Protective effect of ginseng on radiation-induced DNA double strand breaks and repair in murine lymphocytes

We have examined the effects of ginseng on the induction and repair of gamma-ray-induced DNA double strand breaks (dsb) using neutral filter elution technique at pH 9.6 in cultured murine spleen lymphocytes. Ginseng water extract 500 micrograms/ml was added to the culture medium either for 48 hours prior to irradiation. Ginseng extract showed protective effect against the formation of dsb when it was treated for 48 hours before 100 Gy gamma-ray-irradiation. While repair was almost completed until 220.2 minutes after irradiation, DNA repair of irradiated cells in the presence of ginseng extract was did not return to the corresponding control levels even after 621.8 minutes. From these data, it could be calculated that ginseng reduced the relative strand scission factor (RSSF) by about 2. Therefore, it could be concluded that ginseng has radioprotective effect against gamma-ray induced DNA dsb and repair in cultured mouse lymphocytes.

Transcriptional enhancement of tyrosine hydroxylase by prostaglandin E2 in SK-N-BE(2) C cells

Transcriptional regulation of the rat tyrosine hydroxylase (TH) gene by prostaglandin E2 (PGE2) was investigated in human neuroblastoma SK-N-BE(2)C cells. Prostaglandins increased intracellular cAMP in the presence of 3-isobutyl-1-methylxanthine (IBMX), a cAMP phosphodiesterase inhibitor. Among the prostaglandins tested for their cAMP raising property PGE2 was the most effective. The results suggest that the cells express adenylyl cyclase-linked prostanoid receptors that have a higher affinity for PGE2 than for any other naturally occurring prostaglandin. The treatment of cells with PGE2 increased the TH gene expression approximately 2-fold, even though the cAMP accumulation induced by PGE2 alone was almost negligible. Simultaneous treatment with PGE2 and IBMX enhanced the gene expression concomitantly with a marked accumulation of cAMP. Transient transfection assays with 5' upstream serially deleted constructs of the rat TH gene promoter region fused to the chloramphenicol acetyltransferase (CAT) gene revealed that a cAMP response element (CRE) located at -45 to -38 from the start of the TH gene was essential for the enhancement of TH gene expression by PGE2. Site-directed mutagenesis and specific deletion within the sequence of the CRE motif abolished the transcriptional enhancement by PGE2. In addition, a protein kinase A (PKA) inhibitor, H89, specifically blocked the PGE2 effect on TH gene expression. Northern blot analysis revealed that the increase in TH gene transcription with PGE2 is associated with an elevated TH mRNA level. Gel retardation and competition assays confirmed that the binding of nuclear factors to the CRE site was sequence specific and was augmented by PGE2. Our data indicate that PGE2 enhances transcription of the TH gene mediated by the CRE motif through the activation of PKA. They also suggest that the signal flow from the adenylyl cyclase-linked prostanoid receptor to the nucleus is efficient although cAMP accumulation is not prominent.

Characterization of Na+ influx mediated by ATP(4-)-activated P2 purinoceptors in PC12 cells

1. Micromolar levels of extracellular ATP increased cytosolic Na+ concentration ([Na+]i) as well as cytosolic Ca2+ concentration ([Ca2+]i) in PC12 cells. 2. Pretreatment of cells with tetrodotoxin, benzamil or thapsigargin did not alter the ATP-induced Na+ influx. 3. Increased extracellular Mg2+ concentration decreased the ATP effect. Furthermore, when the extracellular ATP pool was treated to contain corresponding calculated concentrations of ATP4-, the increase in [Na+]i stayed linked to the ATP4- concentration rather than to the total ATP concentrations in the stimulants. 4. Extracellular ATP does not create nonselective pores as shown by the fact that ethidium bromide does not enter the cells upon ATP stimulation. 5. Among the tested nucleotides, only adenosine 5'-O-(3-thiotriphosphate), 2-methylthio ATP and 2-chloro ATP also caused Na+ influx. 6. Reactive Blue 2 specifically decreased the ATP effect in a concentration-dependent manner. 7. The results suggest that extracellular ATP triggers Na+ influx through a P2 purinoceptor which is activated by ATP4- in PC12 cells.

