Mechanisms for the biomechanical destruction of L1210 leukemia cells: a rate regulator for metastasis.

Mechanical trauma appears to be one significant cause of the rapid intravascular death of cancer cells and, as such, could act as an important rate regulator for the metastatic process. Intravascular mechanical trauma to cancer cells is thought to be a consequence of shape transitions, occurring when they are deformed from spherical shape by entry into, and passage along, capillaries having smaller diameters than themselves. These transitions from spherical shape require increases in surface area; first, an apparent increase in surface area is accomplished by a reversible, nonlethal surface membrane unfolding. If this is insufficient to meet geometric demands, it is followed by a true increase in surface area, resulting in increased tension in the cancer cell surface membrane, leading to its lethal rupture.     

An exogenous albumin promoter can become silent in dedifferentiated hepatoma variants as well as intertypic hybrids

In order to evaluate the ability of an exogenous tissue-specific promoter to undergo the same dynamic changes in activity as the endogenous one, a 400-base pair fragment of the rat albumin proximal promoter, upstream of the bacterial gpt gene, has been introduced into rat hepatoma cells. Four clones containing a single integrated copy of the construct and producing substantial amounts of albumin and of xanthine phosphoribosyltransferase were isolated. These clones were subjected to two treatments known to result in silencing of the albumin gene: selection for dedifferentiated variants, and fusion with L-cell fibroblasts. In most cases, the albumin-negative progeny obtained no longer expressed the gpt gene: the exogenous promoter of 400 base pairs must contain the sequences required to respond to the mechanisms that block activity of the endogenous gene. However, exceptions were observed: the albumin-deficient variants of one clone remained xanthine phosphoribosyltransferase positive, and some of the albumin-negative hybrids from a different clone continued to produce xanthine phosphoribosyltransferase. These cases of dissociation in expression of the endogenous and the exogenous genes indicate that the site of integration of the alb-gpt construct in one clone renders the sequences insensitive to the mechanisms responsible for albumin gene silencing in dedifferentiated variants, and in the other clone to the mechanism of extinction. Consequently, the mechanisms causing gene silencing in variants and in intertypic hybrids must be different.     

Prion protein PrPc interacts with molecular chaperones of the Hsp60 family.

Prions mediate the pathogenesis of certain neurodegenerative diseases, including bovine spongiform encephalopathy in cattle and Creutzfeldt-Jakob disease in humans. The prion particle consists mainly, if not entirely, of PrPSc, a posttranslationally modified isoform of the cellular host-encoded prion protein (PrPc). It has been suggested that additional cellular factors might be involved in the physiological function of PrPc and in the propagation of PrPSc. Here we employ a Saccharomyces cerevisiae two-hybrid screen to search for proteins which interact specifically with the Syrian golden hamster prion protein. Screening of a HeLa cDNA library identified heat shock protein 60 (Hsp60), a cellular chaperone as a major interactor for PrPc. The specificity of the interaction was confirmed in vitro for the recombinant proteins PrPc23-231 and rPrP27-30 fused to glutathione S-transferase with recombinant human Hsp60 as well as the bacterial GroEL. The interaction site for recombinant Hsp60 and GroEL proteins was mapped between amino acids 180 and 210 of the prion protein by screening with a set of recombinant PrPc fragments. The binding of Hsp60 and GroEL occurs within a region which contains parts of the putative alpha-helical domains H3 and H4 of the prion protein.     

The catalytic activity of the CD45 membrane-proximal phosphatase domain is required for TCR signaling and regulation.

Cell surface expression of CD45, a receptor-like protein tyrosine phosphatase (PTPase), is required for T cell antigen receptor (TCR)-mediated signal transduction. Like the majority of transmembrane PTPases, CD45 contains two cytoplasmic phosphatase domains, whose relative in vivo function is not known. Site-directed mutagenesis of the individual catalytic residues of the two CD45 phosphatase domains indicates that the catalytic activity of the membrane-proximal domain is both necessary and sufficient for restoration of TCR signal transduction in a CD45-deficient cell. The putative catalytic activity of the distal phosphatase domain is not required for proximal TCR-mediated signaling events. Moreover, in the context of a chimeric PTPase receptor, the putative catalytic activity of the distal phosphatase domain is not required for ligand-induced negative regulation of PTPase function. We also demonstrate that the phosphorylation of the C-terminal tyrosine of Lck, a site of negative regulation, is reduced only when CD45 mutants with demonstrable in vitro phosphatase activity are introduced into the CD45-deficient cells. These results demonstrate that the phosphatase activity of CD45 is critical for TCR signaling, and for regulating the levels of C-terminal phosphorylated Lck molecules.     

