity among all these cells, DGH fibroblasts possessed approximately two-fold more EGF receptors than either NG or GF cells. In addition, the growth-promoting effect of exogenously added EGF was concentration-dependent in DGH fibroblasts but was not in either NG or GF cells. All of the above findings clearly demonstrate that DGH and GF fibroblasts exhibit distinct disparity in proliferative responsiveness to EGF and suggest that different mechanisms may be involved in the pathogenesis of these two forms of gingival hyperplasia. These observations also suggest a possible therapeutic approach for blocking EGF-induced cell proliferation in DGH.

Differential inhibition of telomerase activity during induction of differentiation in hematopoietic, melanoma, and glioma cells in culture

Accumulating evidence indicates that telomerase activity is stringently repressed in normal human somatic cells but reactivated in cancers and immortal cells, suggesting that activation of telomerase activity may play a role in carcinogenesis and immortalization. Recently, down-regulation of telomerase activity by induction of differentiation has been reported for cells of pre-myelocytic and myelocytic leukemia as well as embryonic carcinoma. To gain further insight about the regulation of telomerase activity following induction of differentiation, telomerase activity was examined in a human hematopoietic progenitor cell line (D2), a melanoma cell line (CM73-36) and a glioma cell line (Ast812) before and after addition of differentiation inducing agents. The state of differentiation was assessed by growth inhibition and cell morphological maturation. Telomerase activity was assayed by a PCR-based telomeric repeat amplification protocol (TRAP). Our data show that telomerase activity was inhibited only in differentiation-induced D2 cells but not in differentiation-induced melanoma and glioma cells. A model for the differential inhibition of telomerase activity following induction of differentiation in different cancer cells will be presented.

Evolutionary advantages of cell specialization: save and protect DNA

As the transcribed regions of nuclear DNA are in a more open state, they are liable to be damaged by naturally or environmentally produced mutagens. Cell specializations make it possible to express fewer genes in individual cells of multicellular organisms, thus protecting genes from the damage of mutagens. We propose that this might account for the advantage of cell specialization, as an alternative to the traditional conception that cell specializations result in increased efficiency. The most efficient cell specialization to protect DNA is in the segregation of germ cell(s) and somatic cell(s). But in optimal environments, such specialization is expected to reduce the rate of reproduction, which might counteract its advantage of protecting DNA.

Identification of amino acid residues of abrin-a A chain is essential for catalysis and reassociation with abrin-a B chain by site-directed mutagenesis

Abrin is a toxic protein consisting of two subunits, an enzymatic A chain (ABRaA) and a lectin-active B chain (ABRaB), linked by a disulfide bond. Site-directed mutagenesis was performed using PCR to study how the conserved amino acid residues, Tyr74, Tyr113, Glu164 and Trp198, around the active site of ABRaA are involved in enzyme catalysis, enzyme-substrate recognition and reassociation of ABRaA with ABRaB. The protein biosynthesis inhibitory activities of Y74F, Y113F and W198F were decreased moderately to that of wild type reABRaA, while that of E164Q decreased dramatically. Kinetic analysis showed that the kat of Y74F, Y113F and W198F resembled that of wild type, while the Km increased significantly. W198F did not reassociate with ABRaB to form heterodimers, while Y74F, Y113F and E164Q did. SDS-PAGE analysis of ABRaA treated with trypsin showed that reABRaA, Y74F, Y113F and E164Q survived digestion, whereas W198F was not protected from digestion. CD spectra revealed that W198F showed significant conformational changes. These observations suggest that E164 is directly involved in catalysis, and Tyr74, Tyr113 and Trp198 in substrate binding, while Trp198 also plays an important role in maintaining the conformation of ABRaA required for its reassociation with ABRaB.

Oxidized LDL inhibits vascular endothelial cell morphogenesis in culture

Human umbilical cord vein endothelial cells can be induced to undergo morphogenesis (tube formation) by phorbol ester (TPA) when cultured on or in three-dimensional collagen gels. Induction of morphogenesis by TPA is accompanied by increased activity of the collagenase gene transcription factors, ETS1 and API, and the elaboration of collagenase by the endothelial cells. In the present study, we used endothelial cell elongation as a measure of morphogenesis and showed that oxidized low density lipoprotein (oxLDL) inhibited endothelial cell migration in monolayer cultures and TPA-induced morphogenesis in collagen gels in a dose-dependent manner. Moreover, the inhibition was positively correlated with the extent of LDL oxidation. In contrast, native LDL stimulated cell migration and TPA-induced morphogenesis under the same culture conditions. However, in the absence of TPA, LDL showed no effect on EC morphogenesis. Further studies showed that inhibition of TPA-induced endothelial cell morphogenesis by oxLDL is correlated with suppression of the protein kinase C (PKC) and ETS1/AP1 activities. The results indicated that the inhibition of endothelial cell morphogenesis by oxLDL is probably mediated through inhibition of the TPA-activated PKC pathway and its subsequent suppression of the ETS1/AP1 activity. The results also indicated that EC migration can be mediated through PKC-dependent and independent pathways and only the former pathway can induce EC morphogenesis as well.

