Nadia Maria Sposi

TfR2 localizes in lipid raft domains and is released in exosomes to activate signal transduction along the MAPK pathway.

Transferrin receptor 2 (TfR2) possesses a YQRV motif similar to the YTRF motif of transferrin receptor 1 (TfR1) responsible for the internalization and secretion through the endosomal pathway. Raft biochemical dissection showed that TfR2 is a component of the low-density Triton-insoluble (LDTI) plasma membrane domain, able to co-immunoprecipitate with caveolin-1 and CD81, two structural raft proteins. In addition, subcellular fractionation experiments showed that TfR1, which spontaneously undergoes endocytosis and recycling, largely distributed to intracellular organelles, whereas TfR2 was mainly associated with the plasma membrane. Given the TfR2 localization in lipid rafts, we tested its capability to activate cell signalling. Interaction with an anti-TfR2 antibody or with human or bovine holotransferrin showed that it activated ERK1/ERK2 and p38 MAP kinases. Integrity of lipid rafts was required for MAPK activation. Co-localization of TfR2 with CD81, a raft tetraspanin exported through exosomes, prompted us to investigate exosomes released by HepG2 and K562 cells into culture medium. TfR2, CD81 and to a lesser extent caveolin-1, were found to be part of the exosomal budding vesicles. In conclusion, the present study indicates that TfR2 localizes in LDTI microdomains, where it promotes cell signalling, and is exported out of the cells through the exosome pathway, where it acts as an intercellular messenger.

Expression of protein kinase C genes during ontogenic development of the central nervous system.

We have analyzed the RNA expression of three protein kinase C (PKC) genes (alpha, beta, and gamma) in human and murine central nervous systems during embryonic-fetal, perinatal, and adult life. Analysis of human brain poly(A)+ RNA indicates that expression of PKC alpha and beta genes can be detected as early as 6 weeks postconception, undergoes a gradual increase until 9 weeks postconception, and reaches its highest level in the adult stage, and that the PKC gamma gene, although not expressed during embryonic and early fetal development, is abundantly expressed in the adult period. Similar developmental patterns were observed in human spinal cord and medulla oblongata. A detailed analysis of PKC gene expression during mammalian ontogeny was performed on poly(A)+ RNA from the brain cells of murine embryos at different stages of development and the brain cells of neonatal and adult mice. The ontogenetic patterns were similar to those observed for human brain. Furthermore, we observed that the expression of PKC gamma is induced in the peri- and postnatal phases. These results suggest that expression of PKC alpha, beta, and gamma genes possibly mediates the development of central neuronal functions, and expression of PKC gamma in particular may be involved in the development of peri- and postnatal functions.

Transferrin receptor 2 protein is not expressed in normal erythroid cells

Human TFR2 (transferrin receptor 2) is a membrane-bound protein homologous with TFR1. High levels of TFR2 mRNA were found mainly in the liver and, to a lesser extent, in erythroid precursors. However, although the presence of the TFR2 protein in hepatic cells has been confirmed in several studies, evidence is lacking about the presence of the TFR2 protein in normal erythroid cells. Using two anti-TFR2 monoclonal antibodies, G/14C2 and G/14E8, we have provided evidence that TFR2 protein is not expressed in normal erythroid cells at any stage of differentiation, from undifferentiated CD34+ cells to mature orthochromatic erythroblasts. In contrast, erythroleukaemic cells (K562 cells) exhibited a high level of expression of TFR2 at both the mRNA and the protein level. We can therefore conclude that an elevated expression of TFR2 protein is observed in leukaemic cells, but not in normal erythroblasts. The implications of this observation for the understanding of the phenotypic features of haemochromatosis due to mutation of the TFR2 gene are discussed.

Heterocellular hereditary persistence of fetal hemoglobin (HPFH). Molecular mechanisms of abnormal γ-gene expression in association with β thalassemia and linkage relationship with the β-globin gene cluster

SummaryWe report a study of four families of Italian origin in which heterocellular HPFH is inherited linked to β thalassemia over two or three generations. The HPFH + β thalassemia carriers showed thalassemic blood pictures and elevated HbF and F-cell number without increase in the HbF/F-cell content. Association of this gene complex with a second β thalassemia trait gives rise to a mild clinical picture characterized by 9–12 g/dl of mainly HbF in peripheral blood and no transfusion requirement. In two families, independent segregation of the HPFH or β-thal trait was observed, and in one case the study of the DNA polymorphisms within the γδβ gene cluster indicated that the HPFH mutation lies outside that DNA region. In one family the coexistence of a polymorphic variant of the Aγ chain (the AγT chain) allowed us to demonstrate that the increased γ chain synthesis caused by the heterocellular HPFH determinant is directed by both chromosomes.

