Periodontal infection as a possible risk factor for preterm low birth weight

Peridontal diseases are gram-negative anaerobic infections that can occur in women of childbearing age (18 to 34 years). In the present investigation we sought to determine whether the prevalence of maternal periodontal infection could be associated with preterm low birth weight (PLBW), controlling for known risk factors and potential covariates. A case-control study of 124 pregnant or postpartum mothers was performed. PLBW cases were defined as a mother with a birth of less than 2,500 g and one or more of the following: gestational age < 37 weeks, preterm labor (PTL), or premature rupture of membranes (PROM). Controls were normal birth weight infants (NBW). Assessments included a broad range of known obstetric risk factors, such as tobacco use, drug use, alcohol consumption, level of prenatal care, parity, genitourinary infections, and nutrition. Each subject received a periodontal examination to determine clinical attachment level. PLBW cases and primiparous PLBW cases (n = 93) had significantly worse periodontal disease than the respective NBW controls. Multivariate logistic regression models, controlling for other risk factors and covariates, demonstrated that periodontal disease is a statistically significant risk factor for PLBW with adjusted odds ratios of 7.9 and 7.5 for all PLBW cases and primiparous PLBW cases, respectively. These data indicate that periodontal diseases represent a previously unrecognized and clinically significant risk factor for preterm low birth weight as a consequence of either PTL or preterm PROM.

Measuring acute postoperative pain using the visual analog scale: the minimal clinically important difference and patient acceptable symptom state

Background

The 100 mm visual analog scale (VAS) score is widely used to measure pain intensity after surgery. Despite this widespread use, it is unclear what constitutes the minimal clinically important difference (MCID); that is, what minimal change in score would indicate a meaningful change in a patient's pain status.

Methods

We enrolled a sequential, unselected cohort of patients recovering from surgery and used a VAS to quantify pain intensity. We compared changes in the VAS with a global rating-of-change questionnaire using an anchor-based method and three distribution-based methods (0.3 sd , standard error of the measurement, and 5% range). We then averaged the change estimates to determine the MCID for the pain VAS. The patient acceptable symptom state (PASS) was defined as the 25th centile of the VAS corresponding to a positive patient response to having made a good recovery from surgery.

Results

We enrolled 224 patients at the first postoperative visit, and 219 of these were available for a second interview. The VAS scores improved significantly between the first two interviews. Triangulation of distribution and anchor-based methods resulted in an MCID of 9.9 for the pain VAS, and a PASS of 33.

Conclusions

Analgesic interventions that provide a change of 10 for the 100 mm pain VAS signify a clinically important improvement or deterioration, and a VAS of 33 or less signifies acceptable pain control (i.e. a responder), after surgery.

Macrophage oxidation of low density lipoprotein generates a modified form recognized by the scavenger receptor

Incubation of low density lipoprotein (LDL) with endothelial cells or smooth muscle cells overnight has resulted in an oxidative modification of LDL that results in its recognition by macrophages by way of the acetyl LDL receptor. In the present study, we examined whether macrophages themselves can oxidize and modify LDL in a manner similar to that of endothelial cells. Incubation of 125I-labeled LDL with resident or thioglycollate-elicited macrophages for 24 hours in Ham's F-10 medium resulted in the appearance of thiobarbituric acid (TBA) reactive materials and trichloroacetic acid (TCA) soluble radioactivity in the medium. The LDL harvested from these incubations showed increased electrophoretic mobility and was degraded rapidly when added to fresh macrophages as compared to LDL previously incubated in the absence of cells. These macrophage-induced modifications could be prevented if the first incubation was carried out in the presence of the antioxidant butylated hydroxytoluene (BHT) or in Dulbecco's modified Eagle's medium (DMEM). The degradation of 125I-labeled macrophage-modified LDL by macrophages was competitively inhibited by unlabeled acetyl LDL or unlabeled endothelial cell-modified LDL but not by native LDL, indicating that the degradation was mediated by the acetyl LDL receptor.

