A novel means of limiting mechanical signalling maintains normal tissue architecture and homeostasis

MS Samuel

Tumour Microenvironment Laboratory, Centre for Cancer Biology, SA Pathology and the University of South Australia

The importance of mechanical force in regulating tissue architecture and homeostasis is becoming increasingly evident. However, the molecular mechanisms underlying the interplay between force and cell signalling are poorly understood. The ROCK signalling pathway lies at the interface between mechanical and biochemical signalling. In the skin, ROCK signalling promotes epidermal proliferation by increasing ECM production, elevating dermal stiffness and enhancing integrin-mediated mechanotransduction signalling. In turn, elevated dermal stiffness further stimulates ROCK activation, initiating a mechano-reciprocal positive feedback loop that promotes cutaneous tumours. We reasoned therefore, that mechanisms negatively regulating mechano-reciprocity must exist to protect against hyper-proliferation during normal tissue homeostasis. Using an incisional wound healing model of disrupted mechano-reciprocity, we have identified a novel mechanism that limits ROCK signalling in the skin under normal homeostatic conditions, but that is lost in cutaneous squamous cell carcinoma (SCC). Signalling through ROCK is selectively tuned down by the molecular adaptor protein 14-3-3zeta, which promotes the function of an antagonist of ROCK signalling, Mypt1, by hindering its inactivation by ROCK. In 14-3-3zeta-deficient mice, hyper-activated ROCK signalling at wound margins led to elevated ECM production via paracrine communication between keratinocytes and dermal fibroblasts, thereby increasing dermal stiffness. Moreover, 14-3-3zeta-deficient dermal fibroblasts failed to remodel the ECM, further increasing dermal stiffness and causing enhanced mechanotransduction signalling, which increased epidermal proliferation and accelerated the healing of 14-3-3zeta-deficient skin wounds. Accordingly, 14-3-3zeta-deficient mice developed larger, SCCs with stiffer ECM than wild-type mice when placed on the multi-stage chemical carcinogenesis protocol. Significantly, inhibition of 14-3-3zeta using a novel pharmacological inhibitor more than halved wound healing times in mice. These results reveal a novel mechanism that negatively regulates mechano-reciprocity, suggesting new therapeutic opportunities.