Activation of SHP2 Protein-tyrosine Phosphatase Increases HoxA10-induced Repression of the Genes Encoding gp91PHOX and p67PHOX

SHP-2 and PD-1-SHP-2 signaling regulate myeloid cell differentiation and antitumor responses

The inhibitory receptor PD-1 suppresses T cell activation by recruiting the phosphatase SHP-2. However, mice with a T-cell-specific deletion of SHP-2 do not have improved antitumor immunity. Here we showed that mice with conditional targeting of SHP-2 in myeloid cells, but not in T cells, had diminished tumor growth. RNA sequencing (RNA-seq) followed by gene set enrichment analysis indicated the presence of polymorphonuclear myeloid-derived suppressor cells and tumor-associated macrophages (TAMs) with enriched gene expression profiles of enhanced differentiation, activation and expression of immunostimulatory molecules. In mice with conditional targeting of PD-1 in myeloid cells, which also displayed diminished tumor growth, TAMs had gene expression profiles enriched for myeloid differentiation, activation and leukocyte-mediated immunity displaying >50% overlap with enriched profiles of SHP-2-deficient TAMs. In bone marrow, GM-CSF induced the phosphorylation of PD-1 and recruitment of PD-1-SHP-2 to the GM-CSF receptor. Deletion of SHP-2 or PD-1 enhanced GM-CSF-mediated phosphorylation of the transcription factors HOXA10 and IRF8, which regulate myeloid differentiation and monocytic-moDC lineage commitment, respectively. Thus, SHP-2 and PD-1-SHP-2 signaling restrained myelocyte differentiation resulting in a myeloid landscape that suppressed antitumor immunity.

MEKK4-mediated Phosphorylation of HOXA10 at Threonine 362 facilitates embryo adhesion to the endometrial epithelium

Embryo adhesion is a very important step in the embryo implantation process. Homeobox A10 (HOXA10), a key transcriptional factor of endometrial receptivity, is indispensable for embryo adhesion. However, how to control the activation status of HOXA10 remains elusive. Here, we found that Mitogen-activated protein kinase kinase kinase 4 (MEKK4) was associated with HOXA10 and directly phosphorylated HOXA10 at threonine 362. This MEKK4-mediated phosphorylation enhanced HOXA10-mediated transcriptional responses and adhesion between the embryo and endometrial epithelium. Specific deletion or kinase inactivation of MEKK4 in endometrial epithelial cells attenuates adhesion between embryo and epithelium. Therefore, the identification of MEKK4 as a novel physiological positive regulator of HOXA10 activation provides mechanistic insights to improve embryo implantation success. Moreover, when Thr362 was mutated to alanine (T362A) to mimic its dephosphorylation, the protein stability and transcriptional regulation of HOXA10 were decreased. In addition, HOXA10 -promoted embryo adhesion was weakened after the mutation of Thr362, suggesting that the phosphorylation of HOXA10 at this site may be a new indicator for evaluating endometrial receptivity and judging the ‘implantation window’.

SHP-2 Interacts with CD81 and Regulates the Malignant Evolution of Colorectal Cancer by Inhibiting Epithelial-Mesenchymal Transition

PURPOSE

Colon cancer is a common malignant tumor of the digestive system. This project verified the negative role of protein tyrosine phosphatase (SHP-2) in the regulation of colon cancer and further clarified the key targets and molecular mechanisms in the regulation process.

PATIENTS AND METHODS

The expression levels of SHP-2 in colon cancer tissues, adjacent tissues, normal colon cell lines, and cancer cell lines were detected via Quantitative Real-time PCR (qRT-PCR). The effect of SHP-2 on colon cancer cell function was verified using cell proliferation, Transwell, scratch, and apoptotic assays. CD81 was identified as the interaction protein of SHP-2 by immunoprecipitation.

RESULTS

The expression of SHP-2 was decreased in colorectal cancer compared with that in adjacent tissues. This expression was also decreased in colon cancer cells compared with that in intestinal epithelial cells. In addition, the tumor tissues of patients with metastatic colon cancer exhibited downregulated expression of SHP-2 compared with those of patients with non-metastatic colon cancer. Cell proliferation, Transwell, scratch, and apoptotic assay showed that the overexpression of SHP-2 inhibited proliferation, adhesion, and metastasis of colon cancer cell lines and promoted apoptosis. CO-IP proved that SHP-2 could interact with CD81 and inhibit the function of CD81. Recovery experiments confirmed that the overexpression of CD81 reversed the anti-cancer effect of SHP-2.

CONCLUSION

Overexpression of SHP-2 inhibited malignant progression of colon cancer. Mechanism experiments showed that the anti-cancer effect of SHP-2 was realized through the interaction with CD81. This study elucidated the molecular mechanism of SHP-2 regulation in colon cancer and provided guidance for the diagnosis and prognosis assessment of colon cancer.

The O-GlcNAc transferase OGT interacts with and post-translationally modifies the transcription factor HOXA1

HOXA1 belongs to the HOX family of transcription factors which are key regulators of animal development. Little is known about the molecular pathways controlling HOXA1. Recent data from our group revealed distinct partner proteins interacting with HOXA1. Among them, OGT is an O-linked N-acetylglucosamine (O-GlcNAc) transferase modifying a variety of proteins involved in different cellular processes including transcription. Here, we confirm OGT as a HOXA1 interactor, we characterise which domains of HOXA1 and OGT are required for the interaction, and we provide evidence that OGT post-translationally modifies HOXA1. Mass spectrometry experiments indeed reveal that HOXA1 can be phosphorylated on the AGGTVGSPQYIHHSY peptide and that upon OGT expression, the phosphate adduct is replaced by an O-GlcNAc group.

