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R H Michell

Publications and source records attributed to R H Michell.

At least 37 records · Page 2Linked to original sources
PubMed1996

Synthesis and iron binding studies of myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate, and iron binding studies of all myo-inositol tetrakisphosphates.

The first syntheses of the natural products myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate are described. The protected key intermediates 4,5,6-tri-O-benzoyl-myo-inositol and (+/-)-3,4,5,6-tetra-O-benzyl-myo-inositol were phosphorylated with dibenzyl N,N-di-isopropylphosphoramidite in the presence of 1H-tetrazole and subsequent oxidation of the phosphite. The crystal structures of the synthetic intermediates (+/-)-1-O-(tert-butyldiphenylsilyl)-2,3,O-cyclohexylidene-myo-inos itol and (+/-)-4,5,6-tri-O-benzoyl-1-O-(tert-butyldiphenylsilyl)-2,3-O-cycl ohexylidene- myo-inositol are reported. myo-Inositol 1,2,3-trisphosphate, (+/-)-myo-inositol 1,2-bisphosphate, and all isomeric myo-inositol tetrakisphosphates were evaluated for their ability to alter HO. production in the iron-catalysed Haber-Weiss reaction. The results demonstrated that a 1,2,3-grouping of phosphates in myo-inositol was necessary for inhibition, also that (+/-)-myo-inositol 1,2-bisphosphate potentiated HO. production. myo-Inositol 1,2,3-trisphosphate resembled myo-inositol hexakisphosphate (phytic acid) in its ability to act as a siderophore by promoting iron-uptake into Pseudomonas aeruginosa.

Binding Sites↗
PubMed1995

Regulation of neurite outgrowth from differentiated human neuroepithelial cells: a comparison of the activities of prothrombin and thrombin.

The mechanism by which thrombin and prothrombin control neurite retraction was studied in Ad12E1HER10 human neuroepithelial cells. Morphological changes in differentiated cells were apparent within minutes of the addition of very low concentrations of thrombin (3 pM). Higher concentrations (2 nM) of prothrombin were required to elicit a similar response. Doses of thrombin and prothrombin sufficient to cause neurite retraction stimulated protein tyrosine kinase activity. Protein tyrosine kinase activation also correlated positively with thrombin- and prothrombin-induced phosphoinositide 3-kinase activation and InsP6 dephosphorylation. However, thrombin-stimulated Ins(1,4,5)P3 generation and intracellular Ca2+ mobilization only occurred at concentrations in excess of those needed to induce retraction. No fluctuations in Ins(1,4,5)P3 were detected after stimulation with prothrombin, and no rapid synchronized release of Ca2+ was observed, even at very high concentrations. Prothrombin did, however, cause small oscillations in the intracellular Ca2+ concentration, similar to those produced by low concentrations of thrombin, after approximately 30 min. We conclude that prothrombin- and thrombin-induced neurite retractions are not dependent on PtdIns(4,5)P2 and Ca2+ mobilization, but are more probably mediated through an effector mechanism involving protein tyrosine kinase activation. No intracellular Ca2+ mobilization, protein tyrosine kinase activity or neurite retraction was observed after treatment of cells with proteolytically inactive mutant thrombin (S205-->A). Prothrombin-mediated intracellular Ca2+ mobilization and neurite retraction were inhibited by hirudin, which was shown to interact with thrombin but not prothrombin. It is concluded that cleavage of prothrombin to thrombin is a necessary prerequisite for biological activity on differentiated Ad12E1HER10 cells and that differences in agonist concentration are capable of coupling the thrombin receptor to different pathways within the cell.

Blotting, Western↗
PubMed1995

Inositol 1,2,3-trisphosphate and inositol 1,2- and/or 2,3-bisphosphate are normal constituents of mammalian cells.

