Senescent stroma induces nuclear deformations in cancer cells via the inhibition of RhoA/ROCK/myosin II-based cytoskeletal tension

Senescent stroma induces nuclear deformations in cancer cells via the inhibition of RhoA/ROCK/myosin II-based cytoskeletal tension

Recent studies of senescent cells suggest that they can induce tissue dysfunction in part through the secretion of soluble factors, a process that has been termed senescence-associated secretory phenotype (SASP).  Several studies suggest that SASP can affect tumor cell proliferation, and invasion, and even modulated the tumor microenvironment.  New research from Aifuwa et al. found that SASP disrupts proper outside-in mechanotransduction resulting in nuclear lobulations that propagates malignant transformations.  The group treated epithelial breast carcinoma cells with conditioned media from senescent fibroblasts and observed profound morphological changes in the cancer-cell nucleus.  Under basal conditions roughly 5% of cancer cells had an elongated morphology; conversely, after CM treatment the group found that 70% of cancer cells displayed elongated nuclei.  These findings coincided with similar changes in the total cellular shape as well and were confirmed with multiple microscopy approaches.  It was determined that a reduction in actin levels and cortical actin structures played a role in the formation of the elongated nuclei. The group utilized particle tracking microrheology to measure cytoplasmic compliance, and found the senescence CM resulted in robust bead displacement correlating with reduced F-actin content.  They further attributed the structural nuclear changes to the lamin A/C nuclear scaffolding proteins, as lamin A/C depleted cells formed much fewer nuclear lobulations in response to senescence CM.  Finally, the group determined that increasing the contractility of the cells could prevent senescence CM-induced changes to the nucleus.  They utilized the constitutive RhoA activator, CN03, in the presence of senescence CM and found that this activation of the RhoA-ROCK-Myosin II contractile pathway was sufficient to preserve normal rounded cell morphology, robust actin stress fibers, and prevented SASP-induced nuclear lobulations.  They also performed the reverse experiment by treating cells with various inhibitors of the RhoA-ROCK-Myosin II pathway, including the RhoA inhibitor, CT04, and found it was sufficient to induce nuclear lobulations.  Cytoskeleton Inc tools such as the RhoA activator (Cat. # CN03) and the RhoA inhibitor (Cat. # CT04) were essential for defining the signaling mechanism regulating senescence CM-induced changes.