Ferroportin and Erythroid Cells: An Update

In recent years there have been major advances in our knowledge of the regulation of iron metabolism that have had implications for understanding the pathophysiology of some human disorders like beta-thalassemia and other iron overload diseases. However, little is known about the relationship among ineffective erythropoiesis, the role of iron-regulatory genes, and tissue iron distribution in beta-thalassemia. The principal aim of this paper is an update about the role of Ferroportin during human normal and pathological erythroid differentiation. Particular attention will be given to beta-thalassemia and other diseases with iron overload. Recent discoveries indicate that there is a potential for therapeutic intervention in beta-thalassemia by means of manipulating iron metabolism.

C-fms expression correlates with monocytic differentiation in PML-RAR alpha+ acute promyelocytic leukemia

We have investigated the expression of the M-CSF receptor (c-fms) in 16 freshly isolated acute promyelocytic leukemias (APL) expressing the PML/RARα fusion protein. In parallel, we evaluated the capacity of these cells to differentiate along the granulocytic and monocytic pathways. c-fms was constitutively and constantly expressed in all cases sensitive in vivo to all-trans retinoic acid (ATRA) and its expression was further potentiated following in vitro induction with ATRA. Furthermore, gel-shift analysis of APL cells showed elevated levels of PU.1 binding activity to the M-CSF receptor promoter, particularly after ATRA stimulation. Interestingly, the rise of PU.1 binding activity as well as of PU.1 levels after ATRA treatment was significantly higher in APL patients exhibiting monocytic maturation, as compared to those that did not undergo monocytic differentiation. A variable proportion of ATRA-induced APL cells exhibited monocyte-like morphology and immunophenotype: the proportion of monocytic cells was consistently increased by combined treatment with ATRA and diverse hematopoietic growth factors cocktails, which always comprised M-CSF. Monocytic cells originating from in vitro ATRA-induced maturation of APL cells derive from the leukemic clone as suggested by two lines of evidence: (1) monocytic cells harbor the 15;17 translocation; (2) monocytic cells possess Auer bodies. The c-fmsbright leukemic blasts preferentially showed the capacity for monocytic differentiation as compared to the c-fmsdim/− subset: indeed, enforced expression of c-fms into NB4, a PML/RARα+ cell line, favored the onset of monocytic maturation. Finally, low c-fms expression was observed in an APL relapsing patient resistant to ATRA, as well as in an APL case with t(11;17), PLZF/RARα+. These observations indicate that PML/RARα+ APL blasts are bipotent for differentiation through both neutrophilic and monocytic lineages, whereby monocytic differentiation is linked to c-fms expression and stimulation.

Expression of interleukin 3 and granulocyte–macrophage colony-stimulating factor receptor common chain βc, βIT in normal haematopoiesis: lineage specificity and proliferation-independent induction

Interleukin 3 (IL‐3), granulocyte–macrophage colony‐stimulating factor (GM‐CSF) and interleukin 5 (IL‐5) exert their biological activities through interaction with cell‐surface receptors that consist of two subunits, a specific α subunit and a common β transducing subunit (βc). We have evaluated the expression of βc on purified haematopoietic progenitor cells (HPCs) induced to unilineage differentiation/maturation through the erythroid (E), granulocytic (G), megakaryocytic (Mk) or monocytic (Mo) lineage. HPCs displayed low βc expression, which increased during the initial stages of HPC differentiation along the E, G, Mo or Mk lineages. At later stages of differentiation, βc chain expression increased in both G and Mo lineages, was expressed at low levels in the Mk lineage and declined to undetectable levels in the E lineage. Analysis of the full‐length βc and intracytoplasmically truncated βc (βIT) mRNAs showed that the former was predominant in the G and Mo lineages, whereas the latter was prevalent in the E and Mk lineages. The βc induction takes place even in the absence of cell cycling. Thus, incubation of HPCs with graded amounts of IL‐3 showed that the initial induction of βc expression is unrelated to cell proliferation. Furthermore, circulating monocytes and granulocytes exhibit a low level of βc expression that is greatly stimulated following incubation with either IL‐3 or GM‐CSF.

