Genotoxic agents promote the nuclear accumulation of annexin A2: role of annexin A2 in mitigating DNA damage

Annexin A2 is an abundant cellular protein that is mainly localized in the cytoplasm and plasma membrane, however a small population has been found in the nucleus, suggesting a nuclear function for the protein. Annexin A2 possesses a nuclear export sequence (NES) and inhibition of the NES is sufficient to cause nuclear accumulation. Here we show that annexin A2 accumulates in the nucleus in response to genotoxic agents including gamma-radiation, UV radiation, etoposide and chromium VI and that this event is mediated by the nuclear export sequence of annexin A2. Nuclear accumulation of annexin A2 is blocked by the antioxidant agent N-acetyl cysteine (NAC) and stimulated by hydrogen peroxide (H2O2), suggesting that this is a reactive oxygen species dependent event. In response to genotoxic agents, cells depleted of annexin A2 show enhanced phospho-histone H2AX and p53 levels, increased numbers of p53-binding protein 1 nuclear foci and increased levels of nuclear 8-oxo-2'-deoxyguanine, suggesting that annexin A2 plays a role in protecting DNA from damage. This is the first report showing the nuclear translocation of annexin A2 in response to genotoxic agents and its role in mitigating DNA damage.Natural Sciences and Engineering Research Council of Canada (NSERC); European Union [PCOFUND-GA-2009-246542]; Foundation for Science and Technology of Portugal; Beatrice Hunter Cancer Research Institute; Terry Fox Foundationinfo:eu-repo/semantics/publishedVersio

Annexin A2 Binds RNA and Reduces the Frameshifting Efficiency of Infectious Bronchitis Virus

Annexin A2 (ANXA2) is a protein implicated in diverse cellular functions, including exocytosis, DNA synthesis and cell proliferation. It was recently proposed to be involved in RNA metabolism because it was shown to associate with some cellular mRNA. Here, we identified ANXA2 as a RNA binding protein (RBP) that binds IBV (Infectious Bronchitis Virus) pseudoknot RNA. We first confirmed the binding of ANXA2 to IBV pseudoknot RNA by ultraviolet crosslinking and showed its binding to RNA pseudoknot with ANXA2 protein in vitro and in the cells. Since the RNA pseudoknot located in the frameshifting region of IBV was used as bait for cellular RBPs, we tested whether ANXA2 could regulate the frameshfting of IBV pseudoknot RNA by dual luciferase assay. Overexpression of ANXA2 significantly reduced the frameshifting efficiency from IBV pseudoknot RNA and knockdown of the protein strikingly increased the frameshifting efficiency. The results suggest that ANXA2 is a cellular RBP that can modulate the frameshifting efficiency of viral RNA, enabling it to act as an anti-viral cellular protein, and hinting at roles in RNA metabolism for other cellular mRNAs

Proteomes and Signalling Pathways of Antler Stem Cells

As the only known example of complete organ regeneration in mammals, deer antler in the growing or velvet phase is of major interest in developmental biology. This regeneration event initiates from self-renewing antler stem cells that exhibit pluripotency. At present, it remains unclear how the activation and quiescence of antler stem cells are regulated. Therefore, in the present study proteins that were differentially expressed between the antler stem cells and somatic cells (facial periosteum) were identified by a gel-based proteomic technique, and analysed using Ingenuity Pathway Analysis software. Several molecular pathways (PI3K/Akt, ERK/MAPK, p38 MAPK, etc.) were found to be activated during proliferation. Also expressed were the transcription factors POU5F1, SOX2, NANOG and MYC, which are key markers of embryonic stem cells. Expression of these proteins was confirmed in both cultured cells and fresh tissues by Western blot analysis. Therefore, the molecular pathways and transcription factors identified in the current study are common to embryonic and adult stem cells. However, expression of embryonic stem cell transcription factors would suggest that antler stem cells are, potentially, an intermediary stem cell type between embryonic and the more specialized tissue-specific stem cells like those residing in muscle, fat or from a hematopoietic origin. The retention of this embryonic, pluripotent lineage may be of fundamental importance for the subsequent regenerative capacity of antlers

Annexin2 coating the surface of enlargeosomes is needed for their regulated exocytosis

Enlargeosomes are small cytoplasmic vesicles that undergo rapid, Ca(2+)-dependent exo/endocytosis. The role of the cytoskeleton in these processes was unknown. In PC12-27 cells, microtubule disassembly had little effect on enlargeosomes, whereas microfilament disassembly increased markedly both their resting and stimulated exocytosis, and inhibited their endocytosis. Even at rest enlargeosomes are coated at their cytosolic surface by an actin-associated protein, annexin2, bound by a dual, Ca(2+)-dependent and Ca(2+)-independent mechanism. In contrast, the other enlargeosome marker, desmoyokin/Ahnak, is transported across the organelle membrane, apparently by an ABC transporter, and binds to its lumenal face. Annexin2-GFP expression revealed that, upon stimulation, the slow and random enlargeosome movement increases markedly and becomes oriented toward the plasma membrane. After annexin2 downregulation enlargeosome exocytosis induced by both [Ca(2+)](i) rise and cytoskeleton disruption is inhibited, and the NGF-induced differentiation is blocked. Binding of annexin2 to the enlargeosome membrane, the most extensive ever reported (>50% annexin2 bound to ∼3% of total membrane area), seems therefore to participate in the regulation of their exocytosis

Functional involvement of Annexin-2 in cAMP induced AQP2 trafficking.

Contains fulltext : 70255.pdf (publisher's version ) (Closed access)Annexin-2 is required for the apical transport in epithelial cells. In this study, we investigated the involvement of annexin-2 in cAMP-induced aquaporin-2 (AQP2) translocation to the apical membrane in renal cells. We found that the cAMP-elevating agent forskolin increased annexin-2 abundance in the plasma membrane enriched fraction with a parallel decrease in the soluble fraction. Interestingly, forskolin stimulation resulted in annexin-2 enrichment in lipid rafts, suggesting that hormonal stimulation might be responsible for a new configuration of membrane interacting proteins involved in the fusion of AQP2 vesicles to the apical plasma membrane. To investigate the functional involvement of annexin-2 in AQP2 exocytosis, the fusion process between purified AQP2 membrane vesicles and plasma membranes was reconstructed in vitro and monitored by a fluorescence assay. An N-terminal peptide that comprises 14 residues of annexin-2 and that includes the binding site for the calcium binding protein p11 strongly inhibited the fusion process. Preincubation of cells with this annexin-2 peptide also failed to increase the osmotic water permeability in the presence of forskolin in intact cells. Altogether, these data demonstrate that annexin-2 is required for cAMP-induced AQP2 exocytosis in renal cells