Browsing by Author "Sun, Li"

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    Cancer-Associated Fibroblasts Induce a Collagen Cross-link Switch in Tumor Stroma
    (American Association for Cancer Research, 2016) Pankova, Daniela; Chen, Yulong; Terajima, Masahiko; Schliekelman, Mark J.; Baird, Brandi N.; Fahrenholtz, Monica; Sun, Li; Gill, Bartley J.; Vadakkan, Tegy J.; Kim, Min P.; Ahn, Young-Ho; Roybal, Jonathon D.; Liu, Xin; Cuentas, Edwin Roger Parra; Rodriguez, Jaime; Wistuba, Ignacio I.; Creighton, Chad J.; Gibbons, Don L.; Hicks, John M.; Dickinson, Mary E.; West, Jennifer L.; Grande-Allen, K. Jane; Hanash, Samir M.; Yamauchi, Mitsuo; Kurie, Jonathan M.
    Intratumoral collagen cross-links heighten stromal stiffness and stimulate tumor cell invasion, but it is unclear how collagen cross-linking is regulated in epithelial tumors. To address this question, we used KrasLA1 mice, which develop lung adenocarcinomas from somatic activation of a KrasG12D allele. The lung tumors in KrasLA1 mice were highly fibrotic and contained cancer-associated fibroblasts (CAF) that produced collagen and generated stiffness in collagen gels. In xenograft tumors generated by injection of wild-type mice with lung adenocarcinoma cells alone or in combination with CAFs, the total concentration of collagen cross-links was the same in tumors generated with or without CAFs, but coinjected tumors had higher hydroxylysine aldehyde–derived collagen cross-links (HLCC) and lower lysine-aldehyde–derived collagen cross-links (LCCs). Therefore, we postulated that an LCC-to-HLCC switch induced by CAFs promotes the migratory and invasive properties of lung adenocarcinoma cells. To test this hypothesis, we created coculture models in which CAFs are positioned interstitially or peripherally in tumor cell aggregates, mimicking distinct spatial orientations of CAFs in human lung cancer. In both contexts, CAFs enhanced the invasive properties of tumor cells in three-dimensional (3D) collagen gels. Tumor cell aggregates that attached to CAF networks on a Matrigel surface dissociated and migrated on the networks. Lysyl hydroxylase 2 (PLOD2/LH2), which drives HLCC formation, was expressed in CAFs, and LH2 depletion abrogated the ability of CAFs to promote tumor cell invasion and migration.
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    Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma
    (American Society for Clinical Investigation, 2015) Chen, Yulong; Terajima, Masahiko; Yang, Yanan; Sun, Li; Ahn, Young-Ho; Pankova, Daniela; Puperi, Daniel S.; Watanabe, Takeshi; Kim, Min P.; Blackmon, Shanda H.; Rodriguez, Jaime; Liu, Hui; Behrens, Carmen; Wistuba, Ignacio I.; Minelli, Rosalba; Scott, Ken
    Epithelial tumor metastasis is preceded by an accumulation of collagen cross-links that heighten stromal stiffness and stimulate the invasive properties of tumor cells. However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links. Utilizing resected human lung cancer tissues and a p21CIP1/WAF1-deficient, K-rasG12D-expressing murine metastatic lung cancer model, we showed that, relative to normal lung tissues, tumor stroma contains higher levels of hydroxylysine aldehyde–derived collagen cross-links (HLCCs) and lower levels of lysine aldehyde–derived cross-links (LCCs), which are the predominant types of collagen cross-links in skeletal tissues and soft tissues, respectively. Gain- and loss-of-function studies in tumor cells showed that lysyl hydroxylase 2 (LH2), which hydroxylates telopeptidyl lysine residues on collagen, shifted the tumor stroma toward a high-HLCC, low-LCC state, increased tumor stiffness, and enhanced tumor cell invasion and metastasis. Together, our data indicate that LH2 enhances the metastatic properties of tumor cells and functions as a regulatory switch that controls the relative abundance of biochemically distinct types of collagen cross-links in the tumor stroma.
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    Probing Mechanical Properties of Proteins by Molecular Dynamics Simulations
    (2017-10-13) Sun, Li; Onuchic, José N.; Levine, Herbert
    Many proteins have force-related functions, such as force transducers and force sensors. Experimental efforts, such as protein structure determination, mutagenesis studies, single-molecule force experiments, fluorescent molecular probes, and traction force microscopy, have provided an insightful understanding of the mechanical properties of force-related proteins. Molecular dynamics simulations have also been widely performed and have become an increasingly useful technique for understanding the mechanisms of force regulation at the molecular level. By means of molecular simulations, one often aims to obtain a global picture of the free energy landscape and relevant kinetic data in an effort to understand the thermodynamic properties of the molecular system and kinetic pathways of reaction processes. However, the complete free energy landscape of a molecular system requires sufficient sampling of the multi-dimensional configuration space, which often involves applications of enhanced sampling techniques, such as umbrella sampling. This dissertation presents applications of molecular simulations and free energy landscape theory to biomolecular systems of different complexities. The first study investigates the force-dependent unfolding rates of an immunoglobulin-like domain ddFLN4. When constant forces of opposite directions are applied on the two terminal residues to mimic a physiological context, we observe distinct relations between the unfolding rate and applied force at different force levels, indicating that the force-induced unfolding behavior of ddFLN4 can be characterized into three force regimes. More detailed insights are obtained by making connections between unfolding kinetics and the underlying free energy landscape. The second study applies molecular dynamics techniques to a multidomain protein vinculin, an important force sensor and force transducer in focal adhesion mechanotransduction. This study aims to provide a molecular mechanism for vinculin activation, an important conformational change in focal adhesion assembly. Using constant forces applied on the experimentally determined ligand binding sites to mimic the in vivo mechanical context of vinculin, we propose a force-sensitive activation mechanism, and provide detailed analyses on the kinetic bottleneck and order of events in a physiological context.