Localization of FtsI (PBP3) to the septal ring requires its membrane anchor, the Z ring, FtsA, FtsQ, and FtsL

Assembly of the division septum in bacteria is mediated by several proteins that localize to the division site. One of these, FtsI (also called penicillin-binding protein 3) of Escherichia coli, consists of a short cytoplasmic domain, a single membrane-spanning segment, and a large periplasmic domain that encodes a transpeptidase activity involved in synthesis of septal peptidoglycan. We have constructed a merodiploid strain with a wild-type copy of ftsI at the normal chromosomal locus and a genetic fusion of ftsI to the green fluorescent protein (gfp) at the lambda attachment site. gfp-ftsI was expressed at physiologically appropriate levels under control of a regulatable promoter. Consistent with previous results based on immunofluorescence microscopy GFP-FtsI localized to the division site during the later stages of cell growth and throughout septation. Localization of GFP-FtsI to the cell pole(s) was not observed unless the protein was overproduced about 10-fold. Membrane anchor alterations shown previously to impair division but not membrane insertion or transpeptidase activity were found to interfere with localization of GFP-FtsI to the division site. In contrast, GFP-FtsI localized well in the presence of beta-lactam antibiotics that inhibit the transpeptidase activity of FtsI. Septal localization depended upon every other division protein tested (FtsZ, FtsA, FtsQ, and FtsL). We conclude that FtsI is a late recruit to the division site, and that its localization depends on an intact membrane anchor.

Cytotoxic T-cell activity antagonized by naturally occurring HIV-1 Gag variants

Most asymptomatic individuals infected with HIV-1 have a cytotoxic T lymphocyte (CTL) response to the virus Gag proteins which can be demonstrated in vitro. Epitopes have been mapped in p17 Gag and p24 Gag restricted by HLA-B8 (p17-3 and p24-13) and -B27 (p24-14). Viruses isolated from patients who make CTL responses to these peptides vary within the genetic sequences encoding these epitopes and some mutations lead to reduction in killing activity in vitro. This was attributed to either failure of the variant epitope to bind major histocompatibility complex class I or failure of T-cell receptors to bind the presented peptide. But peptide variants of class I-restricted epitopes cause 'antagonism', that is, the presence of a variant epitope (in the form of peptide) inhibits normal lysis of targets presenting the original epitope. This mirrors similar findings in class II-restricted systems. Here we report that naturally occurring variant forms of p17-3, p24-13 and p24-14 may cause antagonism of CTL lines derived from the same individuals. The effect is present if the epitopes are derived from synthetic peptides and when they are processed from full-length proteins expressed by either recombinant vaccinia constructs or replicating HIV.

Complete nucleotide sequence of a 43-kilobase genomic island associated with the multidrug resistance region of Salmonella enterica serovar Typhimurium DT104 and its identification in phage type DT120 and serovar Agona

This study describes the characterization of the recently described Salmonella genomic island 1 (SGI1) (D. A. Boyd, G. A. Peters, L.-K. Ng, and M. R. Mulvey, FEMS Microbiol. Lett. 189:285-291, 2000), which harbors the genes associated with the ACSSuT phenotype in a Canadian isolate of Salmonella enterica serovar Typhimurium DT104. A 43-kb region has been completely sequenced and found to contain 44 predicted open reading frames (ORFs) which comprised approximately 87% of the total sequence. Fifteen ORFs did not show any significant homology to known gene sequences. A number of ORFs show significant homology to plasmid-related genes, suggesting, at least in part, a plasmid origin for the SGI1, although some with homology to phage-related genes were identified. The SGI1 was identified in a number of multidrug-resistant DT120 and S. enterica serovar Agona strains with similar antibiotic-resistant phenotypes. The G+C content suggests a potential mosaic structure for the SGI1. Emergence of the SGI1 in serovar Agona strains is discussed.

Stimulation of 92-kDa gelatinase B promoter activity by ras is mitogen-activated protein kinase kinase 1-independent and requires multiple transcription factor binding sites including closely spaced PEA3/ets and AP-1 sequences

