Hematopoiesis is coordinated by a complex regulatory network of transcription factors and among them PU.1 (Spi1, Sfpi1) represents a key molecule. This review summarizes the indispensable requirement of PU.1 during hematopoietic cell fate decisions and how the function of PU.1 can be modulated by protein-protein interactions with additional factors. The mutual negative regulation between PU.1 and GATA-1 is detailed within the context of normal and leukemogenic hematopoiesis and the concept of 'differentiation therapy' to restore normal cellular differentiation of leukemic cells is discussed.

BackgroundMicroRNAs (miRs) represent a distinct class of posttranscriptional modulators of gene expression with remarkable stability in sera. Several miRs are oncogenic (oncomiRs) and are deregulated in the pathogenesis of breast cancer and function to inhibit tumor suppressors. Routine blood monitoring of these circulating tumor-derived products could be of significant benefit to the diagnosis and relapse detection of early-stage breast cancer (EBC) patients.MethodsAim of this project was to determine expression of miR-155, miR-19a, miR-181b, miR-24, relative to let-7a in sera of 63 patients with EBC and 21 healthy controls. Longitudinal multivariate data analysis was performed to stochastically model the serum levels of each of the oncomiRs during disease phases: from diagnosis, after surgery, and following chemo/radiotherapy. Moreover, this analysis was utilized to evaluate oncomiR levels in EBC patients subgrouped using current clinical prognostic factors including HER2, Ki-67, and grade III.ResultsEBC patients significantly over-express the oncomiRs at the time of diagnosis. Following surgical resection the serum levels of miR-155, miR-181b, and miR-24 significantly decreased (p = 1.89e-05, 5.41e-06, and 0.00638, respectively) whereas the miR-19a decreased significantly after the therapy (p = 0.00869). Furthermore, in case of high-risk patients serum levels of miR-155, miR-19a, miR-181b, and miR-24 are significantly more abundant in comparison to low-risk group (p = 0.026, 0.02567, 0.0250, and 0.00990) and show a decreasing trend upon therapy.ConclusionsOncomiRs are significantly more abundant in the sera of EBC patients compared to controls at diagnosis. Differences in oncomiR levels reflecting EBC risk were also observed. Testing the oncomiRs may be useful for diagnostic purpose and possibly also for relapse detection in follow-up studies of EBC.

BackgroundMicroRNAs are important regulators of transcription in hematopoiesis. Their expression deregulations were described in association with pathogenesis of some hematological malignancies. This study provides integrated microRNA expression profiling at different phases of chronic myeloid leukemia (CML) with the aim to identify microRNAs associated with CML pathogenesis. The functions of in silico filtered targets are in this report annotated and discussed in relation to CML pathogenesis.ResultsUsing microarrays we identified differential expression profiles of 49 miRNAs in CML patients at diagnosis, in hematological relapse, therapy failure, blast crisis and major molecular response. The expression deregulation of miR-150, miR-20a, miR-17, miR-19a, miR-103, miR-144, miR-155, miR-181a, miR-221 and miR-222 in CML was confirmed by real-time quantitative PCR. In silico analyses identified targeted genes of these miRNAs encoding proteins that are involved in cell cycle and growth regulation as well as several key signaling pathways such as of mitogen activated kinase-like protein (MAPK), epidermal growth factor receptor (EGFR, ERBB), transforming growth factor beta (TGFB1) and tumor protein p53 that are all related to CML. Decreased levels of miR-150 were detected in patients at diagnosis, in blast crisis and 67% of hematological relapses and showed significant negative correlation with miR-150 proved target MYB and with BCR-ABL transcript level.ConclusionsThis study uncovers microRNAs that are potentially involved in CML and the annotated functions of in silico filtered targets of selected miRNAs outline mechanisms whereby microRNAs may be involved in CML pathogenesis.

