Microcin E492 is a polypeptide antibiotic that is produced and excreted by Klebsiella pneumoniae RYC492. The genetic determinants for microcin synthesis and immunity were cloned in Escherichia coli VCS257 into the cosmid vector pHC79, starting from total DNA of K. pneumoniae RYC492. The microcin E492 expressed in E. coli had the same properties as that of K. pneumoniae, i.e., the same molecular weight, the ability to form ionic channels in planar phospholipid bilayers, and essentially identical biological properties. Microcin E492 expression in E. coli, like that in K. pneumoniae, was mainly in the exponential phase of growth, declining in the stationary phase. The immunity determinant was subcloned into the same vector, and its expression was found to disappear in the stationary phase. This phenomenon is not dependent on rpoS, the stationary-phase sigma factor.Microcins are a family of low-molecular-weight antibiotics produced by members of the family Enterobacteriaceae. Microcins, unlike colicins, are not induced by DNA-damaging agents, but like for colicins, bacterial strains producing a specific microcin are immune to the same microcin (3).Microcin E492 is a polypeptide with an M r of 6,000 (14) that is produced by Klebsiella pneumoniae RYC492 and is active on strains of Escherichia coli, Klebsiella, Salmonella, Citrobacter, Enterobacter, and Erwinia (6). The mechanism of action is through membrane depolarization (9) induced by the formation of pores in the bacterial membrane (14). Studies on channel-forming bacteriocins produced by gram-negative bacteria have been reported only for colicins, all of them of high molecular weight (reviewed in reference 5). The other described bacteriocin which has the cytoplasmic membrane as target is colicin V. This bacteriocin has been reclassified as a microcin because it has a molecular weight of 6,000 and does not have most of the properties which are associated with colicins (10). Despite the fact that microcin E492 has many feature in common with colicin V, they are not closely related, because ColV ϩ strains that have high-level immunity to colicin V are fully susceptible to microcin E492 (9). Those colicins which act by depolarizing the bacterial energy-transducing membrane in vivo are able to form aqueous channels in both closed liposomes and planar membranes. However, despite the fact that colicin V inhibits the capacity of E. coli to carry out active transport of proline and to generate a membrane potential (26), it has not been possible to find an effect of colicin V on asolectin liposomes, and it remains to be established whether this difference reflects a difference in the in vivo mode of action. Thus, so far the only microcin described to be a channel-forming bacteriocin is microcin E492 (14). Nevertheless, low-molecular-weight pore-forming bacteriocins of gram-positive bacteria have been described, among them the lantibiotic nisin and lactococcins A and B, which are nonlantibiotic heatstable bacteriocins (reviewed in references 1, 13, and 24). The former has...

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BackgroundKaiso protein has been identified as a new member of the POZ-ZF subfamily of transcription factors that are involved in development and cancer. There is consistent evidence of the role of Kaiso and its involvement in human tumorigenesis but there is no evidence about its role in hematopoietic differentiation or establishment of chronic myeloid leukemia (CML). We used, normal K562 cell line, established from a CML patient in blast crisis, and imatinib-resistant K562 cell line, to investigate the specific distribution of Kaiso and their contribution to the cell differentiation status of the blast crisis of CML (CML-BP).ResultsWe found cytoplasmic expression of Kaiso, in K562 cells and patients, confirmed by immunofluorescence, immunohistochemistry and western blot of cytoplasmic protein fraction. Kaiso was weakly expressed in the imatinib-resistant K562 cell line confirmed by immunofluorescence and western blot. The cytoplasmic expression of Kaiso was not modified when the K562 cells were treated for 16 h with imatinib 0.1 and 1 μM. In our study, small interfering RNA (siRNA) was introduced to down regulate the expression of Kaiso and p120ctn in K562 cell line. Kaiso and p120ctn were down regulated individually (siRNA-Kaiso or siRNA-p120ctn) or in combination using a simultaneous co-transfection (siRNA-Kaiso/p120ctn). We next investigated whether knockdown either Kaiso or p120ctn alone or in combination affects the cell differentiation status in K562 cells. After down regulation we analyzed the expression of hematopoietic cell differentiation and proliferation genes: SCF, PU-1, c-MyB, C/EBPα, Gata-2 and maturation markers of hematopoietic cells expressed in the plasma membrane: CD15, CD11b, CD33, CD117. The levels of SCF and c-MyB were increased by 1000% and 65% respectively and PU-1, Gata-2 and C/EBPα were decreased by 66%, 50% and 80% respectively, when Kaiso levels were down regulated by siRNA. The results were similar when both Kaiso and p120ctn were down regulated by siRNA. The increased expression of SCF and decreased expression of GATA-2 could be responsible by the higher cell viability detected in K562 cells double knock-down of both Kaiso and p120ctn. Finally, we studied the effect of knock-down either Kaiso or p120ctn, alone or in combination on CD15, CD11b, CD33 and Cd117 expression. Using siRNA approach a reduction of 35%, 8% and 13% in CD15, CD33 and CD117 levels respectively, were achieved in all transfections, when compared to scrambled knock-down cells.ConclusionThese results suggest that both Kaiso and p120ctn, contributes to maintaining the differentiated state of the K562 cells and similar to other cancers, cytoplasmic localization of Kaiso is related to a poor prognosis in CML-BP. By the broad and profound effects on the expression of genes and markers of hematopoietic differentiation produced by Kaiso knock-down, these findings reveal Kaiso as a potential target for selective therapy of CML.

Polycomb proteins form multiprotein complexes that repress target genes by chromatin remodeling. In this work, we report that the SUZ12 polycomb gene is over-expressed in bone marrow samples of patients at the blastic phase of chronic myeloid leukemia. We also found a direct interaction between polycomb group genes and the WNT signaling pathway in chronic myeloid leukemia transformation. Electrophoretic mobility shift assay (EMSA), Chromatin immunoprecipitation assay (ChIP), and mass spectrometry assays identified noncanonical WNT pathway members, such as WNT5A and WNT11, bound to the SUZ12 promoter. Immunohistochemistry and immunofluorescence with WNT5A and WNT11 antibodies confirmed nuclear localization. Knockdown of WNTs 1, 5A, and 11 with RNAi approaches showed that WNT members are capable of activating SUZ12 transcription with varying promoter affinities. Finally, we suggest that SUZ12 is blocking cellular differentiation, as SUZ12 knockdown release differentiation programs in chronic myeloid blastic phase (CML-BP) transformed cell line.