Phosphorylation and activation of the Jak-3 Janus kinase in response to interleukin-2

Interleukin-2 is an autocrine growth factor for T cells which also activates other cells including B cells and natural killer cells. The subunits of the interleukin-2 receptor (IL-2R) lack intrinsic enzymatic activity, but protein tyrosine phosphorylation is a critical event following ligand binding and src family kinases, such as Lck, are known to be activated by IL-2 (refs 5-9). However, IL-2 signalling can occur in the absence of receptor interaction with Lck, suggesting that other protein tyrosine kinases might be important. Here we report that a new member of the Janus family of kinases (Jak-3) is coupled to the IL-2R in human peripheral blood T cells and natural killer cells.

Crystal structure of p50/p65 heterodimer of transcription factor NF-kappaB bound to DNA

The NF-kappaB p50/p65 heterodimer is the classical member of the Rel family of transcription factors which regulate diverse cellular functions such as immune response, cell growth, and development. Other mammalian Rel family members, including the proteins p52, proto-oncoprotein c-Rel, and RelB, all have amino-terminal Rel-homology regions (RHRs). The RHR is responsible for the dimerization, DNA binding and cytosolic localization of these proteins by virtue of complex formation with inhibitor kappaB proteins. Signal-induced removal of kappaB inhibitors allows translocation of dimers to the cell nucleus and transcriptional regulation of kappaB DNA-containing genes. NF-kappaB specifically recognizes kappaB DNA elements with a consensus sequence of 5'-GGGRNYYYCC-3' (R is an unspecified purine; Y is an unspecified pyrimidine; and N is any nucleotide). Here we report the crystal structure at 2.9 A resolution of the p50/p65 heterodimer bound to the kappaB DNA of the intronic enhancer of the immunoglobulin light-chain gene. Our structure reveals a 5-base-pair 5' subsite for p50, and a 4-base-pair 3' subsite for p65. This structure indicates why the p50/p65 heterodimer interface is stronger than that of either homodimer. A comparison of this structure with those of other Rel dimers reveals that both subunits adopt variable conformations in a DNA-sequence-dependent manner. Our results explain the different behaviour of the p50/p65 heterodimer with heterologous promoters.

Tyrosine phosphorylation and activation of STAT5, STAT3, and Janus kinases by interleukins 2 and 15

The cytokines interleukin 2 (IL-2) and IL-15 have similar biological effects on T cells and bind common hematopoietin receptor subunits. Pathways that involve Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) have been shown to be important for hematopoietin receptor signaling. In this study we identify the STAT proteins activated by IL-2 and IL-15 in human T cells. IL-2 and IL-15 rapidly induced the tyrosine phosphorylation of STAT3 and STAT5, and DNA-binding complexes containing STAT3 and STAT5 were rapidly activated by these cytokines in T cells. IL-4 induced tyrosine phosphorylation and activation of STAT3 but not STAT5. JAK1 and JAK3 were tyrosine-phosphorylated in response to IL-2 and IL-15. Hence, the JAK and STAT molecules that are activated in response to IL-2 and IL-15 are similar but differ from those induced by IL-4. These observations identify the STAT proteins activated by IL-2 and IL-15 and therefore define signaling pathways by which these T-cell growth factors may regulate gene transcription.

Arachidonate lipoxygenases as essential regulators of cell survival and apoptosis

Arachidonic acid (AA) metabolites derived from both cyclooxygenase (COX) and lipoxygenase (LOX) pathways transduce a variety of signals related to cell growth. Here, we report that the AA LOX pathway also functions as a critical regulator of cell survival and apoptosis. Rat Walker 256 (W256) carcinosarcoma cells express 12-LOX and synthesize 12(S)- and 15(S)-hydroxyeicosatetraenoic acids as their major LOX metabolites. W256 cells transfected with 12-LOX-specific antisense oligonucleotide or antisense oligonucleotides directed to conserved regions of LOXs underwent time- and dose-dependent apoptosis. Likewise, treatment of W256 cells with various LOX but not COX inhibitors induced apoptotic cell death, which could be partially inhibited by exogenous 12(S)- or 15(S)-hydroxyeicosatetraenoic acids. The W256 cell apoptosis induced by antisense oligos and LOX inhibitors was followed by a rapid downregulation of bcl-2 protein, a dramatic decrease in the bcl-2/bax ratio, and could be suppressed by bcl-2 overexpression. In contrast, p53, which is wild type in W256 cells, did not undergo alterations during apoptosis induction. The results suggest that the LOX pathway plays an important physiological role in regulating apoptosis.

