Optineurin mediates negative regulation of Rab8 function by TBC1D17, a GTPase activating protein

Advance Online Publication August 1, 2012 doi: 10.1242/?jcs.102327 Rab GTPases regulate various membrane trafficking pathways but the mechanisms by which GTPase activating proteins recognize specific Rabs are not clear. Rab8 is involved in controlling several functions including the trafficking of transferrin receptor from early endosome to recycling endosome. Here we provide evidence to show that TBC1D17, a Rab GTPase activating protein, through its catalytic activity, regulates Rab8-mediated endocytic trafficking of transferrin receptor. Optineurin, a Rab8-binding effector protein, mediates interaction and colocalisation of TBC1D17 with Rab8. A non-catalytic region of TBC1D17 is required for direct interaction with optineurin. Co-expression of Rab8, but not other Rabs tested, rescues the inhibition of transferrin receptor trafficking by TBC1D17. Activated GTP-bound form of Rab8 is localized to the tubules emanating from the endocytic recycling compartment. Through its catalytic activity, TBC1D17 inhibits recruitment of Rab8 to the tubules and reduces colocalisation between transferrin receptor and Rab8. Knockdown of optineurin or TBC1D17 resulted in enhanced recruitment of Rab8 to the tubules. A glaucoma-associated mutant of optineurin, E50K causes enhanced inhibition of Rab8 by TBC1D17 resulting in defective endocytic recycling of transferrin receptor. Our results show that TBC1D17, through its interaction with optineurin, regulates Rab8-mediated endocytic recycling of transferrin receptor and recruitment of Rab8 to the tubules. We describe a mechanism of regulating a Rab GTPase by an effector protein (optineurin) that acts as an adaptor to bring together a Rab (Rab8) and its GTPase activating protein (TBC1D17).

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Modeling the self-organized phosphatidylinositol lipids signaling system in chemotactic cells based on quantitative image analysis

Advance Online Publication August 16, 2012 doi: 10.1242/?jcs.108373 The phosphatidylinositol (PtdIns) lipids reaction is a key signaling event; this signal is responsible for gradient sensing in eukaryotic cell chemotaxis. The self-organization activity of the PtdIns lipids reaction induces an inherent polarity even in the absence of an external chemoattractant gradient by producing a localized PtdIns 3,4,5-trisphosphate [PtdIns(3,4,5)P3]-enriched domain on the membrane. Experimentally, we found that such a domain could exhibit two types of behavior: 1) persistent domain formation that travels on the membrane and 2) stochastic formation of transient domains. Taking advantage of the simultaneous visualization of PtdIns(3,4,5)P3 and its enzyme, phosphatase and a tensin homolog (PTEN), the inter-dependence of their spatiotemporal dynamics was demonstrated statistically. Based on this statistical analysis, we developed a theoretical model for the self-organization of PtdIns lipids signaling that can accurately reproduce both persistent and transient domain formation; these types of formations can be explained by the oscillatory and excitability properties of the system, respectively.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Share Alike License (http://creativecommons.org/licenses/by-nc-sa/3.0), which permits unrestricted non-commercial use, distribution and reproduction in any medium provided that the original work is properly cited and all further distributions of the work or adaptation are subject to the same Creative Commons License terms.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Functional involvement of Rab1A in microtubule-dependent anterograde melanosome transport in melanocytes

Advance Online Publication August 1, 2012 doi: 10.1242/?jcs.109314 Morié Ishida, Norihiko Ohbayashi, Yuto Maruta, Yuka Ebata and Mitsunori Fukuda*?*Correspondence: Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan. Tel.: +81-22-795-7731; Fax: +81-22-795-7733; E-mail: nori{at}m.tohoku.ac.jp. Melanosomes are transported to the cell periphery of melanocytes by coordination between bidirectional microtubule-dependent movements and unidirectional actin-dependent movement. Although both the mechanism of the actin-dependent melanosome transport and the mechanism of the microtubule-dependent retrograde melanosome transport in mammalian skin melanocytes have already been determined, almost nothing is known about the mechanism of the microtubule-dependent anterograde melanosome transport. Small GTPase Rab proteins are common regulators of membrane traffic in all eukaryotes, and in this study we performed genome-wide screening for Rab proteins that are involved in anterograde melanosome transport by expressing 60 different constitutive active (and negative) mutants and succeeded in identifying Rab1A, originally described as a Golgi-resident Rab, as a prime candidate. Endogenous Rab1A protein was found to be localized on mature melanosomes in melanocytes, and its functional ablation either by siRNA-mediated knockdown or by overexpression of a cytosolic form of Rab1A-GTPase-activating protein/TBC1D20 induced perinuclear melanosome aggregation. The results of time-lapse imaging further revealed that long-range anterograde melanosome movements were specifically suppressed in Rab1A-deficient melanocytes, whereas retrograde melanosome transport occurred normally. Taken together, these findings indicate that Rab1A is the first crucial component of the anterograde melanosome transport machinery to be identified in mammalian skin melanocytes.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Diverse, but not yet pluralistic

The question of pluralism in Egypt is becoming more relevant with every passing day, writes Ayman Abdel-Wahab

Egypt is not a pluralistic society -- not yet. But it is an open society, one in which cultural and social diversity have always been a source of vitality and societal prowess.

