Rac1 Dynamics in the Human Opportunistic Fungal Pathogen Candida albicans

The small Rho G-protein Rac1 is highly conserved from fungi to humans, with approximately 65% overall sequence identity in Candida albicans. As observed with human Rac1, we show that C. albicans Rac1 can accumulate in the nucleus, and fluorescence recovery after photobleaching (FRAP) together with fluorescence loss in photobleaching (FLIP) studies indicate that this Rho G-protein undergoes nucleo-cytoplasmic shuttling. Analyses of different chimeras revealed that nuclear accumulation of C. albicans Rac1 requires the NLS-motifs at its carboxyl-terminus, which are blocked by prenylation of the adjacent cysteine residue. Furthermore, we show that C. albicans Rac1 dynamics, both at the plasma membrane and in the nucleus, are dependent on its activation state and in particular that the inactive form accumulates faster in the nucleus. Heterologous expression of human Rac1 in C. albicans also results in nuclear accumulation, yet accumulation is more rapid than that of C. albicans Rac1. Taken together our results indicate that Rac1 nuclear accumulation is an inherent property of this G-protein and suggest that the requirements for its nucleo-cytoplasmic shuttling are conserved from fungi to humans

RhoD regulates cytoskeletal dynamics via the actin nucleation-promoting factor WASp homologue associated with actin Golgi membranes and microtubules

The Rho GTPases have mainly been studied in association with their roles in the regulation of actin filament organization. These studies have shown that the Rho GTPases are essential for basic cellular processes, such as cell migration, contraction, and division. In this paper, we report that RhoD has a role in the organization of actin dynamics that is distinct from the roles of the better-studied Rho members Cdc42, RhoA, and Rac1. We found that RhoD binds the actin nucleation–promoting factor WASp homologue associated with actin Golgi membranes and microtubules (WHAMM), as well as the related filamin A–binding protein FILIP1. Of these two RhoD-binding proteins, WHAMM was found to bind to the Arp2/3 complex, while FILIP1 bound filamin A. WHAMM was found to act downstream of RhoD in regulating cytoskeletal dynamics. In addition, cells treated with small interfering RNAs for RhoD and WHAMM showed increased cell attachment and decreased cell migration. These major effects on cytoskeletal dynamics indicate that RhoD and its effectors control vital cytoskeleton-driven cellular processes. In agreement with this notion, our data suggest that RhoD coordinates Arp2/3-dependent and FLNa-dependent mechanisms to control the actin filament system, cell adhesion, and cell migration

A Novel Rho-Like Protein TbRHP Is Involved in Spindle Formation and Mitosis in Trypanosomes

Background: In animals and fungi Rho subfamily small GTPases are involved in signal transduction, cytoskeletal function and cellular proliferation. These organisms typically possess multiple Rho paralogues and numerous downstream effectors, consistent with the highly complex contributions of Rho proteins to cellular physiology. By contrast, trypanosomatids have a much simpler Rho-signaling system, and the Trypanosoma brucei genome contains only a single divergent Rho-related gene, TbRHP (Tb927.10.6240). Further, only a single RhoGAP-like protein (Tb09.160.4180) is annotated, contrasting with the.70 Rho GAP proteins from Homo sapiens. We wished to establish the function(s) of TbRHP and if Tb09.160.4180 is a potential GAP for this protein. Methods/Findings: TbRHP represents an evolutionarily restricted member of the Rho GTPase clade and is likely trypanosomatid restricted. TbRHP is expressed in both mammalian and insect dwelling stages of T. brucei and presents with a diffuse cytoplasmic location and is excluded from the nucleus. RNAi ablation of TbRHP results in major cell cycle defects and accumulation of multi-nucleated cells, coinciding with a loss of detectable mitotic spindles. Using yeast two hybrid analysis we find that TbRHP interacts with both Tb11.01.3180 (TbRACK), a homolog of Rho-kinase, and the sole trypanosome RhoGAP protein Tb09.160.4180, which is related to human OCRL. Conclusions: Despite minimization of the Rho pathway, TbRHP retains an important role in spindle formation, and henc

A Novel Testis-specific GTPase Serves as a Link to Proteasome Biogenesis: Functional Characterization of RhoS/RSA-14-44 in Spermatogenesis

We functionally characterized RhoS/RSA-14-44 as a new member of Rho GTPase subfamily in spermatogenesis, which provides a direct link between Rho family GTPase and the proteasome biogenesis

La prosodia. Aspetti teorici e metodologici nell\u2019apprendimento-insegnamento delle lingue straniere