1. An inositol trisphosphate (InsP3) distinct from Ins(1,4,5)P3 and Ins(1,3,4)P3, which we previously observed in myeloid and lymphoid cells [French, Bunce, Stephens, Lord, McConnell, Brown, Creba and Michell (1991) Proc R. Soc. London B 245, 193-201; Bunce, French, Allen, Mountford, Moore, Greaves, Michell and Brown (1993) Biochem. J. 289, 667-673], is present in WRK1 rat mammary tumour cells and pancreatic endocrine beta-cells. 2. It has been identified as Ins(1,2,3)P3 by a combination of oxidation to ribitol, a structurally diagnostic polyol, and ammoniacal hydrolysis to identified inositol monophosphates. 3. Ins(1,2,3)P3 concentration in HL60 cells changed little during stimulation by ATP or fMetLeuPhe or during neutrophilic or monocytic differentiation, and Ins(1,2,3)P3 was unresponsive to vasopressin in WRK1 cells. 4. Ins(1,2,3)P3 was usually more abundant than Ins(1,4,5)P3, often being present at concentrations between approximately 1 microM and approximately 10 microM. 5. HL60, WRK-1 and lymphoid cells also contain Ins(1,2)P2 or Ins(2,3)P2, or a mixture of these two enantiomers, as a major InsP2 species. 6. Ins(1,2,3)P3 and Ins(1,2)P2/Ins(2,3)P2 are readily detected in cells labelled for long periods, but not in acutely labelled cells. This behaviour resembles that of InsP6, the most abundant cellular inositol polyphosphate that includes the 1,2,3-trisphosphate motif, which also achieves isotopic equilibrium with inositol only slowly. 7. Ins(1,2,3)P3 is the major InsP3 that accumulates during metabolism of InsP6 by WRK-1 cell homogenates. 8. Possible metabolic relationships between Ins(1,2,3)P3, Ins(1,2)P2/Ins(2,3)P2 and other inositol polyphosphates in cells, and a possible role for Ins(1,2,3)P3 in cellular iron handling, are considered.

Animals↗
PubMed1995

Altered T lymphocyte signaling in rheumatoid arthritis.

Synovial and peripheral blood T cells from patients with rheumatoid arthritis are functionally deficient. This may be secondary to their reduced cytokine (e.g. interleukin-2) synthesis. We have investigated the possibility of an alteration in pathways common to interleukin-2 production and proliferation in peripheral blood T cells from patients with active rheumatoid arthritis. Intracellular calcium levels ([Ca2+]i) were analyzed by flow cytometric methods in Indo1-loaded T cells. These were purified by negative selection from patients or age/sex-matched controls, and stimulated with phytohemagglutinin-P or anti-CD3. Rheumatoid [Ca2+]i responses to both stimuli were reduced (p < 0.005). Patient cell samples included a larger proportion of non-responding cells, but even in the responsive population the magnitude of the response in rheumatoid cells was impaired compared with those in normal cell samples (p < 0.0001) for both stimuli. Proliferation responses were also impaired (p < 0.005), and there was a positive correlation between the paired [Ca2+]i elevation and proliferative responses for both stimuli. CD2 and CD3 expression were normal, and the proportions of CD4, CD8 and CD45RO and CD45RA subsets were also unaffected by disease. Thus a signaling defect downstream of CD2 or CD3 surface molecules may contribute to functional deficiencies in rheumatoid T lymphocytes. This effect is not due to non-steroidal anti-inflammatory drugs which some patients were taking. We have demonstrated similar alterations in [Ca2+]i responses and proliferation in a smaller study of patients with inflammatory bowel disease, indicating that such changes might be present in other chronic inflammatory states.

Antigens, CD↗
PubMed1995

Phosphatidylinositol 4,5-bisphosphate hydrolysis accompanies T cell receptor-induced apoptosis of murine thymocytes within the thymus.

Regulation of the development of thymocytes into mature T cells within the thymus is now known to involve antigen-induced deletion, by apoptosis, of potentially autoreactive thymocytes, and it can be mimicked either by stimulating the T cell receptor (TcR) complex by monoclonal antibody (mAb) or by ionophore-induced elevation of cytosolic [Ca2+]. To identify signaling pathways employed by the TcR complex of immature thymocytes, we examined the effects of anti-CD3 and anti-TcR beta constant (c) region mAb, staphylococcal enterotoxin B (SEB) and pharmacological agents on the generation of inositol phosphates through hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] both in cultured fetal mouse thymic lobes and in the CD4+CD8+ immature thymocyte cell line, TM10G. Stimulation of the TcR complex with anti-CD3 mAb provoked an accumulation of inositol phosphates diagnostic of the occurrence of receptor-stimulated phosphoinositidase C (PLC) activation. Anti-TcRC beta mAb and SEB provoked smaller but similar responses. The PLC activation evoked by anti-CD3 mAb was suppressed by inhibitors of receptor tyrosine kinases and was unmodified by protein kinase C activation or elevation of cytosolic [Ca2+]. It thus appears that apoptosis triggered by TcR stimulation is associated with PLC activation by a receptor-regulated tyrosine kinase. Treatment of thymic lobes or TM10G cells with fluoroaluminate provoked apoptosis of a wider range of thymocyte subtypes and such stimulation also provoked an accumulation of inositol phosphates. The responses to fluoroaluminate were not prevented by inhibitors of tyrosine kinases, suggesting that unidentified GTP-binding proteins which couple to PLC activation may also be capable of initiating apoptosis by a route independent of the TcR. These results, when considered alongside previous studies of mature T cells, indicate that stimulation of immature thymocytes or of mature T cells through their TcR complex activates the PLC-catalyzed PtdIns(4,5)P2 hydrolysis signaling pathway, and thus that this signaling pathway may be implicated both in provoking apoptosis in immature T cells and in initiating proliferation in mature T cells.

