Silencing Livin improved the sensitivity of colon cancer cells to 5-fluorouracil by regulating crosstalk between apoptosis and autophagy

Tumor Suppressor Protein p53 and Inhibitor of Apoptosis Proteins in Colorectal Cancer-A Promising Signaling Network for Therapeutic Interventions

Simple Summary

Tumor suppressor 53 (p53) is a multifunctional protein that regulates cell cycle, DNA repair, apoptosis and metabolic pathways. In colorectal cancer (CRC), mutations of the gene occur in 60% of patients and are associated with a more aggressive tumor phenotype and resistance to anti-cancer therapy. In addition, inhibitor of apoptosis (IAP) proteins are distinguished biomarkers overexpressed in CRC that impact on a diverse set of signaling pathways associated with the regulation of apoptosis/autophagy, cell migration, cell cycle and DNA damage response. As these mechanisms are further firmly controlled by p53, a transcriptional and post-translational regulation of IAPs by p53 is expected to occur in cancer cells. Here, we aim to review the molecular regulatory mechanisms between IAPs and p53 and discuss the therapeutic potential of targeting their interrelationship by multimodal treatment options.

Abstract

Despite recent advances in the treatment of colorectal cancer (CRC), patient’s individual response and clinical follow-up vary considerably with tumor intrinsic factors to contribute to an enhanced malignancy and therapy resistance. Among these markers, upregulation of members of the inhibitor of apoptosis protein (IAP) family effects on tumorigenesis and radiation- and chemo-resistance by multiple pathways, covering a hampered induction of apoptosis/autophagy, regulation of cell cycle progression and DNA damage response. These mechanisms are tightly controlled by the tumor suppressor p53 and thus transcriptional and post-translational regulation of IAPs by p53 is expected to occur in malignant cells. By this, cellular IAP1/2, X-linked IAP, Survivin, BRUCE and LIVIN expression/activity, as well as their intracellular localization is controlled by p53 in a direct or indirect manner via modulating a multitude of mechanisms. These cover, among others, transcriptional repression and the signal transducer and activator of transcription (STAT)3 pathway. In addition, p53 mutations contribute to deregulated IAP expression and resistance to therapy. This review aims at highlighting the mechanistic and clinical importance of IAP regulation by p53 in CRC and describing potential therapeutic strategies based on this interrelationship.

BIRC7 promotes epithelial-mesenchymal transition and metastasis in papillary thyroid carcinoma through restraining autophagy

Papillary thyroid carcinoma (PTC) is the most common cancer of the endocrine system, which is usually associated with a favorable therapeutic response and prognosis. However, metastatic spreading occurs in around 5% of the PTC patients. Identification of molecular markers could early predict the metastatic potential, which is essential for reducing the patient's overtreatment. Baculoviral IAP Repeat Containing 7 (BIRC7) is an inhibitor of apoptosis protein (IAP) family gene that is known to be linked to tumor progression, but its role in the setting of PTC metastasis remains unknown. This study, therefore, aims to explore the role of BIRC7 in the metastasis and autophagy of PTC and elucidate its underlying molecular mechanisms. BIRC7 expression was assessed in fresh samples of human PTC and normal tissues via qRT-PCR and immunohistochemistry. In addition, BIRC7 was overexpressed and silenced in PTC cell lines followed by transmission electron microscopy, western blotting, immunofluorescence microscopy, wound healing and invasion assays. We further explored the relevance of BIRC7 in vivo using a tumor xenograft model. Our results demonstrated that BIRC7 plays a pro-invasive role in PTC. BIRC7 expression is significantly upregulated in PTC compared with matched thyroid normal tissues. In addition, we found that BIRC7 knockdown induced a significant reduction in PTC cell EMT and metastasis in vitro and in vivo, while overexpression of BIRC7 markedly enhanced PTC cell migration and invasion. Moreover, our data showed that BIRC7 was able to suppress autophagy through modulating the expression of ATG5 and BECN1, and that this suppression is responsible for BIRC7 silence induced suppression of EMT and metastasis of PTC cell. We further found that targeting both BIRC7 and mTOR enhances autophagy in PTC cells and to achieve synergistic antimetastatic efficacy in vitro and in vivo. These findings indicate that the suppression of autophagy by BIRC7 drives the invasion and metastasis of PTC cells, thus suggesting that the activation of autophagy may inhibit metastasis of PTC with high BIRC7 expression.

Livin Regulates H2A.XY142 Phosphorylation and Promotes Autophagy in Colon Cancer Cells via a Novel Kinase Activity

Objective: To investigate Livin-mediated regulation of H2A.X^Y142 phosphorylation via a novel kinase activity and its effect on autophagy in colon cancer cells.

Methods: The interaction between Livin and H2A.X was tested by immunoprecipitation. H2A.X–/– HCT116 cells were transfected with human influenza hemagglutinin (HA)-tagged WT or Y142F phospho-dead mutantH2A.X plasmids. GST-tagged recombinant Livin protein was used to perform in vitro pull-down experiment and kinase assay. H2A.X–/–Livin+/+ SW480 cells were co-transfected with H2A.X^WT/H2A.X^Y142F plasmid and LC3 EGFP-tagged plasmid to explore whether H2A.X^Y142F was involved in Livin-mediated autophagy induced by starvation in colon cancer cells.

Results: Co-immunoprecipitation studies confirmed that Livin interacted with H2A.X and that it was phosphorylation dependent. In vitro kinase assay confirmed that Livin could phosphorylate H2A.X. Knockdown of Livin (Livin–/–) in SW480 cells or HCT116 cells canceled the starvation-induced autophagy in colon cancer cells; H2A.X–/–Livin+/+ SW480 cells transfected with H2A.X^WT activated autophagy induced by starvation while cells transfected with H2A.X^Y142F had no significant difference; Livin-H2A.X^Y142F axis activated autophagy in colon cancer cells through transcriptionally regulating ATG5 and ATG7.

Conclusion: Livin promotes autophagy in colon cancer cells via regulating the phosphorylation of H2A.X^Y142.