BBB seminar: Anni Vedeler
Annexin A2 as an mRNA-binding protein
Department of Biomedicine, University of Bergen
Annexin A2 (anxA2) is a multifunctional protein implicated in cellular processes such as signal transduction, membrane trafficking, mRNA transport and membrane/cytoskeleton interactions. AnxA2 binds different intracellular and extracellular ligands and is subjected to numerous post-translational modifications. In addition to Ca2+, its core domain binds F-actin, 14.3.3 regulatory proteins, cholesterol, phospholipids and mRNA intracellularly while p11, a member of the S100 family, binds to its N-terminal tail. Extracellularly, anxA2 binds heparin and is a cellular receptor for t-PA and plasminogen. Thus, it has been proposed to be involved in angiogenesis. The protein also appears to have a key role in cell transformation and its expression is modulated in numerous cancers. Furthermore, we have shown that anxA2 interacts specifically with mRNAs translated on cytoskeleton-bound polysomes and it has recently been identified as an RNA-binding protein that interacts with the localisation signal in the 3'untranslated region (3'UTR) of c-myc mRNA. Cytoskeleton-associated anxA2 is ubiquitinated; this ubiquitination is stable and does not appear to target the protein to degradation by the 26S proteasome. We have used surface plasmon resonance in addition to conventional RNA-protein binding assays to obtain information about the mRNA-anxA2 binding process and its affinity. Moreover, we have been able to produce the mRNA-binding domain IV of anxA2 in a stable and soluble form and we are currently producing mutants to detect the amino acids involved in mRNA-binding. As another approach, we are currently optimising the assay conditions to obtain crystals of a complex containing a smaller region of the 3'UTR of anxA2 mRNA bound to anxA2 protein. We have already generated excellent crystals of anxA2 providing a resolution of 1.8 Å. We are also in the process of identifying other anxA2-associated mRNAs as well as additional proteins present in the anxA2 mRNP complexes in order to understand the biological role of the anxA2 interaction with specific mRNAs. This seminar will focus on our recent data.