The response to brain tumor-derived growth factors is altered in radioresistant human brain endothelial cells.
BACKGROUND
Radioresistant brain tumor vasculature is thought to hamper the efficiency of adjuvant cancer therapies. However, little is known regarding the signalling pathways involved in the angiogenic response to brain tumor-derived growth factors in irradiated human brain microvascular endothelial cells (HBMEC). The goal of this study is to assess the effect of ionizing radiation (IR) on HBMEC survival, migration and tubulogenesis.


METHODS
HBMEC were cultured and irradiated at sublethal single doses. Cell survival was assessed by nuclear cell counting and flow cytometry. HBMEC migration in response to brain tumor-derived growth factors (U-87 GF) and tubulogenesis were assayed using modified Boyden chambers and Matrigel, respectively.


RESULTS
We observed that single administration of 3-10 Gy IR doses only reduced cell survival by 30%. Radioresistant HBMEC overexpressed RhoA, a small GTPase protein regulating cellular adhesion and migration, and Rho-kinase (ROK), a serine-threonine protein kinase and one of RhoA's major targets. HBMEC migration was induced by vascular endothelial growth factor (VEGF), but even more so in response to sphingo-sine-1-phosphate (S1P) and to U-87 GF. Following IR exposure, HBMEC basal migration increased more than two-fold, whereas the response to S1P and to U-87 GF was significantly diminished. Similarly, the inhibitor of ROK Y-27632 decreased HBMEC migration in response to S1P and U-87 GF. Overexpression of RhoA decreased tubulogenesis, an effect also observed in irradiated HBMEC.


CONCLUSIONS
Our results suggest that radioresistant HBMEC migration response to tumor-secreted growth factors and tubulogenesis are altered following IR. The RhoA/ROK signalling pathway is involved in the IR-altered angiogenic functions and may represent a potential molecular target for enhancing the impact of radiotherapy on tumor-associated endothelial cells.
McLaughlin
Nancy
N
Laboratoire de Médecine Moléculaire, Centre de Cancérologie Charles-Bruneau, Hôpital Sainte-Justine-UQAM, Montreal, Quebec, Canada.
Annabi
Borhane
B
Sik Kim
Kwang
K
Bahary
Jean-Paul
JP
Moumdjian
Robert
R
Béliveau
Richard
R
D017209:Apoptosis; D001921:Brain / Q000166:cytology / Q000473:pathology / Q000502:physiology / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D002560:Cerebrovascular Circulation / Q000528:radiation effects*; D004730:Endothelium, Vascular / Q000528:radiation effects*; D005434:Flow Cytometry; D006133:Growth Substances / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D008833:Microcirculation / Q000528:radiation effects*; D009336:Necrosis; D042461:Vascular Endothelial Growth Factor A / Q000528:radiation effects; D020742:rhoA GTP-Binding Protein / Q000528:radiation effects
D006133:Growth Substances; D042461:Vascular Endothelial Growth Factor A; D020742:rhoA GTP-Binding Protein