Human brain GABA transaminase is immunologically distinct from those of other mammalian brains

Monoclonal antibodies (mAbs) to bovine brain gamma-aminobutyric acid (GABA) transaminase were characterized by epitope mapping analysis, and used as probes to compare the epitopes of the enzymes from several mammalian brains including man. From the epitope mapping analysis, three subgroups of mAbs recognizing different peptide fragments were identified. In the immunoblots probed with the mAbs, only one out of the three subgroups of mAbs reacted with a protein band of 50 kDa from human brain; the two other mAbs failed to detect any signal on the blots. In contrast, all of the mAbs did recognize a GABA-T protein band on immunoblots of all other mammalian brains tested. The results suggest that human brain GABA transaminase is immunologically distinct from those of other mammalian brains.

Inactivation of an NADPH-dependent succinic semialdehyde reductase by o-phthalaldehyde

Incubation of an NADPH-dependent succinic semi-aldehyde reductase from bovine brain with o-phthalaldehyde resulted in a time-dependent loss of enzyme activity. The inactivation followed pseudo first-order kinetics with the second-order rate constant of 28 M(-1) s(-1). The inactivation was prevented by preincubation of the enzymes with NADPH, but not by succinic semialdehyde. There was a linear relationship between isoindole formation and the loss of enzyme activity. Spectrophotometric studies indicated that complete inactivation of the enzyme resulted from the formation of one isoindole derivative per molecule of enzyme, which was formed from the reaction of cysteine and lysine residues with o-phthalaldehyde at or near the enzyme active site.

Measurement of apoptotic fragments in growing hair follicles following gamma-ray irradiation in mice

The usefulness of apoptotic fragments assay for investigating radiation response of hair follicles was examined. Frequency was defined as the ratio of the total number of apoptotic fragments to the number of hair follicles per section examined. The curve of dose-effect relationship for the data of apoptotic fragments was obtained by fitting the linear-quadratic model y= a+bD+cD2. When plotting on a linear scale against radiation dose, the line of best fit was y= 0.549 +/- 1.775) + 3.578 +/- 1.236)D + (-0.124 +/- 0.139)D2. The dose-response curves were linear-quadratic and a significant relationship was found between the frequency of apoptotic fragments and dose. The morphological findings of the irradiated groups were typical apoptotic fragments in the matrix region of hair follicles, but the spontaneous occurrence of apoptotic fragments was not observed. Since the apoptotic fragments was not observed. Since the apoptotic fragment assay is simple and reproducible in the whole body irradiation range of 0.5 to 8 Gy, it may be a good tool for evaluating the dose response of low dose radiation in vivo and provide a potentially valuable biological dosimeter for dose distribution determinations following accidental exposure.

A transcript from the long terminal repeats of a murine retrovirus associated with trans activation of cellular genes

Infection of human or murine cells with murine leukemia viruses rapidly increases the expression of a number of genes that belong to the immunoglobulin superfamily and are involved in T-lymphocyte activation, including the class I major histocompatibility complex antigens. We have reported recently that the long terminal repeat (LTR) of Moloney murine leukemia virus encodes a trans activator which induces transcription and expression of class I major histocompatibility complex genes and certain cytokine genes. The portion of the LTR responsible for trans activation was mapped by deletions to lie within the U3 region. We demonstrate here that a transcript is initiated within the U3 region and that its presence correlates with the trans-activating activity. Analysis of the LTR region reveals a potential internal promoter element for RNA polymerase III transcription within the U3 region. Studies with polymerase inhibitors suggest that this LTR transcript, designated let (LTR-encoded trans activator), is a product of RNA polymerase III. The mechanisms whereby RNA leukemia viruses cause lymphoid neoplasia after a long latent period have been extensively studied but are only partially understood. The region of the LTR identified here as being important in trans activation has recently been shown to be a critical determinant of the leukemogenicity and latency of Moloney murine leukemia virus. These findings suggest a novel mechanism of retrovirus-induced activation of cellular gene expression, potentially contributing to leukemogenesis.

Two soluble forms of glutamate dehydrogenase isoproteins from bovine brain

Two soluble forms of novel glutamate dehydrogenase isoproteins, designated GDH I and GDH II, have been purified from bovine brain. GDH I and GDH II were separated on a hydroxyapatite column and eluted by a step gradient at different phosphate concentrations (30 mM and 50 mM for GDH I and GDH II, respectively). The preparations were homogeneous on SDS/PAGE. GDH I and GDH II showed similarity in their molecular sizes and are composed of six identical subunits having a molecular size of 57,500 Da. Differences between the biochemical properties of GDH I and GDH II, such as N-terminal amino acid sequences of intact and tryptic-digested enzymes, kinetic parameters, optimum pH and heat stability, were extensively examined in both reductive amination of alpha-oxoglutarate and oxidative deamination of glutamate. The different effects of ADP on GDH isoproteins were also studied under various conditions. These results indicate that GDH I and GDH II, isolated from bovine brain, are novel and distinct polypeptides.

