Analysis Of Transcriptional Regulation And Tumorigenic Ability Of The Structure Subunit Aα Of PP2A

Protein phosphorylation and dephosphorylation is prevalent in cellular regulatory activity. About one third of cellular protein is regulated by phosphorylation and dephosphorylation. In eukaryotic cells, 98% phosphorylation add phosphate group to Ser/Thr amino acid. Researchers discovered 411 Ser/Thr kinases, but there are only about 40 protein phosphatases. Of all the protein phosphatases, PP2A is one of the most important protein phosphatase. PP2A exists almost in all tissues and organisms, and above all, it dephosphorizes more than 1% protein in human brain. PP2A also takes effect in cell proliferation, differetiation, aging and apoptosis and so on.PP2A consists of catalytic subunit C, structural subunit A and regulatory subunit B. Its a heterotrimer. PP2A exists in two forms:corenzyme and holoenzyme. Coremzyme is madeup of 65kd structrual subunit A and 36kd catalytic subunit C. Coreenzyme take 30-50% of PP2A enzyme. In celluar activity, corenzyme can only be stable when combining with regulatary subunit B as holoenzyme.Our recent study show us that PP2A-Aa is regulated by multiple transcriptional factors, including AP-2a, CREB, ETS-1 and SP-1. These factors bind to normal promoter of mice PP2A-Aα, positively or negtively regulating PP2A-Aαtranscription.In order to confirm whether PP2A-Aαis regulated by the same transcriptional factors in cancer cells, we choose human prostate cancer cells DU145 and LNCaP, analysing the transcriptional mechanism and tumorigenic ability. We find that CREB may play an important role in transcriptional regualtion. Overexpression of CREB in DU145 show us the strong regulation of PP2A-AαIn order to confirm the physiological function, we conduct two related experiments. Firstly, comparing to the control(empty vector) transfected DU145 cells, the cell migration ability of CREB overexpressed DU145 cells enhanced 12.5μm/hr, In nude mice tumorigenic experiment, we find the enhancement of tumorigenic ability. This results is much different from the former results in other research articles. This show us the dual nature of PP2A-Aa in tumorigenic process.When we looking at the CREB activity, we find even with overexpressed CREB, the phosphrylation of CREB can not be enhanced. This result give us the hint that there maybe defects in CREB upstream pathways. Using different inhibitors, we find that PKA is a key protein kinase regulating CREB. The activity of PKA decreased in DU145 than in LNCaP.In summary, our research indicate it is the downregulation of PKA-Ca lead to the decrease of phosphrylation of CREB, at the same time, the stability of CREB decline. Correspondingly, the downregulation of expression of CREB and p-CREB also decrease the tumorigenic ability of DU145 cells. These results provide us brand new imformaiton of the generation of prostate cancer, and this maybe a new break point for the healing of prostate cancer.