Ajuba, a Novel LIM Protein, Interacts with Grb2, Augments Mitogen-Activated Protein Kinase Activity in Fibroblasts, and Promotes Meiotic Maturation of Xenopus Oocytes in a Grb2- and Ras-Dependent Manner

Abstract

LIM domain-containing proteins contribute to cell fate determination, the regulation of cell proliferation and differentiation, and remodeling of the cell cytoskeleton. These proteins can be found in the cell nucleus, cytoplasm, or both. Whether and how cytoplasmic LIM proteins contribute to the cellular response to extracellular stimuli is an area of active investigation. We have identified and characterized a new LIM protein, Ajuba. Although predominantly a cytosolic protein, in contrast to other like proteins, it did not localize to sites of cellular adhesion to extracellular matrix or interact with the actin cytoskeleton. Removal of the pre-LIM domain of Ajuba, including a putative nuclear export signal, led to an accumulation of the LIM domains in the cell nucleus. The pre-LIM domain contains two putative proline-rich SH3 recognition motifs. Ajuba specifically associated with Grb2 in vitro and in vivo. The interaction between these proteins was mediated by either SH3 domain of Grb2 and the N-terminal proline-rich pre-LIM domain of Ajuba. In fibroblasts expressing Ajuba mitogen-activated protein kinase activity persisted despite serum starvation and upon serum stimulation generated levels fivefold higher than that seen in control cells. Finally, when Ajuba was expressed in fully developed Xenopus oocytes, it promoted meiotic maturation in a Grb2-and Ras-dependent manner.The LIM domain defines a unique double zinc finger structure found in a class of proteins involved in cell identity, differentiation, and growth control (10, 33). The LIM motif,

MicroRNAs direct rapid deadenylation of mRNA

“…2B). Ajuba is a LIM-domain protein that plays an important role in controlling the entry of vertebrate cells into mitosis and meiosis (20,21). In P19 cells induced to differentiate, the concentration of this protein initially rises and then declines (22), suggesting a delayed-onset repression mechanism to which miR-125b may contribute as it accumulates over time.…”

Aurora A, mitotic entry, and spindle bipolarity

“…Ajuba, a protein that may enhance Aur-A activity during G 2 , promotes translation of both cyclin B and cdc2 and advance entry into M phase. Moreover, Ajuba binds to the N terminus of Aur-A (17,39). Regarding chromosome alignment, one obvious target is CENP-A, a variant of histone H3 that resides in nucleosomes of the centromeric chromatin at the inner plate of the kinetochore (40).…”

The LIM protein Ajuba promotes adipogenesis by enhancing PPARγ and p300/CBP interaction

“…The Ajuba/ Zyxin subfamily has not yet been uncovered to bind the DNA elements, and their LIM domains mainly function as proteinprotein interface. [16][17][18] An unique nucleus exporting signal is localized in the preLIM region of Ajuba (aa NO. 289-297) and deletion of the nucleus exporting signal or the whole preLIM region will result in the nucleus accumulation of Ajuba.…”

“…289-297) and deletion of the nucleus exporting signal or the whole preLIM region will result in the nucleus accumulation of Ajuba. 16,19 In addition, the preLIM region also mediates the protein-protein interaction, such as HDACs and Prmt5. 20,21 Depending on cell types, Ajuba can be located near the membrane, in the cytoplasm and/or in the nucleus and the stimulation of signals or interaction with proteins will also change its localization in cells.…”

“…20,21 Depending on cell types, Ajuba can be located near the membrane, in the cytoplasm and/or in the nucleus and the stimulation of signals or interaction with proteins will also change its localization in cells. [16][17][18]22 Ajuba functions as a scaffold involving assembly of multiple protein complexes to regulate cell adhesion, migration, mitosis, microRNA maturation, cell differentiation and tissue development. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Ajuba can directly participate in transcriptional regulation where it serves as a transcriptional co-repressor and downregulate gene expression.…”