RESUMO
AMP-activated protein kinase (AMPK), a biologic sensor for cellular energy status, has been shown to act upstream and downstream of known tumor suppressors. However, whether AMPK itself plays a tumor suppressor role in cancer remains unclear. Here, we found that the α2 catalytic subunit isoform of AMPK is significantly downregulated in hepatocellular carcinoma (HCC). Clinicopathologic analysis revealed that underexpression of AMPK-α2 was statistically associated with an undifferentiated cellular phenotype and poor patient prognosis. Loss of AMPK-α2 in HCC cells rendered them more tumorigenic than control cells both in vitro and in vivo. Mechanistically, ectopic expression of AMPK enhanced the acetylation and stability of p53 in HCC cells. The p53 deacetylase, SIRT1, was phosphorylated and inactivated by AMPK at Thr344, promoting p53 acetylation and apoptosis of HCC cells. Taken together, our findings suggest that underexpression of AMPK is frequently observed in HCC, and that inactivation of AMPK promotes hepatocarcinogenesis by destabilizing p53 in a SIRT1-dependent manner.
Assuntos
Proteínas Quinases Ativadas por AMP/metabolismo , Carcinoma Hepatocelular/genética , Carcinoma Hepatocelular/metabolismo , Neoplasias Hepáticas/genética , Neoplasias Hepáticas/metabolismo , Sirtuína 1/genética , Proteína Supressora de Tumor p53/metabolismo , Proteínas Quinases Ativadas por AMP/antagonistas & inibidores , Proteínas Quinases Ativadas por AMP/genética , Acetilação , Apoptose/genética , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Masculino , Fosforilação , Ligação Proteica , Inibidores de Proteínas Quinases/farmacologia , Sirtuína 1/metabolismo , Ativação Transcricional , Proteína Supressora de Tumor p53/genéticaRESUMO
UNLABELLED: Deregulation of cellular-signaling pathways by the inactivation of tumor-suppressor genes is one of the major causes of hepatocellular carcinoma (HCC). In this study, we identified Tax1 binding protein 2 (TAX1BP2) as a novel tumor-suppressor gene in HCC. TAX1BP2 transcript was frequently underexpressed (42.2% with T/NT <0.5; P < 0.03) in HCCs, and underexpression of TAX1BP2 was associated with poorer overall survival rates in patients after surgical resection. An effector domain (ED) for TAX1BP2 tumor-suppressor activity was mapped to the amino-acid residues 267-756. Transient or stable expression of either full-length or ED of TAX1BP2 significantly suppressed HCC cell tumorigenicity through the activation of the p38/p53/p21 pathway. In contrast, silencing of TAX1BP2 by short interfering RNA remarkably suppressed the activation of the p38/p53/p21 pathway. Finally, phosphorylation of TAX1BP2 at serine-763 by cyclin-dependent kinase (CDK)2 abolished the TAX1BP2-mediated p38 activation and tumor-suppressive activity, indicating that TAX1BP2 can adapt CDK2 signaling to the p38/p53/p21 pathway. CONCLUSION: Taken together, our data provide the first evidence that TAX1BP2 is a CDK2-regulated tumor-suppressor gene in HCC and is a novel activator of the p38/p53/p21 pathway.
Assuntos
Carcinoma Hepatocelular/genética , Quinase 2 Dependente de Ciclina/metabolismo , Regulação Neoplásica da Expressão Gênica , Neoplasias Hepáticas/genética , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Carcinoma Hepatocelular/metabolismo , Carcinoma Hepatocelular/patologia , Centrossomo/metabolismo , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Regulação para Baixo , Inativação Gênica , Células Hep G2 , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Estimativa de Kaplan-Meier , Neoplasias Hepáticas/metabolismo , Neoplasias Hepáticas/patologia , Sistema de Sinalização das MAP Quinases/genética , Fosforilação , Proteína Supressora de Tumor p53/metabolismoRESUMO
The CDK5 kinase regulatory subunit-associated protein 3 (CDK5RAP3 or C53/LZAP) regulates apoptosis induced by genotoxic stress. Although CDK5RAP3 has been implicated in cancer progression, its exact role in carcinogenesis is not well established. In this article, we report that CDK5RAP3 has an important prometastatic function in hepatocarcinogenesis. An examination of human hepatocellular carcinoma (HCC) samples revealed at least twofold overexpression of CDK5RAP3 transcripts in 58% (39/67) of HCC specimens when compared with corresponding nontumorous livers. CDK5RAP3 overexpression was associated with more aggressive biological behavior. In HCC cell lines, stable overexpression of CDK5RAP3 promoted, and small interfering RNA-mediated knockdown inhibited, tumorigenic activity and metastatic potential. We found that overexpression of CDK5RAP3 and p21-activated protein kinase 4 (PAK4) correlated in human HCCs, and that CDK5RAP3 was a novel binding partner of PAK4, and this binding enhanced PAK4 activity. siRNA-mediated knockdown of PAK4 in CDK5RAP3-expressing HCC cells reversed the enhanced cell invasiveness mediated by CDK5RAP3 overexpression, implying that PAK4 is essential for CDK5RAP3 function. Taken together, our findings reveal that CDK5RAP3 is widely overexpressed in HCC and that overexpression of CDK5RAP3 promotes HCC metastasis through PAK4 activation.
