Salarin C inhibits the maintenance of chronic myeloid leukemia progenitor cells.

We previously showed that incubation of chronic myeloid leukemia (CML) cells in very low oxygen selects a cell subset where the oncogenetic BCR/Abl protein is suppressed and which is thereby refractory to tyrosine kinase inhibitors used for CML therapy. In this study, salarin C, an anticancer macrolide extracted from the Fascaplysinopsis sponge, was tested as for its activity on CML cells, especially after their incubation in atmosphere at 0.1% oxygen. Salarin C induced mitotic cycle arrest, apoptosis and DNA damage. Salarin C also concentration-dependently inhibited the maintenance of stem cell potential in cultures in low oxygen of either CML cell lines or primary cells. Surprisingly, the drug also concentration-dependently enforced the maintenance of BCR/Abl signaling in low oxygen, an effect which was paralleled by the rescue of sensitivity of stem cell potential to IM. These results suggest a potential use of salarin C for the suppression of CML cells refractory to tyrosine kinase inhibitors.

Chromatin-associated CSF-1R binds to the promoter of proliferation-related genes in breast cancer cells.

The colony-stimulating factor-1 (CSF-1) and its receptor CSF-1R physiologically regulate the monocyte/macrophage system, trophoblast implantation and breast development. An abnormal CSF-1R expression has been documented in several human epithelial tumors, including breast carcinomas. We recently demonstrated that CSF-1/CSF-1R signaling drives proliferation of breast cancer cells via 'classical' receptor tyrosine kinase signaling, including activation of the extracellular signal-regulated kinase 1/2. In this paper, we show that CSF-1R can also localize within the nucleus of breast cancer cells, either cell lines or tissue specimens, irrespectively of their intrinsic molecular subtype. We found that the majority of nuclear CSF-1R is located in the chromatin-bound subcellular compartment. Chromatin immunoprecipitation revealed that CSF-1R, once in the nucleus, binds to the promoters of the proliferation-related genes CCND1, c-JUN and c-MYC. CSF-1R also binds the promoter of its ligand CSF-1 and positively regulates CSF-1 expression. The existence of such a receptor/ligand regulatory loop is a novel aspect of CSF-1R signaling. Moreover, our results provided the first evidence of a novel localization site of CSF-1R in breast cancer cells, suggesting that CSF-1R could act as a transcriptional regulator on proliferation-related genes.

AML1/ETO sensitizes via TRAIL acute myeloid leukemia cells to the pro-apoptotic effects of hypoxia.

We determined the effects of severe hypoxia (∼0.1% O2) on acute myeloid leukemia cells expressing the AML1/ETO oncogene. Incubation of Kasumi-1 cells in hypoxia induced growth arrest, apoptosis and reduction of AML1/ETO protein expression. The conditional expression of AML1/ETO in U937-A/E cells showed that hypoxia induces marked apoptosis in AML1/ETO-expressing cells only, pointing to AML1/ETO as a factor predisposing cells to hypoxia-induced apoptosis. In AML1/ETO-expressing cells, hypoxia enhanced TRAIL expression and its proapoptotic effects. AML1/ETO was found to bind TRAIL promoter and induce TRAIL transcription, although TRAIL expression was restrained by a concomitant relative transcription block. In hypoxia, such a TRAIL repression was removed and an increase of TRAIL expression was induced. Finally, blocking anti-TRAIL antibodies markedly reduced (Kasumi-1 cells) or completely inhibited (U937-A/E cells) hypoxia-induced apoptosis. Taken together, these results indicated that hypoxia induces apoptosis in AML1/ETO-expressing cells via a TRAIL/caspase 8-dependent autocrine loop and that TRAIL is a key regulator of hypoxia-induced apoptosis in these cells.

Selective anti-leukaemic activity of low-dose histone deacetylase inhibitor ITF2357 on AML1/ETO-positive cells.

