Molecular cloning and differential expression patterns of the regulatory subunit B' gene of PP2A in goldfish,Carassius auratus

It is well established that the protein serine/threonine phosphatase 2A(PP2A) plays very important roles in many different cellular processes,including cell proliferation and differentiation,gene expression,neurotransmission,apoptosis,and aging.PP2A consists of three heterogenic subunits:the scaffold subunit A,the catalytic subunit C,and the regulatory subunit B.While both the scaffold and the catalytic subunits contain only two forms,at least four families of the regulatory subunits,B,B',B'',and B''' have been identified.These regulatory subunits from different families are encoded by different genes and bear other functions besides directing the specificity of PP2A.To study the functions of the regulatory subunits of PP2A in lower vertebrates,we have cloned the full-length cDNA sequence of the gene encoding the regulatory subunit B'δ of PP2A from gold fish,Carassius auratus using 3'-RACE and 5'-RACE cloning strategies.Our results revealed that the full-length B'δ cDNA contains 2415 bp and encodes a protein of 555 amino acids.The B'δ protein displays a very high level of sequence identity with the B'δ regulatory subunit from other species of vertebrates.Regarding its expression pattern,RT-PCR revealed that the highest level of mRNA was detected in brain,a less level detected in liver,spermary,ovary,kidney and gill,and the lowest level detected in the fin.During different developmental stages of gold fish,the highest level of mRNA expression was detected at the stages of two-cell,multiple-cell,blastula and gastrula,and a decreased level of B'δ mRNA was detected in other developmental stages.At the protein level,the highest expression level of B'δ protein was found in spermary,ovary,brain and heart,a less amount found in liver and the lowest level detected in kidney,gill and fin.Developmentally,B'δ protein was strongly expressed at the stages of two-cell,multiple-cell,blastula,gastrula,neurula,and optic vesicle,and then decreased at the stages of brain differentiation and eye pigmentation.These results suggest that B'δ appears to play a very important role during gold fish development and also in adult tissue homeostasis.

HBV Infection Promotes the Occurrence and Development of Hepatocellular Carcinoma through Impairing the Inhibitory Effect of PPP2R5A on MAPK/AKT/WNT Signaling Pathway

Reversible phosphorylation and dephosphorylation play important roles in cell function and cell signal transduction. PPP2R5A (protein phosphatase 2 regulatory subunit B’ alpha) is responsible for specifically regulating the catalytic function, substrate specificity and intracellular localization of the tumor suppressor phosphatase PP2A (serine/threonine protein phosphatase 2A). Therefore, the abnormal expression and function of PPP2R5A may be related to canceration. The aim of this study was to reveal its role in the occurrence and development of hepatocellular carcinoma (HCC). It is hoped that the results of this study can provide guidance for the prevention and treatment of HCC. The results showed that PPP2R5A inhibited the proliferation and metastasis of HCC cells, and acted as a tumor suppressor in HCC cells, but it had no significant effect on cell cycle. Further research found that PPP2R5A exerted tumor suppressor efficacy by inhibiting the MAPK/AKT/WNT signaling pathway. Combined with analysis of clinical tissue samples and TCGA database, it was found that the expression of PPP2R5A in tumor tissues of Chinese HCC patients was down-regulated and significantly correlated with the progression-free survival (PFS) of HCC patients. On the contrary, PPP2R5A showed an up-regulation trend in HCC cases in TCGA database although its effect on PFS was the same with that in Chinese HCC patients. Hepatitis B virus (HBV) infection is the main pathogenic factor of HCC in China. It was found that HBV infection reduced the content of PPP2R5A in cells. It was concluded that HBV inhibited the initiation of the protective mechanism mediated by PPP2R5A, making the occurrence and progress of HCC more “unimpeded”. This conclusion will further reveal the role of PPP2R5A in HBV-induced and HBV-unrelated HCC, therefore, providing clues for the prevention and treatment of the two types of HCC, respectively.