Integrated study of the effects of epithelial-mesenchymal transition on cell mechanics, mitotic rounding and proliferation in tumor spheroids

动物细胞需要获得圆形，为有丝分裂纺锤体提供空间，以便成功进行有丝分裂。这种有丝分裂变圆依赖于周围组织的机械变形，并由细胞肌动蛋白皮质的肌动球蛋白收缩性产生的力驱动。有丝分裂圆化的失败可以显著延迟有丝分裂甚至导致细胞死亡。癌细胞能够在机械挑战性环境中维持成功的有丝分裂，例如生长肿瘤的日益拥挤的环境。因此，已经假设癌细胞的肌动蛋白皮质表现出致癌适应，允许在越来越致密的肿瘤组织内进行有丝分裂变圆和分裂。上皮间质转化（EMT）是一种细胞转化，已被证明是癌症进展的标志。它通常与促进细胞迁移和癌细胞侵袭的转移的早期步骤有关。在初步的工作中，我们可以表明，EMT引起相反的细胞力学变化的间期和有丝分裂在非贴壁乳腺上皮细胞。EMT后，间期细胞变软，收缩性降低，而有丝分裂期细胞变硬，收缩性增强。这些细胞力学的变化表明EMT后有丝分裂变圆强度增强。这一推测得到了我们在机械限制的EMT后肿瘤球体中有丝分裂圆度增加和增殖增加的发现的支持。在所提出的项目中，我们的目标是进一步测试我们的假设，即EMT诱导的皮质力学和有丝分裂圆化的变化引起增强的细胞增殖的肿瘤球体中的机械约束。此外，我们的目标是阐明参与EMT诱导的皮质机械表型的产生的细胞信号传导途径。受我们以前的研究结果的启发，我们将特别阐明RhoA和Rac1活性变化的作用。本研究的发现可能揭示EMT如何促进体内肿瘤生长的新方案。总之，我们的发现不仅将为细胞生物学领域提供高影响力的结果，而且还将确定癌症治疗的潜在新靶点。

Animal cells need to acquire a round shape to provide space for the mitotic spindle in order to undergo mitosis successfully. This mitotic rounding relies on mechanical deformation of surrounding tissue and is driven by forces emanating from actomyosin contractility of the cellular actin cortex. Failure of mitotic rounding can significantly delay mitosis or even lead to cell death.Cancer cells are able to maintain successful mitosis in mechanically challenging environments such as the increasingly crowded environment of a growing tumor. Thus, it has been hypothesized that the actin cortex of cancer cells exhibits oncogenic adaptations that allow for ongoing mitotic rounding and division inside increasingly dense tumor tissue. Epithelial Mesenchymal Transition (EMT) is a cellular transformation which was shown to be a hallmark in cancer progression. It is commonly linked to the early steps in metastasis promoting cell migration and cancer cell invasiveness. In preliminary work, we could show that EMT gives rise to opposite cell-mechanical changes in interphase and mitosis in non-adherent breast epithelial cells. While interphase cells become softer and less contractile, mitotic cells become stiffer and more contractile after EMT. These cell-mechanical changes suggest enhanced mitotic rounding strength after EMT. This conjecture is supported by our findings of increased mitotic roundness and increased proliferation in mechanically confined post-EMT tumor spheroids. In the proposed project, we aim to further test our hypothesis that EMT-induced changes of cortical mechanics and mitotic rounding give rise to enhanced cell proliferation in tumor spheroids in mechanical confinement. In addition, we aim to elucidate cellular signaling pathways involved in the generation of the EMT-induced cortex-mechanical phenotype. Motivated by our previous findings, we will in particular, elucidate the role of RhoA and Rac1 activity changes. The insight of this research may reveal a new scheme of how EMT promotes growth of carcinoma in the body. In summary, our findings will not only provide high impact results to the field of cell biology but will also identify potential new targets for cancer therapeutics.