PHLPP:一种天然肿瘤抑制因子被发现

近美国加州大学圣地亚哥分校(UCSD)医学院药理学系的科研人员在人体中发现了一种天然抗癌基因,如果此抗癌基因在人体中的表达及活性得到增强,就可以抑制肿瘤的生长,此抗癌基因被命名为PHLPP(PH domain Leucine-rich repeat Protein Phosphatase).

CIP2A与肿瘤关系的研究进展

蛋白磷酸酶2A(protein phosphatase 2A,PP2A)的癌性抑制因子(cancerous inhibitor of protein phosphatase 2A,CIP2A),又名KIAA1524或p90,是近被鉴别出的一种人类癌蛋白,多项研究表明,CIP2A能够直接与癌转录因子c-Myc蛋白相互作用,抑制PP2A对其丝氨酸62位(S62)的去磷酸化作用,从而抑制了细胞内c-Myc蛋白的水解,稳定了其蛋白表达水平.CIP2A在维持细胞的恶性表型,促进细胞的增殖和恶性转化过程中起重要作用.近研究证实,CIP2A在正常组织中几乎不表达或呈低水平表达,相反,CIP2A在人类多种恶性肿瘤中均呈广泛高表达,其过表达可促使细胞发生恶变,终导致恶性肿瘤的发生,但有关CIP2A在人类肿瘤发生发展过程中的具体作用机制及其与临床相关性目前仍不十分清楚,本文就CIP2A与肿瘤关系的研究进展作一综述.

It is well known that the main brain lesion in Alzheimer's disease (AD) brain is neurofibrillary tangles (NFT) and senile plaques (SP). The amount of NFT is positively correlated with clinical degree of dementia in AD. It is also well studied that the major component of NFT is abnormally hyperphosphorylated microtubule associated protein tau that is caused by an imbalance of protein kinase and protein phosphatase (PP). To reconstitute a specific AD model based on the above hypothesis, we have injected separately calcium calmodulin dependent protein kinase (CaMKKII) activator, bradykinin and PP-2B inhibitor, cyclosporin A into rat hippocampus in the present study. The results showed that the injection of bradykinin caused learning and memory deficient in rats as well as Alzheimer-like tau phosphorylation, including Ser-262/356, Thr-231/235 and Ser-396/404. On the other hand, the injection of cyclosporin A induced the same phosphorylation sites as above except Ser-262/356, however, it did not mimic rat behavior abnormality as bradykinin injection did. The data suggested that activating of CaMKII and the phosphorylation of Ser-262/356 at tau might responsible for the lesion of learning and memory in our model rats. We also incubated PP-2A and PP-1 inhibitor, okadaic acid with human neuroblastoma cell line (SH-SY5Y), and found that (1) inhibition of above PPs induced Alzheimer-like phosphorylation and accumulation of neurofilaments, and Alzheimer-like microtubule disruption, (2) melatonin showed certain protection of the cell from okadaic acid toxicity. The data obtained from this study is significant in AD specific model study.

Bradykinin (BK) is a calcium/calmodulin dependent protein kinase Ⅱ (CaMKⅡ) specific activator, and Cyclosporin A (CSA) is reported to suppress protein phosphotase (PP)-2B activity. In vitro studies have shown that CaMKⅡ and PP-2B play an important role in Alzheimer-like phosphorylation of microtube-associated protein tau. To reconstitute an animal model based on the imbalance of protein kinase (s) and protein phosphatase (s) seen in Alzheimer brain, we injected BK and/or CSA into rat hippocampus. The results from behavioral study showed that an obvious disturbance in learning and memory was seen with BK or BK plus CSA injected rats. Moreover, the behavior abnormality appeared earlier in aged rats than young adults of the same kind after the injection. On the other hand, no obvious dysfunction in living and behavior was observed with CSA alone injected rats. The results obtained by immunohistochemical assay indicated that the staining for M4\, 12E8\, PHF-1 and CaMKⅡ was stronger, and for Tau-1 was weaker in BK injected rats compared with Control group. It was also found that the binding of M4 and PHF-1 but not 12E8 to tau was significantly increased in CSA injected rats. As the same as BK injection, binding of Tau-1 to tau was decreased after CSA injection. The immunostaining for 12E8\,PHF-1 and CaMKⅡ was increased, whereas for Tau-1\, M4\, and GSK-3 was decreased after combination injection of BK and CSA. In addition, the staining of PP-2B decreased in all the three models. To our knowledge, this is the first data shown in vivo that the activation of CaMKⅡ induces both Alzheimer-like tau phosphorylation and behavioral disturbance.

Alzheimer disease (AD) neurofibrillary degeneration is characterized by a disruption of the cytoskeleton. The alteration of microtubule system and the microtubule-associated protein has been extensively investigated in this pathology. In the present study, we decided to explore the role of neurofilament (NF) proteins in AD neurofibrillary degeneration. We first investigated the content and the phosphorylation level of NF proteins in AD brain by using a panel of anti-NF antibodies. It was found by quantitative Western blot that the NF subunits were exclusively detected in an insoluble fraction from AD brain grey matter. The level of phosphorylated (p)-NF-H and (p)-NF-M was increased 1.5 and 1.3 times (P＜0.05) respectively at phosphorylation specific antibody SMI31 epitope in AD as compared to neurological controls of Huntington disease (HD). A 1.6 fold elevation (P＞0.05) of p-NF-H to another phosphate reactive antibody SMI34 was also seen in AD. The level of non-phosphorylated (np)-NF-H/M recognized by SMI33 was similar before alkaline phosphatase (ALP) treatment, but the total level of NF-H/M was 1.5 and 1.6 times (P＜0.01) higher in AD than HD after dephosphorylation. Furthermore, a 1.8 fold increase of NF-M to SMI32 was observed in AD only after ALP treatment, suggesting that the NF-H/M are increased in the phosphorylated form. The amount of NF-L determined by NR-4 was 1.6 fold (P＜0.01) higher in AD than HD. To our knowledge, this is the first biochemical data shown definite abnormality of NF subunits in AD brain. To understand the possible mechanism for the abnormal hyperphosphorylation and elevation of NF in AD brain, we treated human SY5Y neuroblastoma cell with protein phosphatase(PP)-2A and PP-1 inhibitor okadaic acid(OA). Then, we determined the relationship between an AD-like PP-A and PP-1 activity deficiency and NF phosphorylation as well as intracellular translocation in modeled cell system. It was demonstrated that p-NF-H/M detected by SMI31 and SMI34 were increased, and the elevated p-NF-H/M tended to be condensed in the proximal end of the cell processes after treated with 15 nmol/L OA. Further accumulation of p-NF-H/M to the cell plasma and parikarya was seen after increasing the concentration of OA to 30 nmol/L. On the other hand, the majority of np-NF-H/M bound to SMI32 and SMI33 were seen in the cell body although it was also detected in cell processes before OA treatment. The immunoreaction of np-NF-H/M was significantly decreased in the cell body and it became to be condensed in the proximal end of the cell processes after treatment of the cell by 15 nmol/L of OA. Further decreasing of the staining was observed when the concentration of OA was raised to 30 nmol/L. The data demonstrated that an Alzheimer-like inhibition of PP-2A and PP-1 induced hyperphosphorylation and accumulation of NF proteins as seen in AD brain, indicating that abnormality of NF might be involved in AD neurofibrillary degeneration. As SY5Y contains negligible amount of tau protein which was reported to cross-react with p-NF subunits, it might be served as a proper cell model for NF study.