Molecular cloning of L-JAK, a Janus family protein-tyrosine kinase expressed in natural killer cells and activated leukocytes

Protein-tyrosine kinases (PTKs) are critical enzymes for receptor-mediated signaling in lymphocytes. Because natural killer (NK) cells are large granular lymphocytes with specialized effector function, we set out to identify PTKs preferentially expressed in these cells. One such PTK was identified and molecularly cloned. The predicted amino acid sequence shows that this kinase lacks SH2 or SH3 domains typical of src family kinases but has tandem nonidentical catalytic domains, indicating that it is a member of the Janus family of PTKs. Immunoprecipitation using antiserum generated against a peptide corresponding to the deduced amino acid sequence of this gene revealed a kinase with a molecular weight of approximately 125,000. The pattern of expression of this kinase contrasted sharply with that of other Janus kinases, which are ubiquitously expressed. The kinase described in the present study was found to be more limited in its expression; expression was found in NK cells and an NK-like cell line but not in resting T cells or in other tissues. In contrast, stimulated and transformed T cells expressed the gene, suggesting a role in lymphoid activation. Because of its homology and tissue expression, we have tentatively termed this PTK gene L-JAK for leukocyte Janus kinase.

A novel DNA recognition mode by the NF-kappa B p65 homodimer

The crystal structure of the NF-kappa B p65 (RelA) homodimer in complex with a DNA target has been determined to 2.4 A resolution. The two p65 subunits are not symmetrically disposed on the DNA target. The homodimer should optimally bind to a pseudo-palindromic nine base pair target with each subunit recognizing a 5'GGAA-3' half site separated by a central A-T base pair. However, one of the subunits (subunit B) encounters a half site of 5'-GAAA-3'. The single base-pair change from G-C to A-T results in highly unfavorable interactions between this half site and the base contacting protein residues in subunit B, which leads to an 18 degrees rotation of the N-terminal terminal domain from its normal conformation. Remarkably, subunit B retains all the interactions with the sugar phosphate backbone of the DNA target. This mode of interaction allows the NF-kappa B p65 homodimer to recognize DNA targets containing only one cognate half site. Differences in the sequence of the other half site provide variations in conformation and affinity of the complex.

Tumor necrosis factor-alpha and interferon-gamma suppress the activation of human type I collagen gene expression by transforming growth factor-beta 1. Evidence for two distinct mechanisms of inhibition at the transcriptional and posttranscriptional levels

Regulation of human type I procollagen gene expression was studied in cultured fibroblasts both at the transcriptional and posttranscriptional level. Transcriptional regulation was examined in cultures transfected with a human pro alpha 2(I) collagen promoter/reporter gene (chloramphenicol acetyltransferase) construct, while posttranscriptional regulation was assessed by parallel determinations of type I procollagen mRNA steady-state levels. Transforming growth factor-beta 1 (TGF-beta 1) elicited a marked, approximately 5-23-fold, enhancement of pro alpha 2(I) collagen promoter activity, which was accompanied by an elevation of type I procollagen mRNA levels. This enhancement of gene expression was suppressed by tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), as determined at mRNA steady-state level, but two distinct mechanisms were involved. TNF-alpha suppressed the pro alpha 2(I) collagen promoter activity, whereas IFN-gamma had only a minimal effect at transcriptional level. The effects of TNF-alpha and IFN-gamma were synergistic, suggesting that combination of these two factors may potentially provide pharmacologic means to counteract tissue deposition of collagen in diseases involving TGF-beta.

