MLF1-interacting protein is mainly localized in nucleolus through N-terminal bipartite nuclear localization signal.

Background: The myelodysplasia/myeloid leukemia factor 1-interacting protein (MLF1LP, also called KLIP1 and CENP-50) is reported to localize in both the nucleus and the cytoplasm. To investigate the functions of MLF1IP, its subnuclear localization was studied.

Materials And Methods: MLF1IP was tagged with green fluorescent protein (EGFP). Fibrillarin was tagged with red fluorescent protein (DsRed). EGFP-tagged MLF1IP deletion vectors were also constructed. Plasmid-constructs were transfected into human cervical adenocarcinoma HeLa cells or monkey kidney fibroblast COS-7 cells, and the localization was studied by either confocal fluorescence microscopy or fluorescence microscopy.

Results: Ectopically expressed MLF1IP was localized mainly in the nucleolus. In some cells, small dot-like particles of MLF1IP fluorescence were observed in the nucleoplasm. Co-staining of fibrillarin disclosed that MLF1IP was co-localized with fibrillarin in the nucleolus. Deletion mutants of MLF1IP revealed that the N-terminal bipartite nuclear localization signal (NLS) was responsible for nucleolar targeting.

Conclusion: MLF1IP was localized mainly in the nucleolus through the N-terminal bipartite NLS and partly in the nucleoplasm featuring small dot-like particles. These findings suggest that MLF1IP may have multi-functions and its different localizations may contribute to carcinogenesis.