Syndecan-4 tunes cell mechanics by activating the kindlin-integrin-RhoA pathway

A mechanism of cell response to localized tension shows that syndecan-4 synergizes with EGFR to elicit a mechanosignalling cascade that leads to adaptive cell stiffening through PI3K/kindlin-2 mediated integrin activation. Extensive research over the past decades has identified integrins to be the primary transmembrane receptors that enable cells to respond to external mechanical cues. We reveal here a mechanism whereby syndecan-4 tunes cell mechanics in response to localized tension via a coordinated mechanochemical signalling response that involves activation of two other receptors: epidermal growth factor receptor and beta 1 integrin. Tension on syndecan-4 induces cell-wide activation of the kindlin-2/beta 1 integrin/RhoA axis in a PI3K-dependent manner. Furthermore, syndecan-4-mediated tension at the cell-extracellular matrix interface is required for yes-associated protein activation. Extracellular tension on syndecan-4 triggers a conformational change in the cytoplasmic domain, the variable region of which is indispensable for the mechanical adaptation to force, facilitating the assembly of a syndecan-4/alpha-actinin/F-actin molecular scaffold at the bead adhesion. This mechanotransduction pathway for syndecan-4 should have immediate implications for the broader field of mechanobiology.Peer reviewe

Mechanotransduction in health and disease

Physical forces regulate cellular behaviour and function during all stages of life. Mechanotransduction, the process by which cells convert mechanical stimuli into biochemical signalling events is central to a number of physiological and pathological processes. The first part of this work focuses on the effect of retinoid therapy on the mechanobiology of pancreatic cancer. Pancreatic cancer is characterised by a persistent activation of stromal fibroblasts, known as pancreatic stellate cells (PSCs), which can perturb the biomechanical homeostasis of the tumour microenvironment to favour tumour invasion. Using biophysical and biological techniques, we report that all-trans retinoic acid (ATRA), an active vitamin A metabolite restores mechanical quiescence in PSCs via a mechanism involving a retinoic acid receptor beta (RAR-β)-mediated downregulation of actomyosin (MLC-2) contracility. We show that ATRA reduces the ability of PSCs to generate high traction forces and adapt to extracellular mechanical cues (mechanosensing), as well as suppresses force-mediated extracellular matrix remodelling to inhibit local cancer cell invasion in 3D organotypic models. We thus suggest that ATRA may serve as a stroma reprogramming agent for the treatment of pancreatic cancer. In the second part of this work, we focus on syndecan-4 (Syn-4) - a ubiquitous transmembrane proteoglycan receptor. We identify Syn-4 as a cellular mechanotransducer that tunes cell mechanics by eliciting a global mechanosignalling response. We outline a mechanotransduction model whereby localised tension on Syn-4 triggers a synergistic cell-wide activation of β1 integrins, in a PI3K-dependent manner, to subsequently activate the RhoA pathway and induce adaptive cell stiffening. Furthermore, syndecan-4 mediated mechanosensing is required for YAP activation and downstream changes in gene expression. We propose that this newly identified mechanotransductive ability of Syn-4 should have direct implications for the field of mechanobiology.Open Acces

Evaluation of Femoral Bone Fracture Healing in Rats by the Modal Damping Factor and Its Correlation With Peripheral Quantitative Computed Tomography

Introduction Monitoring the progress of fracture healing is essential in order to establish the appropriate timing that ensures adequate bone strength for weight-bearing. In the present experimental study on a rat model of femoral fracture healing, the measurement of bone density and strength by peripheral quantitative computerized tomography (pQCT) was correlated with the modal damping factor (MDF) method. Methods Four groups of 12 male six-month-old Wistar rats each were anesthetized and submitted to baseline femoral pQCT and MDF scanning, followed by aseptic midshaft osteotomy of the right femur which was fixed by a locking intramedullary nail technique. The animals were left to recover and re-scanned following euthanasia of each group after six, eight, 10, and 12 weeks, respectively. The parameters measured by the pQCT method were total bone mineral density (BMD) and polar strength strain index (SSIp). Results Fracture healing progressed over time and at 12 weeks post-osteotomy there was no statistically significant difference between the osteotomized right and the control left femurs regarding MDF, BMD, and SSIp measurements. The highest correlations for the osteotomized femurs were observed between MDF and BMD (r = -0.647, P = 0.043), and between MDF and SSIp (r = -0.350, P = 0.321), at 10 weeks postoperatively. The high to moderate correlations between MDF and BMD, and between MDF and SSIp respectively, support the validity of MDF in assessing fracture healing. Conclusions Based on our findings in this fracture healing animal model, the results from the MDF method are reliable and correlate highly with the total BMD and moderately with the SSI polar values obtained by the pQCT method of bone quality measurement. Further studies are needed which may additionally support that the MDF method can be an attractive portable alternative to monitor fracture healing in the community

ALK upregulates POSTN and WNT signaling to drive neuroblastoma

Neuroblastoma is the most common extracranial solid tumor of childhood. While MYCN and mutant anaplastic lymphoma kinase (ALKF1174L) cooperate in tumorigenesis, how ALK contributes to tumor formation remains unclear. Here, we used a human stem cell-based model of neuroblastoma. Mis-expression of ALKF1174L and MYCN resulted in shorter latency compared to MYCN alone. MYCN tumors resembled adrenergic, while ALK/MYCN tumors resembled mesenchymal, neuroblastoma. Transcriptomic analysis revealed enrichment in focal adhesion signaling, particularly the extracellular matrix genes POSTN and FN1 in ALK/MYCN tumors. Patients with ALK-mutant tumors similarly demonstrated elevated levels of POSTN and FN1. Knockdown of POSTN, but not FN1, delayed adhesion and suppressed proliferation of ALK/MYCN tumors. Furthermore, loss of POSTN reduced ALK-dependent activation of WNT signaling. Reciprocally, inhibition of the WNT pathway reduced expression of POSTN and growth of ALK/MYCN tumor cells. Thus, ALK drives neuroblastoma in part through a feedforward loop between POSTN and WNT signaling

ALK upregulates POSTN and WNT signaling to drive neuroblastoma

Summary: Neuroblastoma is the most common extracranial solid tumor of childhood. While MYCN and mutant anaplastic lymphoma kinase (ALKF1174L) cooperate in tumorigenesis, how ALK contributes to tumor formation remains unclear. Here, we used a human stem cell-based model of neuroblastoma. Mis-expression of ALKF1174L and MYCN resulted in shorter latency compared to MYCN alone. MYCN tumors resembled adrenergic, while ALK/MYCN tumors resembled mesenchymal, neuroblastoma. Transcriptomic analysis revealed enrichment in focal adhesion signaling, particularly the extracellular matrix genes POSTN and FN1 in ALK/MYCN tumors. Patients with ALK-mutant tumors similarly demonstrated elevated levels of POSTN and FN1. Knockdown of POSTN, but not FN1, delayed adhesion and suppressed proliferation of ALK/MYCN tumors. Furthermore, loss of POSTN reduced ALK-dependent activation of WNT signaling. Reciprocally, inhibition of the WNT pathway reduced expression of POSTN and growth of ALK/MYCN tumor cells. Thus, ALK drives neuroblastoma in part through a feedforward loop between POSTN and WNT signaling