Enhanced elastin and fibrillin gene expression in chronically photodamaged skin

Cutaneous aging consists of chronologic aging as well as actinic damage, referred to as photoaging. Most of the morphologic changes associated with an aged appearance result from actinic damage to the skin. The morphologic changes in sun-damaged skin are associated with accumulation of material having the staining characteristics of elastin, known as solar elastosis, in the superficial dermis. Previous studies have demonstrated the presence of elastin within areas of solar elastosis; however, little is known about the mechanisms leading to elastin accumulation in photoaged skin. In addition, fibrillin, the fibrillar component of elastic fibers, has been found in small amounts in solar elastosis. In this study we demonstrate increased elastin mRNA levels in photoaged skin, as well as increased elastin and fibrillin mRNAs in skin explant-derived fibroblasts using Northern hybridizations, compared with controls from sun-protected sites of the same individual. Increased elastin mRNA levels result from transcriptional upregulation of the gene, as demonstrated by transient transfections with a human elastin promoter/chloramphenicol acetyltransferase construct. Elevated mRNA levels were also correlated with increased elastin and fibrillin deposition in paired biopsy specimens from photodamaged and non-sun-exposed skin, as demonstrated by immunohistochemical staining. Thus, approaches to counteract transcriptional activation of elastin gene expression may be useful in preventing the changes associated with cutaneous photoaging.

Effect of inhaled interleukin-5 on airway hyperreactivity and eosinophilia in asthmatics

In order to investigate the role of interleukin-5 (IL-5) in airway hyperreactivity and eosinophilia, we observed the effect of inhaled recombinant human IL-5 on airway responsiveness to methacholine and cell populations in induced sputum in eight patients with allergic bronchial asthma using a placebo-controlled study design. Our results demonstrated that the inhalation of IL-5 did not alter lung function in allergic asthmatics. In the control experiments receiving either vehicle or 0.4 ng of endotoxin, methacholine PC20 values did not change nor did the numbers of eosinophils or eosinophil cationic protein (ECP) sputum values change from baseline. In contrast, after IL-5 inhalation, methacholine PC20 fell from baseline (0.90 +/- 166 mg/ml) to 0.32 +/- 1.63 mg/ml (p < 0.01) at 24 h, and to 0.55 +/- 1.49 mg/ml (p < 0.05) at 48 h. Accompanying this increased airway sensitivity was a significant eosinophilia and elevated concentrations of ECP in induced sputum. Our data provided direct evidence that IL-5 increases airway responsiveness and infiltration of activated eosinophils into the airway in patients with allergic bronchial asthma. It also could be concluded that the observed airway hyperreactivity and eosinophilia were not endotoxin related.

Long-term sun exposure alters the collagen of the papillary dermis. Comparison of sun-protected and photoaged skin by northern analysis, immunohistochemical staining, and confocal laser scanning microscopy

BACKGROUND

Long-term solar irradiation produces both morphologic and functional changes in affected skin. Because collagen is the major structural component of skin, any alteration in its production or degradation could have profound effects on cutaneous functional integrity.

OBJECTIVE

Our purpose was to investigate alterations in the production and morphology of collagen fibers brought about by long-term sun exposure.

METHODS

We compared collagen and collagenase gene expression and collagen immunohistochemical staining and used confocal laser scanning microscopy for morphologic examination of dermal collagen fibers in photodamaged compared with sun-protected skin from the same persons.

RESULTS

Despite a large increase in elastin messenger RNA in sun-damaged skin, collagen and collagenase gene expression remained essentially unchanged. However, striking alterations in the papillary dermis of photoaged skin were found, which revealed large, abnormally clumped elastic fibers and deformed collagen fibers of various diameters, replacing the normal architecture of the papillary dermis.

CONCLUSION

Our data provide evidence for normal collagen gene expression in sun-damaged skin and suggest that degradation and remodeling of collagen take place in the papillary dermis accompanied by deposition of other matrix components, predominantly abnormal elastic fibers.