Reliability and validity of the cognitive impairment diagnosing instrument (CIDI) in the elderly

The reliability and validity of the Cognitive Impairment Diagnosing Instrument (CIDI) were studied in 67 nursing home elderly subjects and 251 elderly psychiatric patients. Its possible highest score is 77 and covers 10 subscales: short-term memory, long-term memory, concentration/calculation, abstract thinking, judgement, memory registration, higher cortical functions, orientation in time, orientation in place and object naming. Test-retest correlations were between 0.827 and 0.990 for the subscale scores and 0.984 for the total score. Inter-tester kappas for each item ranged from 0.200 to 1.000 with a mean of 0.698. Concordance rates were between 50.0 and 100.0% with a mean of 87.2%. Cronbach's alphas for the items of the individual subscales ranged from 0.702 to 0.915. Inter-subscale and subscale-total correlations ranged from 0.503 to 0.820 with a mean of 0.684 and from 0.721 to 0.883, respectively. Cronbach's alpha of the subscales was 0.934. Sensitivity and specificity were 93.3% and 93.8% at the cut-off point of 57.0/57.5 for dementia. Subscale and total scores were significantly different between the demented and non-demented. The total CIDI score was significantly correlated with scores of the Blessed Dementia Rating Scale and the Korean version of the Mini-Mental State Examination.

Ginsenosides activate DNA polymerase delta from bovine placenta

The activation of a DNA polymerase delta (pol delta) purified from bovine placenta by ginsenosides from Panax Ginseng C. A. Meyer has been studied. Preincubation of the enzyme with ginsenosides increased the polymerase activity 2.2-fold in a dose-dependent manner. There was a reproducible decrease in Km, in addition to a substantial increase in Vmax, in response to increasing concentrations of ginsenosides. Ginsenosides also activated the proofreading ability of 3'- to 5'-exonuclease activity associated with DNA pol delta. The coordinated activation of both polymerase and exonuclease activities of DNA pol delta by ginsenosides is consistent with the view that its polymerase and its exonuclease activities residue on the same protein molecule. UV/Vis difference spectroscopic studies suggested that the activation of DNA pol delta by ginsenosides might be due to the conformational change induced by ginsenosides binding.

The Moloney leukemia retroviral long terminal repeat trans-activates AP-1-inducible genes and AP-1 transcription factor binding

Moloney murine leukemia virus (Mo-MuLV) is a thymotropic and leukemogenic retrovirus which causes T lymphomas. The long terminal repeat (LTR) of Mo-MuLV affects the regulation of a number of cellular genes, including collagenase IV, monocyte chemoattractant protein-1, and c-jun genes, all of which contain 12-O-tetradecanoylphorbol-13-acetate-responsive element consensus sites within their promoters. We report here that Mo-MuLV stimulates the collagenase IV gene through transcription factor AP-1, and that the expression of a subgenomic portion of Mo-MuLV LTR alone is sufficient for this effect. Transient or stable expression of the viral LTR increases cellular AP-1 DNA binding activity. The collagenase IV 12-O-tetradecanoylphorbol-13-acetate-responsive element consensus sequence was shown to be required for this trans-activation. Deletions or mutations of this consensus site which abolished AP-1 binding also abolished trans-activation by the LTR. Transient or stable transfection of the viral LTR into cells stimulated c-jun gene expression, suggesting one mechanism whereby the viral LTR may induce cellular AP-1 activity. Thus, the Mo-MuLV LTR, through activation of the transcription factor AP-1, is capable of regulating cellular gene expression, including the induction of proto-oncogenes. This activity may be relevant to the mechanisms whereby retroviruses which do not contain oncogenes induce neoplasia.

