The stiffness of the extracellular matrix induces differential tension within integrin-based adhesions, triggering differential mechanoresponses. However, it has been unclear if the stiffness-dependent differential tension is induced solely by myosin activity. Here, we report that in the absence of myosin contractility, 3T3 fibroblasts still transmit stiffness-dependent differential levels of traction. This myosin-independent differential traction is regulated by polymerizing actin assisted by actin nucleators Arp2/3 and formin where formin has a stronger contribution than Arp2/3 to both traction and actin flow. Intriguingly, despite only slight changes in F-actin flow speed observed in cells with the combined inhibition of Arp2/3 and myosin compared to cells with sole myosin inhibition, they show a 4-times reduction in traction than cells with myosin-only inhibition. Our analyses indicate that traditional models based on rigid F-actin are inadequate for capturing such dramatic force reduction with similar actin flow. Instead, incorporating the F-actin network’s viscoelastic properties is crucial. Our new model including the F-actin viscoelasticity reveals that Arp2/3 and formin enhance stiffness sensitivity by mechanically reinforcing the F-actin network, thereby facilitating more effective transmission of flow-induced forces. This model is validated by cell stiffness measurement with atomic force microscopy and experimental observation of model-predicted stiffness-dependent actin flow fluctuation.

细胞外基质的硬度会引起基于整合素的粘连内的张力差异，从而引发差异的机械反应。然而，尚不清楚硬度依赖性张力差是否仅由肌球蛋白活性引起。在这里，我们报告说，在缺乏肌球蛋白收缩性的情况下，3T3 成纤维细胞仍然传递依赖于刚度的不同水平的牵引力。这种不依赖于肌球蛋白的差异牵引力是通过肌动蛋白成核剂 Arp2/3 和福明辅助的聚合肌动蛋白来调节的，其中福明对牵引力和肌动蛋白流动的贡献比 Arp2/3 更强。有趣的是，尽管与单独抑制肌球蛋白的细胞相比，联合抑制 Arp2/3 和肌球蛋白的细胞中 F-肌动蛋白流速仅观察到轻微变化，但与仅抑制肌球蛋白的细胞相比，它们的牵引力降低了 4 倍。我们的分析表明，基于刚性 F-肌动蛋白的传统模型不足以捕获具有类似肌动蛋白流的如此显着的力减小。相反，结合 F-肌动蛋白网络的粘弹性特性至关重要。我们的包含 F-肌动蛋白粘弹性的新模型表明，Arp2/3 和 formin 通过机械强化 F-肌动蛋白网络来增强刚度敏感性，从而促进更有效地传递流引起的力。该模型通过原子力显微镜的细胞刚度测量和模型预测的刚度依赖性肌动蛋白流波动的实验观察得到验证。