We analysed the in vitro effects of a new hydroxamate derivative, ITF2357, on AML cells. ITF2357 potently induced histone acetylation. ITF2357 0.1 microM blocked proliferation and induced apoptosis in AML1/ETO-positive Kasumi-1 cells, while AML1/ETO-negative HL60, THP1 and NB4 cell lines were sensitive only to 1 microM ITF2357. Apoptosis was induced by 0.1 microM ITF2357 in AML1/ETO-positive primary blasts and U937-A/E cells induced to express AML1/ETO, but not in U937-A/E cells non-expressing AML1/ETO. In Kasumi-1 cells 0.1 microM ITF2357 induced AML1/ETO degradation through a caspase-dependent mechanism. ITF2357 0.1 microM also determined DNMT1 efflux from, and p300 influx to, the nucleus. Moreover, 0.1 microM ITF2357 determined local H4 acetylation and release of DNMT1, HDAC1 and AML1/ETO, paralleled by recruitment of p300 to the IL-3 gene promoter. ITF2357 treatment, however, did not induce re-expression of IL-3 gene. Accordingly, the methylation level of IL-3 promoter, as well as of several other genes, was unmodified. In conclusion, ITF2357 emerged as an anti-leukaemic agent very potent on AML cells, and on AML1/ETO-positive cells in particular. More relevantly, clearly emerged from our results that ITF2357 could be an ideal agent to treat AML subtypes presenting AML1/ETO fusion protein which determine HDAC involvement in leukaemogenesis.

TNF-alpha-converting enzyme cleaves the macrophage colony-stimulating factor receptor in macrophages undergoing activation.

We previously reported that macrophage activators such as LPS, IL-2, and IL-4 down-modulate the M-CSFR via a mechanism involving protein kinase C and phospholipase C. In this study, we showed that M-CSFR is shed from macrophage surface and identified the protease responsible for M-CSFR cleavage and down-modulation. The shedding of M-CSFR elicited by phorbol esters (tetradecanoylphorbol myristate acetate (TPA)) or LPS in murine BAC.1-2F5 macrophages was prevented by cation chelators, as well as hydroxamate-based competitive inhibitors of metalloproteases. We found that the protease cleaving M-CSFR is a transmembrane enzyme and that its expression is controlled by furin-like serine endoproteases, which selectively process transmembrane metalloproteases. M-CSFR down-modulation was inhibited by treating cells in vivo, before TPA stimulation, with an Ab raised against the extracellular, catalytic domain of proTNF-converting enzyme (TACE). TACE expression was confirmed in BAC.1-2F5 cells and found inhibited after blocking furin-dependent processing. Using TACE-negative murine Dexter-ras-myc cell monocytes, we found that in these cells TPA is unable to down-modulate M-CSFR expression. These data indicated that TACE is required for the TPA-induced M-CSFR cleavage. The possibility that the cleavage is indirectly driven by TACE via the release of TNF was excluded by treating cells in vivo with anti-TNF Ab. Thus, we concluded that TACE is the protease responsible for M-CSFR shedding and down-modulation in mononuclear phagocytes undergoing activation. The possible physiological relevance of this mechanism is discussed.

The possible influences of B2A2 and B3A2 BCR/ABL protein structure on thrombopoiesis in chronic myeloid leukaemia.

The Philadelphia chromosome, t(9;22)(q34;q11) gives rise more frequently, in chronic myeloid leukaemia (CML), to two BCR/ABL chimeric transcripts differing only by the absence of 75 nucleotides and defined as b2a2 and b3a2 types, encoding two 210-kDa tyrosine kinase proteins differing only by the absence of 25 amino acids coded by the b3 exon. In the present study the two transcripts, detected by RT-PCR in 88 consecutive unselected CML patients, were correlated with haematological findings at diagnosis and with the megakaryocyte size and frequency by morphometric evaluation of 45 bone marrow biopsies. The secondary structure prediction and hydrophobicity of the b2a2 and b3a2 type BCR/ABL protein were also obtained. The prediction results for the b3 exon amino acids using GOR IV and NnPredict methods showed a short beta strand corresponding to the hydrophobic portion of the peptide. Significantly higher values were found in the platelet count of patients carrying b3a2 transcripts. The megakaryocyte size and frequency in bone marrow biopsies did not show significant differences between the two groups of patients. Stratifying the patients on the basis of white blood cell (WBC) count below or above 100x10(9)/l we still had, in both groups, a significant difference in the platelet count between the b2a2 and b3a2 patients. The possible relationships between the structure of b2a2 and b3a2 types of BCR/ABL fused protein and thrombopoiesis are discussed.

Constitutive activation of the MAPK pathway mediates v-fes-induced mitogenesis in murine macrophages.

