Biomedical subjects
Publications and source records attributed to Y Gazitt.
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A correlation was found between dephosphorylation of chicken erythrocyte membrane proteins, aggregation of intramembrane particles, increase in the lipid bilayer phase of the membrane and exposure of membrane phospholipids toward phospholipase A and trinitrobenzene sulfonic acid. Most of the covalently bound phosphate of the membrane proteins turns over and is associated with 5 major bands. It is suggested that phosphorylation and dephosphorylation of these proteins causes changes in their charge and conformation. Such changes might affect the interaction of these proteins with the neighbouring lipids or lipoprotein complexes and results in the aggregation of intramembrane particles and relative increase in the exposed free lipid bilayer phase of the membrane.
About 20 and 43% of the total membrane phospholipids are hydrolized in fresh rat erythrocytes by treatment with phospholipase C (Bacillus cereus), or both sphingomyelinase and phospholipase C, respectively, without causing cell lysis. Treatment of ATP-depleted cells with phospholipase C alone results in 50% hydrolysis and extensive lysis. Depletion of ATP causes a marked increase in the aggregation of intramembranous particles accompanied by a similar increase in the smooth area between the particle clusters as revealed by the freeze-etch technique. Such changes are not induced by extensive phospholipid hydrolysis in absence of cell lysis in fresh cells. Based on these and additional data, it is suggested that the membrane phospholipid organization can be divided into 3 types: phospholipids exposed to phospholipase C; phospholipids protected against phospholipase C by presence of sphingomyelin; phospholipids which can be exposed following alteration of the proteinlipid interactions. Such alterations which might be induced by a variety of means, including ATP depletion, might result in clustering of intramembranous particles and increase of the free lipid bilayer phase of the membrane.
About half of the sphingomyelin content of fresh and ATP-depleted chicken erythrocytes is hydrolysed by sphingomyelinase. Removal of spingomyelin exposes the rest of the membrane phospholipids to hydrolysis by phospholipase C only in ATP-depleted but not in fresh cells. Addition of both sphinogomyelinase and phospholipase C to ATP-depleted cells causes about 60-70 percent hydrolysis of the total phospholipids accompanied by extensive (90 percent) hemolysis. The phospholipids of toad erythrocytes are partially available to phospholipase C activity in fresh cells (17-25 percent hydrolysis) without prior sphingomyelinase treatment. However, in ATP-depleted toad cells phospholipase C hydrolyses 66 percent of phospholipids and causes extensive lysis. Treatment of either fresh or ATP-depleted toad erythrocytes by sphingomyelinase together with phospholipase C induces hydrolysis of most of the phospholipds with complete lysis. Restoration of ATP to ATP-depleted cells endows them with resistance to the attack of phospholipase C. The correlation between changes in ATP level and membrane organization as revealed by increased susceptibility toward phospholipases is discussed.
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Mononuclear cells concentrated from the blood of 16 non-Hodgkin's lymphoma (NHL) patients in the leukemic phase, were exposed to 10 ng/ml of TPA in an attempt to induce differentiation. Immunoglobulin (Ig) secretion, surface markers (SmIg, GP-70), tartrate resistant acid phosphatase (TRAP) and surface features were followed for up to six days in vitro. TPA induced 'hairy cell' like features in NHL cells as defined by cell morphology, ultrastructure, cell surface markers and the presence of TRAP. Unlike the results obtained in patients with CLL, cells from different patients at the same stage of disease reacted in a similar way. Differences were evident between NHL mononuclear cells obtained from patients in partial remission and active disease when compared with those derived from patients in complete remission. In the former group, NHL cells were maximally induced by TPA to secrete Ig and higher proportions of TRAP positive cells. In addition hairy cell features as seen by light and scanning electron microscopy were also more pronounced. TPA also induced the maximal expression of SmIg and GP-70 in cells derived from patients in this group. Patients with NHL in leukemic phase in complete remission did not express surface membrane GP-70 before or after TPA treatment while SmIg was expressed to some degree before TPA treatment and further induced following treatment with TPA. GP-70 appears to be a more reliable marker for follow-up of NHL patients than any other marker studied here.
PBMC concentrated from 12 patients with CLL were incubated for up to 6 days with various doses of TPA or RA in an attempt to induce differentiation. The results show a great heterogeneity in the cellular response to both inducers. TPA produced two major changes in B-CLL cells, namely the development of some hairy-cell leukemia features with an increase in Ig secretion and the expression of Leu M5 and TAC receptors. In contrast to TPA, RA induced only modest or no changes in surface, but increased numbers of large macrophages were seen as assessed by latex-bead ingestion, expression of Fc receptors and cytochemistry. These changes were more obvious after exposure to RA than to TPA. Thus, while TPA induces mostly differentiation and hairy-cell features in B-lymphocytes, RA induces activation of the monocyte pool with no obvious changes in the lymphocytic compartment.