miR-15a-5p and miR-21-5p contribute to chemoresistance in cytogenetically normal acute myeloid leukaemia by targeting PDCD4, ARL2 and BTG2

Cytarabine and daunorubicin are old drugs commonly used in the treatment of acute myeloid leukaemia (AML). Refractory or relapsed disease because of chemotherapy resistance is a major issue. microRNAs (miRNAs) were incriminated in resistance. This study aimed to identify miRNAs involved in chemoresistance in AML patients and to define their target genes. We focused on cytogenetically normal AML patients with wild-type NPM1 without FLT3-ITD as the treatment of this subset of patients with intermediate-risk cytogenetics is not well established. We analysed baseline AML samples by small RNA sequencing and compared the profile of chemoresistant to chemosensitive AML patients. Among the miRNAs significantly overexpressed in chemoresistant patients, we revealed miR-15a-5p and miR-21-5p as miRNAs with a major role in chemoresistance in AML. We showed that miR-15a-5p and miR-21-5p overexpression decreased apoptosis induced by cytarabine and/or daunorubicin. PDCD4, ARL2 and BTG2 genes were found to be targeted by miR-15a-5p, as well as PDCD4 and BTG2 by miR-21-5p. Inhibition experiments of the three target genes reproduced the functional effect of both miRNAs on chemosensitivity. Our study demonstrates that miR-15a-5p and miR-21-5p are overexpressed in a subgroup of chemoresistant AML patients. Both miRNAs induce chemoresistance by targeting three pro-apoptotic genes PDCD4, ARL2 and BTG2

Regulation of HBP1 via the AKT/FOXO pathway and impact on cell proliferation

Phosphatidylinositol-3-kinase (PI3K) and AKT control key signal transduction pathways that are activated by growth factor receptors, leading to cell proliferation, survival and growth. In this thesis, we identified a novel target of these pathways, the HMG-box protein 1 (HBP1), a ubiquitous transcriptional regulator that promotes cell cycle arrest and premature senescence. In line with its functional roles, HBP1 has been proposed to act as a tumor suppressor. In our first study, we showed that activation of the PI3K/AKT pathway by growth factors repressed HBP1 expression at the transcriptional level by inhibiting forkhead-box O (FOXO) binding to the HBP1 gene promoter. This regulation was observed in human fibroblasts as well as in cancer cell lines. In addition, we noticed that HBP1 and FOXO1 expression were both down-regulated in breast cancer samples compared to normal samples. In our second study, we identified HBP1 as a novel substrate of AKT. We found that AKT phosphorylated HBP1 at three conserved sites: Ser380, Thr484 and Ser509. HBP1 phosphorylation was induced by growth factors that activate the PI3K/AKT pathway and was blocked by AKT inhibition or knock-down. In addition, we observed that HBP1 transcriptional activity was modified by mutating its phosphorylation sites. HBP1 phosphorylation by AKT reduced its transcriptional activity. Using small-hairpin RNA (shRNA), we found that HBP1 knock-down increased human glioblastoma cell proliferation. Conversely, HBP1 overexpression reduced glioma cell growth and transformation. Finally, we showed that the effect of HBP1 on glioma cell growth was altered by its phosphorylation, indicating that HBP1 might be down-regulated by the PI3K/AKT pathway in gliomas. To conclude, our results showed that the PI3K/AKT pathway regulates HBP1 downstream of growth factors by two parallel mechanisms, at the post-translational and transcriptional levels, preventing its inhibitory effect on cell proliferation.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201

The HMG box transcription factor HBP1: a cell cycle inhibitor at the crossroads of cancer signaling pathways

HMG box protein 1 (HBP1) is a transcription factor and a potent cell cycle inhibitor in normal and cancer cells. HBP1 activates or represses the expression of different cell cycle genes (such as CDKN2A, CDKN1A, and CCND1) through direct DNA binding, cofactor recruitment, chromatin remodeling, or neutralization of other transcription factors. Among these are LEF1, TCF4, and MYC in the WNT/beta-catenin pathway. HBP1 also contributes to oncogenic RAS-induced senescence and terminal cell differentiation. Collectively, these activities suggest a tumor suppressor function. However, HBP1 is not listed among frequently mutated cancer driver genes. Nevertheless, HBP1 expression is lower in several tumor types relative to matched normal tissues. Several micro-RNAs, such as miR-155, miR-17-92, and miR-29a, dampen HBP1 expression in cancer cells of various origins. The phosphatidylinositol-3 kinase (PI3K)/AKT pathway also inhibits HBP1 transcription by preventing FOXO binding to the HBP1 promoter. In addition, AKT directly phosphorylates HBP1, thereby inhibiting its transcriptional activity. Taken together, these findings place HBP1 at the center of a network of micro-RNAs and oncoproteins that control cell proliferation. In this review, we discuss our current understanding of HBP1 function in human physiology and diseases

FOXO1 forkhead domain mutants in B-cell lymphoma lack transcriptional activity.