What we need to do is manage the diversity to make it an asset, not a liability. In the heat of political rivalry, the line may be blurred between diversity as a natural phenomenon and the political and social framework this diversity needs in order to survive.

To put it in a nutshell, diversity has to be institutionalised, ensconced into our legal system, defended and channelled into productive courses. Things like the status of women, social inequities, as well as urgent regional matters need to be addressed in a systematic manner. The demands of Upper Egypt for development cannot be ignored, nor can the rights of the Bedouins of Sinai and the inhabitants of Nubia be overlooked. Sectarian strife between the Muslims and Christians and discrimination against certain sections of society must also be confronted.

Our society may be diverse, but the diversity needs to be managed, or it will backfire. Egypt has always been a melting pot, and we need to work harder to keep it so.

Political groups are apt to exploit factional issues for their own benefit. This will happen, no doubt. But we need to keep an eye on what's going on. We need to work double time to make sure that diversity becomes a source of inspiration, not of frustration.

For one thing, we have to boost civil society so it may act as a magnet for the immense energy of our younger generations. The youth deserves to have its say in the future of its country. And it needs to learn how to appreciate civil rights and respect the special needs of certain parts of society. The key to diversity is civil society. If it is fully engaged in development and democratisation, Egypt will remain the melting pot it always was.

The writer is director of the Civil Society Unit at Al-Ahram Centre for Political and Strategic Studies.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

PA vows to hold elections

Local elections are on the cards, but Hamas continues to protest that it has no freedom to campaign in the West Bank, reports Khaled Amayreh in Ramallah

The Palestinian Authority (PA) is planning to hold local elections in the West Bank in mid-October despite Hamas's refusal to do likewise in the Gaza Strip.

The Fatah-dominated PA views elections as the ultimate arbiter between itself and Islamist Hamas, which is in control of the Gaza Strip. Hamas views elections as the would-be fruit of national reconciliation with Fatah.

Despite several agreements and understandings reached through active Arab -- especially Egyptian -- mediation, the two main Palestinian political groups have failed to reach a solid final agreement that would end more than five years of tension, starting soon after Hamas defeated Fatah in the 2006 general elections.

With a supposedly large chunk of eligible Palestinian voters set to boycott the upcoming elections, it is expected that the turnout will be modest, which would allow Hamas to further question the credibility of the elections under current circumstances.

Most of the municipal and local councils in the West Bank are already controlled by Fatah following the sacking of pro-Hamas councils and mayors in the context of the oft-bitter hostility between the two groups.

In many cities and localities, the PA has been refusing to organise elections, fearing Islamists would win the polls.

However, with Hamas substantially weakened in the West Bank due to a combined repression campaign by the PA security agencies and the Israeli occupation army, which saw most Hamas's community leaders and members of parliament thrown behind bars, the PA seems fairly encouraged to hold the elections.

Hamas has been demanding, but to no avail, that the PA introduce preparations for genuine elections, including allowing freedom of speech and other civil liberties that would allow Islamists to campaign freely.

Israel, for its part, has kept up its vehement hostility towards Hamas, vowing to detain Islamist candidates for their "affiliation with a terrorist organisation".

The PA admits it can do nothing to prevent Israel from targeting Hamas, apart from appealing to the international community to pressure Tel Aviv.

But international pressure on Israel may not be good enough for Hamas to risk delivering its leaders and candidates into the jaws of the lion -- risking having a new generation of Islamist leaders languishing in open-ended detention in Israeli jails and detention camps without charge or trial.

The holding of local elections in the West Bank, excluding East Jerusalem, comes in the midst of severe political and economic crises facing the PA and threatening its very survival.

Earlier this week, the extremist Israeli foreign minister, Avigdor Lieberman, called for the elimination of President Mahmoud Abbas, calling him a terrorist.

Lieberman is the second most powerful politician in Israel following Prime Minister Binyamin Netanyahu, and his remarks shouldn't be taken lightly.

Abbas has vowed to once again seek United Nations recognition of a Palestinian state. However, it seems that behind-the-scenes pressure by the United States and its allies may have succeeded in convincing the Palestinian leadership to at least postpone its UN recognition bid for the time being.

Another postponement at the UN is guaranteed to weaken Abbas in the view of his people. The aging Palestinian leader has been severely castigated of late after saying during a meeting with a visiting Israeli delegation, which included rabbis, in Ramallah last week that "Israel was created in order to stay forever."

Several Palestinian leaders and intellectuals scoffed at the remarks, calling them "treasonous and catastrophic".

Abdel-Sattar Qassem, a former presidential candidate and university professor, said Abbas had no right whatsoever to sell out the Palestinian cause.

"Palestine is not the property of the Abbas family; he has no right to cede what doesn't belong to him and his family," he said.

Nonetheless, most if not all Fatah leaders have remained mum, refusing to comment on Abbas's remarks, which most Palestinians view as an embarrassing taboo.