Sp1 sites mediate activation of the plasminogen activator inhibitor-1 promoter by glucose in vascular smooth muscle cells

This study was designed to characterize the direct effects of hyperglycemia on plasminogen activator inhibitor-1 (PAI-1) expression in cultured vascular smooth muscle cells. Glucose induced dose- and time-dependent increases of PAI-1 mRNA expression in rat aortic smooth muscle (RASM) cells in vitro. Using a series of luciferase reporter gene constructs containing PAI-1 5'-flanking sequence (from -6.4 kilobase to -42 base pairs (bp)) transfected into RASM, we found that glucose (25 mM) consistently induced a 4-fold increase in luciferase activity, with the response localized to sequence between -85 and -42 bp. Mutagenesis of two putative Sp1-binding sites located in the region of interest essentially obliterated the glucose-response. Electrophoretic mobility shift assays with radiolabeled oligonucleotides containing the two putative Sp1-binding sites from PAI-1 promoter and nuclear extracts from RASM cells revealed that glucose treatment markedly changed the mobility pattern of the major protein-DNA complexes. Supershift assay showed that transcription factor Sp1 was present in the complexes under control and hyperglycemic conditions. These results suggest that glucose regulates PAI-1 gene expression in RASM cells through an effect on two adjacent Sp1 sites located between -85 and -42 bp of the PAI-1 5'-flanking region and that the release of a transcriptional repressor from the Sp1 complexes may explain the activation of the PAI-1 gene under high glucose conditions in RASM cells.

Elevated 12-lipoxygenase mRNA expression correlates with advanced stage and poor differentiation of human prostate cancer

OBJECTIVES

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer death in males in the United States. The mortality is due mainly to distant metastasis. Therefore, predicting the prognosis of prostate cancer patients is an important clinical problem. Previously, we demonstrated that a 12-lipoxygenase (12-LOX) metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid, enhances the invasiveness of prostate cancer cells and that a 12-LOX-selective inhibitor [N-benzyl-N-hydroxy-5-phenylpentanamide] reduces experimental metastasis in animal model systems. In this study, we investigated the potential of 12-LOX as a predictor for the aggressiveness of prostate cancer.

METHODS

The mRNA expression level of 12-LOX in 122 matching prostate normal and cancerous tissues were measured by quantitative reverse transcription- polymerase chain reaction. Possible association between 12-LOX expression and histologic grade, pathologic and clinical stage, margin positivity, age, and race was analyzed.

RESULTS

12-LOX mRNA levels were elevated in cancer cells and the expression associated with poor differentiation and invasiveness of prostate cancer. Overall, 46 (38%) of 122 evaluable patients showed elevated levels of 12-LOX mRNA in prostate cancer tissues compared with the matching normal tissues. A statistically significantly greater number of cases were found to have an elevated level of 12-LOX among T3, high grade, and surgical margin-positive than T2, intermediate, and low grade, and surgical margin-negative prostatic adenocarcinomas.

CONCLUSIONS

Our data suggest that elevation of 12-LOX mRNA expression occurs more frequently in advanced stage, high-grade prostate cancer and that 12-LOX may serve as an indicator for progression and prognosis of prostate cancer. This enzyme also may be a novel target for the development of anti-invasive and antimetastatic agents.

The amino terminus of JAK3 is necessary and sufficient for binding to the common gamma chain and confers the ability to transmit interleukin 2-mediated signals

JAK3 is a protein tyrosine kinase that specifically associates with the common gamma chain (gammac), a shared subunit of receptors for interleukin (IL) 2, 4, 7, 9, and 15. Patients deficient in either JAK3 or gammac presented with virtually identical forms of severe combined immunodeficiency (SCID), underscoring the importance of the JAK3-gammac interaction. Despite the key roles of JAK3 and gammac in lymphocytic development and function, the molecular basis of this interaction remains poorly understood. In this study, we have characterized the regions of JAK3 involved in gammac association. By developing a number of chimeric JAK3-JAK2 constructs, we show that the binding specificity to gammac can be conferred to JAK2 by transferring the N-terminal domains of JAK3. Moreover, those JAK3-JAK2 chimeras capable of binding gammac were also capable of reconstituting IL-2 signaling as measured by inducible phosphorylation of the chimeric JAK3-JAK2 protein, JAK1, the IL-2 receptor beta chain, and signal transducer and activator of transcription 5A. Subsequent deletion analyses of JAK3 have identified the N-terminal JH7-6 domains as a minimal region sufficient for gammac association. Furthermore, expression of the mutant containing only the JH7-6 domains effectively competed with full-length JAK3 for binding to gammac. We conclude that the JH7-6 domains of JAK3 are necessary and sufficient for gammac association. These studies offer clues toward a broader understanding of JAK-mediated cytokine signaling and may provide a target for the development of novel therapeutic modalities in immunologically mediated diseases.