Somatic point mutations of the FOXO1 transcription factor were reported in non-Hodgkin lymphoma including diffuse large B-cell lymphoma, follicular lymphoma and Burkitt lymphoma. These alterations were associated with a poor prognosis and resistance to therapy. Nearly all amino acid substitutions are localized in two major clusters, affecting either the N-terminal region (Nt mutations) or the forkhead DNA-binding domain (DBD mutations). While recent studies have focused on Nt mutations, we characterized FOXO1 DBD mutants. We analyzed their transcriptional activity, DNA binding, phosphorylation and protein-protein interaction. The majority of DBD mutants showed a decrease in activity and DNA binding, while preserving AKT phosphorylation and interaction with the cytoplasmic ATG7 protein. In addition, we investigated the importance of conserved residues of the α-helix 3 of the DBD. Amino acids I213, R214, H215 and L217 appeared to be crucial for FOXO1 activity. Our data underlined the key role of multiple amino-acid residues of the forkhead domain in FOXO1 transcriptional activity and revealed a new type of FOXO1 loss-of-function mutations in B-cell lymphoma

MiR-15a-5p Confers Chemoresistance in Acute Myeloid Leukemia by Inhibiting Autophagy Induced by Daunorubicin.

Anthracyclines remain a cornerstone of induction chemotherapy for acute myeloid leukemia (AML). Refractory or relapsed disease due to chemotherapy resistance is a major obstacle in AML management. MicroRNAs (miRNAs) have been observed to be involved in chemoresistance. We previously observed that was overexpressed in a subgroup of chemoresistant cytogenetically normal AML patients compared with chemosensitive patients treated with daunorubicin and cytarabine. overexpression in AML cells reduced apoptosis induced by both drugs in vitro. This study aimed to elucidate the mechanisms by which contributes to daunorubicin resistance. We showed that daunorubicin induced autophagy in myeloid cell lines. The inhibition of autophagy reduced cell sensitivity to daunorubicin. The overexpression of decreased daunorubicin-induced autophagy. Conversely, the downregulation of increased daunorubicin-induced autophagy. We found that targeted four genes involved in autophagy, namely and . Daunorubicin increased the expression of these four genes, and counteracted this regulation. Inhibition experiments with the four target genes showed the functional effect of on autophagy. In summary, our results indicated that induces chemoresistance in AML cells through the abrogation of daunorubicin-induced autophagy, suggesting that could be a promising therapeutic target for chemoresistant AML patients

HBP1 is a new target of FOXO down-regulated by growth factor signaling

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HBP1: a new regulator of cell proliferation downstream of AKT and FOXO

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HBP1 phosphorylation by AKT regulates its transcriptional activity and glioblastoma cell proliferation.

The HMG-box protein 1 (HBP1) is a transcriptional regulator and a potential tumor suppressor that controls cell proliferation, differentiation and oncogene-mediated senescence. In a previous study, we showed that AKT activation through the PI3K/AKT/FOXO pathway represses HBP1 expression at the transcriptional level in human fibroblasts as well as in cancer cell lines. In the present study, we investigated whether AKT could also regulate HBP1 directly. First, AKT1 phosphorylated recombinant human HBP1 in vitro on three conserved sites, Ser380, Thr484 and Ser509. In living cells, we confirmed the phosphorylation of HBP1 on residues 380 and 509 using phospho-specific antibodies. HBP1 phosphorylation was induced by growth factors, such as EGF or IGF-1, which activated AKT. Conversely, it was blocked by treatment of cells with an AKT inhibitor (MK-2206) or by AKT knockdown. Next, we observed that HBP1 transcriptional activity was strongly modified by mutating its phosphorylation sites. The regulation of target genes such as DNMT1, P47phox, p16INK4A and cyclin D1 was also affected. HBP1 had previously been shown to limit glioma cell growth. Accordingly, HBP1 silencing by small-hairpin RNA increased human glioblastoma cell proliferation. Conversely, HBP1 overexpression decreased cell growth and foci formation. This effect was amplified by mutations that prevented phosphorylation by AKT, and blunted by mutations that mimicked phosphorylation. In conclusion, our results suggest that HBP1 phosphorylation by AKT blocks its functions as transcriptional regulator and tumor suppressor

HBP1 is a new FOXO target down-regulated by growth factor signaling

info:eu-repo/semantics/nonPublishe

HBP1 is a new target of FOXO down-regulated by growth factor signaling

info:eu-repo/semantics/nonPublishe