Protein kinase B (PKB/c-akt) regulates homing of hematopoietic progenitors through modulation of their adhesive and migratory properties

STAT5 is essential for IL-7-mediated viability, growth, and proliferation of T-cell acute lymphoblastic leukemia cells

T-cell acute lymphoblastic leukemia (T-ALL) constitutes an aggressive subset of ALL, the most frequent childhood malignancy. Whereas interleukin-7 (IL-7) is essential for normal T-cell development, it can also accelerate T-ALL development in vivo and leukemia cell survival and proliferation by activating phosphatidylinositol 3-kinase/protein kinase B/mechanistic target of rapamycin signaling. Here, we investigated whether STAT5 could also mediate IL-7 T-ALL-promoting effects. We show that IL-7 induces STAT pathway activation in T-ALL cells and that STAT5 inactivation prevents IL-7-mediated T-ALL cell viability, growth, and proliferation. At the molecular level, STAT5 is required for IL-7-induced downregulation of p27^kip1 and upregulation of the transferrin receptor, CD71. Surprisingly, STAT5 inhibition does not significantly affect IL-7-mediated Bcl-2 upregulation, suggesting that, contrary to normal T-cells, STAT5 promotes leukemia cell survival through a Bcl-2-independent mechanism. STAT5 chromatin immunoprecipitation sequencing and RNA sequencing reveal a diverse IL-7-driven STAT5-dependent transcriptional program in T-ALL cells, which includes BCL6 inactivation by alternative transcription and upregulation of the oncogenic serine/threonine kinase PIM1 Pharmacological inhibition of PIM1 abrogates IL-7-mediated proliferation on T-ALL cells, indicating that strategies involving the use of PIM kinase small-molecule inhibitors may have therapeutic potential against a majority of leukemias that rely on IL-7 receptor (IL-7R) signaling. Overall, our results demonstrate that STAT5, in part by upregulating PIM1 activity, plays a major role in mediating the leukemia-promoting effects of IL-7/IL-7R.

Casein kinase 2 controls the survival of normal thymic and leukemic γδ T cells via promotion of AKT signaling

The thymus is the major site for normal and leukemic T-cell development. The dissection of the molecular determinants of T-cell survival and differentiation is paramount for the manipulation of healthy or transformed T cells in cancer (immuno)therapy. Casein kinase 2 (CK2) is a serine/threonine protein kinase whose anti-apoptotic functions have been described in various hematological and solid tumors. Here we disclose an unanticipated role of CK2 in healthy human thymocytes that is selective to the γδ T-cell lineage. γδ thymocytes display higher (and T-cell receptor inducible) CK2 activity than their αβ counterparts, and are strikingly sensitive to death upon CK2 inhibition. Mechanistically, we show that CK2 regulates the pro-survival AKT signaling pathway in γδ thymocytes and, importantly, also in γδ T-cell acute lymphoblastic leukemia (T-ALL) cells. When compared with healthy thymocytes or leukemic αβ T cells, γδ T-ALL cells show upregulated CK2 activity, potentiated by CD27 costimulation, and enhanced apoptosis upon CK2 blockade using the chemical inhibitor CX-4945. Critically, this results in inhibition of tumor growth in a xenograft model of human γδ T-ALL. These data identify CK2 as a novel survival determinant of both healthy and leukemic γδ T cells, and may thus greatly impact their therapeutic manipulation.