Preventive effect of ginseng intake against various human cancers: a case-control study on 1987 pairs

This study presents the risk of various cancers in relation to ginseng intake based on the data from a case-control study conducted in the Korea Cancer Center Hospital. Ginseng intakers had a decreased risk [odds ratio = 0.50, 95% confidence interval (CI) = 0.44-0.58] for cancer compared with nonintakers. On the type of ginseng, the odds ratios for cancer were 0.37 (95% CI = 0.29-0.46) for fresh ginseng extract intakers, 0.57 (95% CI = 0.48-0.68) for white ginseng extract intakers, 0.30 (95% CI = 0.22-0.41) for white ginseng powder intakers, and 0.20 (95% CI = 0.08-0.50) for red ginseng intakers. Intakers of fresh ginseng slice, fresh ginseng juice, and white ginseng tea, however, showed no decreasing risk. There was a decrease in risk with the rising frequency and duration of ginseng intake, showing a dose-response relationship. On the site of cancer, the odds ratios were 0.47 for cancer of the lip, oral cavity, and pharynx; 0.20 for esophageal cancer; 0.36 for stomach cancer; 0.42 for colorectal cancer; 0.48 for liver cancer; 0.22 for pancreatic cancer; 0.18 for laryngeal cancer; 0.55 for lung cancer; and 0.15 for ovarian cancer. In cancers of the female breast, uterine cervix, urinary bladder, and thyroid gland, however, there was no association with ginseng intake. In cancers of the lung, lip, oral cavity and pharynx, and liver, smokers with ginseng intake showed decreased odds ratios compared with smokers without ginseng intake. These findings support the view that ginseng intakers had a decreased risk for most cancers compared with nonintakers.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein lipase association with lipoproteins involves protein-protein interaction with apolipoprotein B

Lipoprotein lipase (LPL) hydrolyzes chylomicron and very low density lipoprotein (VLDL) triglycerides and potentiates the cellular uptake of lipoproteins. These LPL-lipoprotein associations could involve only protein-lipid interaction, or they could be modulated by apolipoproteins (apo). ApoB is the major protein component of chylomicrons, VLDL, and low density lipoprotein (LDL). ApoB100, a large glycoprotein with a molecular mass of 550 kDa, is composed of several functional domains. A carboxyl-terminal region of the protein is the ligand for the LDL receptor. There are several hydrophobic domains that are believed to be important in lipid binding. The relatively hydrophilic amino-terminal region of apoB, however, has no known function. Using solid phase assays we quantified LPL-lipoprotein complex formation. On a molar basis, severalfold greater amounts of LPL bound to LDL and VLDL than to high density lipoprotein at all the concentrations of LPL tested (0.9-55 nM). To assess the roles of LDL protein versus lipid, we performed competition and ligand blotting experiments. LDL and an amino-terminal fragment of apoB competed better for 125I-LPL binding to LDL than did lipid emulsion particles. Delipidation of LDL-coated plates did not alter LPL binding. On ligand blots, LPL bound to amino-terminal fragments of apoB generated by thrombin digestion but not to apoA1, apoE, or carboxyl-terminal fragments of apoB. Further evidence for LPL interaction with the amino-terminal region of apoB was obtained using anti-apoB monoclonal antibodies. Antibodies directed against the amino-terminal regions of apoB blocked LPL interaction with LDL, whereas those against the carboxyl-terminal region of apoB did not inhibit LPL interaction with LDL. Thus, we conclude that a specific interaction between LPL and the amino-terminal region of apoB may facilitate LPL association with circulating lipoproteins.

Photoaffinity labeling of retinoic acid-binding proteins

Retinoid-binding proteins are essential mediators of vitamin A function in vertebrate organisms. They solubilize and stabilize retinoids, and they direct the intercellular and intracellular trafficking, transport, and metabolic function of vitamin A compounds in vision and in growth and development. Although many soluble retinoid-binding proteins and receptors have been purified and extensively characterized, relatively few membrane-associated enzymes and other proteins that interact with retinoids have been isolated and studied, due primarily to their inherent instabilities during purification. In an effort to identify and purify previously uncharacterized retinoid-binding proteins, it is shown that radioactively labeled all-trans-retinoic acid can be used as a photoaffinity labeling reagent to specifically tag two known retinoic acid-binding proteins, cellular retinoic acid-binding protein and albumin, in complex mixtures of cytosolic proteins. Additionally, a number of other soluble and membrane-associated proteins that bind all-trans-[11,12-3H]retinoic acid with high specificity are labeled utilizing the same photoaffinity techniques. Most of these labeled proteins have molecular weights that do not correspond to any known retinoid-binding proteins. Thus, photoaffinity labeling with all-trans-retinoic acid and related photoactivatable retinoids is a method that should prove extremely useful in the identification and purification of novel soluble and membrane-associated retinoid-binding proteins from ocular and nonocular tissues.

