[Risk factors for surgical site infection after emergency abdominal surgery: a multicenter cross-sectional study in China]

Objective: Surgical site infection (SSI) is the most common infectious complication after emergency abdominal surgery (EAS). To a large extent, most SSI can be prevented, but there are few relevant studies in China. This study mainly investigated the current situation of SSI occurrence after EAS in China, and further explored risk factors for SSI occurrence. Methods: Multi-center cross-sectional study was conducted. Clinical data of patients undergoing EAS in 33 hospitals across China between May 1, 2019 and June 7, 2019 were prospectively collected, including perioperative data and microbial culture results from infected incisions. The primary outcome was the incidence of SSI after EAS, while the secondary outcomes were postoperative hospital stay, ICU occupancy rate, length of ICU stay, hospitalization cost, and mortality within postoperative 30 days. Univariate and multivariate logistic regression models were used to analyze the risk factors of SSI after EAS. Results: A total of 660 EAS patients aged (47.9±18.3) years were enrolled in this study, including 56.5% of males (373/660). Forty-nine (7.4%) patients developed postoperative SSI. The main pathogen of SSI was Escherichia coli [culture positive rate was 32.7% (16/49)]. As compared to patients without SSI, those with SSI were more likely to be older (median 56 years vs. 46 years, U=19 973.5, P<0.001), male [71.4% (35/49) vs. 56.1% (343/611), χ(2)=4.334, P=0.037] and diabetes [14.3% (7/49) vs. 5.1% (31/611), χ(2)=5.498, P=0.015]; with-lower preoperative hemoglobin (median: 122.0 g/L vs. 143.5 g/L, U=11 471.5, P=0.006) and albumin (median: 35.5 g/L vs. 40.8 g/L, U=9452.0, P<0.001), with higher blood glucose (median: 6.9 mmol/L vs. 6.0 mmol/L, U=17 754.5, P<0.001); with intestinal obstruction [32.7% (16/49) vs. 9.2% (56/611), χ(2)=25.749, P<0.001], with ASA score 3-4 [42.9% (21/49) vs. 13.9% (85/611), χ(2)=25.563, P<0.001] and with high surgical risk [49.0% (24/49) vs. 7.0% (43/611), χ(2)=105.301, P<0.001]. The main operative procedure resulting in SSI was laparotomy [81.6%(40/49) vs. 35.7%(218/611), χ(2)=40.232, P<0.001]. Patients with SSI experienced significantly longer operation time (median: 150 minutes vs. 75 minutes, U=25 183.5, P<0.001). In terms of clinical outcome, higher ICU occupancy rate [51.0% (25/49) vs. 19.5% (119/611), χ(2)=26.461, P<0.001], more hospitalization costs (median: 44 000 yuan vs. 15 000 yuan, U=24 660.0, P<0.001), longer postoperative hospital stay (median: 10 days vs. 5 days, U=23 100.0, P<0.001) and longer ICU occupancy time (median: 0 days vs. 0 days, U=19 541.5, P<0.001) were found in the SSI group. Multivariate logistic regression analysis showed that the elderly (OR=3.253, 95% CI: 1.178-8.985, P=0.023), colorectal surgery (OR=9.156, 95% CI: 3.655-22.937, P<0.001) and longer operation time (OR=15.912, 95% CI:6.858-36.916, P<0.001) were independent risk factors of SSI, while the laparoscopic surgery (OR=0.288, 95% CI: 0.119-0.694, P=0.006) was an independent protective factor for SSI. Conclusions: For patients undergoing EAS, attention should be paid to middle-aged and elderly patients and those of colorectal surgery. Laparoscopic surgery should be adopted when feasible and the operation time should be minimized, so as to reduce the incidence of SSI and to reduce the burden on patients and medical institutions.

Patterning small-molecule biocapture surfaces: microcontact insertion printing vs. photolithography

Chemical patterns prepared by self-assembly, combined with soft lithography or photolithography, are directly compared. Pattern fidelity can be controlled in both cases but patterning at the low densities necessary for small-molecule probe capture of large biomolecule targets is better accomplished using microcontact insertion printing (μCIP). Surfaces patterned by μCIP are used to capture biomolecule binding partners for the small molecules dopamine and biotin.

Postural responses during falling with rapid reach-and-grasp balance reaction in patients with motor complete paraplegia

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

To investigate the kinematic, kinetic and electromyographic (EMG) aspects of postural control during falling with rapid reach-and-grasp balance reaction in thoracic cord-injured individuals wearing knee-ankle-foot orthoses (KAFOs).

SETTING

Institutional Motion Analysis Laboratory.

METHODS

Seven T7-T12 cord-injured subjects with complete motor loss (ASIA classes A and B) participated in this study. Subjects with KAFOs first stood steady with a modified walker and then released their hold on the walker to maintain self-supported standing until falling with grasping. The center of pressure (COP), center of mass (COM) and joint angles were measured together with EMG of the triceps (TRI), T4 paraspinal and abdominal muscles.

RESULTS

After release of the walker, there was a rapid increase of COM-COP distance (that is, from 13.32+/-11.79 to 54.29+/-24.56 mm), with COM in front of COP during a forward fall, which was associated with the increases of T4 muscle activities. After the reach-and-grasp reaction, COM moved behind COP, which was associated with the increase of ankle dorsiflexion and the TRI and abdominal muscle activities.

CONCLUSION

The increase of upper back extensor muscle activity might not be enough to correct postural instability during unsupported stance in thoracic spinal cord injury with complete motor loss. The rapid reach-and-grasp reaction is an alternative compensatory mechanism to prevent falling to the ground.

Functional analysis of a minimal mouse serum amyloid A3 promoter in transgenic mice

We report the generation of transgenic mice harboring the SAA3/LacZ transgene and analysis of its expression patterns in vivo following LPS-induced inflammation. Our results show that a 210-bp fragment of the mouse SAA3 promoter when placed in front of the LacZ gene was sufficient to confer basal and inflammation-induced reporter gene expression. Consistent with endogenous SAA3 expression, the basal level of LacZ expression was high in the lung and liver of newborn and 1-week-old transgenic mice. Its expression however decreased with increasing age and at 3-weeks ofage, LacZ expression was very low in the lung and was essentially undetectable in the liver. When SAA3/LacZ transgenic mice were injected with lipopolisaccharide to induce inflammation, beta-gal activities were increased approximately 6- and 16-fold in the lung and liver, respectively. Histological examination of lung and liver tissues stained with X-gal revealed that the LacZ transgene was expressed primarily in the macrophages. Thus, this minimal SAA3 promoter fragment contains the necessary regulatory sequences for its expression and cytokine responsiveness in macrophages albeit is insufficient to confer expression in hepatocytes.

Activation of the human PAX6 gene through the exon 1 enhancer by transcription factors SEF and Sp1

PAX6 is a transcription factor that plays a major role in ocular morphogenesis. PAX6 is expressed in the eye, central nervous system and pancreas. Two alternative promoters, P0 and P1, which are differentially regulated during development, drive PAX6 transcription. We identified a 57 bp cis-regulatory element in exon 1 of the human PAX6 gene exon 1 enhancer (EIE). EIE enhances P1-driven PAX6 expression. Three regions in E1E (E1E-1, E1E-2 and E1E-3) have sequence similarities with binding sites of transcription factors ARP-1, Isl-1 and SEF, respectively. As shown by electrophoretic mobility shift assays, E1E-3, but not E1E-1 or E1E-2, bound to proteins in nuclear extracts of human glioma cells and transcription factor SEF bound to E1E-3. As shown by transient transfection experiments, deletion or site-specific mutations in E1E-3 dramatically decreased P1 promoter activity. Mutations in E1E-2, however, did not affect function of the P1 promoter. Co-transfection of SEF and PAX6 promoter-reporter constructs showed that SEF up-regulates PAX6 gene expression through the P1 promoter. Two Sp1 sites in the E1E region were also shown to be important by transient co-transfection assays. Data from immunoprecipitation and transient transfection assays demonstrated that SEF and Sp1 interacted in vitro and may act together in vivo to regulate PAX6 expression.