The E3 ubiquitin ligase Triad1 influences development of Mll-Ell-induced acute myeloid leukemia

Chromosomal translocations involving the MLL1 gene characterize a poor prognosis subset of acute myeloid leukemia (AML), referred to as 11q23-AML. Transcription of the HOXA9 and HOXA10 genes is enhanced in hematopoietic stem and progenitor cells in these leukemias. We previously found the ARIH2 gene was repressed by HoxA9 in myeloid progenitors, but activated by HoxA10 during granulopoiesis. ARIH2 encodes the Triad1 protein, an anti-proliferative E3 ubiquitin ligase. In the current study, we investigate the role of Triad1 in leukemogenesis induced by an MLL1 fusion protein (Mll-Ell). We found Mll-Ell increased expression of HoxA9, HoxA10, and Triad1 because HoxA9 represses only one of two ARIH2 cis elements that are activated by HoxA10. Although Triad1 antagonized the generally pro-proliferative effects of the Mll-Ell oncoprotein, we found blocking HoxA9 and HoxA10 phosphorylation shifted the balance to ARIH2 repression in Mll-Ell⁺ cells. We investigated the significance of these in vitro results in a murine bone marrow transplant model. We found Triad1 knockdown significantly shortened the latency to development of AML in mice transplanted with Mll-Ell-transduced bone marrow. And, Triad1 expression fell during the prolonged AML latency period in mice transplanted with bone marrow expressing Mll-Ell alone. Our studies identify Triad1 as a leukemia suppressor in 11q23-AML. This suggests defining relevant Triad1 substrates may indicate novel therapeutic targets in this disease.

Cooperation between AlphavBeta3 integrin and the fibroblast growth factor receptor enhances proliferation of Hox-overexpressing acute myeloid leukemia cells

A poor prognosis subtype of acute myeloid leukemia (AML) is characterized by increased expression of a set of homeodomain (HD) transcription factors, including HoxA9, HoxA10 and Cdx4. This encompasses AML with MLL1 gene translocations, because Mll1-fusion proteins aberrantly activate HOX transcription. We previously identified FGF2 (Fibroblast Growth Factor 2) as a target gene for HoxA9 and HoxA10 that was indirectly activated by Mll-Ell (an Mll1-fusion protein). Autocrine stimulation of Mll-Ell⁺ myeloid progenitor cells by Fgf2 stabilized βcatenin and increased expression of βcatenin target genes, including CDX4. Since HOXA9 and HOXA10 are Cdx4 target genes, Fgf2 indirectly augmented direct effects of Mll-Ell on these genes. ITGB3, encoding β3 integrin, is another HoxA10 target gene. In the current studies, we found activation of ITGB3 transcription in Mll-Ell⁺ myeloid progenitor cells via HoxA9 and HoxA10. Increased expression of αvβ3 integrin increased Syk-activation; contributing to cytokine hypersensitivity. However, inhibiting Fgf-R partly reversed αvβ3 activity in Mll-Ell⁺ progenitor cells by decreasing ITGB3 promoter activity in a βcatenin- and Cdx4-dependent manner. Inhibitors of Fgf-R or Syk impaired proliferation of CD34⁺ bone marrow cells from AML subjects with increased Hox-expression; with a greater combined effect. These studies identified a rational therapeutic approach to this AML subtype.

Long non-coding RNAs in the regulation of myeloid cells

Long non-coding RNAs (lncRNAs) have been attracting immense research interests. The relevance of lncRNAs in biological and physiological as well as in pathological processes has increased along with the understanding of their various regulatory mechanisms. Abundant studies have indicated that lncRNAs are involved in the differentiation, proliferation, activation, and initiation of apoptosis in different cell types. However, most studies about the regulating biology of lncRNAs are currently focused on cancer cells. This review is focused on the widely unexplored role of lncRNAs in the cell fate of myeloid cells. In this review, we summarize recent studies that have confirmed lncRNAs to be essential in the development of myeloid cells under normal and pathological conditions.

Regulation of CYBB Gene Expression in Human Phagocytes by a Distant Upstream NF-κB Binding Site

The human CYBB gene encodes the gp91-phox component of the phagocyte oxidase enzyme complex, which is responsible for generating superoxide and other downstream reactive oxygen species essential to microbial killing. In the present study, we have identified by sequence analysis a putative NF-κB binding site in a DNase I hypersensitive site, termed HS-II, located in the distant 5' flanking region of the CYBB gene. Electrophoretic mobility assays showed binding of the sequence element by recombinant NF-κB protein p50 and by proteins in nuclear extract from the HL-60 myeloid leukemia cell line corresponding to p50 and to p50/p65 heterodimers. Chromatin immunoprecipitation demonstrated NF-κB binding to the site in intact HL-60 cells. Chromosome conformation capture (3C) assays demonstrated physical interaction between the NF-κB binding site and the CYBB promoter region. Inhibition of NF-κB activity by salicylate reduced CYBB expression in peripheral blood neutrophils and differentiated U937 monocytic leukemia cells. U937 cells transfected with a mutant inhibitor of κB "super-repressor" showed markedly diminished CYBB expression. Luciferase reporter analysis of the NF-κB site linked to the CYBB 5' flanking promoter region revealed enhanced expression, augmented by treatment with interferon-γ. These studies indicate a role for this distant, 15 kb upstream, binding site in NF-κB regulation of the CYBB gene, an essential component of phagocyte-mediated host defense.

