Metastasis-associated protein S100A4 (Mts1) induces invasiveness of primary 
tumors and promotes metastasis. S100A4 belongs to the family of small 
calcium-binding S100 proteins that are involved in different cellular processes 
as transducers of calcium signal. S100A4 modulates properties of tumor cells via 
interaction with its intracellular targets, heavy chain of non-muscle myosin and 
p53. Here we report identification of a new molecular target of the S100A4 
protein, liprin beta1. Liprin beta1 belongs to the family of leukocyte common 
antigen-related (LAR) transmembrane tyrosine phosphatase-interacting proteins 
that may regulate LAR protein properties via interaction with another member of 
the family, liprin alpha1. We showed by the immunoprecipitation analysis that 
S100A4 interacts specifically with liprin beta1 in vivo. Immunofluorescence 
staining demonstrated the co-localization of S100A4 and liprin beta1 in the 
cytoplasm and particularly at the protrusion sites of the plasma membrane. We 
mapped the S100A4 binding site at the C terminus of the liprin beta1 molecule 
between amino acid residues 938 and 1005. The S100A4-binding region contains two 
putative phosphorylation sites by protein kinase C and protein kinase CK2. 
S100A4-liprin beta1 interaction resulted in the inhibition of liprin beta1 
phosphorylation by both kinases in vitro.