Genomic structure and promoter characterization of an imprinted tumor suppressor gene ARHI

We have recently identified a maternally imprinted tumor suppressor gene, ARHI (aplysia ras homolog I), the expression of which is lost in ovarian and breast cancers. We have now characterized the genomic structure of the gene including its promoter and the methylation status of its upstream CpG islands. The ARHI gene spans approximately 8 kb containing two exons and one intron. Exon 1 contains 81 non-translated nucleotides, connected to exon 2 with a 3.2-kb intron. The entire protein-coding region is located within exon 2 and encodes a 229-residue small GTP-binding protein belonging to the Ras superfamily. Genomic structure analysis has identified three potential CpG islands. Two of them (CpG island I and II) are located within the promoter and adjacent exon 1 of the ARHI gene. Aberrant methylation of these CpG islands has been detected in breast cancer cells but not in normal epithelial cells, supporting the possibility that appropriate methylation status of the CpG islands in the promoter region may play a role in the downregulation of ARHI gene expression. A TATA box is found 27 bp upstream of the transcription start site associated with several putative transcription factor binding sites. Transient transfection with nested deletion constructs of the 2-kb ARHI promoter regions fused to a luciferase reporter indicated a 121-bp sequence upstream of the transcription initiation site is required for basal promoter activity. Interestingly, this is the region where lower promoter activity has been observed in cancer cells than in normal cells.

Transcription factor AP-2 functions as a repressor that contributes to the liver-specific expression of serum amyloid A1 gene

We previously identified transcription factor AP-2 as the nuclear factor that interacts with the tissue-specific repressor element in the rat serum amyloid A1 (SAA1) promoter. In this report, we provide evidence for a second AP-2-binding site and show that both AP-2 sites participate in mediating the transcription repression of SAA1 promoter. This proximal AP-2 site overlaps with the NFkappaB-binding site known to be essential for SAA1 promoter activity. Protein binding competition experiments demonstrated that AP-2 and NFkappaB binding to these overlapping sites were mutually exclusive. Furthermore, the addition of AP-2 easily displaced prebound NFkappaB, whereas NFkappaB could not displace AP-2. These results thus suggest that one mechanism by which AP-2 negatively regulates SAA1 promoter activity may be by antagonizing the function of NFkappaB. Consistent with a repression function, transient expression of AP-2 in HepG2 cells inhibited conditioned medium-induced SAA1 promoter activation. This inhibition was dependent on functional AP-2-binding sites, since mutation of AP-2-binding sites abolished inhibitory effects of AP-2 in HepG2 cells as well as resulted in derepression of the SAA1 promoter in HeLa cells. In addition to SAA1, we found that several other liver gene promoters also contain putative AP-2-binding sites. Some of these sequences could specifically inhibit AP-2.DNA complex formation, and for the human complement C3 promoter, overexpression of AP-2 also could repress its cytokine-mediated activation. Finally, stable expression of AP-2 in hepatoma cells significantly reduced the expression of endogenous SAA, albumin, and alpha-fetoprotein genes. Taken together, our results suggest that AP-2 may function as a transcription repressor to inhibit the expression of not only SAA1 gene but also other liver genes in nonhepatic cells.

NFkappa B interacts with serum amyloid A3 enhancer factor to synergistically activate mouse serum amyloid A3 gene transcription

We had previously identified a distal regulatory element (DRE) in the mouse serum amyloid A3 (SAA3) promoter that functions as a cytokine-inducible transcription enhancer. Within this DRE, three functional elements interact with CCAAT/enhancer-binding protein (C/EBP) and SAA3 enhancer factor (SEF) transcription factors. In this study, we show that cotransfection of the SEF expression plasmid with an SAA3/luciferase reporter resulted in 3-5-fold activation of the SAA3 promoter. When SEF-transfected cells were further stimulated with conditioned medium or interleukin-1, SAA3 promoter activity was dramatically increased, suggesting that SEF may cooperate functionally with other interleukin-1-inducible transcription factors to synergistically up-regulate SAA3 gene transcription. Indeed, cotransfection of SEF and NFkappaBp65 expression DNAs resulted in synergistic activation of the SAA3 promoter. Intriguingly, no consensus NFkappaB-binding site was found in the SAA3 promoter region; rather a putative NFkappaB-binding sequence with 3-base pair mismatches was identified in the DRE. When this sequence was used in an electrophoretic mobility shift assay, it interacted with NFkappaBp50, albeit with binding affinities that were several hundredfold lower than that with the consensus NFkappaB probe. Functional cooperation between SEF and NFkappaB was further strengthened by the finding that SEF and NFkappaB formed stable cytokine-inducible protein-protein complexes. Finally, despite its weak binding, mutation of this NFkappaB-binding site nevertheless dramatically reduced both NFkappaBp65- and cytokine-mediated induction of SAA3 promoter. Therefore, the molecular basis for the functional synergy between SEF and NFkappaB may, in part, be the ability of SEF to recruit NFkappaB through physical interactions that lead to enhancement or stabilization of NFkappaB binding to the SAA3 promoter element.

Phosphatidylinositol 3-kinase as a mediator of TNF-induced NF-kappa B activation

The activation of transcription factor NF-kappa B by TNF involves the stimulation of a novel signaling cascade. In this paper we show that phosphatidylinositol 3-kinase (PI 3-kinase) may play a pivotal role in TNF-mediated activation of NF-kappa B-dependent genes. Consistent with its involvement in TNF signaling, PI 3-kinase activities in HepG2 and U937 cells can be stimulated by TNF in a rapid but transient manner through a mechanism that may involve its association with the insulin receptor substrate-1. A dominant-negative mutant of the p85 regulatory subunit of PI 3-kinase, which is a potent inhibitor of PI 3-kinase signaling, effectively blocked the TNF-induced expression of an NF-kappa B-dependent reporter gene. Although PI 3-kinase may be required for NF-kappa B activation, overexpression of its p110 catalytic subunit alone was unable to induce an NF-kappa B/chloramphenicol acetyltransferase (CAT) reporter gene. However, when TNF was added to p110-overexpressing cells, there was a synergistic activation of the NF-kappa B/CAT reporter, suggesting that other TNF-inducible signals may cooperate with PI 3-kinase to activate NF-kappa B. Consistent with its role in NF-kappa B activation, inhibition of PI 3-kinase activity by wortmannin or LY294002 greatly potentiated TNF-induced apoptosis. This TNF/wortmannin-induced apoptosis was markedly prevented in cells overexpressing Rel A. Taken together, our results indicate that a PI 3-kinase-regulated step in TNF-signaling is critical for the expression of NF-kappa B-dependent genes.