Production and characterization of monoclonal antibodies to bovine brain succinic semialdehyde reductase

Monoclonal antibodies against bovine brain succinic semialdehyde reductase were produced and characterized. A total of nine monoclonal antibodies recognizing different epitopes of the enzyme were obtained, of which two inhibited the enzyme activity and three stained cytosol of rat spinal cord neurons as observed by indirect immunofluorescence microscopy. When unfractionated total proteins of bovine brain homogenate were separated by gel electrophoresis and immunoblotted, the antibodies specifically recognized a single protein band of 34 kDa, which comigrates with purified bovine succinic semialdehyde reductase. Using the antisuccinic semialdehyde reductase antibodies as probes, we investigated the cross-reactivities of brain succinic semialdehyde reductases from some mammalian and an avian species. The immunoreactive bands on western blots appeared to be the same in molecular mass--34 kDa--in all animal species tested, including humans. The result indicates that brain succinic semialdehyde reductase is distinct from other aldehyde reductases and that mammalian brains contain only one succinic semialdehyde reductase. Moreover, the enzymes among the species are immunologically very similar, although some properties of the enzymes reported previously were different from one another.

Bacterial glutamate racemase has high sequence similarity with myoglobins and forms an equimolar inactive complex with hemin

Glutamate racemase (EC 5.1.1.3), an enzyme of microbial origin, shows significant sequence homology with mammalian myoglobins, in particular in the regions corresponding to the E and F helices, which constitute the heme binding pocket of myoglobins. Glutamate racemase binds tightly an equimolar amount of hemin, leading to loss of racemase activity. Although this enzyme shows homology with aspartate racemase, the latter does not bind hemin. The glutamate racemase gene of Pediococcus pentosaceus has a 795-nt open reading frame and encodes 265-amino acid residues, which form a monomeric protein (M(r) 29,000). Neither racemase has cofactors, but they contain essential cysteine residues [Yohda, M., Okada, H. & Kumagai, H. (1991) Biochim. Biophys. Acta 1089, 234-240].

Protective effects of potato extracts and 16,16-dimethyl prostaglandin E2 on the induction of hepatic foci by cotreatment of gamma radiation and diethylnitrosamine

We investigated the effect of potato extracts and 16,16-dimethyl prostaglandin E2 (DiPGE2) on the induction of glutathione S-transferase P-positive (GST-P+) altered hepatic foci in newborn Sprague-Dawley rats given single treatment with 60Co gamma irradiation and diethylnitrosamine (DEN) alone or in sequential combination. Intraperitoneal injection of 0.15 mumol/g body weight of DEN 1 hour after gamma radiation significantly increased the frequencies of GST-P+ hepatic foci compared to DEN or gamma radiation alone and DEN injection 1 hour before irradiation (p < 0.001). Potato extract was given at a dose of 2 mg/ml in drinking water for 3 weeks and DiPGE2 given at a dose of 10 micrograms/mouse 30 minutes before irradiation. Potato extracts and DiPGE2 decreased significantly the number (p < 0.001), area (p < 0.001) and Dmax (p < 0.05) of GST-P+ hepatic foci compared to the corresponding control. These results suggest that potato extracts and DiPGE2 have radio-protective potential and further studies for underlying mechanisms will be necessary.

The long terminal repeats of a murine retrovirus encode a trans-activator for cellular genes

Type C RNA leukemia viruses cause lymphoid neoplasia after an extended latent period by an unknown mechanism. Infection of human or murine cells with murine leukemia viruses rapidly increases the expression of genes belonging to the immunoglobulin superfamily and involved in T-lymphocyte activation, including the class I major histocompatibility complex antigens. We report here that the long terminal repeat (LTR) of Moloney murine leukemia virus encodes a novel trans-activator, which induces transcription and expression of class I major histocompatibility complex genes. The portion of the LTR responsible for trans-activation lies within the U3 region and can be excised from the LTR while maintaining its activity. Analysis of the U3 region of the LTR and its flanking sequences suggests that functional or regulatory elements for the trans-activity exist between nucleotides 32 and 219 of the LTR sequences. The region of the LTR identified here as important in trans-activation has been shown recently to be a critical determinant of leukemogenicity and latency of Moloney murine leukemia virus. These findings suggest a novel mechanism of retrovirus-induced activation of cellular gene expression, potentially contributing to leukemogenesis.

