Morphogenesis - Signal Transduction シグナル伝達

RhoB null mice have retarded vascular development in the retina.

1: Genes Dev. 2003 Nov 1;17(21):2721-32.

RhoB controls Akt trafficking and stage-specific survival of endothelial cells
during vascular development.

Adini I, Rabinovitz I, Sun JF, Prendergast GC, Benjamin LE.

Beth Israel Deaconess Medical Center, Harvard Medical School, Boston,
Massachusetts 02215, USA.

Blood vessel formation is a complex morphological process that is only beginning
to be understood at the molecular level. In this study, we demonstrate a novel
and critical role for the small GTPase, RhoB, in vascular development. RhoB null
mice have retarded vascular development in the retina characterized by altered
sprout morphology. Moreover, pharmaceutical means to deplete RhoB in neonatal
rats is associated with apoptosis in the sprouting endothelial cells of newly
forming vessels. Similarly, acute depletion of RhoB by antisense or
dominant-negative strategies in primary endothelial cell culture models led to
apoptosis and failures in tube formation. We identified a novel link between
RhoB and the Akt survival signaling pathway to explain these changes. Confocal
microscopy revealed that RhoB is highly localized to the nuclear margin with a
small percentage found inside the nucleus. Similarly, total Akt is throughout
the cell but has increased accumulation at the nuclear margin, and active
phosphorylated Akt is found primarily inside the nucleoplasm, where it partially
colocalizes with the RhoB therein. We show that this colocalization is
functionally relevant, because when RhoB was depleted, Akt was excluded from the
nucleus and total cellular Akt protein was decreased in a proteosome-dependent
manner. Because the function of RhoB in vivo appears to only be rate limiting
for endothelial cell sprouting, we propose that RhoB has a novel stage-specific
function to regulate endothelial cell survival during vascular development. RhoB
may offer a therapeutic target in diseases such as cancer, diabetic retinopathy,
and macular degeneration, where the disruption of sprouting angiogenesis would
be desirable.

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

PMID: 14597666 [PubMed - indexed for MEDLINE]

SOS1-/- mice impair placental development.

1: EMBO J. 2000 Feb 15;19(4):642-54.

The Sos1 and Sos2 Ras-specific exchange factors: differences in placental
expression and signaling properties.

Qian X, Esteban L, Vass WC, Upadhyaya C, Papageorge AG, Yienger K, Ward JM, Lowy
DR, Santos E.

Laboratory of, National Cancer Institute, Bethesda, MD 20892, USA.

Targeted disruption of both alleles of mouse sos1, which encodes a Ras-specific
exchange factor, conferred mid-gestational embryonic lethality that was
secondary to impaired placental development and was associated with very low
placental ERK activity. The trophoblastic layers of sos1(-/-) embryos were
poorly developed, correlating with high sos1 expression in wild-type
trophoblasts. A sos1(-/-) cell line, which expressed readily detectable levels
of the closely related Sos2 protein, formed complexes between Sos2, epidermal
growth factor receptor (EGFR) and Shc efficiently, gave normal Ras.GTP and ERK
responses when treated with EGF for < or =10 min and was transformed readily by
activated Ras. However, the sos1(-/-) cells were resistant to transformation by
v-Src or by overexpressed EGFR and continuous EGF treatment, unlike sos1(+/-) or
wild-type cells. This correlated with Sos2 binding less efficiently than Sos1 to
EGFR and Shc in cells treated with EGF for > or =90 min or to v-Src and Shc in
v-Src-expressing cells, and with less ERK activity. We conclude that Sos1
participates in both short- and long-term signaling, while Sos2-dependent
signals are predominantly short-term.

PMID: 10675333 [PubMed - indexed for MEDLINE]

The interaction between DOC and CSW is needed for normal eye development.

1: EMBO J. 1999 Dec 15;18(24):6950-61.

Recruitment of the protein tyrosine phosphatase CSW by DOS is an essential step
during signaling by the sevenless receptor tyrosine kinase.

Herbst R, Zhang X, Qin J, Simon MA.

Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020,
USA.