Aluminum Compounds↗
PubMed1995

Rat testicular myoid cells express vasopressin receptors: receptor structure, signal transduction, and developmental regulation.

Detection of the neurohypophysial hormones vasopressin (AVP) and oxytocin (OT) in the testis of several species has led to the proposal that these peptides may have a physiological role in the regulation of testicular function. Therefore, we investigated whether the contractile myoid cells of rat seminiferous tubules express functional receptors for AVP or OT and, thus, constitute a target for these hormones. This study used primary cultures of purified peritubular myoid cells derived from rats both before and after puberty. By several criteria, myoid cells prepared from adult rats expressed vasopressin receptors (VPRs). We detected specific and saturable [3H]AVP binding to a single population of sites with a Kd of 7.5 nM and a binding capacity of 145 fmol/mg protein. AVP stimulated the accumulation of inositol phosphates in a dose-dependent manner with an EC50 of 1.7 nM. Cloning and sequencing of the myoid cell VPR confirmed it to be the V1a subtype of VPR. VPR expression by myoid cells is under developmental control, as the receptors are present in the adult rat, but absent before puberty. In contrast, OT receptors were not expressed at any stage of development. Peritubular myoid cells are also responsive to endothelin-1 (ET-1), which potently stimulated phosphoinositidase-C. However, unlike AVP, the ET-1 responses were observed both before and after sexual maturity, suggesting different roles for AVP and ET-1 in the control of myoid cell function. Our data establish that the myoid cells of the adult rat seminiferous tubule are a target for AVP. This indicates an additional role for AVP in the regulation of testicular function and male fertility in the adult rat.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Localisation of bradykinin-like immunoreactivity and modulation of bradykinin-evoked phospholipase D activity by 17 beta-oestradiol in human endometrium.

Bradykinin may act as a promoter of endometrial regeneration. Bradykinin-like immunoreactivity was detected immunocytochemically in the glandular epithelium and stroma of human endometrium. The staining was localized around the stroma and especially in the cells undergoing mitosis. Relatively weak staining was seen in the stromal cells of secretory endometrium, which was predominantly localised around the basal vacuoles of endometrial glands. During the late secretory phase, the intensity of staining was diminished throughout the endometrium: the glandular epithelium showed weak staining and stroma appeared negative. As phosphatidate, the product of phospholipase D pathway, may mediate cell proliferation, the effect of 17 beta-oestradiol on bradykinin-evoked phospholipase D activity assayed as accumulation of [3H]phosphatidylbutanol ([3H]PtdBut) was examined in [3H]myristic acid-labelled primary cultures of human endometrial stromal cells. Bradykinin induced a rapid accumulation of [3H]PtdBut in a time-dependent manner, indicating phospholipase D activation. Pretreatment of stromal cells with 17 beta-oestradiol enhanced the bradykinin-evoked phospholipase D activity. These results suggest that bradykinin-like immunoreactivity is strongly associated with proliferative stromal cells undergoing mitosis, a process that may be mediated by phospholipase D activation as the magnitude of this enzyme's activation in vitro appears to be regulated by 17 beta-oestradiol.

Adult↗
PubMed1994

The intracellular distribution of inositol polyphosphates in HL60 promyeloid cells.

