The importance of mechanical force in the regulation of skin homeostasis is becoming increasingly evident. However, the molecular mechanisms underlying the interplay between mechanical force and cell signalling are poorly understood. The Rho-ROCK signalling pathway lies at the interface between mechanical and biochemical signalling. We have previously shown that Rho-ROCK signalling promotes keratinocyte proliferation by increasing ECM production, elevating dermal stiffness and enhancing integrin-mediated mechanotransduction signalling. In turn, elevated dermal stiffness further stimulates ROCK activation, setting up a positive feedback loop that, if left unrestrained, promotes cutaneous tumours.
We have now identified a novel negative feedback mechanism that limits excessive ROCK signalling in the skin during wound healing but that is lost in squamous cell carcinomas. Signalling through ROCK is selectively tuned down by the molecular adaptor protein 14-3-3ζ, which interacts with an antagonist of ROCK signalling, Mypt1, to maintain it in its active state. In 14-3-3ζ-deficient mice, hyper-activated ROCK signalling at wound margins leads to elevated ECM production, thereby increasing dermal stiffness. Furthermore, 14-3-3ζ-deficient dermal fibroblasts fail to remodel the ECM, thus further increasing dermal stiffness and causing enhanced signalling through integrin-mediated mechanotransduction pathways. This leads to rapid regeneration of the epidermis in 14-3-3ζ-deficient wounds. Interestingly, patient histological samples of chronic wounds with long healing times, including diabetic ulcers and some burns, over-expressed 14-3-3ζ whilst conversely, patient samples of cutaneous squamous cell carcinoma (SCC) exhibited greatly reduced levels of 14-3-3ζ, and SCC tumour size was increased in 14-3-3ζ-deficient mice. Significantly, inhibition of 14-3-3ζ using a novel pharmacological inhibitor halved wound healing times in mice. These results reveal a novel mechanism that negatively regulates mechano-reciprocity and regulates epidermal regeneration, suggesting new therapeutic opportunities.