The 92-kDa type IV collagenase (92-kDa gelatinase B also referred to as MMP-9), which plays a critical role in extracellular matrix degradation, is regulated by growth factors that mediate their effects through the ras proto-oncogene. The current study was undertaken to determine the transcriptional requirements for the induction of 92-kDa gelatinase B expression by an activated ras oncogene. Transfection of OVCAR-3 cells with an expression vector encoding an activated Ha-ras increased 92-kDa gelatinolytic activity and stimulated (over 10-fold) the activity of a CAT reporter driven by 670 nucleotides of 5' flanking sequence of the 92-kDa gelatinase B gene. Transient assays using a CAT reporter driven by 5' deleted fragments of the 92-kDa gelatinase B promoter indicated that a region spanning -634 to -531 was required for optimal induction of the promoter. The individual deletion, or mutation, of a PEA3/ets (-540) motif, AP-1 sites (-533, -79), a NF-kappa B (-600) consensus sequence, and a GT box (-52) substantially reduced the activation of the promoter by ras. An expression vector encoding the PEA3 transcription factor caused a 3-fold stimulation of the wild type but not the PEA3/ets-deleted 92-kDa gelatinase B promoter. Coexpression of a dominant negative c-jun antagonized the ras-dependent stimulation of the 92-kDa gelatinase B promoter-driven CAT reporter. The signaling pathway mediating the induction of 92-kDa gelatinase B promoter activity by ras was examined. The expression of a phosphatase (CL100) which inactivates multiple mitogen-activate protein kinase members abrogated the stimulation of 92-kDa gelatinase B promoter activity by ras. However, the expression of a kinase-deficient mitogen-activated protein kinase kinase 1 (MEK1) did not prevent activation of the 92-kDa gelatinase B promoter by ras and a constitutively activated c-raf expression vector was insufficient for 92-kDa gelatinase B promoter activation. Thus, the stimulation of the 92-kDa gelatinase B promoter by ras requires multiple elements including closely spaced PEA3/est and AP-1 sites and is MEK1-independent.

Randomised trial of oral morphine for chronic non-cancer pain

BACKGROUND

The use of opioid analgesics for chronic non-cancer pain is controversial. Some surveys report good pain relief and improvement in performance while others suggest a poor outcome with a propensity to psychological dependence or addiction.

METHODS

We undertook a randomised double-blind crossover study to test the hypothesis that oral morphine relieves pain and improves the quality of life in patients with chronic regional pain of soft tissue or musculoskeletal origin who have not responded to codeine, anti-inflammatory agents, and antidepressants. Morphine was administered as a sustained-release preparation in doses up to 60 mg twice daily and compared with benztropine (active placebo) in doses up to 1 mg twice daily over three-week titration, six-week evaluation, and two-week washout phases. Pain intensity, pain relief, and drug liking were rated weekly and psychological features, functional status, and cognition were assessed at baseline and at the end of each evaluation phase.

FINDINGS

After dose titration in the 46 patients who completed the study, the mean daily doses of drugs were morphine 83.5 mg and benztropine 1.7 mg. On visual analogue scales, the morphine group showed a reduction in pain intensity relative to placebo in period I (p = 0.01) and this group also fared better in a crossover analysis of the sum of pain intensity differences from baseline (p = 0.02). No other significant differences were detected.

INTERPRETATION

In patients with treatment-resistant chronic regional pain of soft-tissue or musculoskeletal origin, nine weeks of oral morphine in doses up to 120 mg daily may confer analgesic benefit with a low risk of addiction but is unlikely to yield psychological or functional improvement.

Determinants of membrane protein topology

The topology of the integral membrane protein MalF, which is required for maltose transport in Escherichia coli, has been analyzed using fusions of alkaline phosphatase (EC 3.1.3.1). The properties of such fusion strains support a MalF structure previously proposed on theoretical grounds. Several transmembrane segments within MalF can act as signal sequences in exporting alkaline phosphatase. Other transmembrane sequences, in conjunction with cytoplasmic domains, can stably anchor alkaline phosphatase in the cytoplasm. Our results suggest that features of the amino acid sequence (possibly the positively charged amino acids) of the cytoplasmic domains of membrane proteins are important in anchoring these domains in the cytoplasm. These studies in conjunction with our earlier results show that alkaline phosphatase fusions to membrane proteins can be an important aid in analyzing membrane topology and its determinants.

Quantitative bone mineral analysis using dual energy computed tomography

This preliminary evaluation indicates that CT scanning permits measurement of cancellous, cortical or integral bone. With the single energy technique, precision is high and with mode, CT scanning may prove an important tool for assessing the axial skeleton is osteoporotic conditions.

