Blocking fatty acid synthase inhibits tumor progression of human osteosarcoma by regulating the human epidermal growth factor receptor 2/phosphoinositide 3-kinase/protein kinase B signaling pathway in xenograft models

In Situ Analysis of mTORC1/C2 and Metabolism-Related Proteins in Pediatric Osteosarcoma

Activation of the mTOR pathway has been observed in osteosarcoma, however the inhibition of mammalian target of rapamycin (mTOR) complex 1 has had limited results in osteosarcoma treatment. Certain metabolic pathways can be altered by mTOR activation, which can affect survival. Our aim was to characterize the mTOR profile and certain metabolic alterations in pediatric osteosarcoma to determine the interactions between the mTOR pathway and metabolic pathways. We performed immunohistochemistry on 28 samples to analyze the expression of mTOR complexes such as phospho-mTOR (pmTOR), phosphorylated ribosomal S6 (pS6), and rapamycin-insensitive companion of mTOR (rictor). To characterize metabolic pathway markers, we investigated the expression of phosphofructokinase (PFK), lactate dehydrogenase-A (LDHA), β-F1-ATPase (ATPB), glucose-6-phosphate dehydrogenase (G6PDH), glutaminase (GLS), fatty acid synthetase (FASN), and carnitin-O-palmitoyltransferase-1 (CPT1A). In total, 61% of the cases showed low mTOR activity, but higher pmTOR expression was associated with poor histological response to chemotherapy and osteoblastic subtype. Rictor expression was higher in metastatic disease and older age at the time of diagnosis. Our findings suggest the importance of the Warburg-effect, pentose-phosphate pathway, glutamine demand, and fatty-acid beta oxidation in osteosarcoma cells. mTOR activation is linked to several metabolic pathways. We suggest performing a detailed investigation of the mTOR profile before considering mTORC1 inhibitor therapy. Our findings highlight that targeting certain metabolic pathways could be an alternative therapeutic approach.

Decreased expression of miR-195 mediated by hypermethylation promotes osteosarcoma

Osteosarcoma (OS) is the most common type of primary malignant bone tumor. The early lung metastasis of osteosarcoma is one of the main factors of poor prognosis. Therefore, searching for new targets and new mechanisms of osteosarcoma metastasis is essential for the prevention and treatment of osteosarcoma. Our previous studies suggested that fatty acid synthase (FASN) was an oncogene and promoted osteosarcoma. In addition, it is reported that the expression of miR-195 was negatively correlated with osteosarcoma. Aberrant DNA methylation can reversely regulate the expression of miRNAs. However, whether miR-195 could target FASN in osteosarcoma and whether ectopic DNA methylation is the upstream regulatory mechanism of miR-195 in metastasis of osteosarcoma are not fully studied. The expressions were detected by qPCR and western blot, and methylation level was determined by methylation-specific PCR. Luciferase reporter assay, MTT, wound healing, and Transwell assay were used. We found that the expression of miR-195 was low in osteosarcoma. The methylation of miR-195 was high. miR-195 targeted and decreased the expression of FASN. In osteosarcoma, miR-195 inhibited cell proliferation, cell migration, and invasion. The methylation of miR-195 was related to decreased miR-195, it might promote osteosarcoma.

Inhibition of fatty acid synthase (FASN) affects the proliferation and apoptosis of HepG2 hepatoma carcinoma cells via the β-catenin/C-myc signaling pathway

INTRODUCTION AND OBJECTIVES

Research in the last few years has proven that inhibition of fatty acid synthase (FASN) suppresses the migration and invasion of hepatoma carcinoma cells. This study aims to explore the effect of fatty acid synthase knockdown on the apoptosis and proliferation of HepG2 cells.

MATERIALS AND METHODS

The human liver cancer cell line HepG2 was cultured and then transfected with FASN-specific siRNA and negative control RNAi. After 48h, cells and protein lysates were used for western blotting, CCK-8 (cell counting kit-8) assays, flow cytometry and other tests. To assess cell apoptosis, Bax, Bcl-2 and caspase-3 were detected; to assess proliferation, CDK4 (cyclin-dependent kinases 4) and P21 were detected; and to determine the signaling pathway involved, β-catenin and C-myc were also detected.

RESULTS

Inhibition of FASN in HepG2 cells can decrease proliferation and promote apoptosis. Flow cytometry and CCK-8 assays demonstrated that the apoptosis rate of FASN-specific siRNA-transfected cells was significantly increased compared to that of the control cells (p<0.01). In addition, the cell cycle analysis revealed that FASN-specific siRNA-transfected cells induced G1 phase arrest (p<0.05), but an increasing trend in G2 (p<0.05). Compared with expression in negative RNAi-transfected cells, the expression of Bcl-2 and CDK-4 was reduced and the expression of Bax, caspase-3 and P21 was increased in FASN-specific siRNA-transfected cells (p<0.05). Regarding the signaling pathway, the expression of β-catenin and C-myc was significantly reduced when compared to that in negative control cells (p<0.05).

CONCLUSIONS

Inhibition of FASN suppressed the cell survival of HepG2 cells by inhibiting the β-catenin/C-myc pathway. This result suggests the potential treatment value of FASN for hepatoma carcinoma (HCC).

Anoikis resistant mediated by FASN promoted growth and metastasis of osteosarcoma

The pulmonary metastasis of osteosarcoma (OS) occurs commonly, which resulted from anoikis resistant (AR) of tumor cells as reported by previous studies, but the exact roles of AR in osteosarcoma were not fully studied. Our previous investigations showed fatty acid synthase (FASN) was relating to clinical features of patients with OS. In this study, we aim to explore the functions of FASN in the AR OS cells in vitro and in vivo and study the downstream effectors of FASN. In the present study, we used our established cell model to study the AR. We revealed that AR promoted cell proliferation and migration as determined by colony formation assay and transwell assay. In addition, AR assisted tumor growth in vivo. In the AR cells, the expression of FASN was higher. Thus, we constructed lentiviruses to silence or overexpress FASN in four cell lines to study functions of FASN. Silence of FASN reduced cell colonies and migration while overexpression of FASN increased colonies and migration in suspended cells. Loss of functions of FASN induced cell apoptosis in suspended OS cells while gain of function of FASN suppressed apoptosis as determined by flow cytometry. We found the levels of p-ERK1/2 and Bcl-xL declined when FASN was silenced while they increased when FASN was overexpressed. In addition, results showed that the levels of FASN and its potential related molecules (p-ERK1/2 and Bcl-xL) increased in 143B-AR and MG-63-AR cells. In vivo study showed that inhibition of FASN decreased pulmonary metastasis of OS. In conclusion, we showed that anoikis resistant and FASN as two interactional factors facilitated the progress of osteosarcoma.