Remodeling of a rat hepatocyte plasma membrane glycoprotein. De- and reglycosylation of dipeptidyl peptidase IV

The present paper demonstrates the terminal de- and reglycosylation of a rat hepatocyte plasma membrane glycoprotein, dipeptidyl peptidase IV (DPP IV). Cultured hepatocytes were used in pulse-chase experiments with [3H]L-fucose and [14C]N-acetyl-D-mannosamine as markers for terminal carbohydrates, [3H]D-mannose as marker of a core-sugar, and [35S]L-methionine for labeling the protein backbone. Membrane DPP IV was immunoprecipitated with a polyclonal antibody which bound selectively at 4 degrees C to the cell-surface glycoprotein. The times of maximal labeling of hepatocyte plasma membrane DPP IV were 6-9 min for [3H]L-fucose, 20 min for [3H]D-mannose, and 25 min for [35S]L-methionine. When antibodies were bound to cell-surface DPP IV at 4 degrees C, the immune complex remained stable for more than 1 h after rewarming to 37 degrees C, despite ongoing metabolic and membrane transport processes. This was shown by pulse labeling with [35S]L-methionine at 37 degrees C, followed by cooling to 4 degrees C, and addition of antibody against plasma membrane DPP IV. During rewarming, the radioactivity in the complex remained constant. In a similar experiment with [3H]L-fucose, the radioactivity in the immune complex declined rapidly, indicating a defucosylation of the plasma membrane glycoprotein. Using the same experimental design with [3H]D-mannose, the radioactivity in the immune complex remained constant, showing that the core-sugar D-mannose is not cleaved from the membrane glycoprotein. Terminal reglycosylation (refucosylation and resialylation) was demonstrated as follows. Hepatocytes were maintained at 37 degrees C in a medium supplemented with tunicamycin in order to block the de novo synthesis of N-glycosidically bound carbohydrate chains. At 4 degrees C the antibody against DPP IV bound only to cell surface glycoprotein. During the rewarming period at 37 degrees C, radioactivity from [3H]L-fucose and [14C]N-acetyl-D-mannosamine became incorporated into the immune complex. This indicates a fucosylation and sialylation of the glycoprotein originally present at the cell surface. The mechanisms whereby terminal de- and reglycosylation of plasma membrane glycoproteins may occur during membrane recycling are discussed.     

Extrafibrillar proteoglycans osmotically regulate the molecular packing of collagen in cartilage

The molecular packing density of collagen and hence the intrafibrillar water content appears to be regulated in cartilage by the osmotic pressure gradient existing between the extrafibrillar and the intrafibrillar compartments.     

Molecular forms of acetylcholinesterases in Alzheimer's disease

In this study, we examined 26 cases of Alzheimer's disease (AD) and 14 age-matched controls. In Brodmann area 21 cerebral cortex of the AD cases, there was no change in soluble G1 and G4 acetylcholinesterase (AChE) (EC 3.1.1.7), a significant 40% decrease in membrane-associated G4 AChE, significant 342 and 406% increases in A12 and A8 AChE, and a significant 71% decrease in choline acetyltransferase (ChAT) (EC 2.3.1.6). Our working hypothesis to account for these changes postulates that soluble globular forms are unchanged because they are primarily associated with intrinsic cortical neurons that are relatively unaffected by AD, that ChAT and membrane-associated G4 AChE decrease because they are primarily associated with incoming axons of cholinergic neurons that are abnormal in AD, and that asymmetric forms of AChE increase because of an acrylamide-type impairment of fast axonal transport in diseased incoming cholinergic axons. In the nucleus basalis of Meynert (nbM) of the 26 AD cases, there was a significant 61% decrease in the number of cholinergic neurons, an insignificant 23% decrease in nbM ChAT, a significant 298% increase in nbM ChAT per cholinergic neuron, and a significant 7% increase in the area of cholinergic perikarya. To account for the increased ChAT in cholinergic neurons and the enlargement of cholinergic perikarya, we propose that slow axonal transport may be impaired in nbM cholinergic neurons in AD.     

Müllerian inclusions in peritoneal washings. Potential source of error in cytologic diagnosis

Müllerian inclusions in peritoneal washings from female patients may be mistaken for adenocarcinoma. Such findings were studied in the peritoneal washing cytology specimens from eight cases. The inclusions usually presented as tubular or papillary structures, often forming a single layer of epithelium surrounding psammoma bodies. The cells forming these structures often displayed some degree of atypia. Recognition of this entity in peritoneal fluids is important to avoid a misdiagnosis of disseminated cancer. A general outline is proposed for interpreting such findings in peritoneal washings, based on the cytomorphology of these structures as well as the microscopic features of the primary neoplasms.     

Reversal of Con A-induced suppression by a platelet-derived factor which binds to activated suppressor T cells

A platelet-derived factor found in serum as well as in platelet releasate prepared either with calcium ionophore or with thrombin was shown to reverse Con A-induced suppression of the plaque forming cell (PFC) response to sheep erythrocytes (SRBC) in vivo in (CB6)F1 mice. In addition, as shown previously, lymphoma cell-induced suppression in SJL mice was similarly reversed. The factor could be injected prior to Con A on the day before SRBC injection, or on the same day as antigen with comparable results. It also enhanced PFC responses in the absence of Con A. Suppressor cell induction by Con A in vivo, as demonstrated by assay on PFC responses of normal spleen cells in vitro, was abrogated by simultaneous injection of the platelet factor. Cells from mouse spleen and lymph node, but not from thymus could absorb the factor from human serum at 4 degrees C. The phenotype of the relevant spleen cells was L3T4-, Ly1-, Ly2+, Thy1+, Ly22+, Qa1+, Qa4+, Qa5+, and Ly6.IE+. These results suggest that this factor binds to activated peripheral T cells of the suppressor cell phenotype.     