Transcriptional regulation of decorin gene expression. Induction by quiescence and repression by tumor necrosis factor-alpha

Decorin, a leucine-rich proteoglycan with ubiquitous tissue distribution, may play essential biological roles during inflammation and cancer growth through its ability to bind extracellular matrix constituents and growth factors. In this study, we demonstrate that decorin gene expression is greatly enhanced after normal diploid fibroblasts reach confluency and cease to proliferate. Elevation of decorin mRNA steady state levels was maintained for up to 16 days postconfluency. In vitro transcription analyses indicated enhanced transcriptional activity in quiescent fibroblasts when compared to cells harvested in their logarithmic phase of growth. This phenotypic trait was reversed by the exogenous addition of tumor necrosis factor-alpha (TNF-alpha). Furthermore, transforming growth factor-beta (TGF-beta) down-regulated decorin gene expression in an additive manner with TNF-alpha. Transient cell transfection assays using plasmid constructs harboring the decorin promoter linked to the chloramphenicol acetyltransferase reporter gene demonstrated a dose-dependent transcriptional repression by TNF-alpha. These findings were further corroborated by in vitro transcription experiments using nuclear extracts from control and TNF-alpha-treated quiescent fibroblasts. In contrast, the decorin promoter constructs failed to respond to TGF-beta, thus suggesting either post-transcriptional regulation by this growth factor or lack of TGF-beta-responsive elements. Further experiments with 5' deletion constructs showed two TNF-alpha response elements, one residing within the 5'-untranslated region (exon Ib), the other one between residues -188 and -140 of the decorin promoter. Collectively, our results indicate that TNF-alpha, through its ability to transcriptionally inhibit decorin gene expression in growth-arrested cells, may be a key modulator of the biological functions of this proteoglycan.

Permanent anatomic closure of the ductus arteriosus in newborn baboons: the roles of postnatal constriction, hypoxia, and gestation

Permanent closure of the ductus arteriosus requires loss of cells from the muscle media and development of neointimal mounds, composed in part of proliferating endothelial cells. We hypothesized that postnatal ductus constriction produces hypoxia of the inner vessel wall; we also hypothesized that hypoxia might lead to cell death and the production of vascular endothelial cell growth factor (VEGF), a hypoxia-inducible growth factor that stimulates endothelial proliferation. We mapped the distribution of hypoxia in newborn baboons and correlated it with the appearance of cell death (TUNEL technique), VEGF expression, and endothelial proliferation (proliferating cell nuclear antigen expression). In the full-term baboon (n=10), the ductus was functionally closed on Doppler examination by 24 h after delivery. Regions of the ductus where the lumen was most constricted were associated with moderate/intense hypoxia; VEGF expression was increased in the hypoxic muscle media, and luminal endothelial cells, adjacent to the hypoxic media, were proliferating. Cells in the most hypoxic regions of the ductus wall were undergoing DNA fragmentation. In contrast, regions of the ductus with mild degrees of hypoxia had no evidence of cell death, VEGF expression, or endothelial proliferation. Cell death and endothelial proliferation seemed to be limited to regions of the full-term ductus experiencing moderate/intense hypoxia. In the premature baboon (67% gestation) (n=24), only 29% closed their ductus by Doppler examination before d 6. None of the premature baboons, including those with a closed ductus by Doppler, had evidence of moderate/intense hypoxia; also, there was no evidence of cell death, VEGF expression, endothelial proliferation, or neointima formation by d 6. Therefore, the premature ductus is resistant to developing hypoxia, even when its lumen is constricted; this may make it susceptible to later reopening.