Risk of breast cancer in relation to the interval since last full term pregnancy.

OBJECTIVE--To examine whether the risk of breast cancer is increased by a recent term pregnancy. DESIGN--Population based case-control study. SETTING--Eight areas in the United States. SUBJECTS--Cases were 2279 multiparous women residents of the eight areas aged 25-49 who were diagnosed as having breast cancer during 1980-2. Controls were 2357 multiparous women selected from the same areas by random digit dialing. MAIN OUTCOME MEASURE--Relative risk of developing breast cancer according to the time interval since last full term pregnancy. RESULTS--The distribution of intervals since the last term pregnancy was similar in cases and controls. Adjusted for age, parity, and age at first term pregnancy, the odds ratios observed for categories of years since the last full term pregnancy were: 0-2 years, odds ratio 1.16 (95% confidence interval 0.84 to 1.59); 3-6 years, odds ratio 1.21 (0.95 to 1.54); 7-9 years, odds ratio 1.04 (0.84 to 1.38); > or = 10 years, odds ratio 1.00 (reference). CONCLUSIONS--Among multiparous women aged 25-49 years there was no association between the risk of breast cancer and the time interval since the last full term pregnancy.     

Polymorphism of the tumor necrosis factor beta gene in systemic lupus erythematosus: TNFB-MHC haplotypes

We investigated the Nco I restriction fragment length polymorphism (RFLP) of the tumor necrosis factor beta (TNFB) gene in 173 patients with systemic lupus erythematosus (SLE), 192 unrelated healthy controls, and eleven panel families, all of German origin. The phenotype frequency of the TNFB*1 allele was significantly increased in patients compared to controls (63.6% vs 47.1%, RR = 1.96, p <0.002). The results of a two-point haplotype statistical analysis between TNFB and HLA alleles show that there is linkage disequilibrium between TNFB*1 and HLA-A1, Cw7, B8, DR3, DQ2, and C4A DE. The frequency of TNFB*1 was compared in SLE patients and controls in the presence or absence of each of these alleles. TNFB*1 is increased in patients over controls only in the presence of the mentioned alleles. Therefore, the whole haplotype A1, Cw7, B8, TNFB*1, C4A DE, DR3, DQ2 is increased in patients and it cannot be determined which of the genes carried by this haplotype is responsible for the susceptibility to SLE. In addition, two-locus associations were analyzed in 192 unrelated healthy controls for TNFB and class I alleles typed by serology, and for TNFB and class II alleles typed by polymerase chain reaction/oligonucleotide probes. We found positive linkage disequilibrium between TNFB*1 and the following alleles: HLA-A24, HLA-B8, DRB1*0301, DRB1*1104, DRB1*1302, DQA1*0501, DQB1*0201, DQB1*0604, and DPB1*0101. TNFB*2 is associated with HLA-B7, DRB1*1501, and DQB1*0602.This study was supported by grants from the Federal Ministry of Research and Technology (BMFT/DFVLR, 01 VM 8608/9), the German Academic Exchange Service (DAAD, 322/501/014/0), and SFB (217).This work is part of the doctoral thesis of M. P. Bettinotti.     

Feeding Response of Rats to No-Fat and High-Fat Cakes

The nutritional effects of high-fat diets have been extensively studied in laboratory animals, but as yet few experiments have examined the feeding response of animals to newly developed fat substitutes. The present study used commercially available no-fat (0% fat, 92% carbohydrate) and high-fat (41% fat, 54% carbohydrate) cake to determine the effects of fat substitutes on food preference and caloric intake in rats. The first experiment showed that nondeprived rats found the high-fat and no-fat cakes equally palatable and highly preferred to lab chow. Food deprived rats, however, preferred the high-fat cake to the no-fat cake, which may be related to its higher caloric density. In the second experiment, rats fed high-fat cake, in addition to chow, for 30 days consumed more calories and gained more weight than did rats fed no-fat cake and chow. The no-fat cake group, however, overate and gained more weight than chow-only controls. The hyperphagic response to the no-fat cake can be attributed to its carbohydrate content, moisture, and high palatability. Thus, removing fat from the cake reduced, but did not eliminate, its obesity-promoting effect. Obviously, low-fat foods must be consumed in moderation if used for weight control.