Sphingosine-1-Phosphate Receptor-3 Supports Hematopoietic Stem and Progenitor Cell Residence Within the Bone Marrow Niche

Hematopoietic stem and progenitor cells (HSPCs) egress from bone marrow (BM) during homeostasis and at increased rates during stress; however, the mechanisms regulating their trafficking remain incompletely understood. Here we describe a novel role for lipid receptor, sphingosine-1-phosphate receptor 3 (S1PR3), in HSPC residence within the BM niche. HSPCs expressed increased levels of S1PR3 compared to differentiated BM cells. Pharmacological antagonism or knockout (KO) of S1PR3 mobilized HSPCs into blood circulation, suggesting that S1PR3 influences niche localization. S1PR3 antagonism suppressed BM and plasma SDF-1, enabling HSPCs to migrate toward S1P-rich plasma. Mobilization synergized with AMD3100-mediated antagonism of CXCR4, which tethers HSPCs in the niche, and recovered homing deficits of AMD3100-treated grafts. S1PR3 antagonism combined with AMD3100 improved re-engraftment and survival in lethally irradiated recipients. Our studies indicate that S1PR3 and CXCR4 signaling cooperate to maintain HSPCs within the niche under homeostasis. These results highlight an important role for S1PR3 in HSPC niche occupancy and trafficking that can be harnessed for both rapid clinical stem cell mobilization and re-engraftment strategies, as well as the opportunity to design novel therapeutics for control of recruitment, homing, and localization through bioactive lipid signaling. Stem Cells 2017;35:1040-1052.

Autophagy Proteins ATG5 and ATG7 Are Essential for the Maintenance of Human CD34(+) Hematopoietic Stem-Progenitor Cells

Autophagy is a highly regulated catabolic process that involves sequestration and lysosomal degradation of cytosolic components such as damaged organelles and misfolded proteins. While autophagy can be considered to be a general cellular housekeeping process, it has become clear that it may also play cell type-dependent functional roles. In this study, we analyzed the functional importance of autophagy in human hematopoietic stem/progenitor cells (HSPCs), and how this is regulated during differentiation. Western blot-based analysis of LC3-II and p62 levels, as well as flow cytometry-based autophagic vesicle quantification, demonstrated that umbilical cord blood-derived CD34(+) /CD38(-) immature hematopoietic progenitors show a higher autophagic flux than CD34(+) /CD38(+) progenitors and more differentiated myeloid and erythroid cells. This high autophagic flux was critical for maintaining stem and progenitor function since knockdown of autophagy genes ATG5 or ATG7 resulted in reduced HSPC frequencies in vitro as well as in vivo. The reduction in HSPCs was not due to impaired differentiation, but at least in part due to reduced cell cycle progression and increased apoptosis. This is accompanied by increased expression of p53, proapoptotic genes BAX and PUMA, and the cell cycle inhibitor p21, as well as increased levels of cleaved caspase-3 and reactive oxygen species. Taken together, our data demonstrate that autophagy is an important regulatory mechanism for human HSCs and their progeny, reducing cellular stress and promoting survival. Stem Cells 2016;34:1651-1663.

Both mTORC1 and mTORC2 are involved in the regulation of cell adhesion

mTOR is a central controller for cell growth/proliferation and survival. Recent studies have shown that mTOR also regulates cell adhesion, yet the underlying mechanism is not known. Here we found that inhibition of mTOR by rapamycin reduced the basal or type I insulin-like growth factor (IGF-1)-stimulated adhesion of cancer cells. Further research revealed that both mTORC1 and mTORC2 were involved in the regulation of cell adhesion, as silencing expression of raptor or rictor inhibited cell adhesion. Also, PP242, an mTORC1/2 kinase inhibitor, inhibited cell adhesion more potently than rapamycin (mTORC1 inhibitor). Of interest, ectopic expression of constitutively active and rapamycin-resistant mutant of p70 kinase 1 (S6K1) or downregulation of eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) conferred resistance to rapamycin inhibition of cell adhesion, whereas expression of constitutively hypophosphorylated 4E-BP1 (4EBP1-5A) or downregulation of S6K1 suppressed cell adhesion. In contrast, neither genetic manipulation of Akt activity nor pharmacological inhibition of Akt affected cell adhesion. The results suggest that both mTORC1 and mTORC2 are involved in the regulation of cell adhesion; and mTORC1 regulates cell adhesion through S6K1 and 4E-BP1 pathways, but mTORC2 regulates cell adhesion via Akt-independent mechanism.

