The molecular basis of muscular dystrophy in the mdx mouse: a point mutation

The mdx mouse is an X-linked myopathic mutant, an animal model for human Duchenne muscular dystrophy. In both mouse and man the mutations lie within the dystrophin gene, but the phenotypic differences of the disease in the two species confer much interest on the molecular basis of the mdx mutation. The complementary DNA for mouse dystrophin has been cloned, and the sequence has been used in the polymerase chain reaction to amplify normal and mdx dystrophin transcripts in the area of the mdx mutation. Sequence analysis of the amplification products showed that the mdx mouse has a single base substitution within an exon, which causes premature termination of the polypeptide chain.

Specific protection against breast cancers by cyclin D1 ablation

Breast cancer is the most common malignancy among women. Most of these cancers overexpress cyclin D1, a component of the core cell-cycle machinery. We previously generated mice lacking cyclin D1 using gene targeting. Here we report that these cyclin D1-deficient mice are resistant to breast cancers induced by the neu and ras oncogenes. However, animals lacking cyclin D1 remain fully sensitive to other oncogenic pathways of the mammary epithelium, such as those driven by c-myc or Wnt-1. Our analyses revealed that, in mammary epithelial cells, the Neu-Ras pathway is connected to the cell-cycle machinery by cyclin D1, explaining the absolute dependency on cyclin D1 for malignant transformation in this tissue. Our results suggest that an anti-cyclin D1 therapy might be highly specific in treating human breast cancers with activated Neu-Ras pathways.

Cyclin D2 is an FSH-responsive gene involved in gonadal cell proliferation and oncogenesis

THE D-type cyclins (D1, D2 and D3) are critical governors of the cell-cycle clock apparatus during the G1 phase of the mammalian cell cycle. These three D-type cyclins are expressed in overlapping, apparently redundant fashion in the proliferating tissues. To investigate why mammalian cells need three distinct D-type cyclins, we have generated mice bearing a disrupted cyclin D2 gene by using gene targeting in embryonic stem cells. Cyclin D2-deficient females are sterile owing to the inability of ovarian granulosa cells to proliferate normally in response to follicle-stimulating hormone (FSH), whereas mutant males display hypoplastic testes. In ovarian granulosa cells, cyclin D2 is specifically induced by FSH via a cyclic-AMP-dependent pathway, indicating that expression of the various D-type cyclins is under control of distinct intracellular signalling pathways. The hypoplasia seen in cyclin D2(-/-) ovaries and testes prompted us to examine human cancers deriving from corresponding tissues. We find that some human ovarian and testicular tumours contain high levels of cyclin D2 messenger RNA.

Rescue of cyclin D1 deficiency by knockin cyclin E

D-type cyclins and cyclin E represent two very distinct classes of mammalian G1 cyclins. We have generated a mouse strain in which the coding sequences of the cyclin D1 gene (Ccnd1) have been deleted and replaced by those of human cyclin E (CCNE). In the tissues and cells of these mice, the expression pattern of human cyclin E faithfully reproduces that normally associated with mouse cyclin D1. The replacement of cyclin D1 with cyclin E rescues all phenotypic manifestations of cyclin D1 deficiency and restores normal development in cyclin D1-dependent tissues. Thus, cyclin E can functionally replace cyclin D1. Our analyses suggest that cyclin E is the major downstream target of cyclin D1.

E2F-4 and E2F-5, two members of the E2F family, are expressed in the early phases of the cell cycle

The E2F transcription factors play a role in regulating the expression of genes required for cell proliferation. Their activity appears to be regulated by association with the retinoblastoma protein (pRb) and the pRb-related proteins p107 and p130. In vivo, pRb is found in complex with a subset of E2F components--namely, E2F-1, E2F-2, and E2F-3. Here we describe the characterization of cDNAs encoding two unusual E2Fs, E2F-4 and E2F-5, each identified by the ability of their gene product to interact with p130 in a yeast two-hybrid system. E2F-4 and -5 share common sequences with E2F-1, E2F-2, and E2F-3 and, like these other E2Fs, the ability to heterodimerize with DP-1, thereby acquiring the ability to bind an E2F DNA recognition sequence with high affinity. However, in contrast to E2F-1, E2F-4 and E2F-5 fail to bind pRb in a two-hybrid assay. Moreover, they show a unique pattern of expression in synchronized human keratinocytes: E2F-4 and E2F-5 mRNA expression is maximal in mid-G1 phase before E2F-1 expression is detectable. These findings suggest that E2F-4 and E2F-5 may contribute to the regulation of early G1 events including the G0/G1 transition.