Signaling via IL-2 and IL-4 in JAK3-deficient severe combined immunodeficiency lymphocytes: JAK3-dependent and independent pathways

Both IL-2 and IL-4 bind to receptors containing the common gamma chain and JAK3. Although JAK3 is required for proper lymphoid development, the precise roles of this kinase in IL-2 and IL-4 signaling in lymphocytes have not been defined. Here, we have studied IL-2 and IL-4 signaling in B cell lines lacking JAK3. Although IL-2-induced phosphorylation of IL-2R beta, JAK1, and STAT5 all required the presence of JAK3, IL-4-mediated phosphorylation of JAK1, STAT6, and insulin receptor substrates 1 and 2 did not. However, IL-4-induced effects were clearly improved following JAK3 expression. These data indicate that IL-4 signaling occurs in the absence of of JAK3, but is comparatively inefficient. These findings may help in understanding the pathogenesis of the immunodeficiency that occurs with mutations of JAK3 and may suggest a mechanism for the pleiotropic effects of IL-4.

Platelets and cancer metastasis: more than an epiphenomenon

In this review we have presented overwhelming evidence that platelets play an important enhancing role in tumor cell-vasculature interactions and cancer metastasis. Tumor cells employ a host of mechanisms to induce platelet aggregation; vice versa, platelets make use of a spectrum of mechanisms to modulate tumor cell-EC and tumor cell-ECM interactions. Various COX and LOX metabolites are closely involved in this bidirectional modulation, thus providing us with a very promising therapeutic avenue by modifying the actions of these metabolites. On the other hand, adhesion molecules are mediators of tumor cell-platelet-EC interactions; therefore interference with these adhesion molecules and various adhesive processes either by soluble peptides, nonpeptidic analogues, or specific antibodies holds great investigational and clinical appeal.

Cloning and expression of cDNA encoding human galactocerebrosidase, the enzyme deficient in globoid cell leukodystrophy

Globoid cell leukodystrophy (Krabbe disease) is an autosomal recessive disorder resulting from the deficiency of galactocerebrosidase (GALC) activity. GALC is responsible for the lysosomal catabolism of galactosylceramide, a major lipid in myelin, kidney and epithelial cells of small intestine and colon. We describe the molecular cloning of human GALC cDNA and its expression in COS-1 cells. Degenerate PCR primers, derived from N-terminal amino acid sequence from the 51 kDa band from human brain, were used to amplify cat testes RNA, and the resulting product was used to screen human testes and brain libraries. Two overlapping clones contained the total protein coding region, while additional clones and PCR amplification were needed to obtain the complete 3' end of the cDNA. The 3795 bp obtained include 47 bp 5' to the initiation start site, 2007 bp of open reading frame (coding for 669 amino acids), and 1741 bp of 3' untranslated sequence. Modification of the sequence surrounding the initiation codon to one more favorable for expression, resulted in a 6-fold increase in GALC activity in transfected COS-1 cells. The isolation of this clone will permit investigations into the causes for GALC deficiency in humans and available animal models, development of more accurate tests for patient and carrier identification, and evaluation of methods for effectively treating GALC deficiency, initially using the animal models.

Dopamine and glutamate release in the nucleus accumbens and ventral tegmental area of rat following lateral hypothalamic self-stimulation

Rewarding hypothalamic brain stimulation is thought to depend on trans-synaptic activation of high-threshold (and thus rarely directly depolarized by rewarding stimulation) dopaminergic fibers of the medial forebrain bundle. We used in vivo microdialysis and high-performance liquid chromatography coupled with electrochemical or fluorometric detection to investigate the concurrent release of dopamine and glutamate in the nucleus accumbens septi and in the ventral tegmental area, as a function of lateral hypothalamic self-stimulation.Self-stimulation at a variety of stimulation frequencies and pulse widths increased levels of dopamine and its primary metabolites, dihydroxyphenylacetic acid and homovanillic acid in the nucleus accumbens. Lateral hypothalamic self-stimulation also induced significant increases in ventral tegmental area dopamine and metabolite levels, and the percentage increase of dopamine was higher in this region than in the nucleus accumbens. Local perfusion with the dopamine uptake inhibitor nomifensine (10 microM) increased dopamine levels in the nucleus accumbens about three-fold and potentiated the increase of dopamine levels induced by self-stimulation. Nomifensine perfusion also induced a delayed decrease in nucleus accumbens glutamate levels, and self-stimulation did not modify this effect of the drug. Local perfusion with the D2-type dopamine receptor antagonist raclopride significantly increased both basal and self-stimulation induced dopamine release in the nucleus accumbens. Neither nomifensine nor raclopride perfusion significantly affected the maximal rates of self-stimulation. Perfusion with tetrodotoxin (2 microM) into nucleus accumbens significantly decreased basal and prevented stimulation-induced increases in accumbens dopamine levels but only slightly decreased the rate of self-stimulation. In contrast, perfusion of tetrodotoxin (0.5 microM) into the ventral tegmental area decreased basal and blocked stimulation-induced increases in both nucleus accumbens and ventral tegmental area dopamine levels; this treatment also blocked or strongly inhibited self-stimulation. While it had no effect on glutamate levels in the nucleus accumbens, lateral hypothalamic self-stimulation induced a significant and tetrodotoxin-sensitive increase in glutamate levels in the ventral tegmental area. Taken together, the present results indicate that, across a broad range of stimulation parameters, rewarding lateral hypothalamus stimulation causes major and persistent activation of the mesolimbic dopamine system, and suggest descending glutamatergic fibers in the medial forebrain bundle as a candidate for the directly activated descending pathway in lateral hypothalamus brain stimulation reward.