Regulation of BAD phosphorylation at serine 112 by the Ras-mitogen-activated protein kinase pathway

The function of the pro-apoptotic molecule BAD is regulated by phosphorylation of two sites, serine-112 (Ser-112) and serine-136 (Ser-136). Phosphorylation at either site results in loss of the ability of BAD to heterodimerize with the survival proteins BCL-XL or BCL-2. Phosphorylated BAD binds to 14-3-3 and is sequestered in the cytoplasm. It has been shown that phosphorylation of BAD at Ser-136 is mediated by the serine/threonine protein kinase Akt-1/PKB which is downstream of phosphatidylinositol 3-kinase (PI3K). The signaling process leading to phophorylation of BAD at Ser-112 has not been identified. In this study, we show that phosphorylation of the two serine residues of BAD is differentially regulated. While Ser-136 phosphorylation is concordant with activation of Akt, Ser-112 phosphorylation does not correlate with Akt activation. Instead, we demonstrate that activated Ras and Raf, which are upstream of mitogen-activated protein kinases (MAPK), stimulate selective phosphorylation of BAD at Ser-112. Furthermore, phosphorylation of Ser-112, but not Ser-136 requires activation of the MAPK pathway as the MEK inhibitor, PD 98059, blocks EGF-, as well as activated Ras- or Raf-mediated phosphorylation of BAD at Ser-112. Therefore, the PI3K-Akt and Ras-MAPK pathways converge at BAD by mediating phosphorylation of distinct serine residues.

Regulation of 92 kDa type IV collagenase expression by the jun aminoterminal kinase- and the extracellular signal-regulated kinase-dependent signaling cascades

The 92 kDa type IV collagenase (MMP-9), which degrades type IV collagen, has been implicated in tissue remodeling. The purpose of the current study was to determine the role of Jun amino-terminal kinase (JNK)- and extracellular signal-regulated kinase- (ERK)-dependent signaling cascades in the regulation of MMP-9 expression. Towards this end, we first determined the transcriptional requirements for MMP-9 promoter activity in a cell line (UM-SCC-1) which is an avid secretor of this collagenase. Transfection of these cells with a CAT reporter driven by progressive 5' deleted fragments of the MMP-9 promoter indicated the requirement of a region spanning -144 to -73 for optimal promoter activity. DNase I footprinting revealed a protected region of the promoter spanning nucleotides -91 to -68 and containing a consensus AP-1 motif at -79. Mutation of this AP-1 motif practically abolished the activity of the MMP-9 promoter-driven CAT reporter. Mobility shift assays indicated c-Fos and Jun-D bound to this motif and transfection of the cells with a mutated c-Jun, which quenches the function of endogenous Jun and Fos proteins, decreased MMP-9 promoter activity by 80%. UM-SCC-1 cells contained a constitutively activated JNK and the expression of a kinase-deficient JNK1 reduced the activity of a CAT reporter driven either by the MMP-9 promoter or by three tandem AP-1 repeats upstream of a thymidine kinase minimal promoter. Conditioned medium collected from UM-SCC-1 cells transfected with the dominant negative JNK1 expression vector diminished 92 kDa gelatinolysis. Similarly, interfering with MEKK, which lies upstream of JNK1, using a dominant negative expression vector reduced MMP-9 promoter activity over the same concentration range which repressed the AP-1-thymidine kinase CAT reporter construct. UM-SCC-1 cells also contained a constitutively activated ERK1. MMP-9 expression, as determined by CAT assays and by zymography, was reduced by the co-expression of a kinase-deficient ERK1. Interfering with MEK1, which is an upstream activator of ERK1, either with PD 098059, which prevents the activation of MEK1, or with a dominant negative expression construct, reduced 92 kDa gelatinolysis and MMP-9 promoter activity respectively. c-Raf-1 is an upstream activator of MEK1 and a kinase-deficient c-Raf-1 expression construct decreased the activity of a promoter driven by either the MMP-9 promoter or three tandem AP-1 repeats. Conversely, treatment of UM-SCC-1 cells with PMA, which activates c-Raf-1, increased 92 kDa gelatinolysis. These data suggest that MMP-9 expression in UM-SCC-1 cells, is regulated by JNK- and ERK-dependent signaling pathways.