Transforming growth factor beta effects on expression of G1 cyclins and cyclin-dependent protein kinases

Transforming growth factor beta 1 (TGF-beta 1) is a potent growth-inhibitory polypeptide. The mechanism of TGF-beta 1 inhibition has been related to its ability to prevent the hyperphosphorylation of retinoblastoma protein (pRb). Several lines of evidence have suggested that cell cycle-regulated protein kinases are responsible for the hyperphosphorylation of pRb. We demonstrate here that TGF-beta 1 has profound effects on the expression of genes encoding certain G1 cyclins and their associated kinases, which provides one explanation of TGF-beta 1 effects on pRb hyperphosphorylation. These results also suggest that the growth-inhibitory effects of TGF-beta 1 in many cells are attributable to its effects on the cell cycle apparatus involved in programming G1 transit.

Neutral endopeptidase 24.11 loss in metastatic human prostate cancer contributes to androgen-independent progression

Neutral endopeptidase 24.11 (NEP) is a cell-surface enzyme expressed by prostatic epithelial cells that cleaves and inactivates neuropeptides implicated in the growth of androgen-independent prostate cancer (PC). We report that NEP expression and catalytic activity are lost in vitro in androgen-independent but not androgen-dependent PC cell lines. In vivo, NEP protein expression is commonly decreased in cancer cells of metastatic PC specimens from patients with androgen-independent but not androgen-dependent PC. Overexpression of NEP in androgen-independent PC cells or incubation with recombinant NEP inhibits PC cell growth. Furthermore, in androgen-dependent PC cells, expression of NEP is transcriptionally regulated by androgen and decreases with androgen withdrawal. These data suggest that decreased NEP expression, common in androgen-independent PCs, is facilitated by the elimination of androgens, and that NEP loss plays an important role in the development of androgen-independent PC by allowing PC cells to use mitogenic neuropeptides as an alternate source to androgen in order to stimulate cell proliferation.

Interferon-gamma and tumor necrosis factor synergize to induce nitric oxide production and inhibit mitochondrial respiration in vascular smooth muscle cells

Nitric oxide (NO) is an important signal substance in cell-cell communication and can induce relaxation of blood vessels by activating guanylate cyclase in smooth muscle cells (SMCs). NO is synthesized from L-arginine by the enzyme NO synthase, which is present in endothelial cells. It was recently shown that SMCs may themselves produce NO or an NO-related compound. We have studied NO production and its effects on energy metabolism in cultured rat aortic smooth muscle cells. It was observed that the cytokines, interferon-gamma and tumor necrosis factor-alpha, synergistically induced an arginine-dependent production of NO in these cells. This was associated with an inhibition of complex I (NADH: ubiquinone oxidoreductase) and complex II (succinate: ubiquinone oxidoreductase) activities of the mitochondrial respiratory chain, suggesting that NO blocks mitochondrial respiration in these cells. Lactate accumulated in the media of the cells, implying an increased anaerobic glycolysis, but there was no reduction of viability. An NO-dependent inhibition of mitochondrial respiration and a switch to anaerobic glycolysis would reduce energy production of the SMCs. This would in turn reduce the contractile capacity of the cell and might represent another NO-dependent vasodilatory mechanism. It could be of particular importance in inflammation, since cytokines released by inflammatory cells may induce autocrine NO production in SMCs.