Fes is a nonreceptor tyrosine kinase expressed at the highest level in macrophages. We previously showed that the overexpression of c-fes in murine macrophages of the BAC-1.2F5 cell line renders these cells independent of macrophage colony-stimulating factor (MCSF) for survival and proliferation, although no direct relationship could be established between tyrosine-phosphorylated substrates of Fes- and MCSF receptor-dependent signaling and mitogenesis. In this study, we investigated whether the mitogen-activated protein kinase (MAPK) pathway is involved in the growth factor-independent growth of v-fes-overexpressing macrophages. We found a constitutively increased phosphorylation of extracellularly regulated kinase (ERK) in v-fes-overexpressing macrophages as compared with mock-infected cells. This finding was associated with activation of mitogen/extracellular signal-regulated kinase (MEK) and with constitutive localization of ERK in the nucleus. Treatment of v-fes-overexpressing cells with the MEK-specific inhibitor PD98059 markedly reduced cell growth, hyperphosphorylation, and nuclear localization of ERK, indicating that the MAPK pathway mediates the mitogenic effect of v-fes. (Blood. 2000;95:3959-3963)

Functional and immunological analysis of recombinant mouse H- and L-ferritins from Escherichia coli.

The production and characterization of recombinant mouse H- and L-ferritin chains from Escherichia coli are described. The proteins were efficiently expressed and purified with yields of 7-40 mg per liter of cell culture. They had the expected molecular mass and showed a physical stability analogous to that of the corresponding human ferritins. Mouse H- and L-ferritins had a very similar mobility on denaturing SDS-PAGE, but could be readily separated on nondenaturing PAGE because of the distinct slow mobility of mouse L-ferritin. Direct comparative experiments showed that mouse and human H-ferritins had the same iron incorporation activity, whereas mouse L-ferritin incorporated iron less efficiently than human L-ferritin. The difference was attributed to the substitution of a residue exposed on the cavity surface (Glu140 --> Lys) in mouse L-ferritin, a hypothesis confirmed by the finding that the mouse L-ferritin mutant Lys140-Glu incorporated iron as efficiently as human L-ferritin. Rabbit antisera elicited by the recombinant mouse ferritins were specific for the H- and L-chains and did not cross-react with the human ferritins. The antibodies and the derived specific ELISA assays allow the determination of H- and L-ferritins in mouse tissues.

The expansion of murine bone marrow cells preincubated in hypoxia as an in vitro indicator of their marrow-repopulating ability.

In liquid cultures of murine bone marrow cells stimulated with interleukin-3 and granulocyte/macrophage colony-stimulating factor, hypoxia (1% oxygen) induced a reversible block of hematopoiesis, maintaining the progenitors' expansion potential unreduced. Progenitors repopulating day-14 hypoxic cultures with cells or granulocyte/macrophage colony-forming units (CFU-GM) were found, on the basis of their maintenance in hypoxia (12% and 76%, respectively), to belong to different subsets, the latter being much more efficiently maintained. The maintenance in hypoxic cultures of progenitors detectable by marrow-repopulating ability (MRA) assay was 18% for MRAcell progenitors and 69% for MRACFU progenitors. Thus, the repopulation of hypoxic cultures with cells or CFU-GM closely reflected the presence of progenitors capable of repopulating, with cells or CFU-GM, the bone marrow of lethally irradiated syngeneic animals. Progenitors repopulating hypoxic cultures were, like MRA progenitors, significantly resistant to 5-fluorouracil, progenitors repopulating cultures with CFU-GM being two-fold more resistant than those repopulating cultures with cells. We concluded that the repopulation of day-14 hypoxic cultures occurring after their transfer to air is to be considered an indicator of the maintenance of MRA progenitors in hypoxia. The relevance of these results to stem cell biology and their potential practical applications are discussed.

Type II protein C deficiency: identification and molecular modelling of two natural mutants with low anticoagulant and normal amidolytic activity.

