Children's Cancer Institute Australia, Lowy Cancer Research Centre, UNSW, Randwick, NSW, Australia.
Cytoskeleton (Hoboken). 2013 Mar;70(3):148-60. doi: 10.1002/cm.21096. Epub 2013 Jan 17.
Actin and microtubule interactions are important for many cellular events, however these interactions are poorly described. Alterations in γ-actin are associated with diseases such as hearing loss and cancer. Functional investigations demonstrated that partial depletion of γ-actin affects cell polarity and induces resistance to microtubule-targeted agents. To determine whether γ-actin alterations directly affect microtubule dynamics, microtubule dynamic instability was analyzed in living cells following partial siRNA depletion of γ-actin. Partial depletion of γ-actin suppresses interphase microtubule dynamics by 17.5% due to a decrease in microtubule shortening rates and an increase in microtubule attenuation. γ-Actin partial depletion also increased distance-based microtubule catastrophe and rescue frequencies. In addition, knockdown of γ-actin delayed mitotic progression, partially blocking metaphase-anaphase transition and inhibiting cell proliferation. Interestingly, in the presence of paclitaxel, interphase microtubule dynamics were further suppressed by 24.4% in the γ-actin knockdown cells, which is comparable to 28.8% suppression observed in the control siRNA treated cells. Paclitaxel blocked metaphase-anaphase transition in both the γ-actin knockdown cells and the control siRNA cells. However, the extent of mitotic arrest was much higher in the control cells (28.4%), compared to the γ-actin depleted cells (8.5%). Therefore, suppression of microtubule dynamics by partial depletion of γ-actin is associated with marked delays in metaphase-anaphase transition and not mitotic arrest. This is the first demonstration that γ-actin can modulate microtubule dynamics by reducing the microtubule shortening rate, promoting paused/attenuated microtubules, and increasing transition frequencies suggesting a mechanistic link between γ-actin and microtubules.
肌动蛋白和微管相互作用对许多细胞事件都很重要，但这些相互作用描述得很差。γ-肌动蛋白的改变与听力损失和癌症等疾病有关。功能研究表明，γ-肌动蛋白的部分耗竭会影响细胞极性，并诱导对微管靶向药物的耐药性。为了确定γ-肌动蛋白的改变是否直接影响微管动力学，在部分 siRNA 耗竭 γ-肌动蛋白后，在活细胞中分析了微管动力学不稳定性。γ-肌动蛋白的部分耗竭通过降低微管缩短速率和增加微管衰减，使有丝分裂期微管动力学抑制 17.5%。γ-肌动蛋白的部分耗竭也增加了基于距离的微管崩溃和恢复频率。此外，γ-肌动蛋白的敲低延迟了有丝分裂进程，部分阻断了中期-后期转换，并抑制了细胞增殖。有趣的是，在紫杉醇存在的情况下，γ-肌动蛋白敲低细胞的有丝分裂期微管动力学进一步抑制了 24.4%，与对照 siRNA 处理细胞中观察到的 28.8%抑制相当。紫杉醇阻断了γ-肌动蛋白敲低细胞和对照 siRNA 细胞的中期-后期转换。然而，对照细胞（28.4%）的有丝分裂停滞程度明显高于γ-肌动蛋白耗竭细胞（8.5%）。因此，γ-肌动蛋白的部分耗竭抑制微管动力学与中期-后期转换的显著延迟有关，而不是有丝分裂停滞。这是首次证明γ-肌动蛋白可以通过降低微管缩短速率、促进暂停/衰减微管和增加转换频率来调节微管动力学，提示γ-肌动蛋白和微管之间存在机制联系。
