Cell growth can be suppressed by stressful environments, but the role of stress pathways in this process is largely unknown. Here we show that a cascade of p38β mitogen activated protein kinase and p38 regulated/activated kinase (PRAK) plays a role in energy starvation-induced suppression of mammalian target of rapamycin (mTOR), that energy starvation activates the p38β-PRAK cascade, and that p38β- or PRAK-deletion diminishes energy depletion-induced suppression of mTORC1 and reduction of cell size. We show that p38β-PRAK operates independent from the known mTORC1 inactivation pathways – phosphorylation of tuberous sclerosis protein 2 (TSC2) and raptor by AMP activated protein kinase (AMPK), and surprisingly, PRAK directly regulates Ras homolog enriched in brain (Rheb), a key component of the mTORC1 pathway by phosphorylation. Phosphorylation of Rheb at serine 130 by PRAK impairs Rheb’s nucleotide-binding ability and inhibits Rheb-mediated mTORC1 activation. The direct regulation of Rheb by PRAK integrates a stress pathway with the mTORC1 pathway in response to energy depletion.

Cell growth is influenced by environmental stress. Mammalian target of rapamycin (mTOR), the central regulator of cell growth, can be positively or negatively regulated by various stresses through different mechanisms. The p38 MAP kinase pathway is essential in cellular stress responses. Activation of MK2, a downstream kinase of p38␣, enhances mTOR complex 1 (mTORC1) activity by preventing TSC2 from inhibiting mTOR activation. The p38␤-PRAK cascade targets Rheb to inhibit mTORC1 activity upon glucose depletion. Here we show the activation of p38␤ participates in activation of mTOR complex 1 (mTORC1) induced by arsenite but not insulin, nutrients, anisomycin, or H 2 O 2 . Arsenite treatment of cells activates p38␤ and induces interaction between p38␤ and Raptor, a regulatory component of mTORC1, resulting in phosphorylation of Raptor on Ser 863 and Ser 771 . The phosphorylation of Raptor on these sites enhances mTORC1 activity, and contributes largely to arsenite-induced mTORC1 activation. Our results shown here and in previous work demonstrate that the p38 pathway can regulate different components of the mTORC1 pathway, and that p38␤ can target different substrates to either positively or negatively regulate mTORC1 activation when a cell encounters different environmental stresses.The p38 mitogen-activated protein kinase (MAPK) signal pathway plays an important role in a variety of biological processes, including inflammation, cell differentiation, and cell death (1-3). The p38 group of MAPK has four members: p38␣, p38␤, p38␥, and p38␦ (4 -7). Although similarities in activation and function have been observed, each p38 isoform also has distinct functions (8). Although activation of p38 MAPKs by different stimuli is cell type-dependent, various stress stimuli appear to activate the p38 pathway in all types of cells, and thus the p38 pathway is considered to be a major stress-activated signaling pathway (9). The activation of transcription factors and subsequent gene expression is a major mechanism by which the p38 pathway mediates biological responses (10 -12). The activation of other types of cellular proteins is also essential for the p38 pathway to execute its function (13).The mammalian target of rapamycin (mTOR) 3 is a serine/ threonine kinase that acts as an environmental sensor to regulate a plethora of cellular biosynthetic processes (14). mTOR activation promotes cell growth and proliferation, whereas mTOR inhibition stops cell growth and initiates catabolic processes (15). The p70 S6 kinase (S6K) and eIF4E-binding protein 1 (4EBP1) are key regulators of mRNA translation, and are the most well characterized targets of mTOR (16,17). Phosphorylation of S6K and 4EBP1 by mTOR leads to increased levels of translation of specific mRNAs (18,19). mTOR exists in two distinct functional complexes, mTOR complex 1 (mTORC1) and mTORC2. mTORC1 is potently and specifically inhibited by rapamycin, and it regulates cell size, autophagy, ribosome biogenesis, protein translation, transcription, and cellular viability (15)...

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Certain children with a history of recurrent signs of vertigo, headache, and syncope were found to be afflicted with congenital variations of the extracranial vertebral artery. Sonography not only revealed the morphologic variations of the extracranial vertebral artery but also allowed an assessment of changes in blood flow such that posterior circulation ischemia could be determined.

Abstract. The ultrastructure of the tegument in Paraechinophallus japonicus (Bothriocephalidea: Echinophallidae), a cestode parasite of the bathypelagic fish Psenopsis anomala, was studied using scanning and transmission electron microscopy. Paraechinophallus japonicus lacks a true scolex. Four different types of microtriches have been observed on the tegumental surface of P. japonicus. Capilliform (B2.3-mm long) and blade-like spiniform (B1.4-mm long) microtriches are intermingled on the surface of the pseudoscolex. Capilliform microtriches are distinct in possessing a short base and a long electron-lucent cap. The strobila is covered with two types of microtriches, namely filiform (B2.1-mm long) and tusk-shaped microtriches (r4.5-mm long). Tusk-shaped microtriches are limited to the posterior border of each proglottid and are characterized by a short and narrow base, and a large and wide, sharply pointed, electron-dense cap. Similar tusk-shaped microtriches were previously found in members of the family Echinophallidae and may represent an autapomorphy of echinophallid cestodes, all of them being parasitic in centrolophid fish. A unified terminology of microthrix parts is proposed.Additional key words: microtriches, unified terminology, TEM, SEM, Bothriocephalidea A remarkable feature of the cestode tegument is the presence of apical structures called microtriches (Rothman 1963). Microtriches may differ in their structure, shape, size, and distribution between different species, between larvae (metacestodes) and adults, and also between regions of the tapeworm (Charles & Orr 1968;Grammeltvedt 1973;Thompson et al. 1980;MacKinnon & Burt 1983;Kuperman 1988;Caira & Ruhnke 1991; %d'a´rska´& Nebesa´rˇova1 999, 2005). Structural variations of microtriches are mostly evident on the surface of the scolex (Lumsden & Hildreth 1983;Kuperman 1988;Jones 1998;Halton 2004; Palm 2004). The morphology and distribution of microtriches of the scolex is considered to be of phylogenetic importance and represent a potentially significant taxonomic character (Richmond & Caira 1991;Caira et al. 1999; Palm 2004;Agustı´et al. 2005;Gil de Pertierra 2005).Cestodes with paired attachment organs called bothria were traditionally placed in the order Pseudophyllidea. However, recent molecular studies have shown that the order is paraphyletic and consists of two unrelated assemblages (orders): Bothriocephalidea and Diphyllobothriidea (Brabec et al. 2006;Kuchta 2007;Kuchta et al. 2008). The existence of these two groups raises the question as to their differentiation on the basis of morphological and ultrastructural characters. Therefore, the fine morphology of the tegument of Paraechinophallus japonicus YAM-AGUTI 1934, a member of the family Echinophallidae belonging to the more derived group of previous pseudophyllidean cestodes, Bothriocephalidea, was studied using transmission and scanning electron microscopy (TEM and SEM).Invertebrate Biology 127(2): 153-161. r