IntroductionTranscriptional regulation of major hematopoietic oncogenes and tumor suppressor genes represents a critical step in tumor formation, tumor aggressiveness, and therapy resistance. [1][2][3] In addition, a posttranscriptional inhibitory mechanism involving microRNA (miRNA) binding to the 3Ј-untranslated region of target mRNAs causes transcript degradation or interferes with the translation initiation and has been linked to tumorigenesis. 4,5 Under physiologic conditions, miRNAs regulate developmental processes and cell fate decisions, and tight regulation of their levels represents an important factor in cell and tissue homeostasis. 6 MiR-155, a well-studied miRNA, regulates hematopoietic cell development as documented by murine gene targeting experiments and also by other studies describing its function during immune B-and T-cell response, in production of cytokines and antibodies and in antigen presentation. 7,8 Next, transgenic miR-155 overexpression in the mouse stimulates B-cell proliferation and frequent development of lymphomas. 9 In humans, miR-155 up-regulation has been repeatedly reported in chronic B-cell lymphocytic leukemia (B-CLL), in its solid indolent form of a small lymphocytic lymphoma [10][11][12] and also in aggressive types, including non-Hodgkin 10,13,14 and Hodgkin lymphomas. 13,15 Deregulation of several microRNAs was repeatedly described in B-CLL. 16,17 B-CLL, the most common adult leukemia, is characterized by clonal accumulation of B celllike mature-appearing elements (Ͼ 5000/L) 18 typically coexpressing the CD5, CD19, CD20, and CD23 surface markers. B-CLL represents a heterogeneous disease, the outcome of which may be predicted by the levels of surface protein CD38, intracellular tyrosine kinase ZAP70, or by a status of IgV H somatic hypermutation. 18,19 Cytogenetic alterations of 2 loci that contain the p53 gene (deletion of 17p) and the ATM gene (deletion of 11q) are associated with poor prognosis, shorter duration of remission, and shortest overall survival, 20 whereas normal karyotype or trisomy 12 is considered intermediate risk and the 13q14 deletion is considered a favorable mark. Subsets of B-CLL patients may progress to non-Hodgkin diffuse large B-cell lymphoma by a mechanism that remains largely unknown. Taken together, miR-155 appears to play a central role in B-cell function, and its up-regulation in lymphoproliferative disorders, including B-CLL, may lead to a block of differentiation and accumulation of lymphoid-like cells.Recent studies brought evidence of a context-dependent transcriptional regulation of the MIR155HG. First, oncogenic properties of miR-155 have been demonstrated in breast cancer cells where MIR155HG is up-regulated by transforming growth factor-␤/ Smad pathway involving a Smad response element at the position Ϫ454 nt from the transcription start site (TSS). 21 This regulatory pathway becomes disabled on inhibition of miR-155, resulting in derepression of miR-155 targets (including the RhoA protein) and in decreased cell migration and invasio...

Follicular lymphoma (FL) is a common indolent B-cell malignancy with a variable clinical course. An unfavorable event in its course is histological transformation to a high-grade lymphoma, typically diffuse large B-cell lymphoma. Recent studies show that genetic aberrations of MYC or its overexpression are associated with FL transformation (tFL). However, the precise molecular mechanisms underlying tFL are unclear. Here we performed the first profiling of expression of microRNAs (miRNAs) in paired samples of FL and tFL and identified 5 miRNAs as being differentially expressed. We focused on one of these miRNAs, namely miR-150, which was uniformly downmodulated in all examined tFLs (∼3.5-fold), and observed that high levels of MYC are responsible for repressing miR-150 in tFL by binding in its upstream region. This MYC-mediated repression of miR-150 in B cells is not dependent on LIN28A/B proteins, which influence the maturation of miR-150 precursor (pri-miR-150) in myeloid cells. We also demonstrated that low miR-150 levels in tFL lead to upregulation of its target, namely FOXP1 protein, which is a known positive regulator of cell survival, as well as B-cell receptor and NF-κB signaling in malignant B cells. We revealed that low levels of miR-150 and high levels of its target, FOXP1, are associated with shorter overall survival in FL and suggest that miR-150 could serve as a good biomarker measurable in formalin-fixed paraffin-embedded tissue. Overall, our study demonstrates the role of the MYC/miR-150/FOXP1 axis in malignant B cells as a determinant of FL aggressiveness and its high-grade transformation.