High-resolution structure of eukaryotic Fibrillarin interacting with Nop56 amino-terminal domain

Trypanosoma cruzi Fibrillarins: Two paralogous proteins with non-identical signals for nuclear transport

Trypanosoma cruzi is a parasitic protozoa causative of Chagas disease. As part of our interest in studying the basic biology of this microorganism, this work reports our observations related to the characterization of motifs and structural domains present in two fibrillarin isoforms (TcFib1 and TcFib2) that were found to be necessary for the nuclear targeting of these nucleolar proteins. Previous characterization of these proteins indicated that they share 68.67% of identical amino acids and are both expressed as nucleolar proteins in T. cruzi epimastigotes. Using an approach based on the transfection of recombinant genes encoding fluorescent fibrillarin-EGFP fusion proteins, this study found evidence for the presence of 4 motifs or protein domains that help target these proteins to the nucleus: The GAR domain and carboxyl terminus in both TcFibs, as well as two lysines and a computationally predicted cNLS in TcFib1. As a distinctive feature, the GAR domain of TcFib2 proved to be essential for the nuclear localization of this protein paralog. Such a difference between TcFib1 and Tcfib2 nuclear localization signals can be explained as the presence of two partially related nuclear import pathways for the two fibrillarin homologues in this organism.

The roles of NOP56 in cancer and SCA36

NOP56 is a highly conserved nucleolar protein. Amplification of the intron GGCCTG hexanucleotide repeat sequence of the NOP56 gene results in spinal cerebellar ataxia type 36 (SCA36). NOP56 contains an N-terminal domain, a coiled-coil domain, and a C-terminal domain. Nucleolar protein NOP56 is significantly abnormally expressed in a number of malignant tumors, and its mechanism is different in different tumors, but its regulatory mechanism in most tumors has not been fully explored. NOP56 promotes tumorigenesis in some cancers and inhibits tumorigenesis in others. In addition, NOP56 is associated with methylation in some tumors, suggesting that NOP56 has the potential to become a tumor-specific marker. This review focuses on the structure, function, related signaling pathways, and role of NOP56 in the progression of various malignancies, and discusses the progression of NOP56 in neurodegenerative and other diseases.