Selective activation of the mitogen-activated protein kinase subgroups c-Jun NH2 terminal kinase and p38 by IL-1 and TNF in human articular chondrocytes

Previous studies suggested that tyrosine kinase activation is an important signal transduction event in the IL-1 response of chondrocytes. The present study identifies the mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase (ERK)-1 and ERK-2 as major tyrosine phosphorylated proteins in IL-1 stimulated chondrocytes. Kinase assays on immunoprecipitates with myelin basic protein as substrate showed that ERK-1 and ERK-2 activation was detectable within 5 min after IL-1 stimulation and decreased to baseline within 60 min. Analysis of other members of the MAP kinase family showed that chondrocytes also express c-Jun NH2 terminal kinase (JNK)-1, JNK-2, and p38 proteins. These kinases were time-dependently activated by IL-1. Among other chondrocyte activators tested, only TNF activated all three of the MAP kinase subgroups. JNK and p38 were not activated by any of the other cytokines and growth factors tested. However, ERK was also activated by PDGF, IGF-1, and IL-6. Phorbol 12-myristate 13-acetate, calcium ionophore, and cAMP analogues only increased ERK activity but had no significant effects on JNK or p38. These results suggest differential activation of MAP kinase subgroups by extracellular stimuli. ERK is activated in response to qualitatively diverse extracellular stimuli and various second messenger agonists. In contrast, JNK and p38 are only activated by IL-1 or TNF, suggesting that these kinases participate in the induction of the catabolic program in cartilage.

Filamin A mutations cause periventricular heterotopia with Ehlers-Danlos syndrome

OBJECTIVE

To define the clinical, radiologic, and genetic features of periventricular heterotopia (PH) with Ehlers-Danlos syndrome (EDS).

METHODS

Exonic sequencing and single stranded conformational polymorphism (SSCP) analysis was performed on affected individuals. Linkage analysis using microsatellite markers on the X-chromosome was performed on a single pedigree. Western blotting evaluated for loss of filamin A (FLNA) protein and Southern blotting assessed for any potential chromosome rearrangement in this region.

RESULTS

The authors report two familial cases and nine additional sporadic cases of the EDS-variant form of PH, which is characterized by nodular brain heterotopia, joint hypermobility, and development of aortic dilatation in early adulthood. MRI typically demonstrated bilateral nodular PH, indistinguishable from PH due to FLNA mutations. Exonic sequencing or SSCP analyses of FLNA revealed a 2762 delG single base pair deletion in one affected female. Another affected female harbored a C116 single point mutation, resulting in an A39G change. A third affected female had a 4147 delG single base pair deletion. One pedigree with no detectable exonic mutation demonstrated positive linkage to the FLNA locus Xq28, an affected individual in this family also had no detectable FLNA protein, but no chromosomal rearrangement was detected.

CONCLUSION

These results suggest that the Ehlers-Danlos variant of periventricular heterotopia (PH), in part, represents an overlapping syndrome with X-linked dominant PH due to filamin A mutations.

A new set of chemotaxis homologues is essential for Myxococcus xanthus social motility

Myxococcus xanthus cells aggregate and develop into multicellular fruiting bodies in response to starvation. A new M. xanthus locus, designated diffor defective in fruiting, was identified by the characterization of a mutant defective in fruiting body formation. Molecular cloning, DNA sequencing and sequence analysis indicate that the dif locus encodes a new set of chemotaxis homologues of the bacterial chemotaxis proteins MCPs (methyl-accepting chemotaxis proteins), CheW, CheY and CheA. The dif genes are distinct genetically and functionally from the previously identified M. xanthus frz chemotaxis genes, suggesting that multiple chemotaxis-like systems are required for the developmental process of M. xanthus fruiting body formation. Genetic analysis and phenotypical characterization indicate that the M. xanthus dif locus is required for social (S) motility. This is the first report of a M. xanthus chemotaxis-like signal transduction pathway that could regulate or co-ordinate the movement of M. xanthus cells to bring about S motility.

Monocyte deactivation by interleukin 10 via inhibition of tyrosine kinase activity and the Ras signaling pathway

Activation of monocytes by bacterial lipopolysaccharides (LPSs) is a central component in the pathogenesis of septic shock syndrome. Interleukin 10 (IL-10) is a potent monocyte-deactivating factor and transcriptionally inhibits LPS-induced expression of proinflammatory mediators. The intracellular signaling pathways of LPS have been only partially characterized and mechanisms of IL-10 signaling remain unknown. We show that LPS activates the protein tyrosine kinase (PTK) p56lyn and that this is associated with tyrosine phosphorylation of the protooncogene product Vav. These events are completely blocked by the tyrosine kinase inhibitor herbimycin A. LPS also increases Ras activation in monocytes. LPS-triggered phosphorylation of mitogen-activated protein kinase is a downstream activation event that is also reduced by herbimycin A. Analysis of the IL-10 effects shows that it completely inhibits the p56lyn tyrosine kinase activation and all other subsequent events in this pathway including Ras activation. The IL-10 effects are selective since it reduced PTK-dependent cytokine mRNA expression but not the PTK independent induction of c-jun and c-fos mRNA in LPS-activated monocytes. These results identify the Ras signaling pathway as a component of intracellular signaling in LPS-stimulated monocytes and define early events in this response as targets of monocyte deactivation by IL-10.