Measurement of matrix metalloproteinases and tissue inhibitors of metalloproteinases in blood and tissues. Clinical and experimental applications

The balance between production and activation of MMPs and their inhibition by TIMPs is a crucial aspect of cancer invasion and metastasis. On the basis of the concept that MMPs synthesized in tissues seep into the bloodstream, we have examined MMP levels in the plasma of patients with cancer. In colorectal, breast, prostate, and bladder cancer, most patients with aggressive disease have increased plasma levels of gelatinase B. In patients with advanced colorectal cancer, high levels of either gelatinase B or TIMP complex were associated with shortened survival. We propose that these assays may be clinically useful in characterizing metastatic potential in selected kinds of cancer. In rheumatoid arthritis and systemic lupus erythematosus (SLE), serum and plasma levels of stromelysin-1 were approximately 3-5-fold increased. Fluctuating serum stromelysin-1 levels in SLE did not correspond with change in disease activity. In SLE, stromelysin-1 may be a component of the chronic tissue repair process rather than being responsible for inciting tissue damage. On the basis of these observations, we conclude that measurement of plasma/serum MMP and TIMP levels may provide important data for selecting and following patients considered for treatment with drugs that interfere with MMP activity.

Towards single-copy gene expression systems making gene cloning physiologically relevant: lambda InCh, a simple Escherichia coli plasmid-chromosome shuttle system

We describe a simple system for reversible, stable integration of plasmid-borne genes into the Escherichia coli chromosome. Most ordinary E. coli strains and a variety of pBR322-derived ampicillin-resistant plasmids can be used. A single genetic element, a lambda phage, is the only specialized vector required. The resultant strains have a single copy of the plasmid fragment inserted stably at the lambda attachment site on the chromosome, with nearly the entire lambda genome deleted.

Genetic analysis of the membrane insertion and topology of MalF, a cytoplasmic membrane protein of Escherichia coli

MalF is an essential cytoplasmic membrane protein of the maltose transport system of Escherichia coli. We have developed a general approach for analysis of the mechanism of integration of membrane proteins and their membrane topology by characterizing a series of fusions of beta-galactosidase to MalF. The properties of the fusion proteins indicate the following. (1) The first two presumed transmembrane segments of MalF are sufficient to anchor beta-galactosidase firmly to the inner membrane. (2) Hybrid proteins with beta-galactosidase fused to a presumed cytoplasmic domain of MalF have high beta-galactosidase specific activity; fusions to periplasmic domains have low activity. We propose therefore, that periplasmic and cytoplasmic domains of integral membrane proteins can be distinguished by the enzymatic properties of such hybrid proteins. In general, it appears that cleaved or non-cleaved signal sequences when attached to beta-galactosidase cause it to become embedded in the membrane, and this results in the inability of the hybrid proteins to assemble into active enzyme. Additional properties of these fusion proteins contribute to our understanding of the regulation of MalF synthesis. The MalF protein, synthesized as part of the malEFG operon of E. coli, is approximately 30-fold less abundant in the cell than MalE protein (the maltose-binding protein). Differential amounts of the fusion proteins indicate that a regulatory signal occurs within the malF gene that is responsible for the step-down in expression from the malE gene to the malF gene.

An inhibitor of c-jun aminoterminal kinase (SP600125) represses c-Jun activation, DNA-binding and PMA-inducible 92-kDa type IV collagenase expression

The 92-kDa type IV collagenase (MMP-9) contributes to tumor invasion and metastases and strategies to down-regulate its expression could ultimately be of clinical utility. Although the expression of this collagenase is regulated by numerous growth factors, the signaling pathways that transduce these signals are fewer in number and therefore represent pharmacological targets. In this regard, we previously reported that MMP-9 expression was regulated by the c-jun amino terminal kinase (JNK) signaling cascade. Therefore, we undertook a study to determine the efficacy of a novel compound (SP600125), which binds to the ATP binding site of all known JNKs, in repressing MMP-9 expression. In OVCAR-3 cells, SP600125 inhibited the PMA-dependent secretion of MMP-9 in a time-dependent manner and over a dose range that blocked c-Jun phosphorylation and AP-1 binding. SP600125 repressed the activity of a PMA-stimulated MMP-9 promoter-driven luciferase reporter, suggesting that diminished secretion of this collagenase reflected reduced transcription. Further, the activity of a GAL4-driven reporter in PMA-treated cells, co-transfected with an expression construct encoding the trans-activation domain of c-Jun fused to the DNA binding domain of GAL4, was repressed by SP600125. These findings indicate the efficacy of SP600125 in inhibiting c-Jun activation, DNA-binding and the PMA-dependent induction of MMP-9 expression.

