Picosecond time-resolved microspectrofluorometry in live cells exemplified by complex fluorescence dynamics of popular probes ethidium and cyan fluorescent protein

AbstractDesign of next-generation therapeutics comes with new challenges and emulates technology and methods to meet them. Characterizing the binding of either natural ligands or therapeutic proteins to cell-surface receptors, for which relevant recombinant versions may not exist, represents one of these challenges. Here we report the characterization of the interaction of five different antibody therapeutics (Trastuzumab, Rituximab, Panitumumab, Pertuzumab, and Cetuximab) with their cognate target receptors using LigandTracer. The method offers the advantage of being performed on live cells, alleviating the need for a recombinant source of the receptor. Furthermore, time-resolved measurements, in addition to allowing the determination of the affinity of the studied drug to its target, give access to the binding kinetics thereby providing a full characterization of the system. In this study, we also compared time-resolved LigandTracer data with end-point KD determination from flow cytometry experiments and hypothesize that discrepancies between these two approaches, when they exist, generally come from flow cytometry titration curves being acquired prior to full equilibration of the system. Our data, however, show that knowledge of the kinetics of the interaction allows to reconcile the data obtained by flow cytometry and LigandTracer and demonstrate the complementarity of these two methods.

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Fluorescent Protein-Based Autophagy Biosensors

Materials ◽

10.3390/ma14113019 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3019

Author(s):

Heejung Kim ◽

Jihye Seong

Keyword(s):

Energy Transfer ◽

Fluorescent Protein ◽

Resonance Energy Transfer ◽

Treatment Strategies ◽

Resonance Energy ◽

Live Cells ◽

Spectral Profile ◽

Spatiotemporal Resolution ◽

Future Directions ◽

Complex Process

Autophagy is an essential cellular process of self-degradation for dysfunctional or unnecessary cytosolic constituents and organelles. Dysregulation of autophagy is thus involved in various diseases such as neurodegenerative diseases. To investigate the complex process of autophagy, various biochemical, chemical assays, and imaging methods have been developed. Here we introduce various methods to study autophagy, in particular focusing on the review of designs, principles, and limitations of the fluorescent protein (FP)-based autophagy biosensors. Different physicochemical properties of FPs, such as pH-sensitivity, stability, brightness, spectral profile, and fluorescence resonance energy transfer (FRET), are considered to design autophagy biosensors. These FP-based biosensors allow for sensitive detection and real-time monitoring of autophagy progression in live cells with high spatiotemporal resolution. We also discuss future directions utilizing an optobiochemical strategy to investigate the in-depth mechanisms of autophagy. These cutting-edge technologies will further help us to develop the treatment strategies of autophagy-related diseases.

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Ligand-Mediated Assembly and Real-Time Cellular Dynamics of Estrogen Receptor α-Coactivator Complexes in Living Cells

Molecular and Cellular Biology ◽

10.1128/mcb.21.13.4404-4412.2001 ◽

2001 ◽

Vol 21 (13) ◽

pp. 4404-4412 ◽

Cited By ~ 115

Author(s):

David L. Stenoien ◽

Anne C. Nye ◽

Maureen G. Mancini ◽

Kavita Patel ◽

Martin Dutertre ◽

...

Keyword(s):

