PRL-3 is a newly identified protein tyrosine phosphatase associated with tumor metastasis. It is over-expressed in various cancers, such as colorectal cancer, gastric cancer, and ovarian cancer, and is correlated with the progression and survival of cancers. Although PRL-3 plays a causative role in promoting cancer cell invasion and metastasis, the molecular mechanism is unknown. To investigate PRL-3's roles in tumorigenesis and signal transduction pathway, we screened the human placenta brain cDNA library with the bait of PRL-3 in yeast two-hybrid system. Then we identified integrin alpha 1 as a PRL-3-interacting protein for the first tinge, and verified this physical association with pull-down and co-immunoprecipitation assays. Furthermore, we found that PRL-3 could down-regulate the tyrosine-phosphorylation level of integrin beta 1 and increased the phosphorylation level of Erk1/2. Our present discovery will provide new cities for elucidating the molecular mechanism of PRL-3 in promoting cancer invasion and metastasis. (c) 2006 Elsevier Inc. All rights reserved.