Le pi\uf9 recenti acquisizioni nel campo della glottodidattica richiamano la nostra attenzione sull'importanza e sulla necessit\ue0 di promuovere una "svolta prosodica" nell'insegnamento delle lingue. Nella didattica, la concentrazione sul solo aspetto segmentale si \ue8 rivelata scarsamente produttiva e il suo effetto poco duraturo. Invece, dall'analisi dei dati di cui disponiamo, un'elementare competenza degli elementi sovrasegmentali fa scomparire molte interferenze fonologiche. Questo dimostra che la prosodia, base fondamentale di ogni comunicazione orale, influisce sulla produzione orale complessiva e deve occupare un posto importante nelle varie fasi dell'apprendimento. Si pu\uf2 evincere che ritmo e intonazione stranieri non si acquistano in modo naturale, ma attraverso mirate proposte didattiche incentrate sulla persona nella sua completezza umana. Risulta dunque rilevante osservare l'onnipresenza naturale di queste manifestazioni foniche in cui intervengono contemporaneamente componenti biologiche, psicologiche, linguistiche e sociologiche. Nello studiare l\u2019impatto di questi elementi su ogni persona nell'acquisizione della lingua madre, potremo evidenziare da una parte il modo in cui vengono acquisite le lingue straniere e dall'altra quanto \ue8 rilevante basare la didattica delle lingue straniere sulla prosodia. Sul piano pratico, di conseguenza, gli studenti impareranno, grazie agli insegnanti, a comportarsi da parlanti e non da scolari. Si delinea cos\uec la necessit\ue0 di conferire all'ascolto un ruolo di primo piano, e di allenare l'orecchio al riconoscimento di un modello autentico che favorisce una pronuncia adeguata della lingua straniera. Dai risultati di un nostro lavoro comparativo sui sistemi fonici del francese e dell\u2019italiano, \ue8 emersa l\u2019importanza degli elementi ritmici come principale porta d'ingresso nel sistema fonico della lingua straniera in questione. Il ritmo \ue8 in effetti l\u2019elemento pi\uf9 caratteristico delle due lingue e favorisce un'immersione pi\uf9 semplice e pi\uf9 piacevole nello studio della lingua straniera. Da queste osservazioni ha preso avvio un cammino di approfondimento, unito all\u2019ideazione e alla programmazione di attivit\ue0 di esercitazione da proporre nelle classi di lingua. La "correzione" fonetica prospettata si fonda sia sull'ascolto, al fine di perfezionare la competenza di comprensione, sia sulla produzione orale, per far ripetere e produrre, in modo sempre pi\uf9 accettabile, enunciati in lingua straniera. Le predette attivit\ue0 sono svolte in modo da incrementare il piacere di produrre enunciati in lingua straniera come composizioni linguistiche e musicali insieme. Introdurre la prosodia come principale porta di avvicinamento e d\u2019ingresso nella didattica delle lingue straniere, rappresenta una svolta innovativa in quanto permette agli studenti, non solo di acquisire una competenza di comunicazione efficace e autentica, ma anche di rafforzare le motivazioni

The tyrosine kinase Abl is required for Src-transforming activity in mouse fibroblasts and human breast cancer cells.

The cytoplasmic tyrosine kinase Src has been implicated in signal transduction induced by growth factors and integrins. Src also shows oncogenic activity when deregulated. Accumulating evidence indicates that the tyrosine kinase Abl is an important substrate for Src signalling in normal cells. Here we show that Abl is also required for Src-induced transformation of mouse fibroblasts. Abl does not mediate tyrosine phosphorylation of Stat3 and Shc, two important regulators of Src oncogenic activity. In contrast, Abl controls the activation of the small GTPase Rac for oncogenic signalling and active Rac partly rescued Src transformation in cells with inactive Abl. Moreover, Abl mediates Src-induced extracellular regulated kinase 5 (ERK5) activation to drive cell transformation. Finally, we find that Abl/Rac and Abl/ERK5 pathways also operate in human MCF7 and BT549 breast cancer cells, where neoplastic transformation depends on Src-like activities. Therefore, Abl is an important regulator of Src oncogenic activity both in mouse fibroblasts and in human cancer cells. Targeting these Abl-dependent signalling cascades may be of therapeutic value in breast cancers where Src-like function is important.Oncogene (2007) 26, 7313-7323; doi:10.1038/sj.onc.1210543; published online 28 May 2007

The Src-like adaptor protein regulates PDGF-induced actin dorsal ruffles in a c-Cbl-dependent manner.

The Src-like adaptor protein (SLAP) belongs to the subfamily of adapter proteins that negatively regulate cellular signalling initiated by tyrosine kinases. SLAP has a unique, myristylated N-terminus, followed by SH3 and SH2 domains with high homology to Src family tyrosine kinases (SFK) and a unique C-terminal tail, which is important for c-Cbl binding. We have previously shown that SLAP negatively regulates platelet-derived growth factor (PDGF)-induced mitogenesis in fibroblasts and we now report that it regulates F-actin assembly for dorsal ruffles formation. c-Cbl mediated SLAP inhibition towards actin remodelling. Moreover, SLAP enhanced PDGF-induced c-Cbl phosphorylation by SFK. In contrast, SLAP mitogenic inhibition was not mediated by c-Cbl, but it rather involved a competitive mechanism with SFK for PDGF-receptor (PDGFR) association and mitogenic signalling. Accordingly, phosphorylation of the Src mitogenic substrates Stat3 and Shc were reduced by SLAP. Thus, we concluded that SLAP regulates PDGFR signalling by two independent mechanisms: a competitive mechanism for PDGF-induced Src mitogenic signalling and a non-competitive mechanism for dorsal ruffles formation mediated by c-Cbl

Maternal mRNA deadenylation and decay by thepiRNA pathway in the early Drosophila embryo

International audienc