Switching-On Survival and Repair Response Programs in Islet Transplants by Bone Marrow–Derived Vasculogenic Cells

OBJECTIVE—Vascular progenitors of bone marrow origin participate to neovascularization at sites of wound healing and transplantation. We hypothesized that the biological purpose of this bone marrow–derived vascular component is to contribute angiogenic and survival functions distinct from those provided by the local tissue-derived vasculature

Novel Role for p110β PI 3-Kinase in Male Fertility through Regulation of Androgen Receptor Activity in Sertoli Cells

We thank Anna-Lena Berg (AstraZeneca, Lund) and Cheryl Scudamore (MRC, Harwell, UK) for histological analysis, Julie Foster (Barts Cancer Institute, London) for CT scans, Johan Swinnen and Frank Claessens (Leuven University, Belgium) for discussion and AR-luciferase reporter plasmids, Florian Guillou (INRA, CNRS, Université de Tours, France) for the AMH-Cre mouse line and Laura Milne (MRC Centre for Reproductive Health, The University of Edinburgh) for technical support. We thank the members of the Cell Signalling group for critical input.International audienceThe organismal roles of the ubiquitously expressed class I PI3K isoform p110β remain largely unknown. Using a new kinase-dead knockin mouse model that mimics constitutive pharmacological inactivation of p110β, we document that full inactivation of p110β leads to embryonic lethality in a substantial fraction of mice. Interestingly, the homozygous p110β kinase-dead mice that survive into adulthood (maximum ~26% on a mixed genetic background) have no apparent phenotypes, other than subfertility in females and complete infertility in males. Systemic inhibition of p110β results in a highly specific blockade in the maturation of spermatogonia to spermatocytes. p110β was previously suggested to signal downstream of the c-kit tyrosine kinase receptor in germ cells to regulate their proliferation and survival. We now report that p110β also plays a germ cell-extrinsic role in the Sertoli cells (SCs) that support the developing sperm, with p110β inactivation dampening expression of the SC-specific Androgen Receptor (AR) target gene Rhox5, a homeobox gene critical for spermatogenesis. All extragonadal androgen-dependent functions remain unaffected by global p110β inactivation. In line with a crucial role for p110β in SCs, selective inactivation of p110β in these cells results in male infertility. Our study is the first documentation of the involvement of a signalling enzyme, PI3K, in the regulation of AR activity during spermatogenesis. This developmental pathway may become active in prostate cancer where p110β and AR have previously been reported to functionally interac

PU.1 binding to the p53 family of tumor suppressors impairs their transcriptional activity

The transcription factor PU.1 is essential for terminal myeloid differentiation, B- and T-cell development, erythropoiesis and hematopoietic stem cell maintenance. PU.1 functions as oncogene in Friend virus-induced erythroleukemia and as tumor suppressor in acute myeloid leukemias. Moreover, Friend virus-induced erythroleukemia requires maintenance of PU.1 expression and the disruption of p53 function greatly accelerates disease progression. It has been hypothesized that p53-mediated expression of the p21(Cip1) cell cycle inhibitor during differentiation of pre-erythroleukemia cells promotes selection against p53 function. In addition to the blockage of erythroblast differentiation provided by increased levels of PU.1, we propose that PU.1 alters p53 function. We demonstrate that PU.1 reduces the transcriptional activity of the p53 tumor suppressor family and thus inhibits activation of genes important for cell cycle regulation and apoptosis. Inhibition is mediated through binding of PU.1 to the DNA-binding and/or oligomerization domains of p53/p73 proteins. Lastly, knocking down endogenous PU.1 in p53 wild-type REH B-cell precursor leukemia cells leads to increased expression of the p53 target p21(Cip1)

Attenuation of EPO-dependent erythroblast formation by death-associated protein kinase-2

The adult erythron is maintained via dynamic modulation of erythroblast survival potentials. Toward identifying novel regulators of this process, murine splenic erythroblasts at 3 developmental stages were prepared, purified and profiled. Stage-to-stage modulated genes were then functionally categorized, with a focus on apoptotic factors. In parallel with BCL-X and NIX, death-associated protein kinase-2 (DAPK2) was substantially up-modulated during late erythropoiesis. Among hematopoietic lineages, DAPK2 was expressed predominantly in erythroid cells. In a Gata1-IE3.9int-DAPK2 transgenic mouse model, effects on steady-state reticulocyte and red blood cell (RBC) levels were limited. During hemolytic anemia, however, erythropoiesis was markedly deficient. Ex vivo ana-lyses revealed heightened apoptosis due to DAPK2 at a Kit(−)CD71(high)Ter119(−) stage, together with a subsequent multifold defect in late-stage Kit(−)CD71(high)Ter119(+) cell formation. In UT7epo cells, siRNA knock-down of DAPK2 enhanced survival due to cytokine withdrawal, and DAPK2's phosphorylation and kinase activity also were erythropoietin (EPO)-modulated. DAPK2 therefore comprises a new candidate attenuator of stress erythropoiesis