DECIPHERING THE MECHANISMS OF MEDULLOBLASTOMA RESISTANCE TO RADIO/CHEMOTHERAPY: TOWARD PERSONALIZED TREATMENTS?

International audienc

INTRINSIC OR INDUCED AGGRESSIVENESS-LINKED REGULATION OF VEGFC IN MEDULLOBLASTOMA CELL LINES

International audienceMedulloblastoma (MDB) is the most common pediatric malignant brain tumor. MDB is a very heterogeneous disease that consists of four subgroups, each of them with different molecular profiles, metastasis status and clinical outcomes. Treatment of MDB includes surgery, radiotherapy and chemotherapy. It cures 70% of the pa'ents nevertheless with many side effects. Relapse is always fatal. Understanding the mechanisms of this relapse might lead to the development of new targeted treatments. VEGFC and lympha'c markers are the main actors of the metasta'c process in many tumors. We thus meant to determine their role and regula'on in MDB-derived cells. We demonstrated that low-aggressiveness MDB-derived cells, DAOY, expressed high basal amounts of lympha'c marker mRNAs and proteins (VEGFC, PROX1, NRP2). Conversely, highly aggressive cells, HD-MB03, presented low amounts of these markers. X-ray irradia'on treatment of the cells induced a rise in VEGFC, at the mRNA and protein levels. We thus ques'oned the regula'on of lympha'c markers in MDB cells. We observed that in the highly aggressive HD-MB03 cells, VEGFC mRNA amount relies upon a very ac've NF-κB-dependent promoter, but that the mRNA gets intensely degraded, hence the low level of VEGFC mRNA in these cells. Conversely, DAOY cells present low ac'vity of VEGFC promoter and high stability of the synthesized mRNA. The promoter ac'vity is independent from NF-κB. Moreover, while VEGFC is secreted in DAOY cells, it is retained inside the cytoplasm of HD-MB03 cells. Since VEGFC is so precisely regulated in MDB cells, it may play an important part in MDB aggressiveness. HSP 90 VEGFC Claudin DAOY Clone 1 HD-MB03 DAPI DAPI DAPI VEGFC VEGFC VEGFC Merge Merge Merge Intrinsic characterisOcs of MB cell lines DAOY (SHH): High expression of lymphaOc markers and VEGFC > Low proliferaOon and high migraOon rates HDMB-03 (Grp3): High expression of lymphaOc markers and VEGFC > High proliferaOon and low migraOon rates VEGFC has a impact on the proliferaOon of HD-MB03 cells. VEGFC DAOY VEGFC promoter VEGFC VEGFC mRNA HD-MB0

LE VEGFC RÉGULE NÉGATIVEMENT LA CROISSANCE ET L'AGRESSIVITÉ DES CELLULES DE MÉDULLOBLASTOME

International audienceMedulloblastoma (MB), the most common brain pediatric tumor, is a pathology composed of four molecular subgroups. Despite a multimodal treatment, 30% of the patients eventually relapse, with the fatal appearance of metastases within 5 years. The major actors of meta-static dissemination are the lymphatic vessel growth factor, VEGFC, and its receptors/co-receptors. Here, we show that VEGFC is inversely correlated to cell aggressiveness. Indeed, VEGFC decreases MB cell proliferation and migration, and their ability to form pseudo-vessel in vitro. Irradiation resistant-cells, which present high levels of VEGFC, lose the ability to migrate and to form vessel-like structures. Thus, irradiation reduces MB cell aggressiveness via a VEGFC-dependent process. Cells intrinsically or ectopically overexpressing VEGFC and irradiation-resistant cells form smaller experimental tumors in nude mice. Opposite to the common dogma, our results give strong arguments in favor of VEGFC as a negative regulator of MB growth.Le médulloblastome (MB), la tumeur pédiatrique maligne cérébrale la plus courante, est une pathologie composée de quatre sous-groupes moléculaires. Malgré un traitement multimodal, 30% des patients rechutent finalement, avec l'apparition fatale de métastases dans les 5 ans. Les principaux acteurs de la dissémination métastatique sont le facteur de croissance des vaisseaux lymphatiques, le VEGFC, et ses récepteurs / co-récepteurs. Ici, nous montrons que le VEGFC est inversement corrélé à l'agressivité cellulaire. En effet, le VEGFC diminue la prolifération et la migration des cellules MB, ainsi que leur capacité à former des pseudo-vaisseaux in vitro. Les cellules résistantes à l'irradiation, qui présentent des niveaux élevés de VEGFC, perdent la capacité de migrer et de former des structures de type « vaisseaux ». Ainsi, l'irradiation réduit l'agressivité des cellules MB via un processus dépendant du VEGFC. Les cellules surexprimant le VEGFC de façon intrinsèque ou ectopique et les cellules résistantes à l'irradiation forment des tumeurs expérimentales plus petites chez la souris nude. Contrairement au dogme commun, nos résultats donnent de solides arguments en faveur du rôle de régulateur négatif du VEGFC sur la croissance du MB