Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Mol Cell Biol. 2012 Apr;32(8):1374-86. doi: 10.1128/MCB.06291-11. Epub 2012 Feb 13.
Our recent studies implicated key and distinct roles for the highly related RalA and RalB small GTPases (82% sequence identity) in pancreatic ductal adenocarcinoma (PDAC) tumorigenesis and invasive and metastatic growth, respectively. How RalB may promote PDAC invasion and metastasis has not been determined. In light of known Ral effector functions in regulation of actin organization and secretion, we addressed a possible role for RalB in formation of invadopodia, actin-rich membrane protrusions that contribute to tissue invasion and matrix remodeling. We determined that a majority of KRAS mutant PDAC cell lines exhibited invadopodia and that expression of activated K-Ras is both necessary and sufficient for invadopodium formation. Invadopodium formation was not dependent on the canonical Raf-MEK-ERK effector pathway and was instead dependent on the Ral effector pathway. However, this process was more dependent on RalB than on RalA. Surprisingly, RalB-mediated invadopodium formation was dependent on RalBP1/RLIP76 but not Sec5 and Exo84 exocyst effector function. Unexpectedly, the requirement for RalBP1 was independent of its best known function as a GTPase-activating protein for Rho small GTPases. Instead, disruption of the ATPase function of RalBP1 impaired invadopodium formation. Our results identify a novel RalB-mediated biochemical and signaling mechanism for invadopodium formation.
我们最近的研究表明，高度相关的 RalA 和 RalB 小 GTPases（82%的序列同一性）在胰腺导管腺癌（PDAC）的肿瘤发生和侵袭性及转移性生长中分别发挥关键且不同的作用。然而，RalB 如何促进 PDAC 的侵袭和转移尚未确定。鉴于 Ral 效应因子在调节肌动蛋白组织和分泌中的已知功能，我们研究了 RalB 在侵袭伪足形成中的可能作用，侵袭伪足是富含肌动蛋白的膜突起，有助于组织侵袭和基质重塑。我们确定大多数 KRAS 突变型 PDAC 细胞系都表现出侵袭伪足，并且激活的 K-Ras 的表达对于侵袭伪足的形成是必要且充分的。侵袭伪足的形成不依赖于经典的 Raf-MEK-ERK 效应途径，而是依赖于 Ral 效应途径。然而，这一过程对 RalB 的依赖性比对 RalA 更高。令人惊讶的是，RalB 介导的侵袭伪足形成依赖于 RalBP1/RLIP76，但不依赖于 Sec5 和 Exo84 外泌体效应因子的功能。出人意料的是，RalBP1 的需求与其作为 Rho 小 GTPases 的 GTP 酶激活蛋白的最知名功能无关。相反，RalBP1 的 ATP 酶功能的破坏会损害侵袭伪足的形成。我们的结果确定了一种新的 RalB 介导的侵袭伪足形成的生化和信号机制。