Acceleration of uptake of LDL but not chylomicrons or chylomicron remnants by cells that secrete apoE and hepatic lipase

ApoE is a ligand for the low density lipoprotein (LDL) receptor as well as for the LDL receptor-related protein (LRP). The enzyme hepatic lipase (HL) may also affect the uptake of lipoproteins by modifying their composition. We have tested the hypothesis that hepatic lipase and apoE can function as co-factors to alter the rate of lipoprotein uptake. Chinese hamster ovary (CHO) cells were transfected with cDNAs for rat hepatic lipase, human apoE or both HL and apoE. The secreted recombinant proteins were thoroughly characterized and had properties identical to the native proteins. Hepatic lipase and apoE were secreted at 0.17 and 1.25 micrograms/mg cell protein per hour, rates comparable to those in normal liver. 125I-labeled LDL, chylomicron remnants, or chylomicrons were added to media at concentrations near their Kd. In cells that secreted either apoE or hepatic lipase, or both apoE and hepatic lipase, LDL binding was significantly greater than with control cells (2.2-, 2-, 2-fold greater, respectively). Similar enhancement of LDL degradation was observed. In the presence of anti-LDL receptor antibodies, these values were reduced to control levels; thus, the enhanced uptake was mediated by the LDL receptor and not the LRP. The amount of LDL receptor protein, as judged by Western blotting, was similar in the various cell types. Incubation of control CHO cells with media from secreting transfected cells also increased the uptake of 125I-labeled LDL. Kinetic studies indicated that, in apoE-secreting cells, increased LDL binding is associated with a lower Kd and an unchanged Vmax as compared to the control cells; furthermore, when LDL were reisolated by column chromatography (but not by ultracentrifugation) from the incubations where apoE was being secreted, apoE was identified adherent to the LDL particles. Together, these results suggest that the effect is due to alteration of the lipoprotein and not the cell. In contrast, the uptake of 125I-labeled chylomicron remnants, and 125I-labeled chylomicrons was not greater in the transfected cells. Thus, in the amounts secreted by these cells, hepatic lipase and apoE do not convert chylomicrons to chylomicron remnants or alter the uptake of chylomicron remnants by either the LDL receptor or the LRP. The enhancement of LDL removal in cells that secrete hepatic lipase or apoE may help determine the amount of LDL removed by a particular tissue.

An amino-terminal fragment of apolipoprotein B binds to lipoprotein lipase and may facilitate its binding to endothelial cells

Lipoprotein lipase (LPL), the principal enzyme which hydrolyzes triglycerides in circulating plasma lipoproteins, functions while bound to the luminal surface of endothelial cells. LPL is a heparin-binding protein and has been assumed to associate with endothelial cell heparan sulfate proteoglycans (HSPG). Recently, using ligand blotting and affinity chromatography we identified a 116-kDa heparin-releasable LPL-binding protein (hrp-116) from endothelial cells which was not a HSPG (Sivaram, P., Klein, M. G., and Goldberg, I. J. (1992) J. Biol. Chem. 267, 16517-16522). This suggested that, like a number of other heparin-binding proteins, LPL binding to cells also involves non-HSPG proteins. Using heparin-agarose affinity chromatography, a 116-kDa LPL-binding protein was purified from endothelial cell extracts. Microsequencing of peptides generated by Lys-C protease digestion revealed complete homology with four different regions in the NH2-terminal part of human apolipoprotein B (apoB). Western blots using anti-apoB monoclonal antibodies (mAb) that recognize the NH2-terminal region of apoB confirmed that a 116-kDa fragment of apoB was present on endothelial cell membranes. Further evidence that LPL associates with the NH2-terminal region of apoB was obtained by showing 1) that an NH2-terminal fragment of apoB obtained from apoB-transfected CHO cells bound LPL on ligand blots and 2) that NH2-terminal fragments of apoB generated by thrombin digestion of low density lipoprotein bind LPL. Evidence that the NH2-terminal region of apoB mediates LPL interaction with endothelial cells was obtained using monoclonal antibodies. mAb3 and mAb19, which recognize epitopes near the NH2 terminus of apoB, inhibited 125I-LPL binding to cells by 60-65%. In contrast, mAb47, which has determinants at the COOH-terminal end of apoB, inhibited LPL binding by only about 10%. The inhibitory effects of mAb3 and mAb19 were abolished following treatment of cells with heparin, which removes the 116-kDa LPL-binding protein. Furthermore, incubation of 125I-LPL in medium containing an NH2-terminal apoB fragment reduced LPL binding to cells. These data suggest that an NH2-terminal fragment of apoB that binds to endothelial surfaces facilitates LPL binding to cells.