Functional characterization of soluble and membrane-bound forms of vaccinia virus complement control protein (VCP).

Vaccinia virus secretes a 35 kD protein, vaccinia virus complement control protein (VCP), that inhibits the classical and alternative pathways of complement at several points, indicating that it may be a viral analogue of human complement receptor type 1 (CR1; CD35). Structurally, however, CR1 is composed of 30 short consensus repeats (SCRs), whereas VCP consists entirely of four SCRs. We have begun a structure-function analysis of VCP to define the minimum number of SCRs necessary for function, the functional differences between VCP and CR1, and the potential therapeutic roles for VCP. We addressed these questions by creating and characterizing recombinant soluble and membrane-bound forms of VCP. We have determined that (1) VCP requires all four SCRs to bind C3b, (2) whereas CR1 binds C3b and iC3b, VCP binds C3b but not iC3b, and (3) although normally secreted, if expressed on the membrane of mammalian cells, VCP effectively protects the cells from complement-mediated lysis. Thus, VCP appears to be a compact and unique complement regulatory protein with the ability to inhibit both arms of the complement cascade, but lacking affinity for iC3b. By releasing rather than capturing iC3b-bearing complexes following inactivation of C3b, VCP may 'recycle' its active site locally among infected cells, and thereby enable the virus to evade more efficiently host immune and inflammatory responses. The unique function, compact structure, and capacity of VCP to protect mammalian cells from complement-mediated attack, suggests that it could be used both to better understand the structure-function relationship of complement regulatory proteins, in general, and also to rationally design and develop novel therapeutic agents.

Viral complement regulatory proteins.

The inactivation of complement provides cells and tissues critical protection from complement-mediated attack and decreases the associated recruitment of other inflammatory mediators. In an attempt to evade the host immune response, viruses have evolved two mechanisms to acquire complement regulatory proteins. They can directly seize the host cell complement regulators onto their outer envelope and/or they can produce their own proteins which are either secreted into the neighboring intercellular space or expressed as membrane-bound proteins on the infected host cell. The following review will concentrate on the viral homologues of the mammalian complement regulatory proteins, specifically those containing complement control protein (CCP) repeats.

Antibody response to a T-dependent antigen requires B cell expression of complement receptors.

Several lines of evidence indicate that antibody responses to T-dependent antigens require complement receptors expressed on either B lymphocytes or follicular dendritic cells. We have used RAG-2 deficient blastocyst complementation to create mice specifically lacking B cell complement receptors. Despite normal expression of complement receptor 1 (CR1[CD35]) and CR2 (CD21) on follicular dendritic cells, these mice have a profound defect in their capacity to mount a T-dependent antibody response. This is the first direct demonstration in vivo that B cell expression of complement receptors is required for a humoral immune response. This is the first direct demonstration in vivo that B cell expression of complement receptors is required for a humoral immune response. This suggests that CD21 and/or CD35 on B lymphocytes may be required for cellular activation, adsorptive endocytosis of antigen, recruitment to germinal centers, and/or protection from apoptosis during the humoral response to T-dependent antigens.

Tissue expression of human complement inhibitor, decay-accelerating factor, in transgenic pigs. A potential approach for preventing xenograft rejection.

Since complement-mediated hyperacute rejection of xenografts prevents the use of pigs as organ donors to man, the development of transgenic animals expressing species-specific complement inhibitors could provide a strategy for overcoming hyperacute rejection. The complement inhibitor, human decay-accelerating factor (hDAF), prevents the assembly of C3 and C5 convertases. In this article, the first histologic analysis of hDAF expression in pig tissues, specifically expression in endothelial cells of pigs transgenic for hDAF, is described. Twenty-seven transgenic pigs were categorized into 4 groups based on the expression patterns in endothelial, vascular smooth muscle, and squamous epithelial cells of skin biopsy specimens. Skin biopsy specimens permitted evaluation of the pigs without the need to kill them or to perform invasive procedures. Sixteen cases demonstrated endothelial cell staining. Complete necropsy evaluation, available in 14 of the 27 pigs, correlated with the skin biopsy specimen expression of hDAF. The immunoperoxidase data matched identically with the presence of the mRNA transcript in 25 of the 26 cases where RNA data were available. Also, the staining patterns of 6 transgenic pig founders and their 9 offspring (total of 9 founder-offspring pairs) correlated. Since transgenes are variably expressed in different cell types and since tissue lysates represent a melange of cell types, histologic evaluation for protein expression in tissues from transgenic animals will be critical if they are to be bred to become clinical organ donors. In addition to endothelial expression of hDAF, its expression on vascular smooth muscle cells may be important in preventing tissue damage when breaks in the endothelium occur.

Low nm23 protein expression in infiltrating ductal breast carcinomas correlates with reduced patient survival.

Protein levels corresponding to nm23 were determined in normal and neoplastic breast tissues by immunoperoxidase staining. Nm23 protein levels were highest in normal breast epithelium, and lower in intraductal carcinomas. Based on nm23 staining, 39 infiltrating ductal carcinomas were separated into two groups: tumors with homogeneously high nm23 protein content, and tumors with low staining in either a homogeneous or heterogeneous pattern. Patients with low nm23 staining tumors, determined by three pathologists independently, had reduced survival times (alpha = 0.034, alpha = 0.012, alpha = 0.052 by the log rank test). Nm23 expression approached significance as an independent predictor of survival in Cox's proportional hazards model. The data provide the first correlation of low nm23 protein expression and reduced breast carcinoma patient survival.