Materno-embryonally transferred antibodies precipitate autoimmune thyroiditis in obese strain (OS) chickens

In Obese strain (OS) chickens the role of maternal antibodies, passively transferred through the egg to the developing chick, was evaluated as a causative factor in the early development of spontaneous autoimmune thyroiditis (SAT). In the egg, passive antibody titers were highest in the yolk and lower in the allantoic fluid and sera of developing embryos. This passage of antibodies was documented by use of radiolabeled antibodies. In dams with high antibody titers, antibodies could be found in the sera of chicks at the time of hatch. Thyroglobulin was absent in the yolk of OS eggs during embryonal life, as compared with its detection in normal eggs. Immune complexes (thyroglobulin-autoantibody) detected in the thyroids of OS, but not CS, chicks at the time of hatch, or earlier, appear to reflect the presence of the maternally transferred antibodies. A pair of crosses between OS chickens, with thyroiditis, and the C strain (CS), without thyroiditis, was made to evaluate the role of transferred antibodies in the pathogenesis of autoimmune disease. When an OS chicken was the dam, maternal antibodies could be passively transferred; when a CS chicken was the dam, no maternal antibodies were present to be transferred. Nevertheless, both hybrids developed full-blown thyroiditis, demonstrating that binding of transferred maternal antibody to thyroglobulin is not a prerequisite for the induction of SAT. However, presence of maternal antibodies precipitated the onset of disease. Immune complexes formed in the embryonic thyroid are likely to participate in early autoimmune disease, although the development of full-blown thyroiditis may await the competency of the chick's immune system to provide the characteristic cellular infiltrate.     

Characterization of corticosteroid receptors in natural killer cells: comparison with circulating lymphoid and myeloid cells

Lymphocytes mediating natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) activities are relatively refractory to the changes in circulatory traffic and intrinsic function induced in other cell types by in vivo and in vitro corticosteroids (CS). To investigate if such drug resistance could be attributed to differences in the CS receptor number of affinity (Kd) of these cells, these characteristics were determined in purified populations of large granular lymphocytes (LGL), monocytes, neutrophils (PMN), and T cells. All cell types displayed a single class of CS receptor of uniform affinity; however, LGL resembled monocytes and PMN in receptor number and Kd while T cells had significantly fewer sites per cell with lower Kd. These studies suggest that the unresponsiveness of NK activity to CS is not secondary to differences in CS receptor capacity or affinity.     

Templeting and self-assembly

Templeting and self-assembly represent the two extremes of the spectrum of determinate pattern-assembly processes. A templeted pattern can be defined as one that requires a prepattern or templet explicitly specifying the final topology of the pattern. Conversely, a self-assembling pattern can be defined as one for which the inherent constraints of the precursor elements alone are sufficient to specify the final pattern. Both concepts can be directly expressed in matrix notation, and a simple matrix measure, the templeting index, characterizes the relative amount of templeting or of self-assembly in any particular system. With this language, a fundamental principle of pattern-assembly becomes evident: in the determinate realm, some patterns can only be assembled using the same-sized templets--templets that are at least as large as the final pattern.     

Coh A,a mutation affecting the post aggregative related (par) cohesive system of Dictyostelium discoideum

Three stage-specific cohesive systems operate in D. discoideum: VEG, elaborated by vegetative cells: AR, by aggregation competent cells; and PAR, by post aggregation stage cells. Previous study of a mutant strain JC-5 had shown the stability of its PAR system (but not the AR) to be temperature sensitive. However, the phenotypic expression of this mutation termed Coh A is complicated by the presence in that strain of a preexisting mutant gene Rde A, which accelerates developmental events generally and alters the pattern of morphogenesis. Genetic evidence presented here indicates that the two mutations have been separated by parasexual recombination yielding a Coh A, Rde A⁺ segregant class of which strain JC-36 is a prototype. At the permissive temperature, JC-36 follows a morphogenetic sequence like that of the wild type in respect to timing, morphogenetic pattern, and spore appearance. At the restrictive temperature, it forms normal aggregates at the usual time but exhibits two morphogenetic aberrancies during post aggregative development. First, fruit construction is arrested at a stage approximating the 16 hr “Bottle” stage of the wild type, though more squat and blunt tipped, and then the aggregate regresses. Cytodifferentiation into spores and stalk cells is also blocked. Second, a shift of slugs migrating normally at the permissive temperature to the restrictive causes the latter to disintegrate progressively as they leave clumps of cells behind them within the flattened sheath. JC-36 cells developing at the restrictive temperature also exhibited a decrease in EDTA resistant cohesivity attributable on two grounds to the sensitivity of the PAR system. In addition, the disappearance of the AR system completed in the wild type by the Mexicanhat (18–19 hr) stage is indefinitely arrested at an intermediate level in JC-36.