Abstract
Ras proteins participate in multiple signal cascades, regulating crucial cellular processes, including cell survival, proliferation, and differentiation. We have previously reported that Ras proteins are modified by sumoylation and that Lys-42 plays an important role in mediating the modification. In the current study, we further investigated the role of Lys-42 in regulating cellular activities of K-Ras. Inducible expression of K-RasV12 led to the activation of downstream components, including c-RAF, MEK1, and extracellular signal-regulated kinases (ERKs), whereas expression of K-RasV12/R42 mutant compromised the activation of the RAF/MEK/ERK signaling axis. Expression of K-RasV12/R42 also led to reduced phosphorylation of several other protein kinases, including c-Jun N-terminal kinase (JNK), Chk2, and focal adhesion kinase (FAK). Significantly, K-RasV12/R42 expression inhibited cellular migration and invasion in vitro in multiple cell lines, including transformed pancreatic cells. Given that K-Ras plays a crucial role in mediating oncogenesis in the pancreas, we treated transformed pancreatic cells of both BxPC-3 and MiaPaCa-2 with 2-D08, a small ubiquitin-like modifier (SUMO) E2 inhibitor. Treatment with the compound inhibited cell migration in a concentration-dependent manner, which was correlated with a reduced level of K-Ras sumoylation. Moreover, 2-D08 suppressed expression of ZEB1 (a mesenchymal cell marker) with concomitant induction of ZO-1 (an epithelial cell marker). Combined, our studies strongly suggest that posttranslational modification(s), including sumoylation mediated by Lys-42, plays a crucial role in K-Ras activities in vivo.