Effects of nicotine on the immune response. I. Chronic exposure to nicotine impairs antigen receptor-mediated signal transduction in lymphocytes

Previous work has demonstrated that chronic exposure of rats to cigarette smoke causes inhibition of the antibody-forming cell (AFC) response and that the particulate phase of cigarette smoke, containing most of the nicotine in cigarette smoke, is essential for immunosuppression. Using intradermally implanted miniosmotic pumps, LEW rats were exposed to nicotine or its principal metabolite, cotinine, at the rate of about 14 micrograms/hr for 3-4 weeks. Serum cotinine levels in nicotine-treated (NT) animals of 219 +/- 40 ng/ml (on Day 10) were comparable to average human smokers. No significant differences between control (CON) and NT animals were observed in the distribution of lymphocyte subsets. However, nicotine, but not cotinine, treatment for 3 to 4 weeks inhibited both the T-dependent and T-independent AFC responses and proliferation to anti-CD3. Con A response was observed in 4-week but not in 3-week NT animals. Cell cycle analysis revealed that upon stimulation with Con A or anti-CD3, in spite of comparable surface expression of IL-2 receptors and class II MHC molecules, significantly fewer NT T cells entered the S and G2/M phases than CON T cells, indicating an arrest in the G0/G1 phase. Furthermore, B and T cells from NT animals were unable to elevate the intracellular calcium levels normally in response to ligation of antigen receptors, although Ca2+ responses of salivary gland cells to acetylcholine were normal. Thus, nicotine may significantly contribute to the immunosuppressive effects of chronic smoking by inducing a state of anergy in lymphocytes and may be related to their impaired response to antigen-induced signaling.

Neutral endopeptidase inhibits prostate cancer cell migration by blocking focal adhesion kinase signaling

Neutral endopeptidase 24.11 (NEP, CD10) is a cell-surface enzyme expressed by prostatic epithelial cells that cleaves and inactivates neuropeptides implicated in the growth of androgen-independent prostate cancer (PC). NEP substrates such as bombesin and endothelin-1 induce cell migration. We investigated the mechanisms of NEP regulation of cell migration in PC cells, including regulation of phosphorylation on tyrosine of focal adhesion kinase (FAK). Western analyses and cell migration assays revealed an inverse correlation between NEP expression and the levels of FAK phosphorylation and cell migration in PC cell lines. Constitutively expressed NEP, recombinant NEP, and induced NEP expression using a tetracycline-repressive expression system inhibited bombesin- and endothelin-1-stimulated FAK phosphorylation and cell migration. This results from NEP-induced inhibition of neuropeptide-stimulated association of FAK with cSrc protein. Expression of a mutated catalytically inactive NEP protein also resulted in partial inhibition of FAK phosphorylation and cell migration. Coimmunoprecipitation experiments show that NEP associates with tyrosine-phosphorylated Lyn kinase, which then binds the p85 subunit of phosphatidylinositol 3-kinase (PI3-K) resulting in an NEP-Lyn-PI3-K protein complex. This complex competitively blocks FAK-PI3-K interaction, suggesting that NEP protein inhibits cell migration via a protein-protein interaction independent of its catalytic function. These experiments demonstrate that NEP can inhibit FAK phosphorylation on tyrosine and PC cell migration through multiple pathways and suggest that cell migration which contributes to invasion and metastases in PC cells can be regulated by NEP.

