Dynamics of the subcellular localization of RalBP1/RLIP through the cell cycle: the role of targeting signals and of protein‐protein interactions

Abstract

The small G protein Ras regulates many cell processes, such as gene expression, proliferation, apoptosis, and cell differentiation. Its mutations are associated with one-third of all cancers. Ras functions are mediated, at least in part, by Ral proteins and their downstream effector the Ral-binding protein 1 (RalBP1). RalBP1 is involved in endocytosis and in regulating the dynamics of the actin cytoskeleton. It also regulates early development since it is required for the completion of gastrulation in Xenopus laevis. RalBP1 has also been reported to be the main transporter of glutathione electrophiles, and it is involved in multidrug resistance. Such a variety of functions could be explained by a differential regulation of RalBP1 localization. In this study, we have detected endogenous RalBP1 in the nucleus of interphasic cells. This nuclear targeting is mediated by nuclear localization sequences that map to the N-terminal third of the protein. Moreover, in X. laevis embryos, a C-terminal coiled-coil sequence mediates RalBP1 retention in the nucleus. We have also observed RalBP1 at the level of the actin cytoskeleton, a localization that depends on interaction of the protein with active Ral. During mitosis RalBP1 also associates with the mitotic spindle and the centrosome, a localization that could be negatively regulated by active Ral. Finally, we demonstrate the presence of post-transcriptional and post-translational isoforms of RalBP1 lacking the Ral-binding domain, which opens new possibilities for the existence of Ral-independent functions.

Hornerin, an S100 family protein, is functional in breast cells and aberrantly expressed in breast cancer

“…Additionally, the ER/PR positive cell lines displayed more hornerin fragmentation than the more aggressive ER/PR negative cell lines. It is possible that the fragmentation of hornerin is an important mechanistic step in controlling hornerin action similar to that previously demonstrated in prostate cancer cells [46] or the MCF7 breast cancer cell line [47]. It is of note that the MCF10A breast cancer cell line progression model showed increasing amounts of hornerin expression as the tumorigenicity of the cells progressed.…”

Emerging treatments in lung cancer – targeting the RLIP76 molecular transporter

“…37 During mitosis, RLIP76 is phosphorylated, redistributes to centrosomes and the mitotic spindle, and interacts with POB1 and mitotic kinase cyclin-dependent kinase (CDK) 1, leading to Ral-dependent shut off of endocytosis during mitosis. 38,39 Nuclear localization of RLIP76 is mediated by nuclear localization sequences in the N-terminal domain, whereas putative coiled coil domains in the C-terminus adjacent to the RalBD are necessary for retention in the nucleus. 39 Additionally, during mitosis, RLIP76 also localizes to the mitochondria where it couples Ral phosphorylation by mitotic kinase Aurora A to signaling necessary for mitochondrial fission and proper distribution in the daughter cells.…”

“…38,39 Nuclear localization of RLIP76 is mediated by nuclear localization sequences in the N-terminal domain, whereas putative coiled coil domains in the C-terminus adjacent to the RalBD are necessary for retention in the nucleus. 39 Additionally, during mitosis, RLIP76 also localizes to the mitochondria where it couples Ral phosphorylation by mitotic kinase Aurora A to signaling necessary for mitochondrial fission and proper distribution in the daughter cells. 29 Furthermore, the role of RLIP76 in endocytosis may be coupled to its transport activity.…”

Complexity of molecular alterations impacts pancreatic cancer prognosis

“…A downstream target of the Ras GTPase is RALBP1, the second protein identified by the protein-protein network analysis. The protein is involved in the cellular stress response and is over expressed in several cancers in which it protects transformed cells from apoptosis and mediates resistance to various drugs [11,12] . Indeed, RALBP1 has been considered as a prognostic biomarker in colorectal cancer and high expression of RALBP1 is associated with shortened overall survival and early relapse [13] .…”