Requirement of phosphatase of regenerating liver‐3 for the nucleolar localization of nucleolin during the progression of colorectal carcinoma

Phosphatase of regenerating liver‐3 (PRL‐3) is a protein tyrosine phosphatase (PTP) that is frequently overexpressed in liver metastases of colorectal carcinomas (CRCs). The PTP activity of the PRL‐3 protein is indispensable for the promotion of distant metastasis of CRC; however, little is known about the effect of PRL‐3 on cell growth. In this study, we investigated a novel protein that can connect to PRL‐3 to modulate the proliferation of CRC cells. In CRC‐derived SW480 cells, transduction of ectopic wild‐type PRL‐3, but not the C104S catalytic “dead” mutant, up‐regulated cell proliferation and increased the population of cells at the S and G 2 /M phases. Also, inhibition of PTP activity of the PRL‐3 protein by treatment with the PRL‐3 inhibitor suppressed cell proliferation in a dose‐dependent manner as well as PRL‐3 knockdown by RNA interference. Using a comparative study of monodimensional gel electrophoresis of immunoprecipitates from PRL‐3 ‐transfected SW480 cells and subsequent mass spectrometry analysis, nucleolar‐specific protein nucleolin (NCL) was identified as a novel PRL‐3‐binding protein. We confirmed physiological interaction between PRL‐3 and NCL, and found that PRL‐3 phosphatase activity was associated with the suppression of the phospho‐NCL levels and nucleolar assembly of NCL protein. In CRC cases, nucleolar NCL expression was correlated not only with higher levels of PRL‐3 expression but also with frequent incidence of lymph node metastasis and a higher clinicopathologic stage. These findings suggest that NCL is involved in PRL‐3‐mediated cancer progression/metastasis signaling, which plays an important role in the acceleration of CRC growth. ( Cancer Sci 2010)