Mechanisms of Specificity for Hox Factor Activity

Metazoans encode clusters of paralogous Hox genes that are critical for proper development of the body plan. However, there are a number of unresolved issues regarding how paralogous Hox factors achieve specificity to control distinct cell fates. First, how do Hox paralogs, which have very similar DNA binding preferences in vitro, drive different transcriptional programs in vivo? Second, the number of potential Hox binding sites within the genome is vast compared to the number of sites bound. Hence, what determines where in the genome Hox factors bind? Third, what determines whether a Hox factor will activate or repress a specific target gene? Here, we review the current evidence that is beginning to shed light onto these questions. In particular, we highlight how cooperative interactions with other transcription factors (especially PBC and HMP proteins) and the sequences of cis-regulatory modules provide a basis for the mechanisms of Hox specificity. We conclude by integrating a number of the concepts described throughout the review in a case study of a highly interrogated Drosophila cis-regulatory module named “The Distal-less Conserved Regulatory Element” (DCRE).

Beta Hairpin Peptide Hydrogels as an Injectable Solid Vehicle for Neurotrophic Growth Factor Delivery

There is intense interest in developing novel methods for the sustained delivery of low levels of clinical therapeutics. MAX8 is a peptide-based beta-hairpin hydrogel that has unique shear thinning properties that allow for immediate rehealing after the removal of shear forces, making MAX8 an excellent candidate for injectable drug delivery at a localized injury site. The current studies examined the feasibility of using MAX8 as a delivery system for nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), two neurotrophic growth factors currently used in experimental treatments of spinal cord injuries. Experiments determined that encapsulation of NGF and BDNF within MAX8 did not negatively impact gel formation or rehealing and that shear thinning did not result in immediate growth factor release. ELISA, microscopy, rheology, and Western blotting experiments collectively demonstrate the functional capabilities of the therapeutic-loaded hydrogels to (i) maintain a protective environment against in vitro degradation of encapsulated therapeutics for at least 28 days; and (ii) allow for sustained release of NGF and BDGF capable of initiating neurite-like extensions of PC12 cells, most likely due to NGF/BDGF signaling pathways. Importantly, while the 21 day release profiles could be tuned by adjusting the MAX8 hydrogel concentration, the initial shear thinning of the hydrogel (e.g., during injection) does not induce significant premature loss of the encapsulated therapeutic, most likely due to effective trapping of growth factors within structurally robust domains that are maintained during the application of shear forces. Together, our data suggests that MAX8 allows for greater dosage control and sustained therapeutic growth factor delivery, potentially alleviating side effects and improving the efficacy of current therapies.

KPC2 relocalizes HOXA2 to the cytoplasm and decreases its transcriptional activity

Regulation of transcription factor activity relies on molecular interactions or enzymatic modifications which influence their interaction with DNA cis-regulatory sequences, their transcriptional activation or repression, and stability or intracellular distribution of these proteins. Regarding the well-conserved Hox protein family, a restricted number of activity regulators have been highlighted thus far. In the framework of a proteome-wide screening aiming at identifying proteins interacting with Hoxa2, KPC2, an adapter protein constitutive of the KPC ubiquitin-ligase complex, was identified. In this work, KPC2 was confirmed as being a genuine interactor of Hoxa2 by co-precipitation and bimolecular fluorescence complementation assays. At functional level, KPC2 diminishes the transcriptional activity and induces the nuclear exit of Hoxa2. Gene expression analyses revealed that Kpc2 is active in restricted areas of the developing mouse embryo which overlap with the Hoxa2 expression domain. Together, our data support that KPC2 regulates Hoxa2 by promoting its relocation to the cytoplasm.

HoxA10 Terminates Emergency Granulopoiesis by Increasing Expression of Triad1

Expression of the E3 ubiquitin ligase Triad1 is greater in mature granulocytes than in myeloid progenitor cells. HoxA10 actives transcription of the gene encoding Triad1 (ARIH2) during myeloid differentiation, but the contribution of increased Triad1 expression to granulocyte production or function is unknown. Mice with bone marrow-specific disruption of the ARIH2 gene exhibit constitutive inflammation with tissue infiltration by granulocytes and B cells. In contrast, disruption of the HOXA10 gene in mice neither constitutively activates the innate immune response nor significantly alters steady-state granulopoiesis. This study explores the impact of HoxA10-induced Triad1 expression on emergency (stress) granulopoiesis. We found that mice with HOXA10 gene disruption exhibited an overwhelming and fatal emergency granulopoiesis response that was characterized by tissue infiltration with granulocytes, but reversed by re-expression of Triad1 in the bone marrow. We determined that HoxA9 repressed ARIH2 transcription in myeloid progenitor cells, antagonizing the effect of HoxA10 on Triad1 expression. Also, we found that differentiation-stage-specific ARIH2 transcription was regulated by the tyrosine phosphorylation states of HoxA9 and HoxA10. Our studies demonstrate a previously undescribed role for HoxA10 in terminating emergency granulopoiesis, suggesting an important contribution by Hox proteins to the innate immune response.