The pleckstrin homology (PH) domain-containing protein Daughter of Sevenless
(DOS) is an essential component of the Sevenless receptor tyrosine kinase (SEV)
signaling cascade, which specifies R7 photoreceptor development in the
Drosophila eye. Previous results have suggested that DOS becomes tyrosine
phosphorylated during SEV signaling and collaborates with the protein tyrosine
phosphatase CSW. We have investigated this possibility by identifying tyrosine
residues 801 and 854 of DOS as the phosphorylated binding sites for the CSW SH2
domains. We show that these sites become phosphorylated in response to SEV
activation and that phosphorylation of both sites is required to allow CSW to
bind DOS. Mutant DOS proteins in which either Y801 or Y854 of DOS has been
changed to phenylalanine are unable to function during signaling by SEV and
other receptor tyrosine kinases. In contrast, we find that a mutant DOS protein
in which all tyrosine phosphorylation sites except Y801 and Y854 have been
removed is able effectively to provide DOS function during SEV signaling and to
rescue the lethality associated with dos loss-of-function mutations. These
results indicate that a primary role for DOS during signaling by SEV and other
receptor tyrosine kinases is to become phosphorylated at Y801 and Y854 and then
recruit CSW.

PMID: 10601017 [PubMed - indexed for MEDLINE]

Gab1 and Gab2 are phosphorylated by EPO signal.

1: Blood. 2004 Jun 15;103(12):4457-65. Epub 2004 Feb 24.

Tyrosine kinase receptor RON functions downstream of the erythropoietin receptor
to induce expansion of erythroid progenitors.

van den Akker E, van Dijk T, Parren-van Amelsvoort M, Grossmann KS, Schaeper U,
Toney-Earley K, Waltz SE, Lowenberg B, von Lindern M.

Department of Hematology, Erasmus MC, PO Box 1738, 3000 DR Rotterdam, the
Netherlands.

Erythropoietin (EPO) is required for cell survival during differentiation and
for progenitor expansion during stress erythropoiesis. Although signaling
pathways may couple directly to docking sites on the EPO receptor (EpoR),
additional docking molecules expand the signaling platform of the receptor. We
studied the roles of the docking molecules Grb2-associated binder-1 (Gab1) and
Gab2 in EPO-induced signal transduction and erythropoiesis. Inhibitors of
phosphatidylinositide 3-kinase and Src kinases suppressed EPO-dependent
phosphorylation of Gab2. In contrast, Gab1 activation depends on recruitment and
phosphorylation by the tyrosine kinase receptor RON, with which it is
constitutively associated. RON activation induces the phosphorylation of Gab1,
mitogen-activated protein kinase (MAPK), and protein kinase B (PKB) but not of
signal transducer and activator of transcription 5 (Stat5). RON activation was
sufficient to replace EPO in progenitor expansion but not in differentiation. In
conclusion, we elucidated a novel mechanism specifically involved in the
expansion of erythroblasts involving RON as a downstream target of the EpoR.

PMID: 14982882 [PubMed - indexed for MEDLINE]

Overexpression of Gab1 in kidney epithelial cells of a mouce results in constitutive and ligand-independent cell scattering and branching morphogenesis.

1: Nature. 1996 Nov 14;384(6605):173-6.

Interaction between Gab1 and the c-Met receptor tyrosine kinase is responsible
for epithelial morphogenesis.

Weidner KM, Di Cesare S, Sachs M, Brinkmann V, Behrens J, Birchmeier W.

Max Delbruck Center for Molecular Medicine, Berlin, Germany.

The proteins Gab1 and the related DOS (for 'daughter of sevenless') each bind to
substrates of tyrosine kinases like Grb2 or Corkscrew, and act in signalling
pathways downstream of tyrosine kinase receptors. Here we show that Gab1
interacts directly with the c-met-encoded receptor tyrosine kinase but not with
a number of other tyrosine kinases from different subfamilies. A newly
identified proline-rich domain of Gab1 is responsible for the binding of this
protein to the tyrosine-phosphorylated bidentate docking site in c-Met.
Expression of Gab1 in epithelial cells is sufficient to induce the
c-Met-specific activities, including branching morphogenesis. Thus we have
discovered a new phosphotyrosine interaction domain in Gab1 and shown that Gab1
is the substrate of the c-Met receptor tyrosine kinase that mediates epithelial
morphogenesis.

PMID: 8906793 [PubMed - indexed for MEDLINE]