Research

Our research is in the area of Mechanobiology, with focused efforts in understanding the molecular mechanisms by which cell generated mechanical forces and associated signaling pathways enable cell and tissue functions. We have contributed to the development and application of new methods for sub-cellular mechanical perturbations including laser ablation of cytoskeletal structures and direct nuclear force probes. A distinctive feature of our work is that experimental findings are either motivated by or interpreted with mathematical modeling/computational predictions. Using these platforms, we have proposed new explanations for why microtubules adopt certain conformations during cell motility, how tension is established in dynamic stress fibers which enables cell adhesion and migration, how cells find their geometric center, and how the cell shapes and positions the nucleus for establishing cell polarity. In addition, we have established the concept that nuclear-cytoskeletal linkages are functionally involved in tissue development and cell mechanotransduction. Current research projects in the laboratory include quantitative measurements of nuclear forces, the effect of mechanical stresses on nuclear functions and gene expression, cellular adaptation to mechanical properties of the extracellular matrix, and the mechanics of tissue development. A key interest is in the field of Cancer Mechanobiology, with a focus on the role of the nucleus in the development of aberrant tissue structure and function.

The Role of the LINC Complex in Health and Disease

The LINC complex refers to nuclear envelope proteins which mechanically connect the nucleoskeleton and the cytoskeleton, which are important protein networks that govern cellular behavior. The role of the LINC complex in cellular functions like migration, mechanotransduction and tissue development is poorly understood. We have found that the LINC complex regulates genome-wide transcriptional responses to substrate rigidity, and enables mechano-chemical responses of cells to matrix strain.

The SYNE-1 and SYNE-2 genes encoding LINC complex proteins nesprin-1 and nesprin-2 are frequently mutated in breast cancer. Some of these alterations result in changes to the length of these large proteins (> 800 kDa), and some are predicted to abrogate LINC complex function by altering the interaction between the nesprin and SUN proteins and/or the cytoskeleton. Yet, how such alterations to the LINC complex might contribute to cancer development is unknown. We have found that the LINC complex contributes to a loss of tissue structure in glandular epithelia, reminiscent of abnormal glandular tissue structures in cancer.

  1. Zhang Q, Narayanan V, Mui KL, O’Bryan CS, Anderson RH, Birendra KC, Roux KJ, Dickinson RB, Angelini TE, Gundersen GG, Conway DE and Lele TP, Current Biology, Mechanical stabilization of the glandular acinus by linker of nucleoskeleton and cytoskeleton complex, 2019 (in press).
  2. Alam SG, Zhang Q, Prasad N, Li Y, Chamala S, Kuchibhotla R, Kc B, Aggarwal V, Shrestha S, Jones AL, Levy SE, Roux KJ, Nickerson JA, Lele TP. The mammalian LINC complex regulates genome transcriptional responses to substrate rigidity. Scientific Reports. 2016 Dec 1;6:38063.
  3. Wu Jun, Kent Ian A, Shekhar Nandini, Chancellor TJ, Mendonca A, Dickinson RB and Lele TP. Actomyosin Pulls to Advance the Nucleus in a Migrating Tissue Cell. Biophysical Journal, 106 (1) 7-15 (2014).
  4. Chancellor TJ, Lee J, Thodeti CK, Lele TP. Actomyosin tension exerted on the nucleus through nesprin-1 connections influences endothelial cell adhesion, migration, and cyclic strain-induced reorientation. Biophysical Journal. 2010 Jul 7;99(1):115-23.

Nuclear Envelope Mechanics and Rupture

The nuclear membrane ruptures in cancer cells spontaneously and also during migration through confined spaces, which promotes DNA damage due to undesirable mixing of nucleoplasm and cytoplasm and tumorigenesis. We are interested in nuclear envelope mechanics in the context of the double nuclear membrane structure and composition, and how this structure ruptures under mechanical stress. In an early paper, we proposed a mechanical explanation for why the nuclear envelope features a (large) 45 nm separation distance between the outer and inner nuclear membranes, and uniformly distributed nuclear pores separated by ~400 nm. More recently we have demonstrated a critical role for Barrier-to-Autointegration-Factor (BAF) in the repair of nuclear membrane rupture. Furthermore, have shown that tensile stress on the nuclear membrane can cause membrane rupture, as opposed to the commonly accepted compressive stress-mediated rupture. Current efforts are focused on understanding how the structure and composition of the nuclear envelope mediates response to external stresses, and in quantifying the mechanical stresses that are generated on the envelope during nuclear envelope rupture.

  1. Agrawal A and Lele TP. Mechanics of nuclear membranes, Journal of Cell Science, 2019 Jul 15;132(14).
  2. Halfmann, C., Sears, R., Katiyar, A., Busselman, B., Aman, L., Zhang, Q., O’Bryan, C., Angelini, T.E., Lele, T.P., Roux, K. (2019), Repair of nuclear ruptures requires barrier-to-autointegration factor, Journal of Cell Biology, Jul 1;218(7):2136-2149.
  3. Zhang, Q., Tamashunas, A., Agrawal, A., Torbati, M., Katiyar, A., Dickinson, R.B., Lammerding, J., Lele, T.P., (2018), Local, transient tensile stress on the nuclear membrane causes membrane rupture, MolecularBiology of the Cell2019 Mar 21;30(7):899-906.
  4. Torbati, M., Lele, T.P., and Agrawal, A. (2016). On the Ultra-Donut Topology of The Nuclear Envelope, Proceedings of the National Academy of Sciences, 113, no. 40, 11094-11099.