Coexpression of hyperactivated AKT1 with additional genes activated in leukemia drives hematopoietic progenitor cells to cell cycle block and apoptosis

The phosphatidylinositol 3-kinase/AKT pathway is an integral component of signaling involved in the development of many cancers, including myeloid leukemias such as chronic myeloid leukemia and acute myeloid leukemia (AML). Increased AKT1 activity is frequently seen in AML patients, providing leukemic cells with growth and survival promoting signals. An important aspect of AKT1 function is its involvement in cellular metabolism and energy production. Under some circumstances, strong activation of AKT1 increases oxidative stress, which can cause apoptosis when cells progressively build up excess free radicals. This has been described in hematopoietic cells overexpressing activated AKT1; however, whether this is true in cells coexpressing other genetic events involved in leukemia is not known. This prompted us to investigate the effect of constitutively active AKT1 (myristoylated AKT1) in hematopoietic progenitor cells expressing constitutively active signal transducer and activator of transcription 5, Fms-related tyrosine kinase 3-internal tandem duplication, or antiapoptotic B-cell lymphoma 2. Surprisingly, myristoylated AKT1 was incompatible with proliferation driven by both signal transducer and activator of transcription 5 and Fms-related tyrosine kinase 3-internal tandem duplication, which triggered cell cycle block and apoptosis. Moreover, transplantable cells of B-cell lymphoma 2-transgenic mice were impaired in their engraftment ability to recipient mice when expressing hyperactivated AKT1. This was linked to AKT1-mediated proapoptotic functions and not to impairment in homing to the bone marrow. Although cells expressing hyperactivated AKT1 displayed higher levels of reactive oxygen species both in vitro and in vivo, the addition of the antioxidant N-acetyl-L-cysteine significantly reduced apoptosis. Taken together, the results indicate that constitutive AKT1 activity is incompatible with growth- and survival-promoting ability of other activated genes in AML.

Shp1 signalling is required to establish the long-lived bone marrow plasma cell pool

Germline or B-cell-specific loss of Ptpn6 gene encoding the Shp1 protein tyrosine phosphatase leads to skewed B lymphopoiesis and systemic autoimmunity. Here, to study its role in B-cell terminal differentiation, we generated Ptpn6^f/fAicda^Cre/+ mice with Shp1 ablated only in activated B cells. We show that Ptpn6^f/fAicda^Cre/+ mice have normal B-cell development but exhibit defective class-switched primary and recalled antibody response to a T-cell-dependent antigen. Germinal centres are present but do not persist and memory B cells are not formed. Interestingly, Shp1-deficient plasma cells are generated in the spleen but do not contribute to the bone marrow long-lived pool. Plasma cells lacking Shp1 exhibit aberrant α4β1 integrin activation due to dysregulated Src- and PI3-kinase signalling and manifest attenuated migration in vitro and defective bone marrow homing when reconstituted in vivo. Interrupting α4β1–VCAM-1 interaction rectifies this defect. These data suggest that Shp1 signalling is required for the establishment of a life-long protective humoral immunity.

SHP-1 signalling is required for the normal development of B lymphocytes but its role in the terminal differentiation of these cells has not been fully established. Here, the authors show that SHP-1 ablation impairs the establishment of long-lived bone marrow-resident plasma cells due to aberrant integrin activation.

Ribonuclease inhibitor up-regulation inhibits the growth and induces apoptosis in murine melanoma cells through repression of angiogenin and ILK/PI3K/AKT signaling pathway