Purification and identification of a tissue-specific repressor involved in serum amyloid A1 gene expression

We have previously demonstrated that the 5'-flanking regions from the rat serum amyloid A1 (SAA1) promoter are necessary and sufficient to confer specific cytokine-induced expression in cultured hepatoma cells. Deletion analysis identified a tissue-specific repressor (TSR) regulatory element, located between bp -289 and -256, that functioned as a silencer, contributing to the transcription repression on SAA1 promoter in nonliver cells. When this 34-base pair TSR-binding element was used as a probe in electrophoretic mobility shift assays, an intense DNA-protein complex was detected in nuclear extracts from HeLa and several other nonliver tissues. This TSR binding activity, however, was undetectable in extracts from liver or liver-derived cells. The distribution of TSR binding activity is therefore consistent with its regulatory role in repressing SAA1 expression in a tissue-specific manner. In this study, we purified TSR protein from HeLa nuclear extracts and showed that it has a molecular mass of approximately 50 kDa. Surprisingly, protein sequencing and antibody supershift experiments identified TSR as transcription factor AP-2. Subsequent functional analysis showed that forced expression of AP-2 in HepG2 cells could indeed inhibit conditioned medium-induced SAA1 promoter activation. Moreover, expression of a dominant-negative mutant of AP-2 in HeLa cells or mutation of the AP-2-binding site led to derepression of the SAA1 promoter, presumably by neutralizing the inhibitory effects of the endogenous wild-type AP-2. Our results therefore demonstrate a novel function for AP-2 in the transcriptional repression of SAA1 promoter. Together with its tissue distribution, AP-2 may contribute to SAA1's highly liver-specific expression pattern by restricting its expression in nonliver cells.

Synergistic induction of mouse serum amyloid A3 promoter by the inflammatory mediators IL-1 and IL-6

Serum amyloid A (SAA), one of the major acute-phase proteins, increases several hundredfold in concentration in plasma following acute inflammation, primarily as a result of a 200-fold increase in its transcription rate. We have previously demonstrated that a 350-bp promoter fragment from the mouse SAA3 gene could confer conditioned medium-induced expression in cultured cells. The induction is mediated through a 42-bp distal response element (DRE) consisting of three functional regulatory elements. In this study, we show that interleukin-1 (IL-1) is the major cytokine in the conditioned medium responsible for SAA3 induction, and the induction by IL-1 can be effectively blocked by H-7, a protein kinase C inhibitor. Although IL-6 alone had no effect on SAA3 promoter activity, the addition of IL-6 and IL-1 resulted in dramatic synergistic activation of the reporter gene. We further show that the DRE is both necessary and sufficient to confer synergistic induction by IL-1 and IL-6. Moreover, individual mutation of the three regulatory elements within DRE either abolished or drastically reduced the synergistic induction. Our results indicate that synergistic activation of SAA3 promoter by IL-1 and IL-6 is achieved through integration of signals triggered by these two cytokines onto the DRE and that all three functionally distinct regulatory elements in the DRE are required to effectively and fully activate SAA3 gene transcription.

An upstream repressor element that contributes to hepatocyte-specific expression of the rat serum amyloid A1 gene

Serum amyloid A (SAA) is a major acute-phase protein whose expression can be dramatically induced in response to tissue damage, infection, and inflammation. Its expression is highly tissue-specific, restricted almost exclusively to liver hepatocytes. We have shown that a 320-bp fragment of the rat SAA1 promoter could confer liver-cell-specific expression on a reporter gene when transfected into cultured cells. Here we report the identification of a 29-bp regulatory element that possesses inhibitory activities on SAA1 promoter in HeLa cells but has no such effects in liver cells. Moreover, this regulatory element has properties of a transcriptional repressor; in that, it can function with a heterologous promoter and is independent of orientation and distance from the transcription initiation site. Protein binding studies showed that this regulatory element can form specific protein-DNA complexes with nuclear proteins from several nonliver cell lines (HeLa, 10T(1/2), and C2) and placenta. However, the same DNA-protein complex was not detected in extracts from liver or liver-derived cell lines (HepG2 and Hep3B). Taken together, our results demonstrate the presence of a DNA-binding protein, termed tissue-specific repressor, found only in nonhepatocytes which may function to repress SAA1 gene expression by interacting with a repressor element. Thus, liver-specific expression of the SAA1 gene is apparently regulated by both positive and negative regulatory elements and their interacting transcription factors to ensure that it is expressed only in suitable cell types.

Purification and characterization of the serum amyloid A3 enhancer factor

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to acute inflammation, its expression may be induced up to 1000-fold, primarily as a result of a 200-fold increase in the rate of SAA gene transcription. We showed previously that cytokine-induced transcription of the SAA3 gene promoter requires a transcriptional enhancer that contains three functional elements: two CCAAT/enhancer-binding protein (C/EBP)-binding sites and a third site that interacts with a constitutively expressed transcription factor, SAA3 enhancer factor (SEF). Each of these binding sites as well as cooperation among their binding factors is necessary for maximum transcription activation by inflammatory cytokines. Deletion or site-specific mutations in the SEF-binding site drastically reduced SAA3 promoter activity, strongly suggesting that SEF is important in SAA3 promoter function. To further elucidate its role in the regulation of the SAA3 gene, we purified SEF from HeLa nuclear extracts to near homogeneity by using conventional liquid chromatography and DNA affinity chromatography. Ultraviolet cross-linking and Southwestern experiments indicated that SEF consisted of a single polypeptide with an apparent molecular mass of 65 kDa. Protein sequencing and antibody supershift experiments identified SEF as transcription factor LBP-1c/CP2/LSF. Cotransfection of SEF expression vector with SAA3-luciferase reporter resulted in approximately a 5-fold increase in luciferase activity. Interestingly, interleukin-1 treatment of SEF-transfected cells caused dramatic synergistic activation (31-fold) of the SAA3 promoter. In addition to its role in regulating SAA3 gene expression, we provide evidence that SEF could also bind in a sequence-specific manner to the promoters of the alpha(2)-macroglobulin and Aalpha-fibrinogen genes and to an intronic enhancer of the human Wilm's tumor 1 gene, suggesting a functional role in the regulation of these genes.

Phosphatidylinositol 3-kinase in interleukin 1 signaling. Physical interaction with the interleukin 1 receptor and requirement in NFkappaB and AP-1 activation

The signaling mechanisms utilized by the proinflammatory cytokine interleukin-1 (IL-1) to activate the transcription factors NFkappaB and activator protein-1 (AP-1) are poorly defined. We present evidence here that IL-1 not only stimulates a dramatic increase in phosphatidylinositol 3-kinase (PI 3-kinase) activity but also induces the physical interaction of its type I receptor with the p85 regulatory subunit of PI 3-kinase. Furthermore, two PI 3-kinase-specific inhibitors, wortmannin and a dominant-negative mutant of the p85 subunit, inhibited IL-1-induced activation of both NFkappaB and AP-1. Transient transfection experiments indicated that whereas overexpression of PI 3-kinase may be sufficient to induce AP-1 and increase nuclear c-Fos protein levels, PI 3-kinase may need to cooperate with other IL-1-inducible signals to fully activate NFkappaB-dependent gene expression. In this regard, cotransfection studies suggested that PI 3-kinase may functionally interact with the recently-identified IL-1-receptor-associated kinase to activate NFkappaB. Our results thus indicate that PI 3-kinase is a novel signal transducer in IL-1 signaling and that it may differentially mediate the activation of NFkappaB and AP-1.

Developmentally and hormonally regulated CCAAT/enhancer-binding protein isoforms influence beta-casein gene expression

A highly conserved CCAAT/enhancer-binding protein (C/EBP)-binding site centered around -134 relative to the transcription start site in the rat beta-casein gene promoter is capable of interacting specifically with recombinant and mammary gland C/EBP proteins. Western blot analysis indicates that C/EBP levels change dramatically throughout mammary gland development. C/EBP alpha expression is barely detectable in mammary glands from virgin and pregnant animals but is expressed at high levels during lactation and at lower levels during involution. The expression of three C/EBP beta isoforms [the liver-enriched activating proteins (LAPs); and the liver-enriched inhibiting protein (LIP)] is elevated throughout pregnancy, with LIP expression increasing more than 100-fold. Thus, during pregnancy, a low LAP/LIP ratio (< 5) is maintained. C/EBP beta expression decreases at parturition, with LIP diminishing to levels observed in the virgin gland. Therefore, during lactation a more than 100-fold increase in the LAP/LIP ratio is observed. Treatment of the HC11 mammary epithelial cell line with hydrocortisone results in a 10- to 20-fold inhibition of LIP expression, with only minor changes in LAP levels. Therefore, glucocorticoids may impinge upon beta-casein gene expression by altering the ratio of the inhibitory to the activating isoforms of C/EBP beta. Several previously defined casein gene promoter regions capable of conferring hormone and extracellular matrix inducibility to reporter genes in mammary cells are suggested to be composite response elements, containing putative binding sites for the same set of hormonally and developmentally regulated factors: C/EBP, MGF/Stat5, and the glucocorticoid receptor.