Mechanisms of Nuclear Shaping and Positioning

We have a long-standing interest in the mechanisms of nuclear shaping and positioning. We have proposed the concept that the nucleus transmits mechanical stresses in migrating cells and nuclear position is determined by a balance of forces from the leading and trailing edge of the cell. Furthermore, we have proposed a new mechanism for how the nucleus is shaped in cells. This mechanism has the following key features to it: 1) the nucleus does not store elastic energy in the cell, 2) stresses on the nuclear surface are generated by moving cell boundaries, 3) Stress transmission occurs through friction generated in the F-actin network that is in between the moving boundary and the nuclear surface (summarized in a perspective article in the Journal of Cell Biology). We have used traction force microscopy to estimate forces on the nucleus in migrating fibroblasts and established the concept that the forces on the nucleus during migration are tensile. Ongoing studies in the lab are focused on the mechanisms of nuclear dysmorphia in cancer. Irregular nuclear shapes characterized by blebs, lobules, micronuclei, or invaginations are hallmarks of many cancers and other human pathologies. Despite the correlation between abnormal nuclear shape and human pathologies, the mechanism by which the cancer nucleus becomes misshapen is not fully understood.

  1. Lele, T.P., Dickinson, R.B., and Gundersen, G.G., (2018), Mechanical principles of nuclear shaping and positioning, Journal of Cell Biology, 2018 Oct 1;217(10):3330-3342.
  2. Kent IA, Zhang Q, Katiyar A, Li Y, Pathak S, Dickinson RB, Lele TP. Apical cell protrusions cause vertical deformation of the soft cancer nucleus. Journal of Cellular Physiology. 2019
  3. Tocco, V.J., Li, Y., Christopher, K.G., Matthews, J.H., Aggarwal, V., Paschall, L, Luesch, H., Licht, J.D., Dickinson, R.B., and Lele, T.P. (2018), The nucleus is irreversibly shaped by motion of cell boundaries in cancer and non-cancer cells, Journal of Cellular Physiology.233(2):1446-1454.
  4. Alam SG, Lovett D, Kim DI, Roux KJ, Dickinson RB, Lele TP. The nucleus is an intracellular propagator of tensile forces in NIH 3T3 fibroblasts. Journal of Cell Science 2015 May 15;128(10):1901-11

Tools and Models for Nuclear Mechanics

We have developed new probes to apply controlled, known mechanical forces to the nucleus. We have proposed and tested computational models for viscous stress transmission from the moving cell boundary to the nuclear surface, and dynein-based torque generation on the nuclear surface. Ongoing studies in the lab are focused on developing new methods for quantifying nuclear forces during cell migration.

  1. Neelam S, Chancellor TJ, Li Y, Nickerson JA, Roux KJ, Dickinson RB, Lele TP. Direct force probe reveals the mechanics of nuclear homeostasis in the mammalian cell. Proceedings of the National Academy of Sciences USA, 2015 May 5;112(18):5720-5.
  2. Wu J., Lee K.C., Dickinson R.B., Lele T.P. (2011). How Dynein and Microtubules Rotate the Nucleus. Journal of Cellular Physiology226: 2666-2674.
  3. Li Y, Lovett D, Zhang Q, Kuchibhotla RA, Neelam S, Zhu R, Gundersen GG, Lele TP and Dickinson RB. Moving Cell Boundaries Drive Nuclear Shaping during Cell Biophysical Journal, 2015 Aug 18;109(4):670-86.

Microtubule and Actomyosin Mechanics

We are interested in understanding the mechanics of cytoskeletal networks. Using laser ablation of sarcomeric actomyosin stress fibers, we have proposed that tension in stress fibers is due entirely to myosin mediated forces, and not due to spring elements that store elastic energy. By performing microtubule ablation, we have shown that dynein motor forces bend microtubules to put them under tension. Further, these tensile forces center the centrosomal array of microtubules. Kent IA,

  1. Rane PS, Dickinson RB, Ladd AJ, Lele TP. Transient Pinning and Pulling: A Mechanism for Bending Microtubules. PLoS One. 2016 Mar 14;11(3):e0151322.
  2. Wu J, Misra G, Russell RJ, Ladd AJC, Lele TP and Dickinson Effect of dynein on microtubule mechanics and centrosome centering. Molecular Biology of the Cell, 22(24): p. 4834-41 (2011).
  3. Russell R, Xia S-L, Dickinson RB and Lele TP. Sarcomere mechanics in capillary endothelial Biophysical Journal, 97 (6), 1578-1585 (2009).
  4. Wu J., Lee K.C., Dickinson R.B., Lele T.P. (2011). How Dynein and Microtubules Rotate the Nucleus. Journal of Cellular Physiology. 226: 2666-2674.