© 2004 Landes Bioscience. Do Not Distribute
for their supports. We would also like to thank Dr.
Jianlin Fu for his help in using fluorescent micro-
scope (Zeiss, M2 Bio Quad) and Dr. Ponniah
Sathivel and his team in animal Facility Unit. We
appreciate Dr. Xiaohang Yang, Mr. Jin Soo Ka and
Jun Mak Kah for help in making the QuickTime
This work was supported by research grants
from The Agency of Science, Technology and
Research (A*STAR), Singapore.
tumor metastatic processes in vivo. Our study reveals that PRL-3 on its own is able to
complete multiple steps of metastasis. Mutation of its catalytic domain essentially abolishes
matastatic processes. We suggest that once PRL-3 is activated, the barriers to development
of tumor metastasis would be broken with the inevitable induction of the event. For the
[Cancer Biology & Therapy 3:10, 945-951, October 2004]; ©2004 Landes Bioscience
Jing Ping Tang
Bin Qi Gan
Institute of Molecular and Cell Biology; Singapore
*Correspondence to: Qi Zeng; Institute of Molecular and Cell Biology; 61 Biopolis
Drive; Singapore 138673 Singapore; Tel.: 65.6586.9664; Fax: 65.6779.1117;
Received 07/20/04; Accepted 07/27/04
Previously published online as a Cancer Biology & Therapy E-publication:
cancer therapy, cancer metastasis, colorectal
cancer, protein-tyrosine phosphatase, angiogenesis
phosphatase of regenerating liver
Chinese hamster ovary
enhanced green fluorescent protein
serial analysis of gene expression
protein tyrosine phosphatase
fetal bovine serum
bovine serum albumin
PBS with CaCl2and MgCl2
von Willebrand Factor
Haematoxylin & Eosin stain
We are very grateful to Drs. Kenneth W. Gross,
Catherine J. Pallen, Edward Manser and Luen Tang
Bor for their critical reading of the manuscript. We
appreciate Drs. Wanjin Hong and Hwee Tan Yin
Catalytic Domain of PRL-3 Plays an Essential Role in Tumor Metastasis
Formation of PRL-3 Tumors Inside the Blood Vessels
PRL-3, a protein tyrosine phosphatase, has attracted much attention as its transcript is
consistently upregulated in the process of colorectal cancer metastases to secondary
organs. We studied mice injected via the tail vein with CHO cells stably expressing
EGFP-tagged PRL-3 or catalytically inactive mutant PRL-3 (C104S). Our data showed that
the EGFP-PRL-3-expressing cells rapidly induce metastatic tumor formation in lung, while
EGFP-PRL-3 (C104S)-expressing cells lose this metastastic activity. Furthermore, detailed
microscopic examinations revealed that some EGF-PRL-3-, but not EGFP-PRL-3 (C104S)-,
expressing cells form micro- and macro-metastatic solid tumors that sprout into blood
vessels. Our studies provide clear evidence for a causative role of PRL-3 phosphatase
activity in cancer metastasis and tumor-related angiogenesis events. The catalytic domain
of PRL-3 could serve as an ideal therapeutic target for drug development to block the
spread of colorectal cancer.
Colorectal cancer (CRC) is the second-leading cause of cancer-related death in the
United States. Using serial analysis of gene expression (SAGE) technology, PRL-3 was
identified as the only gene that is consistently overexpressed in all 18 liver metastases
derived from colorectal cancer, with essentially undetectable expression in normal colorectal
epithelia and intermediate expression in advanced primary cancers.1PRL-3 mRNA
expression was elevated in nearly all metastatic lesions derived from CRCs, regardless of
the sites of metastasis (liver, lung, brain, or ovary).2The consistency of PRL-3 overexpression
in all the metastatic lesions of CRC examined is strikingly important, because only genes
which are switched on during tumor formation are particularly good targets for potential
PRL-3 is a 20-kDa prenylated protein tyrosine phosphatase identified in 1998.3It is
one of the three members (PRL-1, -2 and -3) of the PRL-PTP family. The PRL-PTPs
comprise a distinct subclass of protein tyrosine phosphatases with a C-terminal prenylation
motif; however, the biological functions of these phosphatases remain to be determined.
PRL-1 is expressed at high levels in proliferating cells and a number of human tumor cell
lines, including HeLa cells.4,5Overexpression of PRL-1 and PRL-2 in epithelial cells
results in a transformed phenotype in culture and tumor growth in nude mice.6,7By
PCR-based subtractive hybridization, PRL-2 was shown to be upregulated 1.8, 2.7 and
4.0 times in advanced prostate cancer cell lines LNCaP, PC-3 and DU-145, respectively,
in comparison with normal epithelial cells. Subsequently, PRL-2 was suggested to be asso-
ciated with prostate tumor progression.8Similarly, overexpression of PRL-3 in human
embryonic kidney fibroblast HEK293 cells enhances growth rate versus nontransfected
cells.9We have shown that the PRL-PTPs are mainly associated with the plasma mem-
brane and endosomal structures in a prenylation-dependent manner.10In addition, we
have demonstrated that the overexpression of PRL-3 or PRL-1 in Chinese hamster ovary
(CHO) cells promote cell migration and invasion. Moreover, PRL-1 and -3 overexpressing
CHO cells are capable of inducing metastatic tumor formation in nude mice.7As PRL-3
is a phosphatase, it is important to investigate whether its catalytic activity itself is directly
involved in the cancer metastasis which is a complex multistage process involving local
invasion, intravasation, extravasation, implantation and angiogenesis.11-15
In this report, we provide important evidence that PRL-3 is sufficient for triggering
Cancer Biology & Therapy
Cancer Biology & Therapy
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molecular function of the metastasis associated phosphatase PRL-3. J Biol Chem 2004;
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PRL-3 AND CANCER METASTASIS