YY1 represses rat serum amyloid A1 gene transcription and is antagonized by NF-kappa B during acute-phase response

Serum amyloid A (SAA), one of the major acute-phase proteins, increases several hundredfold in concentration in plasma following acute inflammation, primarily as a result of a 200-fold increase in its transcriptional rate. Functional analysis of the rat SAA1 promoter has identified a 65-bp cytokine response unit (CRU; positions -135 to -71) that could confer cytokine responsiveness on a heterologous promoter. Within this CRU, two cis-regulatory elements, corresponding to NF-kappa B- and C/EBP-binding sites, were found to be functionally important and exerted synergistic effects on induced SAA1 expression. In this report, we show that a third transcription factor interacts with the CRU through a region located between the NF-kappa B- and C/EBP-binding sites. On the basis of its gel mobility shift patterns, ubiquitous binding activity, sequence specificity of DNA binding, zinc-dependent binding activity, and gel mobility supershift by specific antibodies, we concluded that this factor is identical to YY1. Methylation interference studies revealed that YY1 binding sequences overlapped with those of NF-kappa B, and gel mobility studies showed that NF-kappa binding to the CRU was effectively inhibited by YY1. Consistent with its presumed antagonistic role to NF-kappa B, YY1 exerted a negative effect on SAA1 expression, whereas disruption of its binding in the promoter elevated basal and cytokine-induced activities. Furthermore, overexpression of YY1 trans-repressed SAA1 promoter activity. Thus, our results demonstrate that SAA1 expression is tightly regulated by an on-off switch of activators and repressors, presumably to ensure that it is expressed only under appropriate physiological conditions.

Induction of the mouse serum amyloid A3 gene by cytokines requires both C/EBP family proteins and a novel constitutive nuclear factor

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to acute inflammation, its expression may be induced up to 1,000-fold, primarily as a result of a 200-fold increase in the rate of SAA gene transcription. We have previously demonstrated that a 350-bp promoter fragment from the mouse SAA3 gene was necessary and sufficient to confer liver-specific and cytokine-induced expression. Deletion studies identified a distal response element that is responsible for the cytokine response and has properties of an inducible transcriptional enhancer. In this study, we further analyzed the distal response element and showed that it consists of three functionally distinct elements: the A element constitutes a weak binding site for C/EBP family proteins, the B element also interacts with C/EBP family proteins but with a much higher binding affinity, and the C element interacts with a novel constitutive nuclear factor, SEF-1. Site-specific mutation studies revealed that all three elements were required for maximum promoter activity. C/EBP alpha, C/EBP beta, and C/EBP delta were capable of interacting with elements A and B. Under noninduced conditions, C/EBP alpha was the major binding factor; however, upon cytokine stimulation C/EBP beta- and C/EBP delta-binding activities were dramatically increased and became the predominant binding factors. Consistent with these binding studies were the cotransfection experiments in which C/EBP beta and C/EBP delta were shown to be potent transactivators for the SAA3 promoter. Moreover, the transactivation required an intact B element despite the presence of other functional C/EBP-binding sites. Interestingly, although element C did not interact with C/EBP directly, it was nevertheless required for maximum transactivation by C/EBP delta. Our studies thus demonstrate that both C/EBP family proteins and SEF-1 are required to transactivate the SAA3 gene.

Differential acute-phase response of rat kininogen genes involves type I and type II interleukin-6 response elements

The serum concentration of rat T1 kininogen increases 20-30-fold in response to acute inflammation. This increase, induced in the liver, is regulated primarily at the transcriptional level. In contrast, synthesis of a homologous K kininogen is not induced. In this study, we further analyzed a 321-base pair interleukin (IL)-6 response element in the T1 kininogen promoter and showed that it consists of at least three functionally distinct sequences (A, B, and C boxes). All three sequences were required for full promoter activity. The B box, a strong C/EBP-binding site, was crucial for T1 kininogen's basal expression, whereas A and C boxes resembled the type II IL-6 response elements and were critical for the cytokine response. C/EBP alpha, -beta, and -delta interacted with the B box sequence; however, upon IL-6 stimulation, C/EBP delta binding activity was dramatically induced and became the predominant factor binding to this site. Consistent with these binding studies were the cotransfection experiments, revealing that C/EBP delta was the most potent transactivator under induced conditions and that its transactivation on the T1 kininogen promoter required an intact B box. These findings substantiated the importance of the B box in eliciting the full acute-phase response. A sequence comparison showed the K kininogen promoter contained identical A and B boxes but differed from the T1 kininogen promoter by two nucleotides at the C box. This divergence reduced the IL-6 response by approximately 4-fold, thus contributing to the differential inflammatory response. Our studies demonstrate that evolutionary divergence of a few nucleotides at a critical sequence in the promoter regions can profoundly alter the expression patterns of downstream genes.

Molecular analysis of the differential hepatic expression of rat kininogen family genes

Serum concentration of rat T1 kininogen increases 20- to 30-fold in response to acute inflammation, an induced hepatic synthesis regulated primarily at the transcriptional level. We have demonstrated by transient transfection analyses that rat T1 kininogen gene/chloramphenicol acetyltransferase (T1K/CAT) constructs are highly responsive to interleukin-6 and dexamethasone. In these studies we examined the regulation of a highly homologous K kininogen gene promoter and showed that it is minimally induced under identical conditions. The basal expression of the KK/CAT construct was, however, five- to sevenfold higher than that of the analogous T1K/CAT construct. Promoter-swapping experiments to examine the molecular basis of this differentially regulated basal expression showed that at least two K kininogen promoter regions are important for conferring its high basal expression: a distal 19-bp region (C box) constituted a binding site for C/EBP family proteins, and a proximal 66-bp region contained two adjacent binding sites for hepatocyte nuclear factor 3 (HNF-3). While the C box in the K kininogen promoter was able to interact with C/EBP transcription factors, the T1 kininogen promoter C box could not. In addition, HNF-3 binding sites of the K kininogen promoter demonstrated stronger affinities than those of the T1 kininogen promoter. Since C/EBP and HNF-3 are highly enriched in the liver and are known to enhance transcription of liver-specific genes, these differences in their binding activities thus accounted for the K kininogen gene's higher basal expression. Our studies demonstrated that evolutionary divergence of a few critical nucleotides may lead to subtle changes in the binding affinities of a transcription factor to its recognition site, profoundly altering expression of the downstream gene.