Regulation of ductus arteriosus patency by nitric oxide in fetal lambs: the role of gestation, oxygen tension, and vasa vasorum

We hypothesized that nitric oxide (NO) production by the fetal ductus arteriosus is limited because of low fetal PO2, but that at neonatal PO2, NO might be an important regulator of ductus arteriosus tone. We exposed isolated rings of fetal lamb ductus arteriosus to elevated PO2. L-NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and methylene blue and 6-anilino-5,8-quinolinedione (LY83583), inhibitors of guanylate cyclase, produced constriction of the ductus arteriosus. When ductus arteriosus rings were exposed to low PO2, L-NAME had no effect, and methylene blue and LY83583 had only a small effect on ductus arteriosus tone. Sodium nitroprusside and calcium ionophore A23187 relaxed ductus arteriosus rings more than aortic rings, and relaxed ductus arteriosus rings from immature fetuses more than those from late gestation fetuses. In contrast, ductus arteriosus rings from both early and late gestation were equally sensitive to 8-bromo-cGMP. By both reverse transcriptase-polymerase chain reaction and immunohistochemistry, endothelial cell NOS and inducible calcium-independent NOS, but not nerve cell NOS, were detected in the ductus arteriosus. Inducible NOS was expressed only by endothelial cells lining the ductus arteriosus lumen; in contrast, endothelial cell NOS was expressed by both luminal and vasa vasorum endothelial cells. The role of inducible NOS in the ductus arteriosus is uncertain because the potency of a specific inducible NOS inhibitor in constricting the ductus arteriosus was negligible compared with that of an endothelial cell NOS inhibitor. We speculate that NO may be an important regulator of ductus arteriosus tone at high but not low PO2. The endothelial cell NOS isoform found in vasa vasorum may be an important source of NO because removal of ductus arteriosus luminal endothelium only partially blocks the effects of L-NAME, methylene blue, and LY83583.

Distinct tyrosine phosphorylation sites in JAK3 kinase domain positively and negatively regulate its enzymatic activity

Cytokines are critically important for the growth and development of a variety of cells. Janus kinases (JAKs) associate with cytokine receptors and are essential for transmitting downstream cytokine signals. However, the regulation of the enzymatic activity of the JAKs is not well understood. Here, we investigated the role of tyrosine phosphorylation of JAK3 in regulating its kinase activity by analyzing mutations of tyrosine residues within the putative activation loop of the kinase domain. Specifically, tyrosine residues 980 and 981 of JAK3 were mutated to phenylalanine individually or doubly. We found that JAK3 is autophosphorylated on multiple sites including Y980 and Y981. Compared with the activity of wild-type (WT) JAK3, mutant Y980F demonstrated markedly decreased kinase activity, and optimal phosphorylation of JAK3 on other sites was dependent on Y980 phosphorylation. The mutant Y980F also exhibited reduced phosphorylation of its substrates, gammac and STAT5A. In contrast, mutant Y981F had greatly increased kinase activity, whereas the double mutant, YY980/981FF, had intermediate activity. These results indicate that Y980 positively regulates JAK3 kinase activity whereas Y981 negatively regulates JAK3 kinase activity. These observations in JAK3 are similar to the findings in the kinase that is closely related to the JAK family, ZAP-70; mutations of tyrosine residues within the putative activation loop of ZAP-70 also have opposing actions. Thus, it will be important to determine whether this feature of regulation is unique to JAK3 or if it is also a feature of other JAKs. Given the importance of JAKs and particularly JAK3, it will be critical to fully dissect the positive and negative regulatory function of these and other tyrosine residues in the control of kinase activity and hence cytokine signaling.

