6)

6). insight into membrane localization of PTEN. Keywords:PTEN, Membrane localization, Mutational analysis,Dictyostelium == Introduction == Excessive PIP3 signaling caused by alternations in PI3K, PTEN or the PIP3-regualted serine/threonine kinase AKT prospects to tumor formation and metastasis (1-3). While PI3K inhibitors have been developed as anti-cancer drugs to suppress PIP3 production (4,5), activators of PTEN have not been explored. Despite the central role of PTEN in PIP3 signaling at the plasma membrane, the majority of PTEN is present in the cytosol and nucleus (6,7). Stimulating membrane localization of PTEN could potentially enhance its tumor suppressor function. Currnetly, the details of the mechanism of membrane localization are unclear. PTEN has four unique domains; an N-terminal lipid binding domain name (LBD), phosphatase domain name, C2 domain name, and C-terminal tail domain name (Fig. 1A) (7,8). The lipid binding, phosphatase and C2 domains can interact with phospholipidsin vitro(9-11). While the Morinidazole 3-D structure of the phosphatase and C2 domains of PTEN has been revealed, the structure of the tail domain name is not solved and proposed to be a flexible fragment (12). The C-terminal tail binds the other a part of PTEN and blocks its membrane association. This inhibitory, intramolecular conversation requires phosphorylation at S380, T382, T383 and S385 in the tail. When these residues were substituted with alanine (PTENA4), increased association with the plasma membrane and nucleus were observed in cells (9,13). In this study, we developed a heterologous expression system, in which human Mouse monoclonal to BLNK PTEN-GFP was expressed inDictyosteliumcells. Human PTEN is functional inDictyosteliumcells, as it rescues PTEN-null phenotypes (14-17). Using the powerful genetic system and accessible imaging of membrane localization afforded by expression inDictyostelium, we defined the mechanism and regulation of Morinidazole human PTEN localization. == Physique 1. Isolated PTEN mutations. == (A) The domain name structure of PTEN is usually shown. The table summarizes the position and frequency of mutations isolated in the screen. The isolated mutations were indicated in the 3-D structure of PTEN with the phosphatase and C2 domains (R14-V351) (12) (http://www.ncbi.nlm.nih.gov/Structure/mmdb/mmdbsrv.cgi?uid=11638). (B)Dictyosteliumcells expressing GFP fused to PTEN, PTENC124S, PTENA4, and PTENC124S,A4were Morinidazole viewed by fluorescence microscopy. Cells were incubated in the presence or absence of 20 M MG132 or 40 g/ml cycloheximide. Bar, 10 m. (C and D) Fluorescence intensity of GFP fused to WT or the indicated PTEN mutant at the plasma membrane (C) or nucleus (D) was quantified relative to that in the cytosol as explained in Materials and Methods. Values represent the imply SD (n 15). (E) Integrated fluorescence intensity of PTEN-GFP and PTENA4-GFP at the plasma membrane was normalized relative to total fluorescence intensity in cells (n 10). (F) Whole-cell lysates prepared from cells expressing PTEN-GFP or PTENA4-GFP were analyzed by immunoblotting with antibodies against GFP and actin in the presence or absence of MG132. Band intensity was quantified (n= 3). (G) Cells expressing GFP fused to the indicated forms of PTEN were incubated with 40 g/ml cycloheximide. Whole-cell lysates were analyzed by immunoblotting with anti-GFP antibodies at the indicated time points. Band intensity was quantified relative to 0 hour sample (n= 3). == Results == Human PTEN-GFP is mainly located in the cytosol of mammalian andDictyosteliumcells (9,15). We used error-prone PCR to generate a library of randomly mutated human PTEN cDNAs fused to GFP (complexity = 120,000, average mutation rate = 5.5 per molecule) and transfected the library into PTEN-nullDictyosteliumcells. After selecting transformants in the presence of the antibiotic geneticin, we visually inspected ~20,000 colonies and collected 18 colonies that showed increased membrane association of PTEN-GFP (Fig. 1A). After isolation of plasmids and DNA sequencing, the mutations were separated and re-examined Morinidazole for their effects on PTEN localization inDictyosteliumcells. Demonstrating the feasibility of our screen, we isolated mutations that.