Molecular Cloning and Characterization of Phocein, a Protein Found from the Golgi Complex to Dendritic Spines

Abstract

Phocein is a widely expressed, highly conserved intracellular protein of 225 amino acids, the sequence of which has limited homology to the subunits from clathrin adaptor complexes and contains an additional stretch bearing a putative SH3-binding domain. This sequence is evolutionarily very conserved (80% identity between Drosophila melanogaster and human). Phocein was discovered by a yeast two-hybrid screen using striatin as a bait. Striatin, SG2NA, and zinedin, the three mammalian members of the striatin family, are multimodular, WD-repeat, and calmodulinbinding proteins. The interaction of phocein with striatin, SG2NA, and zinedin was validated in vitro by coimmunoprecipitation and pull-down experiments. Fractionation of brain and HeLa cells showed that phocein is associated with membranes, as well as present in the cytosol where it behaves as a protein complex. The molecular interaction between SG2NA and phocein was confirmed by their in vivo colocalization, as observed in HeLa cells where antibodies directed against either phocein or SG2NA immunostained the Golgi complex. A 2-min brefeldin A treatment of HeLa cells induced the redistribution of both proteins. Immunocytochemical studies of adult rat brain sections showed that phocein reactivity, present in many types of neurons, is strictly somato-dendritic and extends down to spines, just as do striatin and SG2NA.

Heavy Metal-induced Metallothionein Expression Is Regulated by Specific Protein Phosphatase 2A Complexes

“…In the course of regulation, PR110 subunit functioned as critical molecular anchors targeting estrogen receptor to the cell membrane and served as a scaffold for the assembly of proteins, facilitating estrogen-induced activation of endothelial NO synthase (eNOS) (52). Several lines of evidence also suggest that PP2A PR110 complexes are involved in regulating vesicular trafficking (53,54) and the remodeling of cellular cytoskeleton (55). Here, we revealed a novel role of PP2A PR110 complexes in regulation of MT expression by directly dephosphorylating MTF-1.…”

Identification of Mob2, a Novel Regulator of Larval Neuromuscular Junction Morphology, in Natural Populations of Drosophila melanogaster

“…For example, Mob2 in Drosophila regulates morphogenesis of photoreceptors and wing hairs (He et al 2005;Liu et al 2009) and Mob4 (pheocin), a divergent member of this gene family negatively regulates NMJ growth apparently through its effects on axonal transport and microtubule dynamics (Schulte et al 2010). In addition, mammalian Mob proteins have been localized to neuronal dendrites where NDR kinases regulate branching and tiling (Zallen et al 2000;Baillat et al 2001). Our discovery of Mob2 as a regulatory protein that acts presynaptically to restrict NMJ growth further emphasizes the importance of a more complete investigation of the signaling pathways through which Mob2 and its relatives act to regulate growth and morphogenesis of presynaptic and postsynaptic structures.…”

“…In Drosophila, Mob2 has previously been shown to regulate photoreceptor and wing hair morphogenesis (He et al 2005;Liu et al 2009) but has not been implicated in regulating NMJ growth. In flies and mammals, Mob proteins and NDR kinases have been found to play a role in regulating growth and development of neuronal dendrites (Zallen et al 2000;Baillat et al 2001;Emoto et al 2004Emoto et al , 2006Lin et al 2011). We show that Mob2 functions presynaptically to negatively regulate NMJ growth in concert with the NDR kinase, Tricornered (Trc), but not with the closely related NDR kinase, Warts (Wts).…”

Mob4 plays a role in spindle focusing in Drosophila S2 cells

“…S4B) and is very distantly related to S. cerevisiae Mob1p (18% identity; Mob1 and Mob3 are more closely related, with 44 and 33% identity to Mob1p, respectively). Phocein appears to function in peripheral ganglia and dendritic spines of many types of neurons, and, in unpolarized HeLa cells, it localizes to the Golgi (Baillat et al, 2002;Baillat et al, 2001;Moreno et al, 2001). The Mob4 branch of the Mob family is otherwise poorly characterized in the literature.…”