Targeting novel signaling pathways for resistant acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematologic malignancy that is the most common type of acute leukemia diagnosed in adults and the second most common type in children. The overall survival is poor and treatment is associated with significant complications and even death. In addition, a significant number of patients will not respond to therapy or relapse. In this review, several new signaling proteins aberrantly regulated in AML are described, including CREB, Triad1, Bcl-2 family members, Stat3, and mTOR/MEK. Identifying more effective and less toxic agents will provide novel approaches to treat AML.

Protein-tyrosine phosphatase Shp2 positively regulates macrophage oxidative burst

Macrophages are vital to innate immunity and express pattern recognition receptors and integrins for the rapid detection of invading pathogens. Stimulation of Dectin-1 and complement receptor 3 (CR3) activates Erk- and Akt-dependent production of reactive oxygen species (ROS). Shp2, a protein-tyrosine phosphatase encoded by Ptpn11, promotes activation of Ras-Erk and PI3K-Akt and is crucial for hematopoietic cell function; however, no studies have examined Shp2 function in particulate-stimulated ROS production. Maximal Dectin-1-stimulated ROS production corresponded kinetically to maximal Shp2 and Erk phosphorylation. Bone marrow-derived macrophages (BMMs) from mice with a conditionally deleted allele of Ptpn11 (Shp2(flox/flox);Mx1Cre+) produced significantly lower ROS levels compared with control BMMs. Although YFP-tagged phosphatase dead Shp2-C463A was strongly recruited to the early phagosome, its expression inhibited Dectin-1- and CR3-stimulated phospho-Erk and ROS levels, placing Shp2 phosphatase function and Erk activation upstream of ROS production. Further, BMMs expressing gain of function Shp2-D61Y or Shp2-E76K and peritoneal exudate macrophages from Shp2D61Y/+;Mx1Cre+ mice produced significantly elevated levels of Dectin-1- and CR3-stimulated ROS, which was reduced by pharmacologic inhibition of Erk. SIRPα (signal regulatory protein α) is a myeloid inhibitory immunoreceptor that requires tyrosine phosphorylation to exert its inhibitory effect. YFP-Shp2C463A-expressing cells have elevated phospho-SIRPα levels and an increased Shp2-SIRPα interaction compared with YFP-WT Shp2-expressing cells. Collectively, these findings indicate that Shp2 phosphatase function positively regulates Dectin-1- and CR3-stimulated ROS production in macrophages by dephosphorylating and thus mitigating the inhibitory function of SIRPα and by promoting Erk activation.

Regulation of CDX4 gene transcription by HoxA9, HoxA10, the Mll-Ell oncogene and Shp2 during leukemogenesis

Cdx and Hox proteins are homeodomain transcription factors that regulate hematopoiesis. Transcription of the HOX and CDX genes decreases during normal myelopoiesis, but is aberrantly sustained in leukemias with translocation or partial tandem duplication of the MLL1 gene. Cdx4 activates transcription of the HOXA9 and HOXA10 genes, and HoxA10 activates CDX4 transcription. The events that break this feedback loop, permitting a decreased Cdx4 expression during normal myelopoiesis, were previously undefined. In the current study, we find that HoxA9 represses CDX4 transcription in differentiating myeloid cells, antagonizing activation by HoxA10. We determine that tyrosine phosphorylation of HoxA10 impairs transcriptional activation of CDX4, but tyrosine phosphorylation of HoxA9 facilitates repression of this gene. As HoxA9 and HoxA10 are phosphorylated during myelopoiesis, this provides a mechanism for differentiation stage-specific Cdx4 expression. HoxA9 and HoxA10 are increased in cells expressing Mll-Ell, a leukemia-associated MLL1 fusion protein. We find that Mll-Ell induces a HoxA10-dependent increase in Cdx4 expression in myeloid progenitor cells. However, Cdx4 decreases in a HoxA9-dependent manner on exposure of Mll-Ell-expressing cells to differentiating cytokines. Leukemia-associated, constitutively active mutants of Shp2 block cytokine-induced tyrosine phosphorylation of HoxA9 and HoxA10. In comparison with myeloid progenitor cells that are expressing Mll-Ell alone, we find increased CDX4 transcription and Cdx4 expression in cells co-expressing Mll-Ell plus constitutively active Shp2. Increased Cdx4 expression is sustained on exposure of these cells to differentiating cytokines. Our results identify a mechanism for increased and sustained CDX4 transcription in leukemias co-overexpressing HoxA9 and HoxA10 in combination with constitutive activation of Shp2. This is clinically relevant, because MLL1 translocations and constitutive Shp2 activation co-exist in human myeloid leukemias.

Long intergenic non-coding RNA HOTAIRM1 regulates cell cycle progression during myeloid maturation in NB4 human promyelocytic leukemia cells

HOTAIRM1 is a long intergenic non-coding RNA encoded in the human HOXA gene cluster, with gene expression highly specific for maturing myeloid cells. Knockdown of HOTAIRM1 in the NB4 acute promyelocytic leukemia cell line retarded all-trans retinoid acid (ATRA)-induced granulocytic differentiation, resulting in a significantly larger population of immature and proliferating cells that maintained cell cycle progression from G1 to S phases. Correspondingly, HOTAIRM1 knockdown resulted in retained expression of many otherwise ATRA-suppressed cell cycle and DNA replication genes, and abated ATRA induction of cell surface leukocyte activation, defense response, and other maturation-related genes. Resistance to ATRA-induced cell cycle arrest at the G1/S phase transition in knockdown cells was accompanied by retained expression of ITGA4 (CD49d) and decreased induction of ITGAX (CD11c). The coupling of cell cycle progression with temporal dynamics in the expression patterns of these integrin genes suggests a regulated switch to control the transit from the proliferative phase to granulocytic maturation. Furthermore, ITGAX was among a small number of genes showing perturbation in transcript levels upon HOTAIRM1 knockdown even without ATRA treatment, suggesting a direct pathway of regulation. These results indicate that HOTAIRM1 provides a regulatory link in myeloid maturation by modulating integrin-controlled cell cycle progression at the gene expression level.