Identification of a second human nm23 gene, nm23-H2.

Reduced RNA and/or protein levels corresponding to the murine nm23-1 and human nm23-H1 complementary DNA clones have been correlated with high tumor metastatic potential in several rodent model systems and human breast carcinomas. We report the identification of a second human nm23 gene, designated nm23-H2. The pNM23-H2S complementary DNA clone predicted a Mr 17,000 protein 88% identical to nm23-H1. nm23-H2 also shared a significant homology with nucleoside diphosphate kinases and a Drosophila developmental gene. Southern blots containing BglII-restricted genomic DNA, which exhibited an allelic restriction fragment length polymorphism for nm23-H1, contained nonallelic bands upon rehybridization to the nm23-H2 probe. Thus, nm23-H1 and nm23-H2 are distinct genes. Northern blot hybridization of nm23-H1- and nm23-H2-specific probes to breast tumors and cell lines indicated that nm23-H1 expression was reduced in high metastatic potential tumor cells to a greater extent than nm23-H2. The data indicate the existence of a family of independently regulated nm23 genes.

Reduced Nm23/Awd protein in tumour metastasis and aberrant Drosophila development.

Tumour metastasis is the principal cause of death for cancer patients. We have identified the nm23 gene, for which RNA levels are reduced in tumour cells of high metastatic potential. In this report we identify the cytoplasmic and nuclear Nm23 protein, and show that it also is differentially expressed in metastatic tumour cells. We also find that the human Nm23 protein has sequence homology over the entire translated region with a recently described developmentally regulated protein in Drosophila, encoded by the abnormal wing discs (awd) gene. Mutations in awd cause abnormal tissue morphology and necrosis and widespread aberrant differentiation in Drosophila, analogous to changes in malignant progression. The metastatic state may therefore be determined by the loss of genes such as nm23/awd which normally regulate development.

Abnormalities in the metabolism of postprandial and fasting triglyceride-rich lipoprotein subfractions in normal and insulin-dependent diabetic subjects: effects of sex.

To investigate the effect of sex and diabetes on postprandial lipoprotein metabolism, 15 normal and 12 normolipidemic subjects with insulin-dependent diabetes mellitus (IDDM) were studied. Plasma triglyceride (TG) levels were measured and three TG-rich lipoprotein subfractions (Sf greater than 400, 100 to 400, and 20 to 100) were isolated and their composition analyzed before and every 1.5 hours for a total of 7.5 hours following ingestion of corn oil. Normal women compared with men had lower postprandial plasma TG levels (P less than .05) mostly due to lower TG in Sf 100 to 400. The composition of Sf 100 to 400 and Sf 20 to 100 lipoproteins differed in the two sexes (P less than .01), with normal women having particles poorer in TG in both the fasting and postprandial states. Diabetic men compared with normal men had smaller Sf greater than 400 particles following fat ingestion, as shown by a lower TG protein (PR) ratio (7.6 v 12.8, respectively, P less than .05). The composition of Sf 100 to 400 and 20 to 100 lipoproteins was abnormal in IDDM men due to enrichment in total cholesterol (TC) as shown by higher TC/TG, TC/PR, and TG/phospholipid (PL) ratios in both the fasting (P less than .03 to P less than .003) and the postprandial state (P less than .03 to P less than .0001). A lower PL and TG content was also consistently present. A similar enrichment in TC was observed in diabetic v normal women following fat ingestion in Sf greater than 400 only (P less than .003).(ABSTRACT TRUNCATED AT 250 WORDS)

Squamous carcinoma of the esophagus in patients with Barrett esophagus.

Adenocarcinoma of the esophagus is a well-known complication of Barrett esophagus, especially in white men. We present three cases of squamous carcinoma of the esophagus in Barrett patients. All three patients were white men. None had a history of symptomatic gastroesophageal reflux or of Barrett esophagus, but all had substantial usage of alcoholic beverages and tobacco. All three tumors were located in squamous-lined mucosa above the Barrett mucosa. Columnar epithelial dysplasia was present in the Barrett mucosa of two of our patients, and the third patient had a squamous carcinoma of the pharynx. Squamous carcinoma represented 2% of Barrett-associated esophageal carcinomas at our institution in 1980 through 1986. Five additional cases were found in the literature, and all were also in white men. This demographic predominance stood in striking contrast to the 26% prevalence of white patients among those with squamous carcinoma of the esophagus at our institution (P less than 0.0002) and to the 50% prevalence of white men among our patients with Barrett esophagus (P less than 0.02). Two of the literature cases also had substantial alcohol and tobacco usage and had synchronous adenocarcinoma arising in Barrett mucosa. Our findings of a strikingly high prevalence of white men and of multifocal neoplastic changes in the upper aerodigestive tract suggest a pathogenetic relationship between squamous carcinoma of the esophagus and Barrett esophagus, possibly due to alcoholic beverage and tobacco usage. Endoscopic surveillance of Barrett patients for early detection of adenocarcinoma has been recommended; contemporaneous evaluation of the squamous-lined esophagus by biopsy and cytopathology may be advisable.(ABSTRACT TRUNCATED AT 250 WORDS)