1. HL60 promyeloid cells contain high intracellular concentrations of inositol polyphosphates, notably inositol 1,3,4,5,6-pentakisphosphate (InsP5) and inositol hexakisphosphate (InsP6). To determine their intracellular location(s), we studied the release of inositol (poly)phosphates, of ATP, and of cytosolic and granule-enclosed enzymes from cells permeabilized by four different methods. 2. When cells were treated with digitonin, all of the inositol phosphates were released in parallel with the cytosolic constituents. Most of the InsP5 and InsP6 was released before significant permeabilization of azurophil granules. 3. Similar results were obtained from cells preloaded with ethylene glycol and permeabilized by osmotic lysis. 4. Electroporation at approximately 500 V/cm caused rapid release of free inositol. Higher field strengths provoked release of most of the ATP, InsP5 and InsP6, but only slight release of the intracellular enzymes. Multiple discharges released approximately 80-90% of total InsP5 and InsP6. In the absence of bivalent-cation chelators, InsP5 and InsP6 were released less readily than ATP. 5. Treatment of cells with Staphylococcus aureus alpha-toxin caused quantitative release of inositol and ATP, without release of intracellular enzymes. However, inositol phosphates were released much less readily than inositol or ATP. Even after prolonged incubation with a high concentration of alpha-toxin, only approximately 50-70% of InsP2, InsP3 and InsP4 and < or = 20% of InsP5 and InsP6 were released, indicating that the high charge or large hydrated radius of InsP5 and InsP6 might limit their release through small toxin-induced pores. 6. These results indicate that most intracellular inositol metabolites are either in, or in rapid exchange with, the cytosolic compartment of HL60 cells. However, they leave open the possibility that a small proportion of cellular InsP5 and InsP6 (< or = 10-20%) might be in some intracellular bound form.

Adenosine Triphosphate↗
PubMed1994

Inhibition of porcine brain inositol 1,3,4-trisphosphate kinase by inositol polyphosphates, other polyol phosphates, polyanions and polycations.

We have partially purified an enzyme activity that phosphorylates inositol 1,3,4-trisphosphate from porcine brain, rat liver and bovine testis by FPLC chromatography on Q-Sepharose anion-exchange resin and Heparin-agarose. The products of this reaction were inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate. The same enzyme appears to be responsible for both 6-kinase and 5-kinase activities against inositol 1,3,4-trisphosphate (the 6-kinase: 5-kinase activity ratio is approximately 4 to 1), has a pH optimum of approximately 6.8 and requires Mg2+ for activity. The Km values of the enzyme for inositol 1,3,4-trisphosphate and ATP were approximately 0.5 microM and approximately 100 microM, respectively. Inositol 3,4,5,6-tetrakisphosphate, inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate are all competitive inhibitors with K(i) values of 0.4 microM, 3 microM and 5 microM, respectively, well within their likely intracellular concentration ranges: they inhibited 6-kinase and 5-kinase activities equally. 2,3-Bisphosphoglycerate and spermine were also competitive inhibitors, with K(i) values of 0.8 mM an 12 mM, respectively. Dextran sulphate was a non-competitive inhibitor with a Ki of approximately 15 microM, and poly-L-lysine (IC50 approximately 200 microM), polyvinylsulphate (IC50 approximately 250 microM) and heparin (IC50 approximately 2 mg/ml) also inhibited. Inhibition by these compounds suggests that inositol 3,4,5,6-tetrakisphosphate (and to a lesser extent inositol 1,3,4,5-tetrakisphosphate and other naturally occurring intracellular ions) may restrict the synthesis of inositol 1,3,4,6-tetrakisphosphate and hence regulate the rate of inositol penta- and hexakisphosphate synthesis from receptor-generated inositol phosphates.

Animals↗
PubMed1994

Intracellular concentrations of inositol, glycerophosphoinositol and inositol pentakisphosphate increase during haemopoietic cell differentiation.

We have analysed the levels of soluble inositol metabolites in HL60 cells as they differentiate towards neutrophils in response to a combination of all-trans-retinoic acid and granulocyte colony-stimulating factor and towards monocytes in response to 1 alpha-25-dihydroxyvitamin D3. In both cases, differentiation was accompanied by increases in intracellular inositol (Ins), glycerophosphoinositol (GroPIns) and inositol pentakisphosphate (InsP5) concentrations. [GroPIns] reached a peak early in the differentiation of both neutrophils and monocytes and subsequently fell to about double the starting level as the cells acquired mature characteristics, and [InsP5] rose later. Similarly, neutrophils derived in culture by the spontaneous differentiation of myeloid blast cells contained increased levels of Ins, GroPIns and InsP5 when compared to their parental blast cells. We have also compared the inositol metabolites present in two pairs of cell lines which are representative of immature and mature B and T lymphocytes. The mature cells again contained the higher levels of GroPIns and InsP5. We have previously demonstrated increases in Ins, GroPIns and Ins(1,3,4,5,6)P5 levels during the differentiation of HL60 cells towards neutrophils in response to DMSO and of GroPIns during the monocytoid differentiation of normal primitive myeloid blast cells in response to PMA. These observations suggest that deacylation of phosphatidylinositol by a phospholipase A/lysophospholipase pathway, forming GroPIns and probably also regulatory arachidonate metabolites, has some role in haemopoietic cell differentiation. The reasons why Ins(1,3,4,5,6)P5 and Ins accumulate during haemopoietic differentiation remain unknown.