Platelets from mice lacking the aryl hydrocarbon receptor exhibit defective collagen-dependent signaling

BACKGROUND

We previously identified aryl hydrocarbon receptor (AHR) as a novel regulator of megakaryocytic differentiation and polyploidization and reported that AHR-null mice have approximately 15% fewer platelets than do wild-type mice, yet they exhibit a dramatic, unexplained bleeding phenotype.

OBJECTIVES

The current work tests our hypothesis that AHR-null platelets are functionally deficient, contributing to the previously reported (yet unexplained) bleeding phenotype present in AHR-null mice.

METHODS

AHR-null bone marrow was ex vivo differentiated with thrombopoietin with or without AHR ligands or AHR inhibitors and analyzed for degree of megakaryopoiesis and polyploidization. Platelet function of AHR-null mice was assessed with aggregation and spreading assays. Platelet signaling was examined using Western analysis and Rac activity assays.

RESULTS

AHR ligands differentiate murine bone marrow-derived progenitors into polyploid megakaryocytes in the absence of thrombopoietin, and AHR inhibitors block thrombopoietin-induced megakaryocytic differentiation. Despite their responsiveness toward thrombin, AHR-null platelets demonstrate decreased aggregation and spreading in response to collagen compared with wild-type platelets. AHR-null platelets bind fibrinogen after stimulation with thrombin or AYPGKF and aggregate in response to AYPGKF and adenosine diphosphate. Mechanistically, AHR absence led to down-regulation of Vav1 and Vav3, altered phospholipase Cγ2 phosphorylation, decreased Rac1 activation, and reduced platelet activation in response to collagen.

CONCLUSIONS

These results are consistent with a role for AHR in platelet function, especially as it relates to platelet aggregation and spreading in response to collagen. Our work suggests AHR is a critical component of the physiologic response that platelets undergo in response to collagen and may provide novel treatment options for patients with bleeding disorders.

The leukemia-associated Mll-Ell oncoprotein induces fibroblast growth factor 2 (Fgf2)-dependent cytokine hypersensitivity in myeloid progenitor cells

The subset of acute myeloid leukemias (AML) with chromosomal translocations involving the MLL gene have a poor prognosis (referred to as 11q23-AML). The MLL fusion proteins that are expressed in 11q23-AML facilitate transcription of a set of HOX genes, including HOXA9 and HOXA10. Because Hox proteins are transcription factors, this suggests the possibility that Hox target genes mediate the adverse effects of MLL fusion proteins in leukemia. Identifying such Hox target genes might provide insights to the pathogenesis and treatment of 11q23-AML. In the current study we found that Mll-Ell (an MLL fusion protein) induced transcriptional activation of the FGF2 gene in a HoxA9- and HoxA10-dependent manner. FGF2 encodes fibroblast growth factor 2 (also referred to as basic fibroblast growth factor). Fgf2 influences proliferation and survival of hematopoietic stem cells and myeloid progenitor cells, and increased Fgf2-expression has been described in AMLs. We determined that expression of Mll-Ell in myeloid progenitor cells resulted in autocrine production of Fgf2 and Fgf2-dependent cytokine hypersensitivity. Therefore, our results implicated increased Fgf2 expression in progenitor proliferation and expansion in 11q23-AML. Because small molecule inhibitors of Fgf-receptors are in human clinical trials, this suggested a potential therapeutic approach to this treatment refractory leukemia.

The regulation of testicular descent and the effects of cryptorchidism

The first half of this review examines the boundary between endocrinology and embryonic development, with the aim of highlighting the way hormones and signaling systems regulate the complex morphological changes to enable the intra-abdominal fetal testes to reach the scrotum. The genitoinguinal ligament, or gubernaculum, first enlarges to hold the testis near the groin, and then it develops limb-bud-like properties and migrates across the pubic region to reach the scrotum. Recent advances show key roles for insulin-like hormone 3 in the first step, with androgen and the genitofemoral nerve involved in the second step. The mammary line may also be involved in initiating the migration. The key events in early postnatal germ cell development are then reviewed because there is mounting evidence for this to be crucial in preventing infertility and malignancy later in life. We review the recent advances in what is known about the etiology of cryptorchidism and summarize the syndromes where a specific molecular cause has been found. Finally, we cover the recent literature on timing of surgery, the issues around acquired cryptorchidism, and the limited role of hormone therapy. We conclude with some observations about the differences between animal models and baby boys with cryptorchidism.