Regulation of two forms of the TNF receptors by phorbol ester and dibutyryl cyclic adenosine 3',5'-monophosphate in human histiocytic lymphoma cell line U-937

Recently the cDNA for two different forms of TNF receptor, with gene products of molecular masses of 60 and 80 kDa, have been cloned. In the present report, we investigated the effects of phorbol ester and dibutyryl cAMP on the regulation of the transcript for each type of TNF receptor in U-937 cells. Our results indicate that exposure of these cells to either phorbol ester or dibutyryl cAMP increases the steady state mRNA levels of the 80 kDa form. This effect is dose- and time-dependent. The induction of the p80 receptor transcript by PMA and dibutyryl cAMP was additive suggesting independent mechanisms of induction. Under identical conditions, both agents failed to induce the transcript for the p60 form of the TNF receptor. As demonstrated by actinomycin D pulse-chase experiment, the mRNA for the p80 receptor was found to be highly stable with an approximate half-life of 16 h. No significant change in the half-life was observed when cells were treated with phorbol ester. The mechanisms by which phorbol ester and dibutyryl cAMP induce the upregulation of p80 receptor mRNA appear to be different. Induction of receptor transcript by cycloheximide suggests the presence of a labile repressor protein. Interestingly, the effect of cycloheximide on the induction of the p80 mRNA was found to be additive with that of dibutyryl cAMP but not with phorbol ester. 1-(5-Isoquinolinylsufonyl)-2-methylpiperazine (H7) and N[2-(methylamino) ethyl]-5-isoquinolinesulfonamide (H-8), inhibitors of protein kinase C and protein kinase A, respectively, both inhibited the phorbol ester-mediated induction of the p80-transcript but not that mediated through dibutyryl cAMP. Since dibutyryl cAMP undergoes intracellular dissociation into cAMP and butyric acid, we found that exposure of cells to sodium butyrate alone could induce p80 mRNA in a dose-dependent manner, thus suggesting the role of histone hyperacetylation. Furthermore forskolin treatment, an intracellular inducer of cAMP, increased the receptor transcript level whereas isobutylmethylxanthine, an inhibitor of phosphodiesterase, had no effect. Interestingly, while the p80 form of the TNF receptor mRNA levels was elevated by both phorbol ester and dibutyryl cAMP, only dibutyryl cAMP increased the TNF binding; phorbol ester treatment decreased the binding activity. Thus, our results demonstrate that the genes for the two forms of TNF receptors are differentially regulated. Furthermore, the mechanism of regulation by PMA differs from that by dibutyryl cAMP.

Cooperative effects of C/EBP-like and NF kappa B-like binding sites on rat serum amyloid A1 gene expression in liver cells

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. In response to inflammation, its expression is increased by 1000-fold, primarily because of a 200-fold increase in the rates of SAA gene transcription. We have shown that when 304 bp of 5' flanking region of the rat SAA1 gene is fused to a reporter gene, the chloramphenicol acetyltransferase (CAT) gene, CAT activity is induced in a cell-specific manner in response to conditioned media prepared from activated mixed lymphocyte cultures and recombinant interleukin-1. In this study, deletion of the SAA1 promoter to -120 bp with respect to the transcriptional start site did not diminish promoter activity; however, deletion to -94 bp renders the promoter completely inactive. Functional analysis have demonstrated that a 66-bp DNA fragment spanning -138 bp to -73 bp could confer cytokine responsiveness to a heterologous thymidine kinase promoter. Within this 66-bp responsive element resided an NF kappa B-like-binding site and a C/EBP-like-binding site. Although each binding site alone could confer responsiveness when stimulated with conditioned media and TPA, the response was much weaker than that observed when both sites were present. Moreover, site-specific mutations of either binding site completely abolished SAA1 promoter activity. Taken together, these results suggest a functional importance for and cooperative interaction of these two nuclear-factor binding sites in the cytokine-induced expression of the rat SAA1 gene.

Expression of rat serum amyloid A1 gene involves both C/EBP-like and NF kappa B-like transcription factors

Serum amyloid A (SAA) is a major acute-phase protein synthesized and secreted mainly by the liver. During inflammation, its expression is increased by 1000-fold as the result of greatly increased gene transcription. In this study, we analyzed the cis-acting regulatory elements and trans-acting factors important for the expression of the rat SAA1 gene. A DNA fragment containing 304 base pairs (bp) of 5'-flanking sequences of the SAA1 gene was fused to a reporter gene, chloramphenicol acetyltransferase (CAT), and the resulting construct, pSAA1/CAT (-304), was used to assess the function of the 5'-flanking sequences by transient transfection assay. pSAA1/CAT (-304) was not expressed or expressed at very low levels in both the liver- and nonliver-derived cells. However, when stimulated with conditioned medium prepared from mixed lymphocyte cultures, recombinant interleukin 1, or 12-O-tetradecanoylphorbol-13-acetate, expression of the pSAA1/CAT (-304) hybrid gene was induced 15-20-fold, but only in liver-derived cells. Further functional analysis demonstrated that a 66-bp DNA fragment conferred cytokine responsiveness onto a heterologous thymidine kinase promoter both in liver and nonliver cells. Footprint analysis with the Hep3B nuclear proteins revealed four protected regions in the 5'-flanking region of the SAA1 gene. The pattern of protection was identical with nuclear extracts prepared from either unstimulated or conditioned medium-treated Hep3B cells. Two of these footprint regions were identified as binding sites for C/EBP or C/EBP-related proteins, with the distal region having about 10-fold higher binding affinity than the proximal region. One additional cis-element formed a specific protein-DNA complex only with the nuclear proteins from TPA- or conditioned medium-treated Hep3B cells. This cis-element shares sequence identity with nuclear factor NF kappa B binding sites. The finding of a NF kappa B binding site within the 66-bp cytokine-responsive fragment further suggests its functional importance in the regulation of SAA1 gene expression. Our results suggest that C/EBP- and NF kappa B-related proteins may be important regulatory factors that contribute both to tissue specificity and to the high rate of SAA transcription in response to inflammatory mediators.

Interleukin-6 responsiveness and cell-specific expression of the rat kininogen gene

The serum concentration of rat T1 kininogen increases 20-30-fold in response to acute inflammation, an induced hepatic synthesis regulated primarily at the transcriptional level. To analyze the cis-regulatory elements responsible for the induced transcription, we fused a 1.6-kilobase segment of the rat T1 kininogen promoter to a reporter gene, chloramphenicol acetyltransferase (CAT). The resultant chimeric DNA was transfected into cultured cells. In transient transfection assays, this 5'-flanking sequence was sufficient to confer cell-specific expression: CAT activity was readily detectable when the construct was transfected into liver-derived cells, but it was not detectable in nonliver cells. Furthermore, when liver cells (Hep3B) transfected with this construct were treated with conditioned medium prepared from activated mixed lymphocyte cultures or with recombinant interleukin-6 (IL-6), a 5-fold increase in CAT activity was detected. Addition of dexamethasone to the conditioned medium or to IL-6 showed synergistic effects and resulted in a 10-fold increase in CAT activity. In contrast, when IL-1 was used with IL-6, induction of CAT activity was inhibited. Deletion analyses revealed two regions important for tissue-specific and induced regulation of T1 kininogen: sequences proximal to base pair -73 conferred enhanced expression in liver-derived cells and a distal region that conferred responsiveness to conditioned medium, recombinant IL-6, and dexamethasone. This responsive element had properties of an inducible transcriptional enhancer, and it was functional in both liver and nonliver cells when placed immediately upstream of a thymidine kinase promoter.

Two adjacent C/EBP-binding sequences that participate in the cell-specific expression of the mouse serum amyloid A3 gene

Serum amyloid A (SAA) is a major acute-phase protein synthesized primarily in the liver. Its expression, very low in normal animals, is increased several hundredfold following acute inflammation. To examine DNA sequences involved in liver-specific expression, 5'-flanking regions of the mouse SAA3 gene were analyzed by transient transfection, band shift, and DNase I protection assays. We found that a 56-bp fragment immediately 5' to the TATA box spanning the region -93 to -38 relative to the transcription start site was sufficient to confer liver cell-specific transcriptional activation onto a heterologous promoter in a dose-dependent and orientation-independent manner. This DNA fragment could form DNA-protein complexes with heat-stable nuclear proteins, and the complexes formed could be specifically competed for by excess oligomers corresponding to the C/EBP- or DBP-binding sites but not by binding sites for three other liver-specific factors, HNF1, HNF3, and HNF4. Footprint analysis using Hep3B nuclear extracts revealed two adjacent footprint regions within this 56-bp fragment, the distal region having at least fivefold-greater affinity than the proximal region. Identical footprint patterns were observed when purified recombinant C/EBP protein was used. These results indicated that binding of C/EBP to this 56-bp fragment plays an important role in vivo in enhancing expression of the mouse SAA3 gene in hepatocytes.