Cell Differentiation↗
PubMed1994

Second messengers. Sphingolipid signalling.

Sphingomyelin metabolites seem increasingly likely to be intracellular messengers controlling a variety of cell activities, but it is not yet clear exactly which metabolites control which functions, or how they do so.

Animals↗
PubMed1994

Bovine testis and human erythrocytes contain different subtypes of membrane-associated Ins(1,4,5)P3/Ins(1,3,4,5)P4 5-phosphomonoesterases.

1. We have purified membrane-associated Ins(1,4,5)P3/Ins(1,3,4,5)P4 5-phosphatases from bovine testis and human erythrocytes by chromatography on several media, including a novel 2,3-bisphosphoglycerate affinity column. 2. The enzymes have apparent molecular masses of 42 kDa (testis) and 70 kDa (erythrocyte), as determined by SDS/PAGE, and affinities for Ins(1,4,5)P3 of 14 microM and 22 microM respectively. 3. The two enzymes hydrolyse both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 and are therefore type I Ins(1,4,5)P3 5-phosphatases [nomenclature of Hansen, Johanson, Williamson and Williamson (1987) J. Biol. Chem. 262, 17319-17326]. 4. On chromatofocusing, the partially purified testicular enzyme migrates as two peaks of activity, with pI values of about 5.8 and 5.5. The erythrocyte enzyme exhibits only the latter peak. 5. The testis 5-phosphatase is labile at 37 degrees C, but its activity can be maintained in the presence of 50 mM phorbol dibutyrate (PdBu). After PdBu treatment, a third form of the enzyme, with pI about 6.2, appears on chromatofocusing, but without change in its Km or Vmax. 6. Consideration of the properties of these enzymes and of the 5-phosphatases from other tissues suggests that type I Ins(1,4,5)P3 5-phosphatases are of two well-defined subtypes. We propose that these be termed type Ia [typified by the testis enzyme: approximately 40 kDa, higher affinity for Ins(1,4,5)P3] and Type Ib [typified by the erythrocyte enzyme: approximately 70 kDa, lower affinity for Ins(1,4,5)P3].

Animals↗
PubMed1994

Simultaneous oscillations of cytoplasmic free Ca2+ concentration and Ins(1,4,5)P3 concentration in mouse pancreatic beta-cells.

Changes in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in stimulated cells are often oscillatory, but the mechanisms that drive these oscillations are still a matter of controversy: different models of the generation of these [Ca2+]i oscillations make different assumptions as to whether oscillations in Ins(1,4,5)P3 concentration are necessary for this process. We have looked for changes in inositol polyphosphate levels that might occur in suspensions of murine pancreatic beta-cells when these cells are induced to display synchronized oscillations in [Ca2+]i by the sequential addition of glucose, an alpha 2-adrenergic stimulus and extracellular Ca2+. The intracellular level of Ins(1,4,5)P3 oscillated in a manner approximately in synchrony with changes in [Ca2+]i. Oscillations in the levels of Ins(1,4,5)P3 metabolites [Ins(1,3,4)P3 and inositol bisphosphates] were slightly delayed relative to the Ins(1,4,5)P3 oscillations, and the concentration of Ins(1,3,4,5,6)P5 remained approximately constant during the [Ca2+]i oscillations. These results demonstrate that [Ins(1,4,5)P3] and [Ca2+]i oscillate in synchrony in at least one type of cell. Whether such oscillations in intracellular [Ins(1,4,5)P3] provide a primary driving force for [Ca2+]i oscillations either in beta-cells or in other stimulated cells remains to be determined. Even if they do not, the [Ins(1,4,5)P3] oscillations will at least provide an amplifying influence on the [Ca2+]i changes.

Animals↗
PubMed1994

Indomethacin potentiates the induction of HL60 differentiation to neutrophils, by retinoic acid and granulocyte colony-stimulating factor, and to monocytes, by vitamin D3.