Photopheresis: clinical applications and mechanism of action

Photopheresis is a leukapheresis-based therapy that utilizes 8-methoxypsoralen and ultraviolet A irradiation. Photopheresis is currently available at approximately 150 medical centers worldwide. Recent evidence suggests that this therapy used as a single agent may significantly prolong life, as well as induce a 50%-75% response rate among individuals with advanced cutaneous T cell lymphoma (CTCL). Furthermore, a 20%-25% complete response rate with photopheresis alone, or in combination with other biologic response modifiers, has been obtained at our institution among patients with Sezary syndrome. These complete responses have been characterized by the complete disappearance of morphologically atypical cells from the skin and blood. The use of sensitive molecular techniques has also confirmed the sustained disappearance of the malignant T cell clone from the blood of patients with complete responses. In addition to the treatment of CTCL, numerous reports indicate that photopheresis is a potent agent in the therapy of acute allograft rejection among cardiac, lung, and renal transplant recipients. Chronic graft versus host disease also appears to be quite responsive to photopheresis therapy. Likewise, there may also be a potential role for photopheresis in the therapy of certain autoimmune diseases that are poorly responsive to conventional therapy. The immunologic basis for the responses of patients with these conditions is likely due to the induction of anticlonotypic immunity directed against pathogenic clones of T lymphocytes. Treatment-induced apoptotic death of pathogenic T cells and activation of antigen presenting cells are postulated to have important effects in this therapeutic process.

Deletion of the p27Kip1 gene restores normal development in cyclin D1-deficient mice

D-type cyclins (cyclins D1, D2, and D3) are key components of cell cycle machinery in mammalian cells. These proteins are believed to drive cell cycle progression by associating with their kinase partners, cyclin-dependent kinases, and by directing phosphorylation of critical cellular substrates. In addition, D-cyclins play a kinase-independent role by sequestering cell cycle inhibitors p27(Kip1) and p21(Cip1). In the past, we and others generated cyclin D1-deficient mice and have shown that these mice display developmental abnormalities, hypoplastic retinas, and pregnancy-insensitive mammary glands. To test the significance of cyclin D1-p27(Kip1) interaction within a living mouse, we crossed cyclin D1-deficient mice with mice lacking p27(Kip1), and we generated double-mutant cyclin D1(-/-)p27(-/-) animals. Here we report that ablation of p27(Kip1) restores essentially normal development in cyclin D1-deficient mice. Our results provide genetic evidence that p27(Kip1) functions downstream of cyclin D1.

Chlamydia pneumoniae inhibits apoptosis in human peripheral blood mononuclear cells through induction of IL-10

Chlamydia pneumoniae is a common cause of pulmonary infection, with serum positivity in at least 50% of the general population. In this study, we report that human PBMCs exposed to C. pneumoniae are resistant to apoptosis induced by the potent photoactivated chemotherapeutic agents 8-methoxypsoralen and hypericin. In contrast, PBMCs treated with a heat-inactivated inoculum exhibit normal susceptibility to apoptosis. We also observed that human PBMCs are responsive to C. pneumoniae infection by secretion of key immune regulatory cytokines, including IL-12 and IL-10. While IL-12 may play an important role in limiting C. pneumoniae proliferation within cells, IL-10 serves an anti-inflammatory function by down-regulating proinflammatory cytokines such as IL-12 and TNF-alpha. Depletion of endogenous IL-10, but not of IL-12, abolished the apoptosis resistance of C. pneumoniae-infected PBMCs. Furthermore, addition of exogenous IL-10, but not IL-12, significantly increased the resistance of control inoculum-treated PBMCs to photoactivated 8-methoxypsoralen- and hypericin-induced apoptosis. Therefore, we conclude that C. pneumoniae possesses an antiapoptotic mechanism. The resistance to apoptosis observed in PBMCs exposed to C. pneumoniae is due, at least partially, to the IL-10 induced during C. pneumoniae infection.

Prognostic nutritional index predicts survival and correlates with systemic inflammatory response in advanced pancreatic cancer

BACKGROUND

Recent studies have implied a prognostic value of the prognostic nutritional index (PNI) in certain types of human cancers. However, the value of PNI for predicting survival in patients with pancreatic cancer remains unknown. The goal of this study was to investigate the predictive significance of PNI in patients with advanced pancreatic cancer.

METHODS

A total of 321 consecutive patients with pathologically-confirmed locally advanced or metastatic pancreatic ductal adenocarcinoma (PDAC) were retrospectively recruited between January 2011 and August 2013. The patients were divided into a test set (n = 110) and a validation set (n = 211). We evaluated the association between PNI and overall survival (OS). The relationship between PNI and systemic inflammatory response markers, including the neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), and lymphocyte/monocyte ratio (LMR) was also assessed. In addition, the associations between PNI and the TNF-α were analyzed.