Estrogen Receptor ◽

Real Time ◽

Fluorescent Protein ◽

Yellow Fluorescent Protein ◽

Steroid Receptor ◽

Estrogen Receptor Α ◽

Living Cells ◽

Live Cells ◽

Creb Binding Protein ◽

High Accumulation

ABSTRACT Studies with live cells demonstrate that agonist and antagonist rapidly (within minutes) modulate the subnuclear dynamics of estrogen receptor α (ER) and steroid receptor coactivator 1 (SRC-1). A functional cyan fluorescent protein (CFP)-taggedlac repressor-ER chimera (CFP-LacER) was used in live cells to discretely immobilize ER on stably integratedlac operator arrays to study recruitment of yellow fluorescent protein (YFP)-steroid receptor coactivators (YFP–SRC-1 and YFP-CREB binding protein [CBP]). In the absence of ligand, YFP–SRC-1 is found dispersed throughout the nucleoplasm, with a surprisingly high accumulation on the CFP-LacER arrays. Agonist addition results in the rapid (within minutes) recruitment of nucleoplasmic YFP–SRC-1, while antagonist additions diminish YFP–SRC-1–CFP-LacER associations. Less ligand-independent colocalization is observed with CFP-LacER and YFP-CBP, but agonist-induced recruitment occurs within minutes. The agonist-induced recruitment of coactivators requires helix 12 and critical residues in the ER–SRC-1 interaction surface, but not the F, AF-1, or DNA binding domains. Fluorescence recovery after photobleaching indicates that YFP–SRC-1, YFP-CBP, and CFP-LacER complexes undergo rapid (within seconds) molecular exchange even in the presence of an agonist. Taken together, these data suggest a dynamic view of receptor-coregulator interactions that is now amenable to real-time study in living cells.

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Monomer–dimer dynamics and distribution of GPI-anchored uPAR are determined by cell surface protein assemblies

The Journal of Cell Biology ◽

10.1083/jcb.200702151 ◽

2007 ◽

Vol 179 (5) ◽

pp. 1067-1082 ◽

Cited By ~ 54

Author(s):

Valeria R. Caiolfa ◽

Moreno Zamai ◽

Gabriele Malengo ◽

Annapaola Andolfo ◽

Chris D. Madsen ◽

...

Keyword(s):

Cell Membrane ◽

Cell Surface ◽

Plasminogen Activator ◽

Fluorescent Protein ◽

Surface Protein ◽

Basal Membrane ◽

Membrane Dynamics ◽

Live Cells ◽

Cell Surface Protein ◽

Protein Assemblies

To search for functional links between glycosylphosphatidylinositol (GPI) protein monomer–oligomer exchange and membrane dynamics and confinement, we studied urokinase plasminogen activator (uPA) receptor (uPAR), a GPI receptor involved in the regulation of cell adhesion, migration, and proliferation. Using a functionally active fluorescent protein–uPAR in live cells, we analyzed the effect that extracellular matrix proteins and uPAR ligands have on uPAR dynamics and dimerization at the cell membrane. Vitronectin directs the recruitment of dimers and slows down the diffusion of the receptors at the basal membrane. The commitment to uPA–plasminogen activator inhibitor type 1–mediated endocytosis and recycling modifies uPAR diffusion and induces an exchange between uPAR monomers and dimers. This exchange is fully reversible. The data demonstrate that cell surface protein assemblies are important in regulating the dynamics and localization of uPAR at the cell membrane and the exchange of monomers and dimers. These results also provide a strong rationale for dynamic studies of GPI-anchored molecules in live cells at steady state and in the absence of cross-linker/clustering agents.

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Ultrafast Proton Shuttling in Psammocora Cyan Fluorescent Protein

The Journal of Physical Chemistry B ◽

10.1021/jp401114e ◽

2013 ◽

Vol 117 (38) ◽

pp. 11134-11143 ◽

Cited By ~ 8

Author(s):

John T. M. Kennis ◽

Ivo H. M. van Stokkum ◽

Dayna S. Peterson ◽

Anjali Pandit ◽

Rebekka M. Wachter

Keyword(s):

Fluorescent Protein ◽

Cyan Fluorescent Protein ◽

Proton Shuttling

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Specific expression of an oxytocin-enhanced cyan fluorescent protein fusion transgene in the rat hypothalamus and posterior pituitary

Journal of Endocrinology ◽

10.1677/joe-09-0289 ◽

2009 ◽

Vol 204 (3) ◽

pp. 275-285 ◽

Cited By ~ 20

Author(s):

Akiko Katoh ◽

Hiroaki Fujihara ◽

Toyoaki Ohbuchi ◽

Tatsushi Onaka ◽

W Scott Young ◽

...