We have confirmed previous observations that HL60 cells treated with a combination of 10 nM retinoic acid (RA), and 30 ng/ml granulocyte colony-stimulating factor (G-CSF) differentiate efficiently towards neutrophils, as characterized by their growth arrest and acquisition of phagocytic ability. Such low concentrations of RA alone provoked only a small proportion of HL60 cells to differentiate, and G-CSF alone provoked no differentiation. In the presence of 30 microM indomethacin (an inhibitor of the enzyme cyclooxygenase that catalyses the first step of prostanoid synthesis), the onset of differentiation provoked by RA plus G-CSF was more rapid, but the final proportion of mature cells was unchanged. Indomethacin also potentiated the growth arrest and differentiation of cells in response to 10 nM RA alone. Although the potentiating effect of indomethacin on RA-induced differentiation occurred at several indomethacin and RA concentrations, it was only apparent when the RA concentration used was alone sufficient to induce a small proportion of cells to differentiate. Indomethacin shifted the G-CSF dose-response curve of cells treated with 10 nM RA to lower G-CSF concentrations. 1 alpha,25-dihydroxy vitamin D3 (VitD3) induces HL60 cells to differentiate to monocytes and indomethacin also potentiated the differentiation of HL60 cells in response to low doses of VitD3 5,8,11-eicosatriynoic acid, an inhibitor of 5-lipoxygenase and 12-lipoxygenase, neither potentiated neutrophil differentiation of HL60 cells, nor prevented indomethacin potentiation of the differentiation of RA-primed cells. Treatment of cells with dexamethasone, a steroid whose effects include inhibition of arachidonate mobilization by phospholipase A2, potentiated RA-primed neutrophil differentiation in a manner similar to indomethacin. These observations suggest that an arachidonate metabolite formed downstream of cyclooxygenase suppresses differentiation of HL60 cells both to neutrophils and monocytes, probably by inhibiting some event essential to commitment to differentiation.

Arachidonic Acid↗
PubMed1993

Stimulation of tyrosine phosphorylation without inositol lipid hydrolysis in human B lymphocytes on engaging CD72.

Occupancy of CD72 on resting tonsillar B cells by monoclonal antibodies (mAb) promotes entry into the G1 phase of the cell cycle with an accompanying increase in MHC Class II expression and provides a co-stimulus to immobilized anti-mu for driving DNA synthesis. We now report that engagement of CD72 by mAb stimulates tyrosine phosphorylation in B cells with a peak of activity seen at 5-10 min. Two major substrates of 29 and 57 kDa showed a basal level of phosphorylation which increased with time, while a 40 kDa protein and several other minor components were phosphorylated de novo on the addition of mAb to CD72. Inositol lipid hydrolysis was found to be unperturbed, although a shallow rise in the basal level of intracellular free Ca2+ was provoked on engaging CD72. Receptor cross-linking was not a requirement for signaling human B cells through CD72: simple occupancy by univalent antibody was sufficient both to trigger the rise in basal [Ca2+]i and to promote DNA synthesis.

Antigens, CD↗
PubMed1993

Comparison of the levels of inositol metabolites in transformed haemopoietic cells and their normal counterparts.

We have compared the levels of inositol metabolites in three pairs of normal and transformed cells which have been matched with respect to their cell lineage, differentiation and proliferation status: (i) normal human myeloid blast cells and the human promyelocytic leukaemic cell line, HL60; (ii) human umbilical-cord T-helper cells and C8166 cells, a HTLV-1-transformed T-helper cell line; and (iii) an interleukin 3-dependent long-term culture of murine pro-B-cells (BAF3) and BAF3 cells transformed by transfection with the bcr-abl oncogene. Complex patterns of inositol metabolites were present in each of the cell populations. Although there were a number of differences in the levels of certain inositol metabolites between individual cell populations in the paired groups, we did not observe any consistent difference in the levels of inositol metabolites between the proliferating normal and transformed cells. In particular, our data do not support the reported correlation between elevated glycerophosphoinositol (GroPIns) levels and transformation of cells by membrane and cytoplasmic oncogenes which has been reported by other workers. All the cells contained high concentrations of Ins(1,3,4,5,6)P5 (between 12 and 55 microM) and InsP6 (between 37 and 105 microM). The HTLV1-transformed T-helper cells had particularly high levels of total inositol phosphates (predominantly GroPIns, an unidentified inositol bisphosphate and InsP6). The observations are discussed with reference to cell transformation and to the differentiation status of the paired populations.

Animals↗