RESULTS

Kaplan-Meier analyses showed that a low PNI correlated significantly with a shorter OS in patients with advanced pancreatic cancer (190 days for patients with a low PNI vs. 290 days for patients with a high PNI, log-rank = 12.566, P < 0.001). Multivariate analysis identified PNI as an independent prognostic factor for OS (hazard ratio [HR]: 0.627, 95% confidence interval [CI]: 0.453-0.868, P = 0.003). PNI also correlated positively with NLR and PLR and negatively with LMR. Additionally, patients with a low PNI exhibited high levels of TNF-α.

CONCLUSIONS

Our results confirm that PNI is associated with the systemic inflammatory response and can be used to predict survival in advanced pancreatic cancer.

Effect of nicotine on the immune system: possible regulation of immune responses by central and peripheral mechanisms

Nicotine (NT) treatment impairs T-cell receptor (TCR)-mediated signaling, leading to the arrest of T cells in the G1 phase of the cell cycle and inhibition of the antibody plaque-forming cell (AFC) response to sheep red blood cells (SRBC). This paper summarizes some of the previous findings related to cigarette smoke/NT and the immune response, and presents preliminary evidence suggesting that mice chronically treated with NT (0.5 mg/day/kg body weight) have a depressed inflammatory response in the turpentine-induced abscess model of inflammation. This ability of nicotine to attenuate an inflammatory response may also be the cause of reduced mortality of chronically nicotine-treated mice from acute influenza A pneumonitis. Moreover, in LEW rats, decreased anti-SRBC AFC responses were also observed after intracerebroventricular (i.c.v.) administration of relatively small concentrations of NT (28 micrograms/day/kg body weight) which, when given peripherally, did not affect the AFC response. In vitro the addition of NT to T cells increased protein tyrosine kinase (PTK) activity and intracellular Ca2+ concentration [Ca2+]i. These results support the hypothesis that NT alters immune responses by directly interacting with T cells, as well as indirectly through brain-immune interactions.

Clinical implications of systemic inflammatory response markers as independent prognostic factors for advanced pancreatic cancer

BACKGROUND

Cancer-associated inflammation is a key molecular feature of pancreatic ductal adenocarcinoma. In this study, we systematically evaluated the prognostic relevance of systemic inflammatory response (SIR) markers in patients with advanced pancreatic cancer.

METHODS

A total of 321 consecutive patients with pathologically-confirmed locally advanced or metastatic pancreatic adenocarcinoma were retrospectively recruited. The patients were divided into a test set (n = 110) and a validation set (n = 211). The associations between overall survival (OS) and clinically available SIR markers including white blood cell (WBC) count, absolute neutrophil count, absolute lymphocyte count, absolute monocyte count, platelet count, neutrophil-lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR) and lymphocyte/monocyte ratio (LMR) were analyzed using Kaplan-Meier curves and multivariate Cox proportional models.

RESULTS

High WBC count, neutrophil count, monocyte count, NLR, PLR and low LMR were significantly associated with decreased OS in the test set. Using the validation set for confirmation, we found also in multivariate analysis an independent value of WBC count (hazard ratio (HR): 2.176, 95% confidence interval (CI): 1.560-3.035, P < 0.001), neutrophil count (HR: 2.807, 95% CI: 2.000-3.940, P < 0.001), monocyte count (HR: 1.848, 95% CI: 1.315-2.598, P < 0.001), NLR (HR: 2.204, 95% CI: 1.590-3.055, P < 0.001), PLR (HR: 1.537, 95% CI: 1.114-2.122, P = 0.009) and LMR (HR: 0.569, 95% CI: 0.412-0.784, P = 0.001) for OS in patients with advanced pancreatic cancer.

CONCLUSIONS

Our study confirmed that SIR markers can be used to determine optimal therapeutic strategies for individual patients and to predict pancreatic cancer prognosis.