Two mutations in exons 3 and 9 of the protein C gene were identified by amplification and sequencing from symptomatic probands referred for venous thromboembolism and thrombophilia screening. The phenotype associated with the mutations is a type II protein C deficiency with normal amidolytic activity. In one family, the mutation in exon 3 (G3545-->A), which predicts an R9 to H substitution in the Gla domain, was identified. A mutation in exon 9 (G10899-->A), which predicts an R352 to W substitution in the catalytic site, was identified in the second family and has been reported previously in association with type II deficiency with low amidolytic activity. Western blotting of the purified proteins from the probands' plasma did not show any abnormal migratory pattern. Molecular modelling suggested a possible impairment in the recently described Na+ binding pocket for the R352-->W mutant. No conclusions could be drawn relative to the R9-->H mutant.

Incubation of murine bone marrow cells in hypoxia ensures the maintenance of marrow-repopulating ability together with the expansion of committed progenitors.

We developed previously a hypoxic culture system in which progenitors endowed with marrow-repopulating ability (MRA), unlike committed progenitors, were selected and maintained better than in air. We report here an improvement to this system targeted at combining the maintenance of progenitors sustaining MRA with the numerical expansion of multipotent and committed progenitors. Murine bone marrow cells were incubated at 1% oxygen in liquid medium supplemented with stem cell factor, granulocyte colony-stimulating factor, interleukin-6 and interleukin-3. In day 8 hypoxic cultures, the numbers of high proliferative potential and granulocyte/macrophage colony-forming cells (HPP-CFC and CFU-GM) were increased with respect to time zero. Colonies generated by HPP-CFC derived from hypoxic cultures exhibited a high replating ability, whereas colonies generated by HPP-CFC derived from control cultures exhibited a low replating ability. MRA was fully maintained in hypoxia and markedly reduced in air. Thus, severe hypoxia is able to ensure a full maintenance of progenitors sustaining MRA, together with a significant expansion of in vitro-detectable clonogenic progenitors, including those endowed with replating ability. This system could contribute to the improvement of current techniques for the in vitro treatment of human haematopoietic cell populations before transplantation.

Low M(r) phosphotyrosine protein phosphatase activity on fibroblast growth factor receptor is not associated with enzyme translocation.

Fibroblast growth factor receptor (class IV) shares a certain degree of similarity with class III members like platelet-derived growth factor and macrophage-colony-stimulating factor receptors, which, once activated, are substrates of low M(r) phosphotyrosine protein phosphatase. Up until now no phosphotyrosine phosphatase has been shown to act on this receptor in vivo. Here we demonstrate that low M(r) phosphotyrosine protein phosphatase is able to reduce receptor tyrosine phosphorylation and cell proliferation in response to basic fibroblast growth factor. Contrary to what was previously observed for platelet-derived growth factor, during cell stimulation with basic fibroblast growth factor, no enzyme redistribution among cellular compartments is observed.

Molecular characterization of a novel endonuclease (Xib) and possible involvement in lysosomal glycogen storage disorders.

We cloned and partially characterized a human endonuclease (Xib) which shows sequence homologies to pancreatic DNase I but an enzymatic activity closer to DNase II. We report on the structural differences found between Xib and other recently cloned human DNases. Fluores cence microscopy analysis of transiently transfected cells with Xib::pEGFP constructs indicate that the protein is located in the cytoplasm and possibly anchored to a membrane, as deduced from a hydrophobic amino acid stretch present at the C-terminal end. Xib is overexpressed in muscle and cardiac tissues and is alternately spliced in several normal and neoplastic cells. In situ hybridization studies using human cardiac and muscle biopsies indicate accumulation of Xib transcript in the vacuoles of muscle cells from patients affected by vacuolar myopathy as acid maltase deficiency; however, no point mutations were detected in their DNA.

The low-molecular-weight phosphotyrosine protein phosphatase, when overexpressed, reduces the mitogenic response to macrophage colony-stimulating factor and tyrosine phosphorylation of its receptor.

The interference of low-molecular-weight phosphotyrosine protein phosphatase with the macrophage response to macrophage colony-stimulating factor was investigated. This paper shows that this phosphatase, already known to be involved in platelet-derived growth factor receptor signaling, is physiologically expressed in murine macrophages and dephosphorylates in vitro macrophage colony-stimulating factor receptor molecules immunoprecipitated from macrophage colony-stimulating factor-stimulated macrophages. We obtained the first demonstration that a phosphotyrosine-specific protein phosphatase dephosphorylates the macrophage colony-stimulating factor receptor in vivo and reduces the mitogenic response to macrophage colony-stimulating factor. The data indicate that low-molecular-weight phosphotyrosine protein phosphatase is a negative regulator of macrophage colony-stimulating factor receptor signaling.