Human ribonuclease inhibitor (RI), a cytoplasmic protein, is constructed almost entirely of leucine rich repeats. RI could suppress activities of ribonuclease and angiogenin (ANG) through closely combining with them. ANG is a potent inducer of blood vessel growth and has been implicated in the establishment, growth, and metastasis of tumors. ILK/PI3K/AKT signaling pathway also plays important roles in cell growth, cell-cycle progression, tumor angiogenesis, and cell apoptosis. Our previous experiments demonstrated that RI might effectively inhibit some tumor growth and metastasis. Our recent study showed that ILK siRNA inhibited the growth and induced apoptosis in bladder cancer cells as well as increased RI expression, which suggest a correlation between RI and ILK. However, the exact molecular mechanism of RI in anti-tumor and in the cross-talk of ANG and ILK signaling pathway remains largely unknown. Here we investigated the effects of up-regulating RI on the growth and apoptosis in murine melanoma cells through angiogenin and ILK/PI3K/AKT signaling pathway. We demonstrated that up-regulating RI obviously decreased ANG expression and activity. We also discovered that RI overexpression could remarkably inhibit cell proliferation, regulate cell cycle and induce apoptosis. Furthermore, up-regulation of RI inhibited phosphorylation of ILK downstream signaling targets protein kinase B/Akt, glycogen synthase kinase 3-beta (GSK-3β), and reduced β-catenin expression in vivo and vitro. More importantly, RI significant inhibited the tumor growth and angiogenesis of tumor bearing C57BL/6 mice. In conclusion, our findings, for the first time, suggest that angiogenin and ILK signaling pathway plays a pivotal role in mediating the inhibitory effects of RI on melanoma cells growth. This study identifies that RI may be a useful molecular target for melanoma therapy.

Inositol tetrakisphosphate limits NK cell effector functions by controlling PI3K signaling

Natural killer (NK) cells have important functions in cancer immunosurveillance, BM allograft rejection, fighting infections, tissue homeostasis, and reproduction. NK cell-based therapies are promising treatments for blood cancers. Overcoming their currently limited efficacy requires a better understanding of the molecular mechanisms controlling NK cell development and dampening their effector functions. NK cells recognize the loss of self-antigens or up-regulation of stress-induced ligands on pathogen-infected or tumor cells through invariant NK cell receptors (NKRs), and then kill such stressed cells. Two second-messenger pathways downstream of NKRs are required for NK cell maturation and effector responses: PIP(3) generation by PI3K and generation of diacylglycerol and IP(3) by phospholipase-Cγ (PLCγ). In the present study, we identify a novel role for the phosphorylated IP(3) metabolite inositol (1,3,4,5)tetrakisphosphate (IP(4)) in NK cells. IP(4) promotes NK cell terminal differentiation and acquisition of a mature NKR repertoire. However, in mature NK cells, IP(4) limits NKR-induced IFNγ secretion, granule exocytosis, and target-cell killing, in part by inhibiting the PIP(3) effector-kinase Akt. This identifies IP(4) as an important novel regulator of NK cell development and function and expands our understanding of the therapeutically important mechanisms dampening NK cell responses. Our results further suggest that PI3K regulation by soluble IP(4) is a broadly important signaling paradigm.

Molecular mechanisms underlying adhesion and migration of hematopoietic stem cells

Hematopoietic stem cell transplantation is the most powerful treatment modality for a large number of hematopoietic malignancies, including leukemia. Successful hematopoietic recovery after transplantation depends on homing of hematopoietic stem cells to the bone marrow and subsequent lodging of those cells in specific niches in the bone marrow. Migration of hematopoietic stem cells to the bone marrow is a highly regulated process that requires correct regulation of the expression and activity of various molecules including chemoattractants, selectins and integrins. This review will discuss recent studies that have extended our understanding of the molecular mechanisms underlying adhesion, migration and bone marrow homing of hematopoietic stem cells.

