(A-16) P38γMAPK regulates invasive breast cancer cell stiffness, influencing metastasis

Introduction:: Despite decades of work on the molecular and genetic characteristics of cancer metastasis, metastasis remains responsible for around 90% of cancer-related death. However, because the stages of the metastatic process are mechanical, recent studies have also investigated the mechanical properties of metastatic cancer cells. During metastasis, tumor cells may undergo extreme deformation and cytoskeletal changes, including possible apoptosis induced by mechanical forces. Yet is not clear how modifications in a single gene of a cancer cell can modulate its degree of metastatic likelihood. In this study, we studied the impact of p38γ MAPK expression on the deformability of the invasive cancer cell line MDA-MB-231 by knocking down p38γ. MDA-MB-231-p38γKD cells showed significantly reduced metastasis compared with the parent MDA-MB-231 human breast cancer cell line.

We studied the cytomechanical effects of this genetic knockdown via particle tracking microrheology (PTM). PTM tracks the Brownian motion of 200nm diameter nanoparticles that were ballistically injected into cytoplasm. Based on the trajectory of particle movements, mean squared displacement functions can be calculated, reflecting the frequency-dependent viscoelasticity of the cytoplasm, including storage and loss moduli, creep compliance, viscosity. High spatiotemporal resolution imaging allowed us to observe the mechanical responses of the cytoplasm at a frequency of 100Hz. These technologies allow us to explore the mechanical differences between these two related cancer cell lines, helping to identify how the cell mechanics may support metastatic success.


Materials and Methods:: We studied the cytomechanical effects of this genetic knockdown via particle tracking microrheology (PTM). PTM tracks the Brownian motion of 200nm diameter nanoparticles that were ballistically injected into cytoplasm. Based on the trajectory of particle movements, mean squared displacement functions can be calculated, reflecting the frequency-dependent viscoelasticity of the cytoplasm, including storage and loss moduli, creep compliance, viscosity. High spatiotemporal resolution imaging allowed us to observe the mechanical responses of the cytoplasm at a frequency of 100Hz. These technologies allow us to explore the mechanical differences between these two related cancer cell lines, helping to identify how the cell mechanics may support metastatic success.


Results, Conclusions, and Discussions:: We calculated the mechanical properties from the mean squared displacements of intracellular nanoparticles. MDA-MB-231-p38γKD cells displayed a higher stiffness than parent MDA-MB-231 cells. The power law slope is 11% lower in MDA-MB-231-p38γKD compared to parent MDA-MB-231 cells, indicating the motion of nanoparticles in p38γ knockdown cells are more restricted. Moreover, MDA-MB-231-p38γKD cells showed a nearly double creep compliance compared with MDA-MB-231 cells at time lag=1s, suggesting that p38γ knockdown cells are substantially stiffer. In combination with prior studies showing that p38γ MAPK expression enhances cancer cell motility and metastasis [1], our results illuminate these prior data in the context of the control of p38γ on cell stiffness through regulation of actin cytoskeletal behavior. Thus, knockdown of p38γ is associated with lower metastatic success likely due in part to the increased cellular stiffness conferred in the tumor cells, which may preclude robust cell migration and intravasation.


Acknowledgements (Optional): :

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