The EL2 Rat Fibroblasts Line: Differential Effects of Growth Factors (EGF, PDGF, FGF, TPA and TGFβ) on Cell Proliferation and c‐fos Expressiona

Fibroblasts growth in culture is controlled by the concentration of serum in the medium. Serum contains a growth factor released by platelets during clot formation’*2 and growth factors derived from platelet-poor p l a ~ m a . ~ The platelet-derived growth factor (PDGF) allows cells to become competent to enter the cell cycle, but is not able to drive them into the S phase. Progression through GO/Gl into S after PDGF stimulus is induced by either plasma supplementation or sequential addition of its active constituents, i.e., epidermal growth factor (EGF) and somatomedin C (IGF I).‘ On the basis of these observations, it has been proposed that PDGF and EGF play a different role in the prereplicative phase, acting as a competence and a progression factor respectively. The competence/progression model has been postulated on the basis of studies on BALB/c 3T3 fibroblasts, but it is not established whether it may be generally applied to normal fibroblasts in culture.’ Recent studies on fibroblasts and lymphoid cells indicated that growth factors induce the activation of proto-oncogenes encoding nuclear proteins of unknown function (c-myc, c-myb, c-fos).It has been suggested that these genes may be directly involved in the regulation of cell proliferation, as transducers of growth factor

cAMP-mediated β-adrenergic signaling negatively regulates Gq-coupled receptor-mediated fetal gene response in cardiomyocytes

The treatment with beta-blockers causes an enhancement of the norepinephrine-induced fetal gene response in cultured cardiomyocytes. Here, we tested whether the activation of cAMP-mediated beta-adrenergic signaling antagonizes alpha(1)-adrenergic receptor (AR)-mediated fetal gene response. To address this question, the fetal gene program, of which atrial natriuretic peptide (ANP) and the beta-isoform of myosin heavy chain are classical members, was induced by phenylephrine (PE), an alpha(1)-AR agonist. In cultured neonatal rat cardiomyocytes, we found that stimulation of beta-ARs with isoproterenol, a beta-AR agonist, inhibited the fetal gene expression induced by PE. Similar results were also observed when cardiomyocytes were treated with forskolin (FSK), a direct activator of adenylyl cyclase, or 8-CPT-6-Phe-cAMP, a selective activator of protein kinase A (PKA). Conversely, the PE-induced fetal gene expression was further upregulated by H89, a selective PKA inhibitor. To evaluate whether these results could be generalized to Gq-mediated signaling and not specifically to alpha(1)-ARs, cardiomyocytes were treated with prostaglandin F(2)alpha, another Gq-coupled receptor agonist, which is able to promote fetal gene expression. This treatment caused an increase of both ANP mRNA and protein levels, which was almost completely abolished by FSK treatment. The capability of beta-adrenergic signaling to regulate the fetal gene expression was also evaluated in vivo conditions by using beta1- and beta2-AR double knockout mice, in which the predominant cardiac beta-AR subtypes are lacking, or by administering isoproterenol (ISO), a beta-AR agonist, at a subpressor dose. A significant increase of the fetal gene expression was found in beta(1)- and beta(2)-AR gene deficient mice. Conversely, we found that ANP, beta-MHC and skACT mRNA levels were significantly decreased in ISO-treated hearts. Collectively, these data indicate that cAMP-mediated beta-adrenergic signaling negatively regulates Gq cascade activation-induced fetal gene expression in cultured cardiomyocytes and that this inhibitory regulation is already operative in the mouse heart under physiological conditions.

Molecular heterogeneity of beta thalassaemia in the Italian population

Summary Fifty‐one subjects originating from Southern Italy and affected by Cooleys anaemia have been studied in order to define the degree of heterogeneity of β thalassaemia mutations in this high incidence area. Restriction endonuclease mapping has been carried out on genomic DNA by the Southern blot technique both to exclude the existence of gross deletions or rearrangements and to establish the relative frequency of four polymorphic restriction sites (i.e. Gγ and Aγ Hind III, β Ava II and β Bam HI) within the γδβ gene region. In 28 subjects unequivocal linkage of the four polymorphic sites has been determined leading to the identification of seven different chromosome haplotypes, six of which had previously been reported associated with specific β0 and β+ thalassaemia mutations. Globin chain synthesis studies on peripheral blood reticulocytes indicated that subjects carrying the same genotype may behave differently as far as the β chain production is concerned relative to both the a and the non‐α chains. Thus, β thalassaemia turns out to be quite heterogeneous even in this limited geographical area. β+ mutations appear to be predominant, particularly those affecting nuclear precursor RNA splicing to mature β globin mRNA.