The main reason for Fatah's refusal to publicly distance itself from the remarks has to do with the fact that Abbas tightly controls Fatah's coffers and any severe criticisms directed at the chairman may cost the critics their financial survival.

Meanwhile, a severe economic crisis, whose harshness has no parallel since the start of the Israeli occupation 1967, is hitting hard in the occupied territories, causing families to adopt unprecedented austerity measures.

With its foreign aid and revenue dwindling, the PA government is barely able to pay salaries for its estimated 160,000 civil servants.

As a result, the PA has failed to pay electricity and water bills to Israel, prompting the Israeli government to threaten to cut off electricity to the West Bank, including Abbas's own office in Ramallah.

On Monday, 4 September, the state-run Israeli TV disclosed the content of a letter sent to Netanyahu by Energy Minister Uzi Landaou in which the latter threatened to cut electricity off to the West Bank.

Landaou, an extreme right winger, was quoted as saying that the PA was indebted to Israel for huge sums of money which would force him to cut off power to the Fayyad government.

The suffocating economic crisis is forcing most Palestinians to prioritise their spending, with many families unable to send their grown up sons and daughters back to college due to poverty.

Demonstrations protesting widespread poverty have been taking place in some areas such as Ramallah and Bethlehem. However, the scope of the protests doesn't seem to pose an immediate threat to the survival of the PA regime in Ramallah.

The PA is not a sovereign entity and is not free to carry out normal economic activities such as free import and export, due to Israeli restrictions and control over border crossings connecting the West Bank to the outside world.

This is the reason most economic experts argue that it is nearly impossible for the PA to successfully overcome its recurrent economic and financial crises as long as Israel remains in control of the Palestinian territories.

Others go as far as arguing that it too late for the Palestinians to establish a viable and territorially contiguous Palestinian state on the West Bank, given the phenomenal expansion of Jewish colonies throughout the occupied territory.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.

Mechanosensitive mechanisms in transcriptional regulation

Advance Online Publication July 13, 2012 doi: 10.1242/?jcs.093005 July 1, 2012 J Cell Sci 125, 3061-3073. Akiko Mammoto1,*, Tadanori Mammoto1,* and Donald E. Ingber1,2,3,‡

1Vascular Biology Program, Children's Hospital and Harvard Medical School, Boston, MA 02115, USA

2Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, MA 02115, USA

3Harvard School of Engineering and Applied Sciences, Cambridge, MA 02139, USA ?‡Author for correspondence (don.ingber{at}wyss.harvard.edu) ?* These authors contributed equally to this work

Transcriptional regulation contributes to the maintenance of pluripotency, self-renewal and differentiation in embryonic cells and in stem cells. Therefore, control of gene expression at the level of transcription is crucial for embryonic development, as well as for organogenesis, functional adaptation, and regeneration in adult tissues and organs. In the past, most work has focused on how transcriptional regulation results from the complex interplay between chemical cues, adhesion signals, transcription factors and their co-regulators during development. However, chemical signaling alone is not sufficient to explain how three-dimensional (3D) tissues and organs are constructed and maintained through the spatiotemporal control of transcriptional activities. Accumulated evidence indicates that mechanical cues, which include physical forces (e.g. tension, compression or shear stress), alterations in extracellular matrix (ECM) mechanics and changes in cell shape, are transmitted to the nucleus directly or indirectly to orchestrate transcriptional activities that are crucial for embryogenesis and organogenesis. In this Commentary, we review how the mechanical control of gene transcription contributes to the maintenance of pluripotency, determination of cell fate, pattern formation and organogenesis, as well as how it is involved in the control of cell and tissue function throughout embryogenesis and adult life. A deeper understanding of these mechanosensitive transcriptional control mechanisms should lead to new approaches to tissue engineering and regenerative medicine.

Key words Funding

This work was supported by the National Institutes of Health [grant numbers CA45548 and DE019023], the Department of Defense [grant number BC074986], AHA, the Hearst Foundation and ABTA. Deposited in PMC for release after 12 months.

This article is part of a Minifocus on Mechanotransduction. For further reading, please see related articles: ‘Deconstructing the third dimension – how 3D culture microenvironments alter cellular cues’ by Brendon M. Baker and Christopher S. Chen (J. Cell Sci. 125, 3015-3024). ‘Finding the weakest link – exploring integrin-mediated mechanical molecular pathways’ by Pere Roca-Cusachs et al. (J. Cell Sci. 125, 3025-3038). ‘Signalling through mechanical inputs – a coordinated process’ by Huimin Zhang and Michel Labouesse (J. Cell Sci. 125, 3039-3049). ‘United we stand – integrating the actin cytoskeleton and cell–matrix adhesions in cellular mechanotransduction’ by Ulrich S. Schwarz and Margaret L. Gardel (J. Cell Sci. 125, 3051-3060). ‘Molecular force transduction by ion channels – diversity and unifying principles’ by Sergei Sukharev and Frederick Sachs (J. Cell Sci. 125, 3075-3083).

© 2012. Published by The Company of Biologists Ltd

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.