Keyword(s):

Fluorescent Protein ◽

Fusion Gene ◽

Plasma Osmolality ◽

Cyan Fluorescent Protein ◽

Posterior Pituitary ◽

Protein Fusion ◽

Transgenic Rats ◽

Salt Loading ◽

Wide Range ◽

Enhanced Cyan Fluorescent Protein

We have generated rats bearing an oxytocin (OXT)-enhanced cyan fluorescent protein (eCFP) fusion transgene designed from a murine construct previously shown to be faithfully expressed in transgenic mice. In situ hybridisation histochemistry revealed that the Oxt–eCfp fusion gene was expressed in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) in these rats. The fluorescence emanating from eCFP was observed only in the SON, the PVN, the internal layer of the median eminence and the posterior pituitary (PP). In in vitro preparations, freshly dissociated cells from the SON and axon terminals showed clear eCFP fluorescence. Immunohistochemistry for OXT and arginine vasopressin (AVP) revealed that the eCFP fluorescence co-localises with OXT immunofluorescence, but not with AVP immunofluorescence in the SON and the PVN. Although the expression levels of the Oxt–eCfp fusion gene in the SON and the PVN showed a wide range of variations in transgenic rats, eCFP fluorescence was markedly increased in the SON and the PVN, but decreased in the PP after chronic salt loading. The expression of the Oxt gene was significantly increased in the SON and the PVN after chronic salt loading in both non-transgenic and transgenic rats. Compared with wild-type animals, euhydrated and salt-loaded male and female transgenic rats showed no significant differences in plasma osmolality, sodium concentration and OXT and AVP levels, suggesting that the fusion gene expression did not disturb any physiological processes. These results suggest that our new transgenic rats are a valuable new tool to identify OXT-producing neurones and their terminals.

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Intact Ca(2+)-binding sites are required for targeting of annexin 1 to endosomal membranes in living HeLa cells

Journal of Cell Science ◽

10.1242/jcs.113.22.3931 ◽

2000 ◽

Vol 113 (22) ◽

pp. 3931-3938 ◽

Cited By ~ 1

Author(s):

U. Rescher ◽

N. Zobiack ◽

V. Gerke

Keyword(s):

Hela Cells ◽

Binding Sites ◽

Fluorescent Protein ◽

Binding Protein ◽

Membrane Binding ◽

Growth Factor Receptor ◽

Intracellular Distribution ◽

Live Cells ◽

Membrane Structures ◽

Annexin 1

Annexin 1 is a Ca(2+)-regulated membrane binding protein and a major substrate of the epidermal growth factor receptor kinase. Because of its properties and intracellular distribution, the protein has been implicated in endocytic trafficking of the receptor, in particular in receptor sorting occurring in multivesicular endosomes. Up to now, however, the localization of annexin 1 to cellular membranes has been limited to subcellular fractionation and immunocytochemical analyses of fixed cells. To establish its localization in live cells, we followed the intracellular fate of annexin 1 molecules fused to the Green Fluorescent Protein (GFP). We show that annexin 1-GFP associates with distinct, transferrin receptor-positive membrane structures in living HeLa cells. A GFP chimera containing the Ca(2+)/phospholipid-binding protein core of annexin 1 also shows a punctate intracellular distribution, although the structures labeled here do not resemble early but, at least in part, late endosomes. In contrast, the cores of annexins 2 and 4 fused to GFP exhibit a cytoplasmic or a different punctate distribution, respectively, indicating that the highly homologous annexin core domains carry distinct membrane specificities within live cells. By inactivating the three high-affinity Ca(2+) binding sites in annexin 1 we also show that endosomal membrane binding of the protein in live HeLa cells depends on the integrity of these Ca(2+) binding sites. More detailed analysis identifies a single Ca(2+) site in the second annexin repeat that is crucially involved in establishing the membrane association. These results reveal for the first time that intracellular membrane binding of an annexin in living cells requires Ca(2+) and is mediated in part through an annexin core domain that is capable of establishing specific interactions.

