Subcellular localization of the metastasis-promoting protein S100A4
The S100A4 protein has been associated with increased metastatic capacity of cancer cells, and several studies have suggested a correlation between the expression level of S100A4 and the prognostic outcome of patients with various types of cancer. S100A4 is located in the extracellular space, the cytoplasm and the nucleus. However, the biological functions of S100A4, and how it is translocated into the nucleus are still uncertain.
The aim of the present study was to elucidate which domains in the S100A4 protein that were responsible for nuclear localization. We constructed a fusion protein consisting of S100A4 and Enhanced Green Fluorescense Protein (EGFP) and three S100A4-EGFP deletion constructs. All constructs were transiently transfected into five different cancer cell lines, and subcellular localization of the overexpressed proteins were studied using fluorescence- and confocal microscopy.
The full-length S100A4-EGFP protein showed a similar subcellular localization as all of the three truncated S100A4-EGFP proteins, with an even protein distribution in the cytoplasm and almost none green fluorescent colour in the nucleus.
In conclusion, we were unable to determine which domains in the S100A4 protein that were important for nuclear localization. Since S100A4 is a small molecule of only 12 kD, it could possibly pass through the nuclear pores without any active transport mechanism being involved.
Supervisors: Gunhild M. Mælandsmo and Kristin Andersen Department of Tumor Biology, The Norwegian Radium Hospital.