crassa(26). is a critical step for many cellular functions. The family of tail-anchored proteins is recognized for anchoring proteins and vesicles to specific membranes, such as the endoplasmic reticulum (ER) and the outer Rabbit polyclonal to Complement C4 beta chain mitochondrial membrane (1), and tail-anchored proteins are characterized by a C-terminal single transmembrane domain, which is posttranslationally inserted into membranes (2, 3). Sarcolemmalmembrane-associatedprotein (SLMAP) is a tail-anchored protein first identified in myocardiac cells (4). In mammals, this protein is known to be involved in myoblast fusion during embryonic development, excitation-contraction coupling in cardiac myocytes, and cell cycle progression (58). Furthermore, SLMAPwas identified to be a disease gene for Brugada syndrome, a cardiac channelopathy (9). The functional diversity of SLMAP is dependent on alternative splicing, leading to at least four different isoforms of the protein (4, 6, 7, 10). Importantly, gene expression analyses have implicatedSLMAPmisexpression with endothelial dysfunctions in diabetes, chromosomal aberrations, and cancer (1114), and currently, SLMAP is the target of lectin-based treatment of drug-resistant cancer cells (15). SLMAP is conserved from yeasts to humans, and characterized fungal SLMAP homologs includeNeurospora crassaHAM-4 (hyphalanastomosis4), Saccharomyces cerevisiaeFar9p (factorarrest9p) and Far10p, as well asSchizosaccharomyces pombeCsc1p (component ofSIPcomplex1p) (1618). HAM-4 is essential for vegetative cell fusion, whereas Far9p and Far10p are required for pheromone-induced cell cycle arrest during yeast mating and Csc1p acts in cytokinesis. Interestingly, in a genome-wide screen forvacuolarproteinsorting (vps)-deficient mutants, Far9p was also identified to be Vps64p and vacuolar morphology was altered inN. crassaham-4mutants, indicating a role for SLMAP homologs in organelle morphology in fungi (18, 19). Recently, SLMAP has been identified to be an accessory protein to the humanstriatin-interactingphosphataseandkinase (STRIPAK) complex, a large multiprotein complex assembled around a core of protein phosphatase 2A (PP2A) subunits (20). In addition to PP2A structural (PP2AA) and catalytic (PP2Ac) subunits, human STRIPAK GW7604 complex contains striatins (regulatory PP2AB subunits), striatin-interactingproteins1and2(STRIP1/2), monopolar spindle-one-binder (MOB) proteins, germinalcenterkinaseIII(GCKIII) protein kinases, andcerebralcavernousmalformation protein3(CCM3). This core GW7604 STRIPAK complex is able to assemble in a mutually exclusive way with other accessory proteins, like SLMAP and the suppressor of IB kinase (SIKE) or a cortactin-binding protein 2 family member (CTTNBP2 or CTTNBP2NL) (21). The high diversity of STRIPAK and STRIPAK-like complexes makes estimation of the molecular weight of the complex difficult. Human STRIPAK was found to play a role in Golgi apparatus polarization and is involved in mitosis by tethering Golgi vesicles to centrosomes and the nuclear membrane in a cell cycle-specific manner (22, 23). STRIPAK-equivalent complexes have been found in a number of diverse organisms from yeasts to humans. GW7604 TheDrosophila melanogasterdSTRIPAK (DrosophilaSTRIPAK) complex is a negative regulator of the Hippo signaling pathway (24). TheS. cerevisiaeFar complex plays a role in cell cycle arrest during mating as well as acts in an antagonistic fashion toward TORC2 (targetofrapamycincomplex2) signaling (17, 25). TheS. pombeSIP (SIN [septationinitiationnetwork]inhibitoryPP2A) complex is required for the coordination of mitosis and cytokinesis by inhibiting SIN (16). TheN. crassaSTRIPAK complex controls nuclear accumulation of the MAK1 mitogen-activated protein (MAP) kinase and regulates chemotropic interactions between conidial germlings (26). Moreover, in the fungal model organismSordaria macrospora(2729), GW7604 the STRIPAK complex is required for cell fusion and sexual reproduction, namely, the formation of multicellular fruiting bodies (30). Discrete STRIPAK components have been characterized in other filamentous fungi, e. g., Aspergillus nidulans, Fusarium graminearum, Magnaporthe oryzae, andSclerotinia sclerotiorum(3134); however , a description of the STRIPAK complex in these fungi is still lacking. S. macrosporaSTRIPAK consists of PP2AA, PP2Ac1, striatin homolog PRO11, STRIP homolog PRO22, and the MOB protein SmMOB3. Strikingly, a mutant lacking the striatin homolog PRO11 can be complemented by mouse striatin cDNA (35), thereby highlighting the suitability ofS. macrosporafor studying the molecular function of STRIPAK components. Finally, defects in multicellular differentiation can easily be observed inS. macrospora, since the fungus forms complex three-dimensional fruiting bodies (perithecia) within 7 days without the need of a mating partner, and early developmental structures (coiled hyphae termed ascogonia and spherical immature fruiting bodies termed protoperithecia) are not masked by any asexual spores (27). The aim of this study was to functionally characterize PRO45, the SLMAP homolog fromS. macrospora, and provide insights into its role within the fungal STRIPAK complex. Protein-protein interaction studies indeed showed that PRO45 is part of fungal STRIPAK. We further established superresolutionstructured-illuminationmicroscopy (SIM) forS. macrosporato distinctly demonstrate that PRO45 cellular localization is dependent on STRIPAK integrity. Here,.