Nuclear localization of the metastasis-associated protein S100A4 has been shown 
to correlate with advanced disease stage in primary colorectal carcinomas (CRC), 
but nuclear function and its relevance for the metastatic capacity of tumor 
cells is still unclear. Among several nuclear interacting protein partners 
suggested for S100A4, the tumor suppressor protein p53 has attracted particular 
interest, and previous studies suggest direct and indirect modes of interaction 
between the two proteins. The present study was undertaken to assess 
coexpression and potential interaction in CRC. TP53 mutational status and S100A4 
expression were investigated in a selected series of primary CRC specimens (n = 
40) and cell lines (n = 17) using DNA sequencing, western blot, and double 
immunostaining. Additionally, S100A4 and p53 were experimentally up- and 
down-regulated in vitro to assess reciprocal effects. For the first time, S100A4 
and p53 coexpression was demonstrated in individual CRC cells, with nuclear 
colocalization as a particularly interesting feature. In contrast to previous 
studies, no correlation was observed between TP53 mutational status and S100A4 
expression, and no evidence was obtained to support reciprocal regulation 
between the two molecules in the HCT116 isogenic cell line model. In conclusion, 
S100A4 and p53 were shown to be colocalized in individual nuclei of CRC cells, 
and it might be speculated whether the proteins interact in this subcellular 
compartment.