Tumor suppressor gene RBM5 delivered by attenuated Salmonella inhibits lung adenocarcinoma through diverse apoptotic signaling pathways

Abstract

BackgroundRBM5 (RNA-binding motif protein 5, also named H37/LUCA-15) gene from chromosome 3p21.3 has been demonstrated to be a tumor suppressor. Current researches in vitro confirm that RBM5 can suppress the growth of lung adenocarcinoma cells by inducing apoptosis. There is still no effective model in vivo, however, that thoroughly investigates the effect and molecular mechanism of RBM5 on lung adenocarcinoma.MethodWe established the transplanted tumor model on BALB/c nude mice using the A549 cell line. The mice were treated with the recombinant plasmids carried by attenuated Salmonella to induce the overexpression of RBM5 in tumor tissues. RBM5 overexpression was confirmed by immunohistochemistry staining. H&E staining was performed to observe the histological performance on plasmids-treated A549 xenografts. Apoptosis was assessed by TUNEL staining with a TUNEL detection kit. Apoptosis-regulated genes were detected by Western blot.ResultsWe successful established the lung adenocarcinoma animal model in vivo. The growth of tumor xenografts was significantly retarded on the mice treated with pcDNA3.1-RBM5 carried by attenuated Salmonella compared to that on mice treated with pcDNA3.1. Overexpression of RBM5 enhanced the apoptosis in tumor xenografts. Furthermore, the expression of Bcl-2 protein was decreased significantly, while the expression of BAX, TNF-α, cleaved caspase-3, cleaved caspase-8, cleaved caspase-9 and cleaved PARP proteins was significantly increased in the pcDNA3.1-RBM5-treated mice as compared to that in the control mice.ConclusionsIn this study, we established a novel animal model to determine RBM5 function in vivo, and concluded that RBM5 inhibited tumor growth in mice by inducing apoptosis. The study suggests that although RBM5’s involvement in the death receptor-mediated apoptotic pathway is still to be investigated, RBM5-mediated growth suppression, at least in part, employs regulation of the mitochondrial apoptotic pathways.

Lentiviral vector-mediated RBM5 overexpression downregulates EGFR expression in human non-small cell lung cancer cells

“…Rac1 and β-catenin were upregulated when RBM5 was knocked down [ 26 ]. Our previous study confirmed previous findings and further demonstrated that exogenous expression of RBM5 inhibited the A549 cell growth in vivo and in vitro , and re-sensitized A549/DDP cells to cisplatin by enhancement of mitochondria apoptosis [ 18 , 19 , 21 ]. Our recent study demonstrated for the first time an inverse correlation between the expression levels of RBM5 , and transforming growth factor alpha (TGF-α) signaling factors, EGFR , and KRAS in NSCLC tissues [ 22 ], which suggested that the presence of a complex regulatory network between those genes was involved in tumor suppression and oncogenic expression.…”

“…The use of animals in this study was in accordance with animal care guidelines, and the protocol was approved by Jilin University Animal Care Committee. A549 xenografts were established and the RBM5 gene was delivered into xenografts by attenuated Salmonella according to a previous study [ 19 ]. Briefly, BALB/c athymic nude female mice (nu/nu); between four and five-weeks-old) were purchased from the Institute of Zoology, Chinese Academy of Sciences (Beijing, China).…”

Role of RNA‑binding protein 5 in the diagnosis and chemotherapeutic response of lung cancer (Review)

“…is able to regulate apoptosis and cell cycle progression by increasing signal transducer and activator of transcription 5B and bone morphogenetic protein 5 expression levels, and reducing nuclear receptor coactivator 3, Pim-1 proto-oncogene serine/threonine kinase, baculoviral IAP repeat containing 3, BCL-2, EGFR and cyclin dependent kinase 2 expression levels (44)(45)(46)(47). In addition, RBM5 was demonstrated to inhibit cyclin A expression and RB phosphorylation, and thereby regulate cell cycle progression and induce G1 arrest (30).…”

Overexpression of RBM5 induces autophagy in human lung adenocarcinoma cells

“…The ectopic expression of RBM5 suppresses the growth of human lung cancer [ 11 ], breast cancer [ 13 ], fibrosarcoma [ 14 ], and hematopoietic cells [ 15 – 17 ]. Our previous study demonstrated that exogenous expression of RBM5 by the pcDNA3.1-RBM5 inhibited the cell growth of human prostate cancer and lung cancer in vivo and in vitro and resensitized the response of A549/DDP cells (cisplatin resistant counterparts of A549 cells) to cisplatin [ 8 , 18 – 20 ]. Although the mechanisms of RBM5-mediated tumor suppression remain not quite clear, recent studies suggest that RBM5 is involved in the regulation of the mitochondrial apoptotic pathway and Bcl-2 family expression [ 8 , 18 , 19 ].…”

“…Our previous study demonstrated that exogenous expression of RBM5 by the pcDNA3.1-RBM5 inhibited the cell growth of human prostate cancer and lung cancer in vivo and in vitro and resensitized the response of A549/DDP cells (cisplatin resistant counterparts of A549 cells) to cisplatin [ 8 , 18 – 20 ]. Although the mechanisms of RBM5-mediated tumor suppression remain not quite clear, recent studies suggest that RBM5 is involved in the regulation of the mitochondrial apoptotic pathway and Bcl-2 family expression [ 8 , 18 , 19 ]. It has been confirmed that Bcl-2 family also function as autophagy regulators via their interaction with the core autophagy factor Beclin family which plays an important role in the initiation of autophagosome formation [ 21 – 24 ].…”