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Overexpressed Pituitary Tumor-Transforming Gene Causes Aneuploidy in Live Human Cells

Endocrinology ◽

10.1210/en.2003-0305 ◽

2003 ◽

Vol 144 (11) ◽

pp. 4991-4998 ◽

Cited By ~ 76

Author(s):

Run Yu ◽

Wenge Lu ◽

Jiandong Chen ◽

Chris J. McCabe ◽

Shlomo Melmed

Keyword(s):

Cancer Cells ◽

Chromosome Segregation ◽

Pituitary Tumor ◽

Fluorescent Protein ◽

Human Cancer ◽

Live Cells ◽

Pituitary Tumor Transforming Gene ◽

Transforming Gene

Abstract The mammalian securin, pituitary tumor-transforming gene (PTTG), is overexpressed in several tumors and transforms cells in vitro and in vivo. To test the hypothesis that PTTG overexpression causes aneuploidy, enhanced green fluorescent protein (EGFP)-tagged PTTG (PTTG-EGFP) was expressed in human H1299 cancer cells (with undetectable endogenous PTTG expression) and mitosis of individual live cells observed. Untransfected cells and cells expressing EGFP alone exhibited appropriate mitosis. PTTG-EGFP markedly prolonged prophase and metaphase, indicating that PTTG blocks progression of mitosis to anaphase. In cells that underwent apparently normal mitosis (35 of 65 cells), PTTG-EGFP was degraded about 1 min before anaphase onset. Cells that failed to degrade PTTG-EGFP exhibited asymmetrical cytokinesis without chromosome segregation (18 of 65 cells) or chromosome decondensation without cytokinesis (9 of 65 cells), resulting in appearance of a macronucleus. Fifty-one of 55 cells expressing a nondegradable mutant PTTG exhibited asymmetrical cytokinesis without chromosome segregation, and some (4 of 55) decondensed chromosomes, both resulting in macronuclear formation. During this abnormal cytokinesis, all chromosomes and spindles and both centrosomes moved to one daughter cell, suggesting potential chaos in the subsequent mitosis. In conclusion, failure of PTTG degradation or enhanced PTTG accumulation, as a consequence of overexpression, inhibits mitosis progression and chromosome segregation but does not directly affect cytokinesis, resulting in aneuploidy. These results demonstrate that PTTG induces aneuploidy in single, live, human cancer cells.

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tdLanYFP, a yellow, bright, photostable and pH insensitive fluorescent protein for live cell imaging and FRET-based sensing strategies

10.1101/2021.04.27.441613 ◽

2021 ◽

Author(s):

Y. Bousmah ◽

H. Valenta ◽

G. Bertolin ◽

U. Singh ◽

V. Nicolas ◽

...

Keyword(s):

Single Molecule ◽

Live Cell Imaging ◽

Cell Imaging ◽

Fluorescent Protein ◽

Fluorescent Proteins ◽

Yellow Fluorescent Protein ◽

Resonance Energy ◽

Live Cell ◽

Live Cells

AbstractYellow fluorescent proteins (YFP) are widely used as optical reporters in Förster Resonance Energy Transfer (FRET) based biosensors. Although great improvements have been done, the sensitivity of the biosensors is still limited by the low photostability and the poor fluorescence performances of YFPs at acidic pHs. In fact, today, there is no yellow variant derived from the EYFP with a pK1/2 below ∼5.5. Here, we characterize a new yellow fluorescent protein, tdLanYFP, derived from the tetrameric protein from the cephalochordate B. lanceolatum, LanYFP. With a quantum yield of 0.92 and an extinction coefficient of 133 000 mol−1.L.cm−1, it is, to our knowledge, the brightest dimeric fluorescent protein available, and brighter than most of the monomeric YFPs. Contrasting with EYFP and its derivatives, tdLanYFP has a very high photostability in vitro and preserves this property in live cells. As a consequence, tdLanYFP allows the imaging of cellular structures with sub-diffraction resolution with STED nanoscopy. We also demonstrate that the combination of high brightness and strong photostability is compatible with the use of spectro-microscopies in single molecule regimes. Its very low pK1/2 of 3.9 makes tdLanYFP an excellent tag even at acidic pHs. Finally, we show that tdLanYFP can be a FRET partner either as donor or acceptor in different biosensing modalities. Altogether, these assets make tdLanYFPa very attractive yellow fluorescent protein for long-term or single-molecule live-cell imaging that is also suitable for FRET experiment including at acidic pH.

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