Anti-PSD-95 was obtained from Zymed Laboratories and was used at 1:250 for immunoblotting and 1:330 for indirect immunofluorescence staining. tightly controlled by specific channels, transporters and exchangers. The temporal and spatial aspects of Ca2+signaling require specific sub-cellular arrangements of these Ca2+handling proteins because an aberrantly located Ca2+channel Colistin Sulfate or transporter could change the nature of the Ca2+signal and subsequently result in an abnormal biological response [1,2]. The plasma membrane Ca2+ATPases (PMCAs) are responsible for removing Ca2+from the cell to the extracellular space. Thus, these proteins play an essential role in maintaining intracellular Ca2+homeostasis. Four genes encode mammalian PMCAs (PMCA1-4) and with alternative splicing occurring at two separate sites over 20 different PMCA isoforms are generated. Although the need for this isoform diversity may be partly explained by the tissue-specific expression of many PMCAs, recent studies also suggest that different isoforms participate in localized Ca2+signaling within specific membrane microdomains (for a recent review, see [3]). Organizing PMCA molecules into discrete Ca2+signaling microdomains or connecting them to other signaling pathways may be achieved through interaction with specific signaling and scaffolding proteins. A consensus sequence E-T/S-X-L/V for binding type-I PDZ (postsynaptic-density-95/discs large/zona occludens-1) domains was identified at the carboxyl terminus of the b-splice variants of all PMCA isoforms. Through this motif the b forms of PMCAs interact with members of the membrane-associated guanylate kinase (MAGUK) family, such as the synapse-associated proteins PSD-95/SAP90, SAP97/hDlg, SAP102, and PSD-93/chapsyn-110 [4] or the Ca2+/CaM-dependent serine protein kinase CASK [5]. In addition, PMCA2b (with the sequence ETSL at the C-terminus) interacts specifically with the Na+/H+exchanger regulatory factor-2 (NHERF2) that may link the apically targeted PMCA2w/b via its ezrin/radixin/moesin (ERM)-binding domain to the actin cytoskeleton [6]. On the other hand, PMCA4b with the sequence of ETSV at the C-terminus binds specifically to the PDZ domain of neuronal nitric oxide synthase (NOS-1) and down regulates NO production most likely due to a PMCA-mediated decrease of local [Ca2+] in the immediate vicinity of Mouse monoclonal to MYL3 NOS-1 [7]. While several proteins have been identified as interacting partners of the PMCA little is known about their involvement in targeting and specific membrane distribution of the pump molecules. Here we show for the first time that the MAGUK family member PSD-95 increases the plasma membrane expression of PMCA4b and – similarly to other Ca2+signaling molecules such as neurotransmitter receptors and channels – redistributes the calcium pump into clusters. We demonstrate that these clusters are restricted to specific regions of the plasma membrane, fenced by the underlying actin cytoskeleton. We also show that in the clustered state the lateral mobility of the PMCA molecules is significantly reduced. Our results suggest that PDZ domain directed clustering could associate the PMCA with complex macromolecular systems at specialized membrane regions such as the post-synaptic density or cell junctions. == 2. Materials and methods == == 2.1. Chemicals and reagents == Fugene 6 Transfection Colistin Sulfate Reagent was obtained from Roche Applied Science. DMEM and OPTIMEM were obtained from Gibco. Monoclonal anti-PMCA antibody 5F10 [8] was used at a dilution of 1 1:5,000 for immunoblotting and 1:100 for indirect immunofluorescence staining. Anti-PSD-95 was obtained from Zymed Laboratories and was used at 1:250 for immunoblotting and 1:330 for indirect immunofluorescence staining. TRITC-phalloidin was obtained from Sigma Chemical Co. Alexa Fluor 488, 594 and 633-conjugated goat anti-mouse IgG and anti-rabbit IgG were obtained from Invitrogen Corp. All other chemicals used were of reagent grade. == 2.2. Plasmid constructs == Plasmid pMM2-PMCA4b for expression of full-length human PMCA4x/b in mammalian Colistin Sulfate cells has been described previously [9]. GFP-PMCA4b encoding human PMCA4x/b fused at its NH2 terminus to GFP was generated by cloning an XhoI fragment carrying the full-length PMCA4x/b sequence into pEGFP-C2 (Clontech) as described [10]. Construct GFP-PMCA4x/bct6 was similarly made by cloning a PCR-generated.