Genetic analysis of membrane protein topology by a sandwich gene fusion approach

We describe a cloning vector that allows the construction of phoA sandwich fusions in which mature alkaline phosphatase is inserted into target proteins. In contrast to previous fusions obtained using the TnphoA transposon, the entire amino acid sequence of the target protein is present in the fusion product. We have constructed a series of sandwich fusions of alkaline phosphatase to the multispanning cytoplasmic membrane protein MalF. Despite the fact that the alkaline phosphatase was tethered to MalF at both its N and its C terminus, the enzyme exhibited high activity when it was fused to a periplasmic domain of the membrane protein. Cells harboring an alkaline phosphatase sandwich fusion to the end of the first membrane-spanning segment of MalF exhibited both MalF and alkaline phosphatase activity. When alkaline phosphatase was inserted into a cytoplasmic domain of MalF, its specific activity was very low. Our results suggest that the alkaline phosphatase activity of phoA sandwich fusions provides a more sensitive monitor than previous methods of the cellular localization of the domain of the target protein to which the enzyme is fused. Thus, the sandwich fusion approach can give a more accurate picture of membrane protein topology.

Sleep and nocturnal acid reflux in normal subjects and patients with reflux oesophagitis

Nocturnal gastro-oesophageal reflux may be important in the pathogenesis of reflux oesophagitis. This study aimed to determine whether: (1) gastro-oesophageal reflux occurs during sleep in patients with reflux oesophagitis and, if so, to explore the mechanism, and (2) the sleep pattern of patients with oesophagitis is different from that of control subjects. After a standard evening meal, simultaneous manometric, oesophageal pH, and polysomnographic recordings were obtained in 11 patients with endoscopic oesophagitis and 11 control subjects. Patients with gastrooesophageal reflux disease had significantly more total reflux episodes throughout the nocturnal monitoring period than control subjects (105 v 6). Ninety two of 105 episodes of gastro-oesophageal reflux in patients occurred during the awake state and 10 during sleep stage II. A number of reflux episodes occurred during brief periods of arousal from the various sleep stages. Of the 105 reflux events recorded in patients, 42 were induced by transient lower oesophageal sphincter relaxation, 20 by stress reflux, 22 by free reflux mechanisms, and in 21 the mechanism was unclear. The sleep pattern and the time spent in each sleep stage was not different between the two groups. It is concluded that the awake state is crucial for the occurrence of nocturnal reflux episodes in normal subjects as well as in patients with reflux oesophagitis and that the difference between the frequency of gastro-oesophageal reflux between normal subjects and patients cannot be explained by different sleep patterns.

How many membrane proteins are there?

One of the basic issues that arises in functional genomics is the ability to predict the subcellular location of proteins that are deduced from gene and genome sequencing. In particular, one would like to be able to readily specify those proteins that are soluble and those that are inserted in a membrane. Traditional methods of distinguishing between these two locations have relied on extensive, time-consuming biochemical studies. The alternative approach has been to make inferences based on a visual search of the amino acid sequences of presumed gene products for stretches of hydrophobic amino acids. This numerical, sequence-based approach is usually seen as a first approximation pending more reliable biochemical data. The recent availability of large and complete sequence data sets for several organisms allows us to determine just how accurate such a numerical approach could be, and to attempt to minimize and quantify the error involved. We have optimized a statistical approach to protein location determination. Using our approach, we have determined that surprisingly few proteins are misallocated using the numerical method. We also examine the biological implications of the success of this technique.

Use of phoA fusions to study the topology of the Escherichia coli inner membrane protein leader peptidase

A topology of the Escherichia coli leader peptidase has been previously proposed on the basis of proteolytic studies. Here, a collection of alkaline phosphatase fusions to leader peptidase is described. Fusions to the periplasmic domain of this protein exhibit high alkaline phosphatase activity, while fusions to the cytoplasmic domain exhibit low activity. Elements within the cytoplasmic domain are necessary to stably anchor alkaline phosphatase in the cytoplasm. The amino-terminal hydrophobic segment of leader peptidase acts as a weak export signal for alkaline phosphatase. However, when this segment is preceded by four lysines, it acts as a highly efficient export signal. The coherence of in vitro studies with alkaline phosphatase fusion analysis of the topology of leader peptidase further indicates the utility of this genetic approach to membrane protein structure and insertion.