The lipoxygenase metabolite 12(S)-HETE induces a cytoskeleton-dependent increase in surface expression of integrin alpha IIb beta 3 on melanoma cells

Integrin receptors are mediators of cell-extracellular matrix and cell-cell interactions. Biochemical and immunocytochemical evidence shows that the platelet integrin receptor alpha IIb beta 3 is present on the cell surface, at focal adhesion plaques and in the perinuclear region of metastatic B16a murine melanoma cells. Antibody to the fibronectin receptor alpha 5 beta i, inhibits basal adhesion by approx. 30%, whereas antibodies to alpha IIb beta 3 are ineffective. The surface immunoreactivity of tumor cells for alpha IIb beta 3 can be enhanced by pre-treatment (5 min) with a lipoxygenase metabolite of arachidonic acid [i.e. 12-(S)-HETE] in a dose-dependent manner (max. effect approx. 0.1 microM). Other lipoxygenase metabolites are ineffective. B16a cells possess a large intracellular pool of alpha IIb beta 3, from which the receptor complex translocates to the cell surface following 12-(S)-HETE pretreatment. This pre-treatment of tumor cells enhances their adhesion to fibronectin, which is mediated exclusively by alpha IIb beta 3 receptors. 12-(S)-HETE also facilitates the redistribution of alpha IIb beta 3 in the plasma membrane with localization at the focal adhesion plaques. The cytoskeleton of the B16a cell is characterized by an absence of distinct microtubules in interphase cells and the presence of prominent microfilaments and vimentin intermediate filaments. In B16a cells, the disruption of intermediate filaments and/or microfilaments prevents the 12-(S)-HETE-induced increase in plasma membrane alpha IIb beta 3 and enhanced tumor-cell adhesion to fibronectin. The microtubule-disrupting agent, colchicine, is ineffective in both respects. We conclude that the lipoxygenase metabolite of arachidonic acid, 12-(S)-HETE, regulates the surface expression and function of the alpha IIb beta 3 integrin in B16a cells. Further, these data support the hypothesis that microfilaments and intermediate filaments have a profound role in regulating the expression of a multifunctional integrin in B16a tumor cells.

Role of p21Waf1/Cip1/Sdi1 in cell death and DNA repair as studied using a tetracycline-inducible system in p53-deficient cells

Postulated roles for p21(Waf1/Cip1/Sdi1) (p21) in DNA repair and apoptosis remain controversial. Studies suggest both stimulatory and inhibitory effects of p21 in DNA repair. p21 has also been implicated in induction or protection from apoptosis. Using the tetracycline inducible expression system, we studied the role of p21 in DNA repair and apoptosis in wild-type p53 deficient DLD1 colorectal carcinoma cells. These cells displayed marked heterogeneity in their ability to tolerate higher levels of exogenous p21. The majority of the p21 overexpressing cells grew slower and did not exhibit apoptotic phenotype, some cells underwent apoptotic death within 5-8 days following p21 induction while other became giant cells prior to undergoing cell death. Induction of p21 transgene neither sensitized to nor protected from adriamycin-induced acute cell death. p21 also did not alter the clonogenic survival following adriamycin treatment. Clonogenic survival after u.v.-irradiation was, however, increased when p21 expression was transiently induced a few hours before and after u.v.-irradiation. Consistent with its effect on clonogenic survival, p21 also enhanced the cellular capacity to repair three different exogenously introduced u.v.-damaged reporter plasmids. Taken together our results demonstrate that p21 may modulate the nucleotide excision repair process to facilitate the repair of u.v.-type DNA damage even in the absence of wild-type p53.