Regulation of mouse serum amyloid A gene expression in transfected hepatoma cells

Expression of mouse serum amyloid A (SAA1, -2, and -3) mRNAs can be induced up to 1,000-fold in the liver in response to acute inflammation. This large increase is primarily the result of a 200-fold increase in the rates of SAA gene transcription. To analyze the cis-acting regulatory element(s) responsible for regulating transcription, we fused 306 base pairs of the mouse SAA3 promoter to a reporter gene, the chloramphenicol acetyltransferase (CAT) gene, and transfected this chimeric DNA into cultured cells. In transient expression assays, this 5' sequence was sufficient to confer cell-specific expression: CAT activity was readily detectable when the construct was transfected into liver-derived cells but was not detectable in nonliver cells. Furthermore, when liver cells transfected with this construct were treated with conditioned media prepared from activated mixed lymphocyte cultures or with recombinant interleukin-1, a 10- to 15-fold increase in CAT activity was detected. Deletion analyses showed two regions of interest: a proximal region that enhanced CAT expression in a cell-specific manner and a distal region that conferred responsiveness to both conditioned media and recombinant interleukin-1. This distal responsive element had properties of an inducible transcriptional enhancer, and deletion of the proximal cell-specific region rendered the distal element responsive to stimulation by conditioned media in nonliver cells.

Molecular and cellular biology of serum amyloid A

Serum amyloid A (SAA) is one of the major acute-phase proteins in humans and mice. It is synthesized predominantly by the liver and secreted as a major component of the apolipoproteins in the high density lipoprotein particle. While the major physiological function of SAA is unclear, prolonged elevation of plasma SAA levels, as in chronic inflammation, however, results in the pathological condition amyloidosis affecting the liver, kidney and spleen. The expression of SAA mRNA is dramatically elevated in response to infection or systemic inflammation and is due primarily to the increased rate of SAA gene transcription. Studies in vitro and in vivo demonstrated that the expression of SAA genes is regulated by the inflammatory cytokine interleukin-1. Moreover, both the interleukin-1-induced expression and the enhanced liver-specific expression of the SAA gene are controlled by the binding of nuclear proteins to specific DNA sequences upstream from the structural gene.

RNA editing of apolipoprotein B mRNA. Sequence specificity determined by in vitro coupled transcription editing

Apolipoprotein (apo) B-48 mRNA is produced by in vivo RNA editing which involves a C----U conversion of the first base of the codon CAA for Gln-2153, changing it to UAA, an in-frame stop codon. We have reproduced the editing reaction in vitro using nuclear extracts. Efficient RNA editing was demonstrated by using apoB mRNA segments as substrate or in a coupled transcription-editing reaction using apoB minigenes as template. ApoB minigenes were constructed by ligating the adenovirus major late promoter to a fragment of apoB-100 DNA containing the editing site and used for the transcription-editing reaction. We defined the sequence specificity of the editing reaction using site-specific single and multiple base mutants constructed by the polymerase chain reaction. Among 22 different mutant apoB-100 minigene constructs containing mutations in the bases immediately flanking the edited C-6666, 20 were edited in the coupled transcription-editing reaction. The results suggest a relatively lax sequence specificity for apoB mRNA editing. Our observation may have important implications for apoB-48 biogenesis as well as for the editing process as a general biologic regulatory mechanism.

Stimulation of the acute-phase response in simian virus 40-hepatocyte cell lines

Seven simian virus 40 (SV40)-hepatocyte cell lines were characterized with respect to the ability to express eight liver acute-phase genes. cDNA clones corresponding to albumin, serum amyloid A, alpha 1-acid glycoprotein, haptoglobin, alpha-, beta-, and gamma-fibrinogen, and alpha 1-major-acute-phase protein mRNAs were used in Northern (RNA) or slot blot analyses. In the noninduced state, six of the seven cell lines showed significant (i.e., liverlike) levels of constitutive expression of all genes examined except that expression of haptoglobin mRNA was considerable lower than in the normal liver. To examine whether these immortalized liver cells can respond appropriately to inflammatory mediators, cells were treated with conditioned medium from activated human monocytes or mixed lymphocyte cultures. Results showed that these SV40-hepatocyte cell lines responded to the conditioned media in culture by down-regulating albumin gene expression and up-regulating other acute-phase genes in a time- and dose-dependent manner. These results indicate that the SV40-hepatocytes retained not only the ability to express a number of acute-phase genes but also the ability to respond to external stimuli. The usefulness of these cell lines for analysis of the molecular mechanisms involved in the regulation of these acute-phase genes is discussed.

Altered expression of acute-phase reactants in mouse liver tumors

We studied the expression of eight liver acute-phase genes in spontaneous and diethylnitrosamine-induced mouse liver tumors (MLTs) under basal and induced conditions. Primary spontaneous and chemically induced MLTs were used for RNA isolation and histopathologic analysis. In the noninduced state, all MLTs showed similar levels of mRNA for albumin, serum amyloid A, alpha 1-acid glycoprotein, haptoglobin, and alpha-, beta-, and gamma-fibrinogens compared with control or background livers. The mRNA for the alpha 1-major acute-phase protein, however, was consistently elevated in both spontaneous and diethylnitrosamine-induced MLTs. The expression of these acute-phase reactants in 11 MLTs was examined following exposure of the mice to turpentine. The relative expression of these mRNAs in these MLTs varied widely compared with mRNA expression in controls. Though all MLTs expressed the same three species of fibrinogen mRNAs as did the controls, no MLT demonstrated downregulation of albumin mRNA levels, and only 1 of 11 MLTs showed a marginal increase in serum amyloid A mRNA levels. Synthesis of mRNA for alpha 1-acid glycoprotein and haptoglobin was intermediate. The study of the response of MLTs to specific acute-phase stimuli may make possible a better understanding of the basis for coordinated expression of acute-phase reactants and of the variable phenotypes associated with cancers.

Effects of experimentally induced nephrosis on protein synthesis in rat liver

A nephrotic syndrome was experimentally induced in rats by a single intravenous injection of aminonucleoside of puromycin. Experimental animals were studied 8 days after the injection, at which time they exhibited marked proteinuria and hypoalbuminemia compared with control animals. The experimental animals also exhibited alterations in protein synthesis in liver as evidenced by a marked increase in the rate of albumin synthesis relative to total hepatic protein synthesis, changes in the relative concentrations of several plasma proteins, an increased protein content of plasma, an increased liver weight relative to body weight, and an increased RNA content of liver. Perfused liver preparations derived from nephrotic rats exhibited an increased release of albumin and other secretory proteins compared with control preparations. In contrast, there was no difference in the rate of synthesis of nonexported proteins between the two groups. The elevation in the relative rate of albumin synthesis was accompanied by a relative increase of the same magnitude in albumin mRNA. Furthermore, the relative amounts of several other mRNAs, including those coding for beta-fibrinogen, haptoglobin, metallothionein II, and two unidentified proteins, were increased, whereas the amount of mRNA coding for alpha 1-acid glycoprotein was decreased in livers of nephrotic rats compared to controls. These results indicate that nephrosis leads to marked alterations in the synthesis of albumin and other plasma proteins. Mechanisms responsible for these alterations include changes in the relative abundance of specific mRNAs and an increase in total cellular RNA.

