Oncogenic signaling alters cell shape and mechanics to facilitate cell division under confinement

Context:

Most animal cells undergo different degrees of rounding up when entering mitosis both in cell culture and in vivo (Cadart et al. 2014). This is important for accurate spindle positioning and metaphase plate formation (Lancaster and Baum, 2014). For cells to survive, they need to maintain division in the complex environments. In order to do so, cells require contractility of acto-myosin cytoskeleton (Champion et al. 2017). To understand how mitosis successfully occurs in different extra-cellular environments, it is imperative to study the role of contractility, the upstream regulators of contractility and mechanics during this process.

Major findings:

To understand how cancer cells, regulate contractility to successfully divide in different environments, the authors transformed epithelial cells (MCF10A) by over-expressing a single oncogene, Rasv12. This is a simple system to look at the role of upstream signaling in regulating mitotic rounding without the caveats of having extra chromosome numbers or centrosome aberrations. The authors find that inducible Ras activation signals through the MEK/ERK pathway and enhances cell rounding during mitosis. They also show that Ras activation alters Rho-based contractility during mitosis. To understand how this transformation effects the mechanics of dividing cells, they measure the stiffness of the cells sitting on the surface by using atomic force microscopy (AFM) and real time deformability cytometry (RT-DC), a high- throughput method to measure the stiffness of cells in suspension. Interestingly, Ras activation leads to softer cells during interphase but stiffer cells during metaphase. The role of Ras activation in enhancing mitotic rounding becomes more obvious under stiff confinement. The authors show that increase in contractility is required for the push to successfully divide and reduce mitotic defects under confinement.

What I liked about the preprint

It is interesting for me that small term activation of Ras is enough for changing the mechanics of the cell undergoing mitosis. Authors show the importance of oncogenic signaling that could provide cancer cells with a capacity to undergo mitosis successfully in confinements like tumor spheroids and cells undergoing EMT. Therefore, this is a study that shows another example of temporal regulation of signaling controlling mechanics and cellular geometry.

What’s next and my questions to the author:

I would be curious to know how the interphase cells with Ras activation show reduced stiffness when attached to the surface and even when in suspension. According to previous studies, I could find that cells are only softer in loosely adhered cells (Gullekson et al. 2017). Ras/ERK activation clearly regulates cortical contractility during mitosis, my view would be that this happens via changes in the cortical thickness that would maintain cortical tension. This could be measured by STORM imaging during various stages of mitosis. It is still not clear to me how Ras activation, even before cells enter interphase, regulate stiffness temporally. One way I could see how cancer cells could achieve this would be regulating mitotic kinases like CDK1, which would then feed on to Rho signaling. A previous study showed that oncogenic Ras suppresses CDK1 expression (Huang et al. 2013). It will be interesting to see how CDK1, ROCK and ECT2 (RhoA-GEF) localization changes with progression of mitosis.

References

Cadart, Clotilde, Ewa Zlotek-Zlotkiewicz, Maël Le Berre, Matthieu Piel, and Helen K. Matthews. 2014. “Exploring the Function of Cell Shape and Size during Mitosis.” Developmental Cell 29 (2): 159–69.

Champion, Lysie, Monika I. Linder, and Ulrike Kutay. 2017. “Cellular Reorganization during Mitotic Entry.” Trends in Cell Biology 27 (1): 26–41.

Gullekson, Corinne, Gheorghe Cojoc, Mirjam Schürmann, Jochen Guck, and Andrew Pelling. 2017. “Mechanical Mismatch between Ras Transformed and Untransformed Epithelial Cells.” Soft Matter 13 (45): 8483–91.

Huang, Tun-Lan, Jerry P. Pian, and Bin-Tao Pan. 2013. “Oncogenic Ras Suppresses Cdk1 in a Complex Manner during the Incubation of Activated Xenopus Egg Extracts.” Archives of Biochemistry and Biophysics. https://doi.org/10.1016/j.abb.2013.01.006.

Lancaster, Oscar M., and Buzz Baum. 2014. “Shaping up to Divide: Coordinating Actin and Microtubule Cytoskeletal Remodelling during Mitosis.” Seminars in Cell & Developmental Biology 34 (October): 109–15.

Tags: cancer signaling, contractility, epithelial mesenchymal transition, mitosis, stiffness

Posted on: 1st May 2019 , updated on: 3rd May 2019

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