Graphical modeling of gene expression in monocytes suggests molecular mechanisms explaining increased atherosclerosis in smokers

Smoking is a risk factor for atherosclerosis with reported widespread effects on gene expression in circulating blood cells. We hypothesized that a molecular signature mediating the relation between smoking and atherosclerosis may be found in the transcriptome of circulating monocytes. Genome-wide expression profiles and counts of atherosclerotic plaques in carotid arteries were collected in 248 smokers and 688 non-smokers from the general population. Patterns of co-expressed genes were identified by Independent Component Analysis (ICA) and network structure of the pattern-specific gene modules was inferred by the PC-algorithm. A likelihood-based causality test was implemented to select patterns that fit models containing a path “smoking→gene expression→plaques”. Robustness of the causal inference was assessed by bootstrapping. At a FDR ≤0.10, 3,368 genes were associated to smoking or plaques, of which 93% were associated to smoking only. SASH1 showed the strongest association to smoking and PPARG the strongest association to plaques. Twenty-nine gene patterns were identified by ICA. Modules containing SASH1 and PPARG did not show evidence for the “smoking→gene expression→plaques” causality model. Conversely, three modules had good support for causal effects and exhibited a network topology consistent with gene expression mediating the relation between smoking and plaques. The network with the strongest support for causal effects was connected to plaques through SLC39A8, a gene with known association to HDL-cholesterol and cellular uptake of cadmium from tobacco, while smoking was directly connected to GAS6, a gene reported to have anti-inflammatory effects in atherosclerosis and to be up-regulated in the placenta of women smoking during pregnancy. Our analysis of the transcriptome of monocytes recovered genes relevant for association to smoking and atherosclerosis, and connected genes that before, were only studied in separate contexts. Inspection of correlation structure revealed candidates that would be missed by expression-phenotype association analysis alone.

A Src family kinase-Shp2 axis controls RUNX1 activity in megakaryocyte and T-lymphocyte differentiation

Hematopoietic development occurs in complex microenvironments and is influenced by key signaling events. Yet how these pathways communicate with master hematopoietic transcription factors to coordinate differentiation remains incompletely understood. The transcription factor RUNX1 plays essential roles in definitive hematopoietic stem cell (HSC) ontogeny, HSC maintenance, megakaryocyte (Mk) maturation, and lymphocyte differentiation. It is also the most frequent target of genetic alterations in human leukemia. Here, we report that RUNX1 is phosphorylated by Src family kinases (SFKs) and that this occurs on multiple tyrosine residues located within its negative regulatory DNA-binding and autoinhibitory domains. Retroviral transduction, chemical inhibitor, and genetic studies demonstrate a negative regulatory role of tyrosine phosphorylation on RUNX1 activity in Mk and CD8 T-cell differentiation. We also demonstrate that the nonreceptor tyrosine phosphatase Shp2 binds directly to RUNX1 and contributes to its dephosphorylation. Last, we show that RUNX1 tyrosine phosphorylation correlates with reduced GATA1 and enhanced SWI/SNF interactions. These findings link SFK and Shp2 signaling pathways to the regulation of RUNX1 activity in hematopoiesis via control of RUNX1 multiprotein complex assembly.

Physiological roles of NOX/NADPH oxidase, the superoxide-generating enzyme

NADPH oxidase is a superoxide (O₂^•−)-generating enzyme first identified in phagocytes, essential for their bactericidal activities. Later, in non-phagocytes, production of O₂^•− was also demonstrated in an NADPH-dependent manner. In the last decade, several non-phagocyte-type NADPH oxidases have been identified. The catalytic subunit of these oxidases, NOX, constitutes the NOX family. There are five homologs in the family, NOX1 to NOX5, and two related enzymes, DUOX1 and DUOX2. Transgenic or gene-disrupted mice of the NOX family have also been established. NOX/DUOX proteins possess distinct features in the dependency on other components for their enzymatic activities, tissue distributions, and physiological functions. This review summarized the characteristics of the NOX family proteins, especially focused on their functions clarified through studies using gene-modified mice.

The aryl hydrocarbon receptor (AHR) transcription factor regulates megakaryocytic polyploidization

We propose that the aryl hydrocarbon receptor (AHR) is a novel transcriptional regulator of megakaryopoietic polyploidization. Functional evidence was obtained that AHR impacts in vivo megakaryocytic differentiation and maturation; compared to wild-type mice, AHR-null mice had lower platelet counts, fewer numbers of newly synthesized platelets, increased bleeding times and lower-ploidy megakaryocytes (Mks). AHR mRNA increased 3·6-fold during ex vivo megakaryocytic differentiation, but reduced or remained constant during parallel isogenic granulocytic or erythroid differentiation. We interrogated the role of AHR in megakaryopoiesis using a validated Mk model of megakaryopoiesis, the human megakaryoblastic leukaemia CHRF cell line. Upon CHRF Mk differentiation, AHR mRNA and protein levels increased, AHR protein shifted from the cytoplasm to the nucleus and AHR binding to its consensus DNA binding sequence increased. Protein and mRNA levels of the AHR transcriptional target HES1 also increased. Mk differentiation of CHRF cells where AHR or HES1 was knocked-down using RNAi resulted in lower ploidy distributions and cells that were incapable of reaching ploidy classes ≥16n. AHR knockdown also resulted in increased DNA synthesis of lower ploidy cells, without impacting apoptosis. Together, these data support a role for AHR in Mk polyploidization and in vivo platelet function, and warrant further detailed investigations.

Phosphorylation of HOX11/TLX1 on Threonine-247 during mitosis modulates expression of cyclin B1

BACKGROUND

The HOX11/TLX1 (hereafter referred to as HOX11) homeobox gene was originally identified at a t(10;14)(q24;q11) translocation breakpoint, a chromosomal abnormality observed in 5-7% of T cell acute lymphoblastic leukemias (T-ALLs). We previously reported a predisposition to aberrant spindle assembly checkpoint arrest and heightened incidences of chromosome missegregation in HOX11-overexpressing B lymphocytes following exposure to spindle poisons. The purpose of the current study was to evaluate cell cycle specific expression of HOX11.

