Hematopoiesis - Signal Transduction シグナル伝達

Hematopoietic cell regulation by Rac1 and Rac2

1: Science. 2003 Oct 17;302(5644):445-9.

Hematopoietic cell regulation by Rac1 and Rac2 guanosine triphosphatases.

Gu Y, Filippi MD, Cancelas JA, Siefring JE, Williams EP, Jasti AC, Harris CE,
Lee AW, Prabhakar R, Atkinson SJ, Kwiatkowski DJ, Williams DA.

Division of Experimental Hematology, Cincinnati Children's Hospital Medical
Center, Cincinnati, OH 45229, USA.

The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling
regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles
leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into
the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to
engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but
not Rac1, regulates superoxide production and directed migration in neutrophils,
and in each cell type, the two GTPases play distinct roles in actin
organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate
unique aspects of hematopoietic development and function.

Publication Types:
Research Support, U.S. Gov't, P.H.S.

PMID: 14564009 [PubMed - indexed for MEDLINE]

BTK-/- mice show impaired responsiveness to Epo.

1: J Exp Med. 2004 Mar 15;199(6):785-95. Epub 2004 Mar 8.

Btk is required for an efficient response to erythropoietin and for
SCF-controlled protection against TRAIL in erythroid progenitors.

Schmidt U, van den Akker E, Parren-van Amelsvoort M, Litos G, de Bruijn M,
Gutierrez L, Hendriks RW, Ellmeier W, Lowenberg B, Beug H, von Lindern M.

Institute of Molecular Pathology, Vienna, Austria.

Regulation of survival, expansion, and differentiation of erythroid progenitors
requires the well-controlled activity of signaling pathways induced by
erythropoietin (Epo) and stem cell factor (SCF). In addition to qualitative
regulation of signaling pathways, quantitative control may be essential to
control appropriate cell numbers in peripheral blood. We demonstrate that
Bruton's tyrosine kinase (Btk) is able to associate with the Epo receptor (EpoR)
and Jak2, and is a substrate of Jak2. Deficiency of Btk results in reduced and
delayed phosphorylation of the EpoR, Jak2, and downstream signaling molecules
such as Stat5 and PLCgamma1 as well as in decreased responsiveness to Epo. As a
result, expansion of erythroid progenitors lacking Btk is impaired at limiting
concentrations of Epo and SCF. In addition, we show that SCF induces Btk to
interact with TNF-related apoptosis-inducing ligand (TRAIL)-receptor 1 and that
lack of Btk results in increased sensitivity to TRAIL-induced apoptosis.
Together, our results indicate that Btk is a novel, quantitative regulator of
Epo/SCF-dependent expansion and survival in erythropoiesis.

Publication Types:
Comparative Study
Research Support, Non-U.S. Gov't

PMID: 15007095 [PubMed - indexed for MEDLINE]

BTK-/-/TEC-/- plateles fail to undergo an inccrease in Ca2+ , aggregation, secretion, and spreading in response to collagen or CRP.

1: Blood. 2003 Nov 15;102(10):3592-9. Epub 2003 Jul 3.

Tec regulates platelet activation by GPVI in the absence of Btk.

Atkinson BT, Ellmeier W, Watson SP.

Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT,
United Kingdom. [email protected]

The Tec family kinase Btk plays an important role in the regulation of
phospholipase C gamma 2 (PLC gamma 2) downstream of the collagen receptor
glycoprotein VI (GPVI) in human platelets. Platelets also express a second
member of this family, Tec; however, its function has not been analyzed. To
address the role of Tec, we analyzed Btk-/-, Tec-/-, and Btk/Tec
double-deficient (Btk-/-/Tec-/-) platelets. Tec-/- platelets exhibit a minor
reduction in aggregation to threshold concentrations of collagen or the
GPVI-specific agonist collagen-related peptide (CRP), whereas responses to
higher concentrations are normal. Tyrosine phosphorylation of PLC gamma 2 by
collagen and CRP is not altered in Tec-/- platelets. However, Btk-/-/Tec-/-
platelets exhibit a greater reduction in PLC gamma 2 phosphorylation than is
seen in the absence of Btk, thus revealing an important role for Tec in this
situation. Furthermore, Btk-/-/Tec-/- platelets fail to undergo an increase in
Ca2+, aggregation, secretion, and spreading in response to collagen or CRP,
whereas they aggregate normally to adenosine diphosphate (ADP) and spread on
fibrinogen. A residual GPVI signal exists in the Btk-/-/Tec-/- platelets as CRP
synergizes with ADP to mediate aggregation. These results demonstrate an
essential requirement for Tec and Btk in platelet activation by GPVI and reveal
a functional role for Tec in the regulation of PLC gamma 2 in the absence of
Btk.

Publication Types:
Research Support, Non-U.S. Gov't

PMID: 12842985 [PubMed - indexed for MEDLINE]

PLCG2 -/- mice impair vasculogenesis and erythropoiesis.