Role and regulation of expression of 92-kDa type-IV collagenase (MMP-9) in 2 invasive squamous-cell-carcinoma cell lines of the oral cavity

The present study was undertaken to determine the role of the metalloproteinase MMP-9 in the invasive phenotype of squamous-cell carcinoma of the oral cavity and the regulation of its expression. Zymographic analysis of conditioned medium from 2 highly invasive squamous-cell-carcinoma cell lines indicated large amounts of an enzyme which was indistinguishable, in size (92 kDa) from the MMP-9 pro-enzyme. Conversion of the 92-kDa gelatinase into a lower-molecular-weight species (84 kDa), identical in size to the activated gelatinase, was evident when both cell lines, which are avid secretors of urokinase, were cultured in the presence of plasminogen. Penetration of an extracellular-matrix-coated filter was dramatically reduced in the presence of the collagenase inhibitor, tissue inhibitor of metalloproteinase-2, suggesting a critical role for MMP-9 in the invasive process. Immunohistochemical studies demonstrating the presence of MMP-9 in tumor cells of resected squamous-cell cancers suggested that secretion of this collagenase by cells in vitro was reflective of the in vivo setting. Since several phorbol-ester response elements are present in the MMP-9 promoter, we determined the role of protein-kinase-C pathways in the regulation of MMP-9 expression in cultured SCC. Treatment of cells with PMA resulted in a more-than-20-fold increase in the level of protein and mRNA. Conversely, culturing of cells in the presence of the protein-kinase-C inhibitor, calphostin-C, led to a dose-dependent decrease in the amount of MMP-9 mRNA and protein, suggesting that the constitutive expression of this collagenase reflects activation of this signal transduction pathway. In summary, our data suggest that, for a sub-population of squamous-cell carcinomas, secreted MMP-9 is an important determinant of the invasive phenotype, and that the expression of this metalloproteinase is regulated by protein-kinase-C pathways.

Positively charged amino acid residues can act as topogenic determinants in membrane proteins

When alkaline phosphatase is fused to the periplasmic domain of a cytoplasmic membrane protein, it is efficiently exported to the periplasm. Such a hybrid protein exhibits high alkaline phosphatase enzymatic activity. When alkaline phosphatase is fused to the cytoplasmic domain of a membrane protein, it remains, for the most part, in the cytoplasm. Such fusions exhibit low enzymatic activity. However, stable retention of alkaline phosphatase in the cytoplasm requires the presence in the fusion protein of the cytoplasmic loop ordinarily present in that position in the native, unfused protein. Using oligonucleotide-directed mutagenesis, we have shown that positively charged amino acids are required for the stable cytoplasmic localization of the fused alkaline phosphatase. We propose that, in addition to hydrophobic transmembrane segments, positively charged amino acids in the hydrophilic cytoplasmic domains of a membrane protein are determinants of the protein's topology.

The topological analysis of integral cytoplasmic membrane proteins

We review three general approaches to determining the topology of integral cytoplasmic membrane proteins. (i) Inspection of the amino acid sequence and use of algorithms to predict membrane spanning segments allows the construction of topological models. For many proteins, the mere identification of such segments and an analysis of the distribution of basic amino acids in hydrophilic domains leads to correct structure predictions. For others, additional factors must come into play in determining topology. (ii) Gene fusion analysis of membrane proteins, in many cases, leads to complete topological models. Such analyses have been carried out in both bacteria and in the yeast Saccharomyces cerevisiae. Conflicts between results from gene fusion analysis and other approaches can be used to explore details of the process of membrane protein assembly. For instance, anomalies in gene fusion studies contributed evidence for the important role of basic amino acids in determining topology. (iii) Biochemical probes and the site of natural biochemical modifications of membrane proteins give information on their topology. Chemical modifiers, proteases and antibodies made to different domains of a membrane protein can identify which segments of the protein are in the cytoplasm and which are on the extracytoplasmic side of the membrane. Sites of such modifications as glycosylation and phosphorylation help to specify the location of particular hydrophilic domains. The advantages and limitations of these methods are discussed.