RESULTS

Cell cycle specific expression studies revealed a phosphorylated form of HOX11 detectable only in the mitotic fraction of cells after treatment with inhibitors to arrest cells at different stages of the cell cycle. Mutational analyses revealed phosphorylation on threonine-247 (Thr247), a conserved amino acid that defines the HOX11 gene family and is integral for the association with DNA binding elements. The effect of HOX11 phosphorylation on its ability to modulate expression of the downstream target, cyclin B1, was tested. A HOX11 mutant in which Thr247 was substituted with glutamic acid (HOX11 T247E), thereby mimicking a constitutively phosphorylated HOX11 isoform, was unable to bind the cyclin B1 promoter or enhance levels of the cyclin B1 protein. Expression of the wildtype HOX11 was associated with accelerated progression through the G2/M phase of the cell cycle, impaired synchronization in prometaphase and reduced apoptosis whereas expression of the HOX11 T247E mutant restored cell cycle kinetics, the spindle checkpoint and apoptosis.

CONCLUSIONS

Our results demonstrate that the transcriptional activity of HOX11 is regulated by phosphorylation of Thr247 in a cell cycle-specific manner and that this phosphorylation modulates the expression of the target gene, cyclin B1. Since it is likely that Thr247 phosphorylation regulates DNA binding activity to multiple HOX11 target sequences, it is conceivable that phosphorylation functions to regulate the expression of HOX11 target genes involved in the control of the mitotic spindle checkpoint.

NOX/NADPH oxidase, the superoxide-generating enzyme: its transcriptional regulation and physiological roles

NADPH oxidase is a superoxide (O(2)(-))-generating enzyme first identified in phagocytes that shows bactericidal activities. It has been reported that O(2)(-) is also produced in an NADPH-dependent manner in non-phagocytes. In the last decade, non-phagocyte-type NADPH oxidases have been identified, and the catalytic subunit NOX family has been found to be composed of five homologs, NOX1 to NOX5, and two related enzymes, DUOX1 and DUOX2. These NOX proteins have distinct features in dependency on other components for maximal enzymatic activity, tissue distribution, expressional regulation, and physiological functions. This review summarized the distinct characteristics of NOX family proteins, especially focusing on their functions and mechanisms of their expressional regulation.

Regulation of leukemic cell differentiation and retinoid-induced gene expression by statins

There is emerging evidence that, beyond their cholesterol-lowering properties, statins exhibit important antileukemic effects in vitro and in vivo, but the precise mechanisms by which they generate such responses remain to be determined. We have previously shown that statins promote differentiation of acute promyelocytic leukemia cells and enhance generation of all-trans retinoic acid (ATRA)-dependent antileukemic responses. We now provide evidence that statin-dependent leukemic cell differentiation requires engagement and activation of the c-Jun NH2-terminal kinase kinase pathway. In addition, in experiments, to define the molecular targets and mediators of statin-induced differentiation, we found a remarkable effect of statins on ATRA-dependent gene transcription, evidenced by the selective induction of over 400 genes by the combination of atorvastatin and ATRA. Altogether, our studies identify novel statin molecular targets linked to differentiation, establish that statins modulate ATRA-dependent transcription, and suggest that combined use of statins with retinoids may provide a novel approach to enhance antileukemic responses in acute promyelocytic leukemia and possibly other leukemias.

Constitutively active SHP2 cooperates with HoxA10 overexpression to induce acute myeloid leukemia

The homeodomain transcription factor HoxA10 is maximally expressed in myeloid progenitor cells. Sustained HoxA10 expression during differentiation has been described in poor prognosis human acute myeloid leukemia (AML). Consistent with this, engineered overexpression of HoxA10 in murine bone marrow induces a myeloproliferative disorder that progresses to AML over time. This murine model suggests that HoxA10 overexpression is sufficient for myeloproliferation but that differentiation block, and therefore AML, requires acquisition of additional mutations. In myeloid progenitor cells, HoxA10 represses transcription of genes that encode phagocyte effector proteins such as gp91PHOX and p67PHOX. Tyrosine phosphorylation of HoxA10 during myelopoiesis decreases binding to these target genes. In immature myeloid cells, HoxA10 also activates transcription of the DUSP4 gene that encodes Mkp2, an anti-apoptotic protein. HoxA10 binding to the DUSP4 promoter decreases during myelopoiesis. Therefore, both myeloid-specific gene repression and DUSP4 activation by HoxA10 decrease during myelopoiesis. This results in phenotypic differentiation and facilitates apoptosis as differentiation proceeds. HoxA10 is de-phosphorylated by SHP2 protein-tyrosine phosphatase in myeloid progenitors. This mechanism maintains HoxA10 in a nonphosphorylated state in immature, but not differentiating, myeloid cells. Constitutively active SHP2 mutants have been described in human AML, which dephosphorylate HoxA10 throughout myelopoiesis. In this study, we hypothesize that constitutive SHP2 activation synergizes with HoxA10 overexpression to accelerate progression to AML. Because both HoxA10 overexpression and constitutive SHP2 activation are found in poor prognosis human AML, these studies contribute to understanding biochemical aspects of disease progression in myeloid malignancy.