Effects of modifications near the 2-, 3- and 4-fold symmetry axes on human ferritin renaturation.

Ferritin is a protein of 24 subunits which assemble into a shell with 432 point symmetry. It can be denatured reversibly in acidic guanidine hydrochloride, with the formation of poorly populated renaturation intermediates. In order to increase the accumulation of intermediates and to study the mechanism of ferritin renaturation, we analysed variants of the human ferritin H-chain altered at the N-terminus (delta(1-13)), near the 4-fold axis (Leu-169 --> Arg), the 3-fold axis (Asp-131 --> Ile + Glu-134 --> Phe) or the 2-fold axis (Ile-85 --> Cys). We also carried out specific chemical modifications of Cys-130 (near the 3-fold axis) and Cys-85 (near the 2-fold axis). Renaturation of the modified ferritins yielded assembly intermediates that differed in size and physical properties. Alterations of residues around the 2-, 4- and 3-fold axes produced subunit monomers, dimers and higher oligomers respectively. All these intermediates could be induced to assemble into ferritin 24-mers by concentrating them or by co-renaturing them with wild-type H-ferritin. The results support the hypothesis that the symmetric subunit dimers are the building blocks of ferritin assembly, and are consistent with a reassembly pathway involving the coalescence of dimers, probably around the 4-fold axis, followed by stepwise addition of dimers until the 24-mer cage is completed. In addition they show that assembly interactions are responsible for the large hysteresis of folding and unfolding plots. The implications of the studies for in vivo heteropolymer formation in vertebrates, which have two types of ferritin chain (H and L), are discussed.

Characterization of a saporin isoform with lower ribosome-inhibiting activity.

We have expressed in Escherichia coli five isoforms of saporin, a single-chain ribosome-inactivating protein (RIP). Translation inhibition activities of the purified recombinant polypeptides in vitro were compared with those of recombinant dianthin 30, a less potent and closely related RIP, and of ricin A chain. Dianthin 30, and a saporin isoform encoded by a cDNA from leaf tissue (SAP-C), both had about one order of magnitude lower activity in translation inhibition assays than all other isoforms of saporin tested. We recently demonstrated that saporin extracted from seeds of Saponaria officinalis binds to alpha2-macroglobulin receptor (alpha2MR; also termed low density lipoprotein-receptor-related-protein), indicating a general mechanism of interaction of plant RIPs with the alpha2MR system [Cavallaro, Nykjaer, Nielsen and Soria (1995) Eur. J. Biochem. 232, 165-171]. Here we report that SAP-C bound to alpha2MR equally well as native saporin. However, the same isoform had about ten times lower cytotoxicity than the other saporin isoforms towards different cell lines. This indicates that the lower cell-killing ability of the SAP-C isoform is presumably due to its altered interaction with the protein synthesis machinery of target cells. Since saporin binding to the alpha2MR is competed by heparin, we also tested in cell-killing experiments Chinese hamster ovary cell lines defective for expression of either heparan sulphates or proteoglycans. No differences were observed in cytotoxicity using native saporin or the recombinant isoforms. Therefore saporin binding to the cell surface should not be mediated by interaction with proteoglycans, as is the case for other alpha2MR ligands.

Interleukin-4 rapidly down-modulates the macrophage colony-stimulating factor receptor in murine macrophages.

The activation of macrophages interferes with their response to macrophage colony-stimulating factor (M-CSF), the main growth and differentiation factor for mononuclear phagocytes. We tested the rapid effects of interleukin-4 (IL-4), the alternative macrophage activator produced by Th2 helper lymphocytes, on the receptor for M-CSF (M-CSFR) expressed on the cell surface of murine macrophages. IL4 rapidly down-modulated M-CSFR in a dose-dependent fashion. This effect was unique to IL-4 among a number of Th2-produced cytokines, none of which, with the exception of IL4 itself, is able to activate macrophages. The down-modulation of M-CSFR by IL4 was partially prevented by the inhibition of the activity of phospholipase C or protein kinase C. The data are consistent with the hypothesis that the down-modulation of M-CSFR is a property common to, and exclusive of, macrophage activators, and is driven by different activators via a common mechanism.