Changes in plasma albumin concentration, synthesis rate, and mRNA level during acute inflammation

Induction of acute inflammation in rats by the subcutaneous injection of turpentine resulted in a marked fall in the concentration of albumin in plasma. This fall, which reached a minimum of 45% of the control level at 36 h after injection of the inflammatory agent, occurred in the presence of no significant change in the concentration of total protein in plasma. It was accompanied by a corresponding decline in the relative abundance of albumin mRNA in liver, which reached a minimum of 25% of the control level at 36 h after initiation of the inflammatory response. Perfused livers from 36-h postinjection rats exhibited albumin secretion rates that were reduced to 38% of control values. In contrast, release of total secretory proteins, secretion of nonalbumin plasma proteins, and synthesis of nonexported proteins by perfused livers were elevated to 166, 266, and 117% of the control values, respectively, as a result of the inflammatory response. These results demonstrate that acute inflammation causes a relative reduction in hepatic albumin mRNA, which leads to a corresponding decrease in albumin synthesis and secretion by liver and a fall in the concentration of albumin in plasma. The concentration of total protein in plasma is maintained during acute inflammation in part by increased synthesis and secretion by liver of nonalbumin plasma proteins, e.g. the acute-phase reactants.

Regulation of carbamoyl phosphate synthetase-aspartate transcarbamoylase-dihydroorotase gene expression in growing and arrested cells

We have studied expression of the carbamoyl-P synthetase-aspartate transcarbamoylase-dihydroorotase (CAD) gene in growing or confluent Syrian hamster cells, and also in cells arrested by depriving them of serum or restimulated by adding fresh serum. In contrast to other biosynthetic enzymes such as dihydrofolate reductase, the amount of the CAD enzyme decreased very little when growth was arrested, as judged by the small change in aspartate transcarbamoylase activity. However, the level of CAD mRNA was about 10-fold lower in arrested cells than in growing cells. The rate of transcription of CAD, measured by the nuclear run-off technique, decreased roughly in parallel with the decrease in the steady-state level of the mRNA, suggesting that control of transcription is probably an important element in the overall regulation of CAD gene expression. Expression of a different gene which lies near the 5' end of CAD changed in parallel with that of CAD, but expression of two other genes in the same region was insensitive to the growth state of the cells. Therefore, control of gene expression as a function of growth was specific rather than a reflection of more general changes in chromatin structure in the vicinity of CAD.

Expression of rat apolipoprotein A-IV and A-I genes: mRNA induction during development and in response to glucocorticoids and insulin

Rat apolipoproteins (apo-) A-IV and A-I share many structural similarities, the most notable of which is a domain of repeated docosapeptides with amphipathic helical potential. Although the genes for apo-A-IV and apo-A-I probably diverged from a common ancestor, these proteins seem to have developed different functions in their evolution. In the present study, cloned cDNAs were used to characterize the expression of apo-A-IV and apo-A-I mRNAs in a wide variety of adult rat tissues, as well as in small intestine and liver obtained from fetal, suckling, and weanling animals; comparisons were made to the expression of apo-E mRNA. The apo-A-IV and apo-A-I mRNAs were most abundant in adult small intestine and liver, with trace amounts detected in other tissues. Substantial amounts of these mRNAs were detected in the yolk sac, suggesting that this fetal tissue plays an important role in lipid metabolism during gestation. Noncoordinate accumulation of apo-A-IV and apo-A-I mRNAs was observed within and between the liver and small intestine during neonatal development. The apo-A-IV mRNA levels in the developing small intestine and liver appeared to correlate with their triglyceride secretion rates, suggesting that this protein plays an important role in the metabolism of triglyceride-rich lipoproteins. When dexamethasone (0.1 microM), insulin (0.01 microM), or insulin and dexamethasone together were incubated with primary cultures of nonproliferating adult rat hepatocytes, apo-A-IV mRNA levels were 4-, 7-, and 11-fold higher, respectively, than in non-hormone-treated control hepatocytes. Hormone administration resulted in a 2-fold greater amount of apo-A-I mRNA in each case, with no significant change in the level of apo-E mRNA. The overall results suggest that these structurally related apolipoproteins are regulated in substantially different ways.

Tissue specific expression and developmental regulation of two genes coding for rat fatty acid binding proteins

We have examined the tissue distribution and developmental regulation of two low molecular weight cytosolic fatty acid binding proteins. Based on their initial site of isolation, they have been referred to as liver and intestinal fatty acid binding proteins (FABP). Cloned cDNAs were used to probe blots of RNAs extracted from a wide variety of adult rat tissues as well as small intestine and liver RNA obtained from fetal, suckling, and weaning animals. The highest concentrations of "liver" FABP mRNA were found in small intestine and liver. "Intestinal" FABP mRNA is most abundant in small bowel RNA while only trace amounts were encountered in liver. Both mRNAs were detectable in stomach, colon, pancreas, spleen, lung, heart, testes, adrenal, and brain RNA at 1-8% the concentrations observed in small intestine. Accumulation of both mRNAs in the small intestinal epithelium increases during development. The mRNAs are first detectable between the 19th and 21st day of gestation. They undergo a coordinated 3-4-fold increase in concentration within the first 24 h after birth. Thereafter, gut levels of intestinal FABP mRNA remain constant during the suckling period while liver FABP mRNA increases an additional 2-fold. Liver FABP mRNA levels are also induced in hepatocytes during the first postnatal day but subsequently do not change during the suckling and weaning phase, despite marked alterations in hepatic fatty acid metabolism. These observations support the concept that the major role of these proteins is to facilitate the entry of lipids into cells and/or their subsequent intracellular transport and compartmentalization. The data also raise questions about the identity of extragastrointestinal FABPs.

Apolipoprotein E mRNA is abundant in the brain and adrenals, as well as in the liver, and is present in other peripheral tissues of rats and marmosets

The relative amount of apolipoprotein (apo-) E mRNA in 12 different tissues of the rat and marmoset was examined by dot blot hybridization using cloned cDNA probes. As expected, it was found to be most abundant in the liver. However, substantial amounts of apo-E mRNA were found in the brain and adrenals at relative levels about one-third of that found in the liver. Significant quantities of apo-E mRNA were detected in all of the other peripheral tissues as well. The apo-E mRNA levels in these tissues were 2-10% of that found in the liver of the rat and 10-30% of that found in the liver of the marmoset. Apo-E mRNA was also abundant in human brain and in each species examined; it was distributed throughout all major areas of this organ. In contrast, apo-A-I mRNA was detected in abundant amounts only in the small intestine and in the liver. Extrahepatic apo-E mRNA appears to be functional, generating a translation product similar or identical to that generated by the liver. During fetal and neonatal development, apo-E mRNA is rapidly induced from low levels to approximately equal to 60% of adult levels in liver at parturition. The fetal yolk sac contains more apo-E mRNA than the fetal liver, suggesting a significant role for the yolk sac as a source of apo-E during gestation.

Evidence that the folate-requiring enzymes of de novo purine biosynthesis are encoded by individual mRNAs

Isolation of the mRNAs encoding for the three folate-requiring enzymes involved in de novo purine biosynthesis followed by their in vitro translation resulted in three separate proteins electrophoretically identical with those previously isolated. The three enzymes are glycinamide ribonucleotide transformylase, 5-aminoimidazole-4-carboxamide ribonucleotide transformylase, and 5,10-methenyl-, 5,10-methylene-, and 10-formyltetrahydrofolate synthetase. Thus these enzymes do not appear to be derived from large multifunctional proteins that are then subject to proteolysis in vivo or during in vitro purification. The levels of these enzymatic activities were increased by approximately 2-fold after raising the concentration of protein in the chicken's diet. The observed response is similar to that noted for glutamine phosphoribosylpyrophosphate amidotransferase, the presumed rate-limiting enzymatic activity for this pathway. For 5-amino-imidazole-4-carboxamide ribonucleotide transformylase and the trifunctional synthetase but not glycinamide ribonucleotide transformylase the increase in enzymatic activity correlates with higher mRNA levels.

