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Hepatocellular carcinoma (HCC) is a deadly form of liver malignancy with limited treatment
options. Amplification and/or overexpression of c-MYC is one of the most frequent genetic events
in human HCC. The mammalian target of Rapamycin Complex 1 (mTORC1) is a major functional
axis regulating various aspects of cellular growth and metabolism. Recently, we demonstrated that
mTORC1 is necessary for c-Myc driven hepatocarcinogenesis as well as for HCC cell growth in vitro.
Among the pivotal downstream effectors of mTORC1, upregulation of Fatty Acid Synthase (FASN) and
its mediated de novo lipogenesis is a hallmark of human HCC. Here, we investigated the importance
of FASN on c-Myc-dependent hepatocarcinogenesis using in vitro and in vivo approaches. In mouse
and human HCC cells, we found that FASN suppression by either gene silencing or soluble inhibitors
more effectively suppressed proliferation and induced apoptosis in the presence of high c-MYC
expression. In c-Myc/Myeloid cell leukemia 1 (MCL1) mouse liver tumor lesions, FASN expression
was markedly upregulated. Most importantly, genetic ablation of Fasn profoundly delayed (without
abolishing) c-Myc/MCL1 induced HCC formation. Liver tumors developing in c-Myc/MCL1 mice
depleted of Fasn showed a reduction in proliferation and an increase in apoptosis when compared
with corresponding lesions from c-Myc/MCL1 mice with an intact Fasn gene. In human HCC samples,
a significant correlation between the levels of c-MYC transcriptional activity and the expression
of FASN mRNA was detected. Altogether, our study indicates that FASN is an important effector
downstream of mTORC1 in c-MYC induced HCC. Targeting FASN may be helpful for the treatment
of human HCC, at least in the tumor subset displaying c-MYC amplification or activation.
Protection against Staphylococcus aureus is determined by the polarization of the anti-bacterial immune effector mechanisms. Virulence factors of S. aureus can modulate these and induce differently polarized immune responses in a single individual. We proposed that this may be due to intrinsic properties of the bacterial proteins. To test this idea, we selected two virulence factors, the serine protease-like protein B (SplB) and the glycerophosphoryl diester phosphodiesterase (GlpQ). In humans naturally exposed to S. aureus, SplB induces a type 2-biased adaptive immune response, whereas GlpQ elicits type 1/type 3 immunity. We injected the recombinant bacterial antigens into the peritoneum of S. aureus-naïve C57BL/6N mice and analyzed the immune response. This was skewed by SplB toward a Th2 profile including specific IgE, whereas GlpQ was weakly immunogenic. To elucidate the influence of adjuvants on the proteins’ polarization potential, we studied Montanide ISA 71 VG and Imject™Alum, which promote a Th1 and Th2 response, respectively. Alum strongly increased antibody production to the Th2-polarizing protein SplB, but did not affect the response to GlpQ. Montanide enhanced the antibody production to both S. aureus virulence factors. Montanide also augmented the inflammation in general, whereas Alum had little effect on the cellular immune response. The adjuvants did not override the polarization potential of the S. aureus proteins on the adaptive immune response.
Staphylococcus aureus(S. aureus) is a pathobiont of humans as well as a multitude of animalspecies. The high prevalence of multi-resistant and more virulent strains ofS. aureusnecessitatesthe development of new prevention and treatment strategies forS. aureusinfection. Major advancestowards understanding the pathogenesis ofS. aureusdiseases have been made using conventionalmouse models, i.e., by infecting naïve laboratory mice with human-adaptedS. aureusstrains. However,the failure to transfer certain results obtained in these murine systems to humans highlights thelimitations of such models. Indeed, numerousS. aureusvaccine candidates showed promising resultsin conventional mouse models but failed to offer protection in human clinical trials. These limitationsarise not only from the widely discussed physiological differences between mice and humans, but alsofrom the lack of attention that is paid to the specific interactions ofS. aureuswith its respectivehost. For instance, animal-derivedS. aureuslineages show a high degree of host tropism and carry arepertoire of host-specific virulence and immune evasion factors. Mouse-adaptedS. aureusstrains,humanized mice, and microbiome-optimized mice are promising approaches to overcome theselimitations and could improve transferability of animal experiments to human trials in the future.