Salameh Joëlle, Cantaloube Isabelle, Benoit Béatrice, Poüs Christian, Baillet Anita
INSERM UMR-S 1193, Faculté de Pharmacie, Université Paris-Saclay, Châtenay-Malabry, France.
INSERM UMR-S 1193, Faculté de Pharmacie, Université Paris-Saclay, Châtenay-Malabry, France; Laboratoire de Biochimie-Hormonologie, Hôpital Antoine Béclère, AP-HP, Clamart, France.
Curr Biol. 2021 Sep 27;31(18):4088-4103.e5. doi: 10.1016/j.cub.2021.07.004. Epub 2021 Jul 29.
Cell resistance to taxanes involves several complementary mechanisms, among which septin relocalization from actin stress fibers to microtubules plays an early role. By investigating the molecular mechanism underlying this relocalization, we found that acute paclitaxel treatment triggers the release from stress fibers and subsequent proteasome-mediated degradation of binder of Rho GTPases 2 (BORG2)/Cdc42 effector protein 3 (Cdc42EP3) and to a lesser extent of BORG3/Cdc42EP5, two Cdc42 effectors that link septins to actin in interphase cells. BORG2 or BORG3 silencing not only caused septin detachment from stress fibers but also mimicked the effects of paclitaxel by triggering both septin relocalization to microtubules and significant drug resistance. Conversely, BORG2 or BORG3 overexpression retained septins on actin fibers even after paclitaxel treatment, without affecting paclitaxel sensitivity. We found that drug-induced inhibition of Cdc42 resulted in a drop in BORG2 level and in the relocalization of septins to microtubules. Accordingly, although septins relocalized when overexpressing an inactive mutant of Cdc42, the expression of a constitutively active mutant acted locally at actin stress fibers to prevent septin release, even after paclitaxel treatment. These findings reveal the role of Cdc42 upstream of BORG2 and BORG3 in controlling the interplay between septins, actin fibers, and microtubules in basal condition and in response to taxanes.
细胞对紫杉烷类药物的耐药性涉及多种互补机制，其中，septin从肌动蛋白应激纤维重新定位到微管在早期发挥作用。通过研究这种重新定位背后的分子机制，我们发现急性紫杉醇处理会触发septin从应激纤维释放，并随后通过蛋白酶体介导降解Rho GTP酶结合蛋白2（BORG2）/Cdc42效应蛋白3（Cdc42EP3），以及在较小程度上降解BORG3/Cdc42EP5，这两种Cdc42效应蛋白在间期细胞中将septin与肌动蛋白连接起来。沉默BORG2或BORG3不仅导致septin从应激纤维脱离，还通过触发septin重新定位到微管和显著的耐药性模拟了紫杉醇的作用。相反，即使在紫杉醇处理后，过表达BORG2或BORG3仍能使septin保留在肌动蛋白纤维上，而不影响紫杉醇敏感性。我们发现药物诱导的Cdc42抑制导致BORG2水平下降以及septin重新定位到微管。因此，尽管过表达无活性的Cdc42突变体时septin会重新定位，但组成型活性突变体的表达即使在紫杉醇处理后也在肌动蛋白应激纤维上局部起作用以防止septin释放。这些发现揭示了在基础状态和对紫杉烷类药物反应中，Cdc42在BORG2和BORG3上游在控制septin、肌动蛋白纤维和微管之间相互作用中的作用。
