Poster S5 - Unraveling YAP Spatio-Temporal Dynamics and Its Implications in Cancer Metastasis within Viscous Microenvironments

Introduction: Cancer metastasis stands as the foremost cause of cancer-related mortality, necessitating a deeper understanding of the molecular mechanisms underlying this process. Yes-associated protein (YAP), a key transcriptional regulator, has emerged as a pivotal player in cancer metastasis, particularly in the context of cellular response to mechanical cues within the tumor microenvironment. Notably, cancer cells exhibit enhanced migratory capacity in high-viscosity environments. Further, it is known that YAP moves into the nucleus under highly viscous conditions, implicating the role of YAP in mechanotransduction processes associated with enhanced cell motility.

Materials and

Methods: Acrylamide (A) with N, N-Methylene bisacrylamide (B) were mixed with distilled water to final concentrations of 3%A/0.06%B, 8% A/0.1% B corresponding to polyacrylamide gels with an elastic modulus of 8kPa. The mixtures were then degassed for 25 min. 10% ammonium persulfate and 0.4% TEMED were used in initiating polymerization. Cells were seeded together on different dishes and cultured in 0.77cP or 8cP as per the required experimental conditions. They were then fixed and stained for YAP or trypsinized and used for migration in PDMS microchannel devices.

Results, Conclusions, and Discussions: Our study elucidates the dynamics of YAP translocation for MDA-MB-231 in response to variations in extracellular viscosity. Under high-viscosity (8cP) conditions, YAP translocates into the nucleus, promoting transcriptional activity associated with enhanced cellular migration. This is also true for cells on soft substrates (Fig.1a), suggesting cell sensitivity to the viscous mechanical cue. Remarkably, cells retain a memory of the viscous surrounding even after transitioning back to basal viscosities (0.77cP), displaying sustained migratory behavior.
To elucidate the spatiotemporal dynamics of YAP in viscous conditions comprehensively, we conducted experiments examining YAP localization at varying timepoints and substrate stiffness levels. Additionally, we investigated the impact of removing the viscous mechanical cue on YAP spatial dynamics. Moreover, using microfluidic devices mimicking the confined physiological microenvironment, we probed the persistence of heightened migratory potential post-transfer to basal viscosities (3µm width x 10µm height channels). Remarkably, we observed that the duration of memory retention varies based on the pre-treatment duration in high viscosity. Specifically, we noted that the memory is retained for a day post-transfer when the cells are treated in high viscosity for 2 days, whereas it persists for 10 days post-transfer to basal viscosities for pre-treatment of 6 days exposure to high viscosity (Fig. 1b) with implications for transcriptional changes underlying altered cell behavior. Interestingly, we also observed a notable difference in YAP nuclear export following the transfer to basal viscosities. Specifically, we found that YAP exports out of the nucleus faster in cells conditioned in high viscosity for 2 days compared to those conditioned for 6 days (Fig.1c). This retention of YAP in the nucleus along with the migratory memory was even more prolonged in cells cultured on 8kPa gels under 8cP (not shown).
Furthermore, our discussion will encompass cellular contractility, along with the Hippo pathway's role in mediating YAP localization, YAP-driven transcriptional alterations (YAP-TEAD activity), and their impact on cellular behavior. The mechanism to YAP nuclear sequestering under high viscosity will be discussed in detail.
Understanding the intricate interplay between YAP localization, contractility, and memory formation holds promise for identifying targeted therapeutic strategies aimed at disrupting metastatic progression.

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