We herein present a novel platform of well-controlled ordered and disordered nanopatterns positioned with a cyclic peptide of arginine-glycine-aspartic acid (RGD) on a bioinert poly(ethylene glycol) background, to study whether the nanoscopic order of spatial patterning of the integrinspecific ligands influences osteoblast adhesion. This is the first time that the nanoscale order of RGD ligand patterns was varied quantitatively, and tested for its impact on the adhesion of tissue cells. Our findings reveal that integrin clustering and such adhesion induced by RGD ligands is dependent on the local order of ligand arrangement on a substrate when the global average ligand spacing is larger than 70 nm; i.e., cell adhesion is "turned off" by RGD nanopattern order and "turned on" by the RGD nanopattern disorder if operating at this range of inter-ligand spacing.Integrin plays a central role in the formation of focal adhesions (FAs), which anchor cells to the extracellular matrix (ECM). 1 High-affinity binding of the integrin transmembrane proteins to ECM ligands has been extensively exploited for tailoring artificial synthetic ECM systems. 2 Thus far, it has been reported that cell responses to the synthetic ECM depend to a large extent on multiple substrate features, such as its chemical composition, 3-6 geometry and topographical features, 7 ligand organization, 8,9 and even substrate stiffness. 10,11 In particular, the spatial organization of the integrin-specific peptide sequence of arginineglycine-aspartic acid (RGD) on non-fouling substrates has attracted much attention. This sequence, contained in many ECM proteins, can be recognized by all five aV integrins (αVβ1, αVβ3, αVβ5, αVβ6, αVβ8), two β1 integrins (α5β1, α8β1) and αIIbβ3. 12 Once ligated, the integrin receptors link the ECM to the cytoskeleton and integrate intracellular and extracellular events. Furthermore, it is known that cellular behaviors such as adhesion, migration, proliferation and differentiation, are quite sensitive to the bioactivity, tether length, interspacing and density of surface RGD ligands in artificial ECM materials. 13-21Recent developments in nanotechnology have given access to the nanoscale organization of RGD ligands in both inorganic and polymeric substrates mimicking ECMs. Research concerning randomly dispersed RGD ligands grafted onto polymeric materials suggested that *Corresponding authors: E-mail: E-mail: Spatz@mf.mpg.de (J.P. Spatz); E-mail: jdding1@fudan.edu.cn (J. Ding). Supporting Information Available: A detailed description of the experimental protocols for sample preparation and characterization is available free of charge via the Internet at http://pubs.acs.org. Nevertheless, there has been no report to date of studies comparing cellular responses to nanostructured surfaces characterized by ordered or disordered organization of biomolecules such as RGD ligands. Herein, we chose to examine this critical issue in cell-nanomaterial interactions by exploring osteoblast adhesion regulated by the nanoscale organ...

Here we show that glioblastoma express high levels of branched-chain amino acid transaminase 1 (BCAT1), the enzyme that initiates the catabolism of branched-chain amino acids (BCAAs). Expression of BCAT1 was exclusive to tumors carrying wild-type isocitrate dehydrogenase 1 (IDH1) and IDH2 genes and was highly correlated with methylation patterns in the BCAT1 promoter region. BCAT1 expression was dependent on the concentration of α-ketoglutarate substrate in glioma cell lines and could be suppressed by ectopic overexpression of mutant IDH1 in immortalized human astrocytes, providing a link between IDH1 function and BCAT1 expression. Suppression of BCAT1 in glioma cell lines blocked the excretion of glutamate and led to reduced proliferation and invasiveness in vitro, as well as significant decreases in tumor growth in a glioblastoma xenograft model. These findings suggest a central role for BCAT1 in glioma pathogenesis, making BCAT1 and BCAA metabolism attractive targets for the development of targeted therapeutic approaches to treat patients with glioblastoma.

SummaryBackgroundCells sense the extracellular environment using adhesion receptors (integrins) linked to the intracellular actin cytoskeleton through a complex network of regulatory proteins that, all together, form focal adhesions (FAs). The molecular basis of how these sensing units are regulated, how they are implicated in transducing mechanical stimuli, and how this leads to a spatiotemporal coordination of FAs is unclear.ResultsHere we show that vinculin, through its links to the talin-integrin complex and F-actin, regulates the transmission of mechanical signals from the extracellular matrix to the actomyosin machinery. We demonstrate that the vinculin interaction with the talin-integrin complex drives the recruitment and release of core FA components. The activation state of vinculin is itself regulated by force, as underscored by our observation that vinculin localization to FAs is dependent on actomyosin contraction. Using a variety of vinculin mutants, we establish which components of the cell-matrix adhesion network are coordinated through direct and indirect associations with vinculin. Moreover, using cyclic stretching, we demonstrate that vinculin plays a key role in the transmission of extracellular mechanical stimuli leading to the reorganization of cell polarity. Of particular importance is the actin-binding tail region of vinculin, without which the cell’s ability to repolarize in response to cyclic stretching is perturbed.ConclusionsOverall our data promote a model whereby vinculin controls the transmission of intracellular and extracellular mechanical cues that are important for the spatiotemporal assembly, disassembly, and reorganization of FAs to coordinate polarized cell motility.

Cells adherent on a cyclically stretched substrate with a periodically varying uniaxial strain are known to dynamically reorient nearly perpendicular to the strain direction. We investigate the dynamic reorientation of rat embryonic and human fibroblast cells over a range of stretching frequency from 0.0001 to 20 s(-1) and strain amplitude from 1% to 15%. We report quantitative measurements that show that the mean cell orientation changes exponentially with a frequency-dependent characteristic time from 1 to 5 h. At subconfluent cell densities, this characteristic time for reorientation shows two characteristic regimes as a function of frequency. For frequencies below 1 s(-1), the characteristic time decreases with a power law as the frequency increases. For frequencies above 1 s(-1), it saturates at a constant value. In addition, a minimum threshold frequency is found below that no significant cell reorientation occurs. Our results are consistent for the two different fibroblast types and indicate a saturation of molecular mechanisms of mechanotransduction or response machinery for subconfluent cells within the frequency regime under investigation. For confluent cell layers, we observe similar behaviors of reorientation under cyclic stretch but no saturation in the characteristic time with frequency, suggesting that cell-cell contacts can play an important role in the response machinery of cells under mechanical strain.