Structure of amplified DNA in different Syrian hamster cell lines resistant to N-(phosphonacetyl)-L-aspartate

Syrian hamster cell lines selected in multiple steps for resistance to high levels of N-(phosphonacetyl)-L-aspartate (PALA) contain many copies of the gene coding for the pyrimidine pathway enzyme CAD. Approximately 500 kilobases of additional DNA was coamplified with each copy of the CAD gene in several cell lines. To investigate its structure and organization, we cloned ca. 162 kilobases of coamplified DNA from cell line 165-28 and ca. 68 kilobases from cell line B5-4, using a screening method based solely on the greater abundance of amplified sequences in the resistant cells. Individual cloned fragments were then used to probe Southern transfers of genomic DNA from 12 different PALA-resistant mutants and the wild-type parents. A contiguous region of DNA ca. 44 kilobases long which included the CAD gene was amplified in all 12 mutants. However, the fragments cloned from 165-28 which were external to this region were not amplified in any other mutant, and the external fragments cloned from B5-4 were not amplified in two of the mutants. These results suggest that movement or major rearrangement of DNA may have accompanied some of the amplification events. We also found that different fragments were amplified to different degrees within a single mutant cell line. We conclude that the amplified DNA was not comprised of identical, tandemly arranged units. Its structure was much more complex and was different in different mutants. Several restriction fragments containing amplified sequences were found only in the DNA of the mutant cell line from which they were isolated and were not detected in DNA from wild-type cells or from any other mutant cells. These fragments contained novel joints created by rearrangement of the DNA during amplification. The cloned novel fragments hybridized only to normal fragments in every cell line examined, except for the line from which each novel fragment was isolated or the parental population for that line. This result argues that "hot spots" for forming novel joints are rare or nonexistent.

Biology of simian virus 40 (SV40) transplantation antigen (TrAg). X. Tumorigenic potential of mouse cells transformed by SV40 in high responder C57BL/6 mice and correlation with the persistence of SV40 TrAg, early proteins and sequences

Primary mouse embryo fibroblasts of C57Bl/6 origin and cells derived from a tumor induced by polyoma virus in a C57Bl/6 mouse were transformed with SV40. The tumorigenic potential of these cells in normal adult and SV40-immunized mice was correlated with the synthesis of SV40 tumor antigens including the transplantation rejection antigen (TrAg) and with the presence of SV40 early region DNA sequences. Primary cells transformed by SV40 (B6/WT-3) induced tumors in immunocompetent adult syngeneic mice after adaptation in the immunosuppressed host. Passage of these tumor cells (B6/WT-3-T) through SV40-immunized mice resulted in the retention of both T and t antigens and TrAg. However, passage of SV40-transformed polyoma tumor cells through SV40-immunized immunocompetent adult mice but not in nonimmunized mice resulted in the loss of expression of SV40 tumor antigens including TrAg. This loss correlated with the loss of SV40 early region sequences from these double transformed cells. These results demonstrate that the establishment of in vitro SV40-transformed primary mouse cells into a tumor capable of progressive growth in high responder mice does not lead to the selection of variants which have lost the expression of early region DNA sequences.

Rapid and selective shutoff of plasma protein production in herpes simplex virus type 2-infected hepatoma cells

The effect of herpes simplex virus type 2 (HSV-2) infection of hepatoma McA-RH7777 cells on the production of alpha-fetoprotein (AFP) and several other secreted plasma proteins was examined. Cells infected with HSV-2 were labeled with [35S]methionine for various times postinfection (p.i.). Culture media and intracellular extracts were immunoprecipitated with plasma protein antibodies and examined by polyacrylamide gel electrophoresis. The relative levels of AFP and several other plasma proteins decreased substantially in infected cells compared with mock-treated controls; however, the level of at least one secreted plasma protein was unchanged after infection and the level of another increased after infection. Hybridization analyses with AFP cDNA showed that AFP RNA decreased to 43 and 30% of controls at 3.5 and 6.5 hr p.i., respectively. These observations were supported by the results of cell-free translation of isolated poly(A)-containing RNA. HSV-2 proteins were not detectable at times p.i. when AFP synthesis, secretion, and mRNA levels were significantly diminished. No decrease in AFP levels was observed in cells infected with ultraviolet-irradiated virus. We conclude that HSV-2 infection of McA-RH7777 cells leads to a rapid decrease in synthesis and secretion of specific plasma proteins which is apparent, at least for AFP, at the level of mRNA. This shutoff is not common to all McA-RH7777 cell proteins and, although seen early after infection, most likely requires the expression of a virus gene(s).

Diabetes-induced alterations in liver protein synthesis. Changes in the relative abundance of mRNAs for albumin and other plasma proteins

Mechanisms responsible for diabetes-induced alterations in liver protein synthesis were investigated in vivo and in perfused liver using Bio-Breeding Worcester (BB/W) control rats, spontaneously diabetic BB/W rats maintained on insulin therapy, and diabetic BB/W rats withdrawn from insulin therapy for 48 h. Withdrawal of insulin therapy in the diabetic rats resulted in marked alterations in a number of parameters related to liver protein synthesis compared to BB/W control or insulin-maintained diabetic rats. Alterations seen in vivo following withdrawal of insulin included changes in the relative concentrations of several plasma proteins, a 40% reduction in total liver RNA relative to DNA, a 5-fold reduction in albumin synthesis relative to the synthesis of total liver proteins, a 5-fold reduction in albumin mRNA relative to total RNA, reductions in the relative abundance of mRNAs for at least four plasma proteins other than albumin, and a relative increase in mRNA for at least one plasma protein. Alterations observed in perfused liver included reductions in total liver protein synthesis (60% of control), albumin production (24% of control), and total secretory protein production (44% of control). All parameters studied were essentially unchanged from BB/W control values when the diabetic rats were maintained on insulin therapy. The results indicate that insulin deficiency leads to marked reductions in liver protein synthesis, particularly the synthesis of albumin and other plasma proteins. The mechanisms responsible for these alterations include changes in the relative abundance of specific mRNAs and a decrease in total cellular RNA.

The role of amino acids in the regulation of protein synthesis in perfused rat liver. II. Effects of amino acid deficiency on peptide chain initiation, polysomal aggregation, and distribution of albumin mRNA

Decreased rates of protein synthesis which occurred in rat livers perfused with amino acid-deficient medium were accompanied by a loss of polysomes and a doubling of concentrations of ribosomal subunits and monomers as compared to unperfused liver or livers perfused with amino acid-supplemented medium. The loss of polysomes was not the result of mRNA degradation because this effect could be reversed by addition of amino acids to the perfusion medium. Instead, loss of polysomes indicated an impairment in peptide chain initiation. To determine whether the block of initiation could be the result of sequestration of mRNA in untranslatable pools, the content of albumin mRNA in membrane-bound and free polysomes and in the non-polysomal fraction isolated on sucrose density gradients was determined by hybridization to an albumin cDNA. In livers perfused with an amino acid-supplemented medium, 90% of the albumin mRNA was found in bound polysomes, and with amino acid-deficient medium, this value was decreased to 80%. Thus, there was no indication of a significant pool of mRNA which was not being translated. The block of initiation was, however, accompanied by a marked change in density and methionine-binding characteristics of the 40 S ribosomal subunit in livers perfused with deficient medium as compared to livers perfused with supplemented medium or to unperfused livers. There was a relative loss of 40 S subunits in a low density form, 1.41 g/cm3, an increase in the proportion in a high density form, 1.48 g/cm3, and a decrease in binding of [35S]methionine to 40 S ribosomal subunits. These changes provide evidence of reduced rates of formation of the 40 S initiation complex.