Dr. Shu Chien Profile

Dr. Shu Chien

Professor at Univ of California San Diego

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Publications (4)

Proceedings Article | 14 March 2012 Paper

Molecular signaling in live cells studied by FRET

Shu Chien, Yingxiao Wang

Proceedings Volume 8329, 832902 (2012) https://doi.org/10.1117/12.919126

KEYWORDS: Fluorescence resonance energy transfer, Biosensors, Visualization, Plasma, Proteins, Cancer, Signaling molecules, Receptors, Live cell imaging, In vitro testing

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Genetically encoded biosensors based on fluorescence resonance energy transfer (FRET) enables visualization of signaling events in live cells with high spatiotemporal resolution. We have used FRET to assess temporal and spatial characteristics for signaling molecules, including tyrosine kinases Src and FAK, small GTPase Rac, calcium, and a membrane-bound matrix metalloproteinase MT1-MMP. Activations of Src and Rac by platelet derived growth factor (PDGF) led to distinct subcellular patterns during cell migration on micropatterned surface, and these two enzymes interact with each other to form a feedback loop with differential regulations at different subcellular locations. We have developed FRET biosensors to monitor FAK activities at rafts vs. non-raft regions of plasma membrane in live cells. In response to cell adhesion on matrix proteins or stimulation by PDGF, the raft-targeting FAK biosensor showed a stronger FRET response than that at non-rafts. The FAK activation at rafts induced by PDGF is mediated by Src. In contrast, the FAK activation at rafts induced by adhesion is independent of Src activity, but rather is essential for Src activation. Thus, Src is upstream to FAK in response to chemical stimulation (PDGF), but FAK is upstream to Src in response to mechanical stimulation (adhesion). A novel biosensor has been developed to dynamically visualize the activity of membrane type-1-matrix metalloproteinase (MT1-MMP), which proteolytically remodels the extracellular matrix. Epidermal growth factor (EGF) directed active MT1-MMP to the leading edge of migrating live cancer cells with local accumulation of EGF receptor via a process dependent on an intact cytoskeletal network. In summary, FRET-based biosensors enable the elucidation of molecular processes and hierarchies underlying spatiotemporal regulation of biological and pathological processes, thus advancing our knowledge on how cells perceive mechanical/chemical cues in space and time to coordinate molecular/cellular functions.

Proceedings Article | 24 August 2010 Paper

3-dimensional forces and molecular dynamics of live cells

Sung Sik Hur, Yi-Shuan Li, Joon Seok Park, Ying-Li Hu, Shu Chien

Proceedings Volume 7759, 77590S (2010) https://doi.org/10.1117/12.861581

KEYWORDS: 3D image processing, Finite element methods, 3D metrology, Digital image correlation, Protactinium, Confocal microscopy, Green fluorescent protein, Proteins, Microscopy, Image processing

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Proceedings Article | 7 May 2007 Paper

On the way to subcellular imaging of mechanotransduction in the developing vasculature

Irina Larina, Yingxiao Wang, Shu Chien, Mary Lane, Mary Dickinson

Proceedings Volume 6535, 653504 (2007) https://doi.org/10.1117/12.740602

KEYWORDS: Fluorescence resonance energy transfer, In vivo imaging, Luminescence, Sensors, Heart, Fluorescent proteins, Blood circulation, In vitro testing, Tissues, Biophysics

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Proceedings Article | 18 August 2005 Paper

Oscillating optical tweezer-based 3-D confocal microrheometer for investigating the intracellular micromechanics and structures

H. Ou-Yang, E. Rickter, C. Pu, O. Latinovic, A. Kumar, M. Mengistu, L. Lowe-Krentz, S. Chien

Proceedings Volume 5930, 593004 (2005) https://doi.org/10.1117/12.618108

KEYWORDS: Optical tweezers, Particles, Confocal microscopy, Optical amplifiers, Cytoskeletons, Microscopes, Proteins, Mirrors, Phase shifts, Motion measurement

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Mechanical properties of living biological cells are important for cells to maintain their shapes, support mechanical stresses and move through tissue matrix. The use of optical tweezers to measure micromechanical properties of cells has recently made significant progresses. This paper presents a new approach, the oscillating optical tweezer cytorheometer (OOTC), which takes advantage of the coherent detection of harmonically modulated particle motions by a lock-in amplifier to increase sensitivity, temporal resolution and simplicity. We demonstrate that OOTC can measure the dynamic mechanical modulus in the frequency range of 0.1-6,000 Hz at a rate as fast as 1 data point per second with submicron spatial resolution. More importantly, OOTC is capable of distinguishing the intrinsic non-random temporal variations from random fluctuations due to Brownian motion; this capability, not achievable by conventional approaches, is particular useful because living systems are highly dynamic and often exhibit non-thermal, rhythmic behavior in a broad time scale from a fraction of a second to hours or days. Although OOTC is effective in measuring the intracellular micromechanical properties, unless we can visualize the cytoskeleton in situ, the mechanical property data would only be as informative as that of "Blind men and the Elephant". To solve this problem, we take two steps, the first, to use of fluorescent imaging to identify the granular structures trapped by optical tweezers, and second, to integrate OOTC with 3-D confocal microscopy so we can take simultaneous, in situ measurements of the micromechanics and intracellular structure in living cells. In this paper, we discuss examples of applying the oscillating tweezer-based cytorheometer for investigating cultured bovine endothelial cells, the identification of caveolae as some of the granular structures in the cell as well as our approach to integrate optical tweezers with a spinning disk confocal microscope.

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