1: J Biol Chem. 2002 Mar 15;277(11):9335-41. Epub 2001 Dec 13.

Absence of erythrogenesis and vasculogenesis in Plcg1-deficient mice.

Liao HJ, Kume T, McKay C, Xu MJ, Ihle JN, Carpenter G.

Department of Biochemistry, Vanderbilt University School of Medicine, Nashville,
Tennessee 37232,USA.

Mice nullizygous for Plcg1 cease growing at early to mid-gestation. An
examination of carefully preserved wild-type embryos shows clear evidence of
erythropoiesis, but erythropoiesis is not evident in Plcg1 nullizygous embryos
at the same stage. The analyses of embryonic materials demonstrate that in the
absence of Plcg1, erythroid progenitors cannot be detected in the yolk sac or
embryo body by three different assays, burst-forming units, colony-forming
units, and analysis for the developmental marker Ter119. However, non-erythroid
granulocyte/macrophage colonies are produced by Plcg1 null embryos. Further
analysis of these embryos demonstrates significantly diminished vasculogenesis
in Plcg1 nullizygous embryos based on the lack of expression of the endothelial
marker platelet endothelial cell adhesion molecule-1. In addition, Plcg1
nullizygous embryos express a greatly reduced level of vascular endothelial
growth factor receptor-2/Flk-1, consistent with significantly impaired
vasculogenesis and erythropoiesis. Interestingly, these early embryos do express
phospholipase C-gamma2, however, it is unable to substitute for the absence of
phospholipase C-gamma1, which can be detected in its tyrosine-phosphorylated
state.

Publication Types:
Research Support, U.S. Gov't, P.H.S.

PMID: 11744703 [PubMed - indexed for MEDLINE]

Jak2 -/- mice show defective erythropoiesis.

1: Cell. 1998 May 1;93(3):397-409.

Jak2 deficiency defines an essential developmental checkpoint in definitive
hematopoiesis.

Neubauer H, Cumano A, Muller M, Wu H, Huffstadt U, Pfeffer K.

Institute of Medical Microbiology, Immunology, and Hygiene, Technical University
of Munich, Germany.

Janus kinases (Jaks) play an important role in signal transduction via cytokine
and growth factor receptors. A targeted inactivation of Jak2 was performed.
Jak2-/- embryos are anemic and die around day 12.5 postcoitum. Primitive
erythrocytes are found, but definitive erythropoiesis is absent. Compared to
erythropoietin receptor-deficient mice, the phenotype of Jak2 deficiency is more
severe. Fetal liver BFU-E and CFU-E colonies are completely absent. However,
multilineage hematopoietic stem cells (CD34low, c-kit(pos)) can be found, and B
lymphopoiesis appears intact. In contrast to IFNalpha stimulation, Jak2-/- cells
do not respond to IFNgamma. Jak2-/- embryonic stem cells are competent for LIF
signaling. The data provided demonstrate that Jak2 has pivotal functions for
signal transduction of a set of cytokine receptors required in definitive
erythropoiesis.

Publication Types:

PMID: 9590174 [PubMed - indexed for MEDLINE]

RasGRP2 -/- mice have a platelet aggregation defect.

1: Nat Med. 2004 Sep;10(9):982-6. Epub 2004 Aug 29.

CalDAG-GEFI integrates signaling for platelet aggregation and thrombus
formation.

Crittenden JR, Bergmeier W, Zhang Y, Piffath CL, Liang Y, Wagner DD, Housman DE,
Graybiel AM.

Department of Brain and Cognitive Sciences, and McGovern Institute for Brain
Research, Massachusetts Institute of Technology, 45 Carleton Street, E25-618,
Cambridge, Massachusetts 02139, USA.

Signaling through the second messengers calcium and diacylglycerol (DAG) is a
critical element in many biological systems. Integration of calcium and DAG
signals has been suggested to occur primarily through protein kinase C family
members, which bind both calcium and DAG. However, an alternative pathway may
involve members of the CalDAG-GEF/RasGRP protein family, which have structural
features (calcium-binding EF hands and DAG-binding C1 domains) that suggest they
can function in calcium and DAG signal integration. To gain insight into the
signaling systems that may be regulated by CalDAG-GEF/RasGRP family members, we
have focused on CalDAG-GEFI, which is expressed preferentially in the brain and
blood. Through genetic ablation in the mouse, we have found that CalDAG-GEFI is
crucial for signal integration in platelets. Mouse platelets that lack
CalDAG-GEFI are severely compromised in integrin-dependent aggregation as a
consequence of their inability to signal through CalDAG-GEFI to its target, the
small GTPase Rap1. These results suggest that analogous signaling defects are
likely to occur in the central nervous system when CalDAG-GEFI is absent or
compromised in function.

Publication Types:
PMID: 15334074 [PubMed - indexed for MEDLINE]