Distribution of p53 and K-ras mutations in human lung cancer tissues

Studies were performed to examine the mutational pattern of K-ras exons 1 and 2 and p53 exons 5-8 in lung cancer tissues from 27 Chinese patients (10 smokers, 17 non-smokers) using single-stranded conformational polymorphism and DNA sequencing. K-ras mutations were found in 13/27 tumors (48%); all mutations were clustered in exon 1 and distributed between codons 9 and 32. The frequency and number of patients with K-ras mutations between smokers and non-smokers were not different, except that a high frequency of G --> A transitions (11/11) was found in non-smokers. Among cell types, K-ras mutations were found in 7/13 (54%) squamous cell carcinoma (SC) and 5/12 (42%) adenocarcinoma (AC) patients. A --> T transversions (all six transversions) were present only in SC. In p53, 18/27 (67%) tumors contained mutations in exons 7 and 8, frequently at codons 226, 270, 275 and 281. The number of tumors with p53 mutations in smokers (70%) and in non-smokers (65%) was similar, and the mutation frequency did not differ except for a higher number of G --> A (6/7) and T --> C (5/6) transitions in non-smokers. Among cell types, the number of tumors with p53 mutations was 9/13 (69%) in SC and 8/12 (67%) in AC. The A --> G (11/16) transitions and A --> C (4/4) transversions in p53 were more frequent in SC than in AC (P < 0.04 for A --> G; P < 0.02 for A --> C). The varying mutation patterns in both the K-ras and p53 genes between smokers and non-smokers and among cell types suggest that other than cigarette smoke, environmental and dietary factors may also be involved in the genesis of lung cancer among these patients.

TGF-beta1 selectively suppresses PDGF receptor signaling pathways in MG-63 human osteosarcoma cell

We previously found that TGF-beta1 inhibits PDGF mitogenicity in MG-63 cells and the inhibition is correlated with a suppression of the PDGF-induced receptor autophosphorylation. In this study, we analyze if all the PDGF receptor signaling pathways are similarly affected by the TGF-beta1 pretreatment. We show that TGF-beta1 suppresses PDGF-stimulated tyrosine phosphorylation of PLC-gamma1, and the phosphorylation of Erk. In contrast, the tyrosine phosphorylation of PI3-kinase is not affected. Thus, TGF-beta1 selectively suppresses two out of three PDGF receptor signaling pathways despite of its prominent inhibition of the PDGF-induced receptor autophosphorylation. The results also indicate that activation of the PI3-kinase pathway alone by PDGF is not sufficient in supporting the optimum growth of MG-63 cells under the culture conditions employed.

Structure-function relationship of trichosanthin

Trichosanthin (TCS), a 27 kDa ribosome inactivating protein extracted from the root tuber of Trichosanthes plant, was subjected to limited chymotrypsin digestion and three peptide fragments designated TCS-F1 72-247, TCS-F2 100-247, and TCS-F3 133-247 were generated. The RNA-N-glycosidase and cytotoxic activities of the TCS fragments were compared with that of inact TCS. TCS-F1 and TCS-F2 were biologically active, while TCS-F3 was completely inactive. Dose-dependent studies showed that TCS-F1 and TCS-F2 were less potent in their trophoblast cytotoxicity than intact TCS, however, full biological effect could still be obtained with a higher dosage. Based on the known three-dimensional structure of TCS, we postulate that the putative active site of TCS is located at amino acid residues 110 to 174.

Probing the Domain Structure of Abrin-a by Tryptic Digestion

Abrin-a is a potent plant toxin that consists of A and B chains linked by a disulfide bond. The abrin-a A chain (AaTA) has N-glycosidase activity while the abrin-a B chain (AaTB) has galactose-binding activity. By partial tryptic digestion, the domain structure of abrin-a was investigated. Seven tryptic fragments with molecular masses greater than 3500 Da were isolated and characterized. One fragment, designated T-21 and consisting of 153 amino acid residues, contained the major part of the second domain of AaTB and, after cross-linking of T-21 with glutaraldehyde, the reaction product had the same level of hemagglutinating activity as native abrin. When the T-21 fragment was conjugated with AaTA, the conjugate inhibited protein biosynthesis in HeLa cells. This suggests that the T-21 fragment is able to bind specifically to cells; its conjugate facilitates membrane translocation of AaTA into cells and consequently inhibits protein biosynthesis. T-21, with a molecular mass less than AaTB, is therefore a potentially useful substance for the preparation of immunotoxins.