Hepatocarcinoma cancer (HCC) is one the most common visceral malignancies in Taiwan, which has a very high incidence and a devastatingly poor prognosis. BMP4, belonging to the TGF-£] super-family of proteins is a multifunctional cytokine, known to exert its biological effects through SMAD and non-SMAD dependent pathways and is also known to be involved in human carcinogenesis. However, the effects of the BMP4 signaling in liver carcinogenesis are not yet clearly defined. In this study, we first demonstrate that BMP4 and its receptor, BMPR1A, are over-expressed in a majority of primary HCC and promote the growth and migration of HCC cell lines in vitro. We also further identify that BMP4 can induce HCC CDK1 and cyclinB1 up-regulation to accelerate cell cycle progression. Our study indicates that the induction of HCC cell proliferation is independent on the SMAD signaling pathway, since Smad4 knockdown of BMP4 induced HCC cell lines still leads to the up-regulation of CDK1 and cyclinB1 expression in HCC. Using MEK kinase selective inhibitors, the induction of CDK1 and cyclinB1 mRNA and protein were shown to be dependent on the activation of MEK/ERK signaling. In vivo xenograft studies confirmed that the BMPR1A- knockdown cells were significantly less tumorigenic than control groups. Taken together, our findings show that the up-regulation of BMP4 and BMPR1A in HCC promote the proliferation and metastasis of HCC cells and that CDK1 and cyclinB1 are important, SMAD-independent molecular targets in BMP4 signaling pathways during the HCC tumorigenesis. We propose here that BMP4 signaling pathways may have potential as new therapeutic targets, in HCC treatment.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第23382号 / 医博第4751号 / 新制||医||1052(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊藤 貴浩, 教授 滝田 順子, 教授 江藤 浩之 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Staphylococcus aureus est une bactérie Gram positive qui colonise la peau des animaux et des humains sains. Dans certaines conditions, telles que la perturbation du microbiote, S. aureus peut induire différentes maladies en déjouant les fonctions de défenses de la cellule hôte. Récemment, notre équipe a montré que les S. aureus méthiciline-résistant (MRSA) souche MW2 (USA400) étaient capables d’induire un retard de la transition de phase G2/M des cellules HeLa. Dans ce travail, nous avons démontré que cette action est initiée par des composants du surnagent de culture de S. aureus.Différentes fractions de surnagents de culture de MW2 ont été obtenues par la chromatographie d’exclusion et analysées par la spectrométrie de masse. Ces techniques nous ont permis d’identifier les peptides phenol-soluble modulins alpha (PSMa) comme responsables du retard du cycle cellulaire des cellules hôtes. Confirmant l’implication de ces modulines, la souche LAC¿psma déficiente en PSMa 1 – 4, n’a pas affecté la progression normale du cyle cellulaire de cellules epitheliales HeLa. De plus, le traitement de ces cellules avec des PSMa1 et PSMa3 synthétiques a induit un retard de la transition de phase G2/M qui a été associé à la diminution de l’expression de gènes codant des défensines ß. Enfin, nous avons démontré que la souche MW2 diminue le niveau d’optineurine et d’optineurine phosphorylée sur la sérine-177, une protéine hôte qui est impliquée dans la transition de phase G2/M. Ce travail représente une étape importante de la compréhension du mécanisme d’interférence de S. aureus / Staphylococcus aureus is a Gram-positive bacterium that colonizes the skin of healthy animals and humans. In certain conditions, including the disruption of the commensal microbiota, S aureus can cause different diseases by deviating the host defense functions. Recently, our group has shown that the methicillin-resistant S. aureus (MRSA) MW2 (USA400) strain causes delay in the transition of the G2/M phase of HeLa cells. In the present work, we demonstrated that this action is initiated by components of the supernatant of the S. aureus culture. Different supernatant fractions were obtained by size exclusion chromatography and were analyzed by mass spectrometry, which allowed to identify phenol-soluble modulins alpha (PSMa) as responsible for the host cell cycle delay.Confirming the involvement of these modulins in the delay, the MRSA LAC¿psma strain, which is deficient in PSMa1–4, did not affect the normal progression of the cycle in HeLa cells. In addition, the treatment of these cells with synthetic PSMa1 and PSMa3 caused delay in the transition of the G2/M phase associated with the decreased production of host ß-defensins. Lastly, we demonstrated that the MW2 strain, which produce PSMa, decreases the level of optineurin and optineurin phosphorylated at serine 177, a host protein that is involved in the G2/M phase transition. The work conducted in this thesis represents an important achievement in the understanding of how S. aureus interferes with the host cell cycle, revealing a new role for PSMa produced by this bacterium.