Identification of a cellular protein that interacts and synergizes with the RTA (ORF50) protein of Kaposi's sarcoma-associated herpesvirus in transcriptional activation

Lytic reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8, from latency requires transcriptional transactivation by the viral protein RTA encoded by the ORF50 gene. Very little is known about how RTA functions and the cellular factors that may be involved in its transactivation function. Using the yeast two-hybrid system, we have identified a human cellular protein that can interact with KSHV RTA. The cellular protein, referred to as the human hypothetical protein MGC2663 by GenBank, is encoded by human chromosome 19. This protein is 554 amino acids (aa) in size and displays sequence similarity with members of the Krueppel-associated box-zinc finger proteins (KRAB-ZFPs). MGC2663 expression could be detected in all primate cell lines tested, and its expression level was neither stimulated nor inhibited by RTA. MGC2663 specifically synergizes with RTA to activate viral transcription, and overexpression of MGC2663 in the presence of RTA further enhances RTA transactivation of several viral promoters that were identified as targets for RTA. Coimmunoprecipitation and pull-down assays further demonstrated that MGC2663 interacts with RTA both in vivo and in vitro, and the N-terminal 273 aa of KSHV RTA and the potential zinc finger domain of MGC2663 are required for their interaction. Our results indicate that this novel human cellular protein, MGC2663, named K-RBP (KSHV RTA binding protein) due to its RTA binding feature, specifically interacts with the KSHV RTA protein and functions as a cellular RTA cofactor to activate viral gene expression. Though its normal cellular function needs to be further studied, K-RBP may play a significant role in mediating RTA transactivation in vivo.

Differential expression of scavenger receptor isoforms during monocyte-macrophage differentiation and foam cell formation

Scavenger receptors mediate binding and uptake of chemically modified lipoproteins. cDNA cloning of the human macrophage scavenger receptor (MSR) reveals the presence of two mRNA species, the type I and II isoforms, which are generated by 3' alternative splicing of a single MSR gene and translated into two proteins with different C-terminal domains. We studied MSR isoform expression during the differentiation from circulating monocytes to adherent macrophages and subsequently to lipid-laden foam cells. Differentiation from monocyte to macrophage was associated with a prominent increase in MSR expression on the mRNA, protein, and cell surface levels, leading to an increased uptake of acetylated low-density lipoprotein (LDL). Further analyses of mRNA and proteins revealed that both MSR isoforms were present in low and approximately equal amounts on the surface of CD14+ peripheral blood monocytes; these cells had approximately similar levels of type I and type II MSR mRNA species. During differentiation to macrophages, there was a rapid, selective increase in type I MSR mRNA, with type II mRNA being expressed at approximately the same level as in the monocyte. This, in turn, resulted in an increase in type I MSR protein on the cell surface during differentiation from monocyte to macrophage. Type I MSR mRNA also dominated during the transformation of macrophages to foam cells in the presence of acetylated LDL. These findings suggest that the increased uptake of modified LDL during differentiation from monocyte to macrophage is accomplished by a selective upregulation of type I MSRs on the mRNA level. The increased expression of type I MSRs may be important for foam cell formation.

Timing of cyclin E gene expression depends on the regulated association of a bipartite repressor element with a novel E2F complex

Transient induction of the cyclin E gene in late G1 gates progression into S. We show that this event is controlled via a cyclin E repressor module (CERM), a novel bipartite repressor element located near the cyclin E transcription start site. CERM consists of a variant E2F-binding site and a contiguous upstream AT-rich sequence which cooperate during G0/G1 to delay cyclin E expression until late G1. CERM binds the protein complex CERC, which disappears upon progression through G0-G1 and reappears upon entry into the following G1. CERC disappearance correlates kinetically with the liberation of the CERM module in vivo and cyclin E transcriptional induction. CERC contains E2F4/DP1 and a pocket protein, and sediments faster than classical E2F complexes in a glycerol gradient, suggesting the presence of additional components in a novel high molecular weight complex. Affinity purified CERC binds to CERM but not to canonical E2F sites, thus displaying behavior different from known E2F complexes. In cells nullizygous for members of the Rb family, CERC is still detectable and CERM-dependent repression is functional. Thus p130, p107 and pRb function interchangeably in CERC. Notably, the CERC-CERM complex dissociates prematurely in pRb-/- cells in correspondence with the premature expression of cyclin E. Thus, we identify a new regulatory module that controls repression of G1-specific genes in G0/G1.