Enhancing the adhesion of hematopoietic precursor cell integrins with hydrogen peroxide increases recruitment within murine gut

Hematopoietic stem cells (HSCs) migrate to injury sites and aid in tissue repair. However, clinical success is poor and is partially due to limited HSC recruitment. We hypothesized that HSC pretreatment with H2O2 would enhance their recruitment to injured gut. As HSCs are rare cells, the number of primary cells obtained from donors is often inadequate for functional experiments. To circumvent this, in this study we utilized a functionally relevant cell line, HPC-7. Anesthetized mice were subjected to intestinal ischemia-reperfusion (IR) injury, and HPC-7 recruitment was examined intravitally. Adhesion to endothelial cells (ECs), injured gut sections, and ICAM-1/VCAM-1 protein were also quantitated in vitro. H2O2 pretreatment significantly enhanced HPC-7 recruitment to injured gut in vivo. A concomitant reduction in pulmonary adhesion was also observed. Enhanced adhesion was also observed in all in vitro models. Increased clustering of α4 and β2 integrins, F-actin polymerization, and filopodia formation were observed in pretreated HPC-7s. Importantly, H2O2 did not reduce HPC-7 viability or proliferative ability. HPC-7 recruitment to injured gut can be modulated by H2O2 pretreatment. This may be through increasing the affinity or avidity of surface integrins that mediate HPC-7 homing to injured sites or through stimulating the migratory apparatus. Strategies that enhance hematopoietic stem/progenitor cell recruitment may ultimately affect their therapeutic efficacy.

The role of PI3K/protein kinase B (PKB/c-akt) in migration and homing of hematopoietic stem and progenitor cells

PURPOSE OF REVIEW

Hematopoietic stem cell (HSC) transplantation is the most powerful treatment modality for a variety of hematological disorders. Successful hematopoietic recovery after transplantation depends on optimal homing of HSCs to the bone marrow and subsequent lodging in the HSC niche. The molecular mechanisms underlying bone marrow homing are, thus far, incompletely understood. This review focuses on recent studies that extended our understanding of how the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (PKB/c-akt) signaling module can regulate migration and homing of HSCs.

RECENT FINDINGS

In addition to regulation of HSC maintenance and lineage development, it has recently become apparent that the PI3K/PKB signaling module plays a critical role in regulation of migration and adhesion of hematopoietic stem and progenitor cells. Activation of this signaling pathway enhances firm adhesion, reduces migration and inhibits bone marrow homing, whereas inhibition of PKB conversely induces bone marrow homing.

SUMMARY

These findings clearly implicate the PI3K/PKB signaling module in playing a critical role in regulation of bone marrow homing, suggesting that pharmacological modulation of this signaling molecule prior to transplantation may provide a clinical means of improving engraftment levels and accelerating hematopoietic recovery.

Small interfering RNA targeting integrin-linked kinase inhibited the growth and induced apoptosis in human bladder cancer cells

Integrin-linked kinase (ILK), an intracellular serine/threonine kinase, is implicated in cell growth and survival, cell-cycle progression, tumor angiogenesis, and cell apoptosis. Recent studies showed that the expression and activity of ILK increased significantly in many types of solid tumors. However, the exact molecular mechanism of ILK underlie tumor has not been fully ascertained. The purpose of our study was to determine whether knockdown of ILK would inhibit cell growth and induce apoptosis in bladder cancer cells using a plasmid vector based small interfering RNA (siRNA). The experiments showed that knockdown of ILK could remarkably inhibit cell proliferation and growth, regulate cell cycle and induce apoptosis of bladder cancer BIU-87 and EJ cells. We demonstrated that knockdown of ILK inhibited phosphorylation of downstream signaling targets protein kinase B/Akt, glycogen synthase kinase 3-beta (GSK-3β), and reduced expression of β-catenin in BIU-87 as well as EJ cells by Western blot and Immunofluorescence analysis. In addition, down-regulation of ILK also could increase expression of Ribonuclease inhibitor (RI), an important acidic cytoplasmic protein with many functions. BALB/C nude mice injected with the BIU-87 cells transfected ILK siRNA showed a significant inhibition of the tumor growth with lighter tumor weight, lower microvessels density and higher apoptosis rate than those in the other two control groups. In conclusion, these results suggest that ILK might be involved in the development of bladder cancer, and could be served as a novel potential therapy target for human bladder cancer. Our study may be of biological and clinical importance.