Defilippi P, Olivo C, Tarone G, Mancini P, Torrisi M R, Eva A
Dipartimento di Genetica, Biologia e Chimica Medica, Universita di Torino, Italy.
Oncogene. 1997 Apr 24;14(16):1933-43. doi: 10.1038/sj.onc.1201027.
The Dbl oncogene is the putative exchange factor for two small GTP-binding proteins, RhoA and CDC42 which are involved in the polymerization of actin to produce stress fibers and filopodia, respectively. We report here that Dbl oncogene-transformed NIH3T3 cells show actin stress fibers only when cells are plated on fibronectin. Plating of cells on collagen I and IV as well as on poly-D-lysine and gelatin induces polymerization of actin to form filopodia, lamellipodia and membrane ruffles but not stress fibers. The putative collagen receptors, alpha1/beta1 and alpha2/beta1 integrins are expressed at reduced level in Dbl-transformed cells compared to untransformed NIH3T3 fibroblasts. Nevertheless, adhesion to collagens is not altered. Inhibitory monoclonal antibody to mouse integrin beta1 subunit blocked adhesion of both Dbl-transformed and untransformed NIH3T3 cells, demonstrating that adhesion to collagen I and IV is mediated by the beta1 family of integrins. Dbl product rapidly induces the depolymerization of actin stress fibers, rounding up of the cells, and formation of filopodia and lamellipodia when microinjected in NIH3T3 cells plated on gelatin. Thus, Dbl may exert its effect on actin cytoskeleton organization in response to extracellular proteins by altering integrin-mediated signalling pathways.
Dbl癌基因被认为是两种小GTP结合蛋白RhoA和CDC42的交换因子，它们分别参与肌动蛋白聚合以产生应力纤维和丝状伪足。我们在此报告，Dbl癌基因转化的NIH3T3细胞仅在细胞接种于纤连蛋白上时才显示肌动蛋白应力纤维。将细胞接种于I型和IV型胶原以及聚-D-赖氨酸和明胶上会诱导肌动蛋白聚合形成丝状伪足、片状伪足和膜皱褶，但不会形成应力纤维。与未转化的NIH3T3成纤维细胞相比，假定的胶原受体α1/β1和α2/β1整合素在Dbl转化细胞中的表达水平降低。然而，对胶原的黏附并未改变。针对小鼠整合素β1亚基的抑制性单克隆抗体可阻断Dbl转化和未转化的NIH3T3细胞的黏附，表明对I型和IV型胶原的黏附是由整合素β1家族介导的。当将Dbl产物显微注射到接种于明胶上的NIH3T3细胞中时，它会迅速诱导肌动蛋白应力纤维解聚、细胞变圆，并形成丝状伪足和片状伪足。因此，Dbl可能通过改变整合素介导的信号通路，对细胞外蛋白做出反应，从而对肌动蛋白细胞骨架组织发挥作用。
