Table Of ContentOncoImmunology1:3,37 4 –37 5 ;May/June2012;G2012LandesBioscience
Egfl7 promotes tumor escape from immunity
Sébastien Pinte and Fabrice Soncin*
CNRSUMR8161;InstitutdeBiologiedeLille;Lille,France
Keywords: endothelium, escape from immunity, angiogenesis, adhesion molecules, extravasation
Egfl7isanendothelial-specificgenewhichexpressionisderegulatedinhumancancers.WeshowedthatEgfl7promotes
tumor escape from immunity by downregulating the expression of leukocyte adhesion molecules in endothelial cells,
thusrepressing immunecellextravasation into tumors.
The tumor blood vessel endothelium lung adenocarcinoma LLC1 cells, and most of these cells infiltrated the tissues
forms an imperfectly tight barrier which analyzed the resulting effects in vitro and of control tumors and few were observed
actively protects the tumor mass from the in vivo. Overexpression of Egfl7 had no in the blood vessels. In parallel, RNA
immune system. Tumor escape from effects on tumor cell proliferation, migra- and protein arrays analyses showed that
immunity is achieved, in part, by the tion, or clone formation in vitro, suggest- IFNc expression was severely reduced in
downregulation of leukocyte adhesion ing that the protein has no major effects tumors overexpressing Egfl7 when com-
molecules normally expressed by activated on tumor cells themselves. On the other pared with controls, suggesting that these
endothelial cells. This endothelium hand, when implanted in Balb/c or tumors were depleted of immune cells.
anergy limits the adhesion and infiltration C57Bl/6 mice, tumors expressing Egfl7 Immunostainings confirmed that T-lym-
of effector immune cells within the grewfasterandinducedahigherincidence phocytes had massively infiltrated control
tumor.1-3 We found that Egfl7 induces of lung metastasis than controls. Egfl7 tumors whereas tumors overexpressing
this mechanism in endothelial cells, increased the tumor vascular density, Egfl7 were much less infiltrated and most
and thus promotes tumor escape from endothelium permeability, necrosis, and T-lymphocytes were sequestered in the
the immune system.4 hypoxia.Ontheotherhand,Egfl7hadno blood vessels lumens (Fig. 1). This was
Egfl7 (also named VE-statin) is a effects on the Ki67 proliferation index of repeatedly observed with all immune cells
secreted protein specifically expressed by tumor cells or on apoptosis. tested, namely CD4 and CD8 T-lympho-
endothelial cells during embryogenesis.5 More interestingly, when tumor cells cytes, B-lymphocytes, dendritic cells,
Egfl7 represses smooth muscle cell migra- were implanted in immune-deficient macrophages and NK cells, which were
tion, suggesting a role for this protein in SCID-Bg mice, Egfl7 had no effects on down-represented in tumors overexpress-
vascular maturation. Egfl7 is also an tumor growth and metastasis anymore, ing Egfl7 when compared with control
endogenousrepressorofendothelialelasto- suggesting that the effects of Egfl7 were tumors. This implied that Egfl7 affected
genesis via its interaction with lysyl strictly dependent on the existence of the infiltration of all types of immune
oxydases and repression of their catalytic an intact immune system in the receiving cells, with no particular specificity.
activity.6Afewreportsshowedthategfl7is mice. Furthermore, control tumors grew However, Egfl7 had no direct effects on
deregulated in human cancer; its expres- in SCID-Bg mice as fast as tumors immunecells,asitwasnotabletodecrease
sion is not anymore restricted to the overexpressing Egfl7 grew in Balb/c mice, the basal or induced proliferation of T
endothelium in human tumors, but is suggesting that, in immunocompetent lymphocytes, nor the basal or induced
also detected in cancer cells themselves. mice, Egfl7 could create an immuno- activation of T-lymphocytes, dendritic
Further, Egfl7 expression levels in human deficient environment within the tumor cells, and NK cells. Second, the effects of
hepatocarcinoma, glioma, and colon which would favor its growth. Egfl7 on immune cells were locally
cancercorrelatewithahighertumorgrade, Adetailedanalysisofthemorphologyof confined to the tumors and not systemic
with a poorer prognosis and higher tumors grown in immunocompetent mice since the spleens of mice bearing control
metastatic scores,7-9 suggesting that Egfl7 revealed the presence of numerous indivi- or tumors expressing Egfl7 were equally
is associated with tumor progression. dualized cells in the blood vessels lumens well populated.
In order to understand its role during of tumors expressing Egfl7, while a small From all these observations, it became
tumor growth and metastasis, we over- number of such cells were infiltrated highly probable that Egfl7 affected the
expressed Egfl7 in breast cancer 4T1 and withinthetumortissues.Onthecontrary, extravasation of immune cells from the
*Correspondenceto:FabriceSoncin;Email:[email protected]
Submitted:12/06/11;Accepted:12/07/11
http://dx.doi.org/10.4161/onci.18964
374 OncoImmunology Volume1Issue3
AUTHOR'SVIEW
than controls (Fig. 1). We found that
expressionoftheseadhesionmoleculeswas
directly controlled by Egfl7 in endothelial
cells, as repressing endogenous egfl7 using
RNA interference promoted the expres-
sion of ICAM-1, VCAM-1 and E-selectin
and lymphocyte adhesion to these cells,
suggesting that Egfl7 is a constitutive
repressor of endothelial cell activation.
When switching to the human disease,
we noticed that in human breast cancer
tumors expressing high levels of Egfl7,
bloodvesselendothelialcellsexpressedless
ICAM-1 and VCAM-1 than in tumors
expressinglowlevelsofEgfl7.Inaddition,
there was a direct and inverse correlation
between the levels of expression of egfl7
and those of ifnc, these two points
suggesting that Egfl7 promotes tumor
escape from immunity in human cancer
as it does in mice.
Egfl7 is therefore an endogenous regu-
lator of endothelial cell activation which,
when expressed in a tumor context, favors
tumorgrowthbydownregulatingimmune
cell extravasation. Tumor escape from
immunity mediated by the endothelium
is undoubtedly an interesting process to
considerforthedesignoftherapeutictools
aimed at preventing cancer progression
Figure1.Controltumors(top)showalargeinfiltrationofCD3ε+T-lymphocytes(brown)and and, following our observations, Egfl7
expresshighlevelsofICAM-1(green)andVCAM-1(red).TumorsexpressingEgfl7(bottom)havea representsanewtargetforinterferingwith
reducedinfiltrationofT-lymphocyteswhichmainlyremaininthebloodcirculation(arrows),blood these processes. It is worth noting that
vesselsexpressmuchlessICAM-1andVCAM-1(inserts).
since Egfl7 maintains the normal endo-
thelium in a non-activated state, interfer-
blood circulation into the tumors. An and showed that endothelial cells from ing with this property when targeting
analysis of expression of leukocyte adhe- tumors expressing Egfl7 expressed much Egfl7 might produce severe adverse side
sion molecules confirmed this hypothesis less ICAM-1, VCAM-1 and E-selectin effects in normal organs.
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