Essential role of nuclear factor-kappaB for NADPH oxidase activity in normal and anhidrotic ectodermal dysplasia leukocytes

This work investigated the functional role of nuclear factor-kappaB (NF-kappaB) in respiratory burst activity and in expression of the human phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase genes CYBB, CYBA, NCF1, and NCF2. U937 cells with a stably transfected repressor of NF-kappaB (IkappaBalpha-S32A/S36A) demonstrated significantly lower superoxide release and lower CYBB and NCF1 gene expression compared with control U937 cells. We further tested Epstein-Barr virus (EBV)-transformed B cells from patients with anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID), an inherited disorder of NF-kappaB function. Superoxide release and CYBB gene expression by EDA-ID cells were significantly decreased compared with healthy cells and similar to cells from patients with X-linked chronic granulomatous disease (X91(0) CGD). NCF1 gene expression in EDA-ID S32I cells was decreased compared with healthy control cells and similar to that in autosomal recessive (A47(0)) CGD cells. Gel shift assays demonstrated loss of recombinant human p50 binding to a NF-kappaB site 5' to the CYBB gene in U937 cells treated with NF-kappaB inhibitors, repressor-transfected U937 cells, and EDA-ID patients' cells. Zymosan phagocytosis was not affected by transfection of U937 cells with the NF-kappaB repressor. These studies show that NF-kappaB is necessary for CYBB and NCF1 gene expression and activation of the phagocyte NADPH oxidase in this model system.

The tyrosine phosphatase Shp2 (PTPN11) in cancer

Diverse cellular processes are regulated by tyrosyl phosphorylation, which is controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs). De-regulated tyrosyl phosphorylation, evoked by gain-of-function mutations and/or over-expression of PTKs, contributes to the pathogenesis of many cancers and other human diseases. PTPs, because they oppose the action of PTKs, had been considered to be prime suspects for potential tumor suppressor genes. Surprisingly, few, if any, tumor suppressor PTPs have been identified. However, the Src homology-2 domain-containing phosphatase Shp2 (encoded by PTPN11) is a bona fide proto-oncogene. Germline mutations in PTPN11 cause Noonan and LEOPARD syndromes, whereas somatic PTPN11 mutations occur in several types of hematologic malignancies, most notably juvenile myelomonocytic leukemia and, more rarely, in solid tumors. Shp2 also is an essential component in several other oncogene signaling pathways. Elucidation of the events underlying Shp2-evoked transformation may provide new insights into oncogenic mechanisms and novel targets for anti-cancer therapy.

Constitutive activation of SHP2 in mice cooperates with ICSBP deficiency to accelerate progression to acute myeloid leukemia

Myeloproliferative disorders (MPDs) are characterized by cytokine hypersensitivity and apoptosis resistance. Development of a block in myeloid differentiation is associated with progression of MPD to acute myeloid leukemia (AML) and portends poor prognosis. Identifying molecular markers of this transition may suggest targets for therapeutic intervention. Interferon consensus sequence binding protein (ICSBP, also known as IRF8) is an interferon-regulatory transcription factor that functions as a leukemia tumor suppressor. In mice, ICSBP deficiency induces an MPD that progresses to AML over time, suggesting that ICSBP deficiency is sufficient for myeloproliferation, but additional genetic lesions are necessary for AML. Since activity of ICSBP is influenced by tyrosine phosphorylation state, we hypothesized that mutations in molecular pathways that regulate this process might synergize with ICSBP deficiency for progression to AML. Consistent with this, we found that constitutive activation of SHP2 protein tyrosine phosphatase synergized with ICSBP haploinsufficiency to facilitate cytokine-induced myeloproliferation, apoptosis resistance, and rapid progression to AML in a murine bone marrow transplantation model. Constitutive SHP2 activation cooperated with ICSBP deficiency to increase the number of progenitors in the bone marrow and myeloid blasts in circulation, indicating a block in differentiation. Since SHP2 activation and ICSBP deficiency may coexist in human myeloid malignancies, our studies have identified a molecular mechanism potentially involved in disease progression in such diseases.

Constitutive activation of SHP2 protein tyrosine phosphatase inhibits ICSBP-induced transcription of the gene encoding gp91PHOX during myeloid differentiation

The IFN consensus sequence-binding protein (ICSBP; also referred to as IFN regulatory factor 8) is a transcription factor which is expressed in myeloid and B cells. In previous studies, we found that ICSBP activated transcription of the gene encoding gp91(PHOX) (the CYBB gene), a rate-limiting component of the phagocyte respiratory burst oxidase expressed exclusively after the promyelocyte stage of myelopoiesis. Previously, we found that CYBB transcription was dependent on phosphorylation of specific ICSBP tyrosine residues. Since ICSBP is tyrosine-phosphorylated during myelopoiesis, this provided a mechanism of differentiation stage-specific CYBB transcription. In the current studies, we found that ICSBP was a substrate for Src homology-containing tyrosine phosphatase 2 (SHP2-PTP) in immature myeloid cells but not during myelopoiesis. Therefore, SHP2-PTP inhibited CYBB transcription and respiratory burst activity in myeloid progenitor cells by dephosphorylating ICSBP. In contrast, we found that ICSBP was a substrate for a leukemia-associated, constitutively active mutant form of SHP2, described previously, throughout differentiation. Consistent with this, constitutive SHP2 activation blocked ICSBP-induced CYBB transcription and respiratory burst activity in differentiating myeloid cells. ICSBP-deficiency and constitutive SHP2 activation have been described in human myelodysplastic syndromes. As these two abnormalities may coexist, our results identified a potential molecular mechanism for impaired phagocyte function in this malignant myeloid disease.