Generation of PRL-3- and PRL-1-specific monoclonal antibodies as potential diagnostic markers for cancer metastases.

PURPOSE: The PRL-3 mRNA is consistently elevated in metastatic samples derived from colorectal cancers. We sought to generate a specific PRL-3 monoclonal antibody (mAb) that might serve as a potential diagnostic marker for colorectal cancer metastasis. EXPERIMENTAL DESIGN: PRL-3 is one of three members (PRL-1, PRL-2, and PRL-3) in a unique protein-tyrosine phosphatase family. Because the three PRLs are 76% to 87% identical in their amino acid sequences, it poses a great challenge to obtain mAbs that are specific for respective phosphatase of regenerating liver (PRL) but not for the other two in the family. We screened over 1,400 hybridoma clones to generate mAbs specific to each PRL member. RESULTS: We obtained two hybridoma clones specifically against PRL-3 and another two clones specifically against PRL-1. These antibodies had been evaluated by several critical tests to show their own specificities and applications. Most importantly, the PRL-3 mAbs were assessed on 282 human colorectal tissue samples (121 normal, 17 adenomas, and 144 adenocarcinomas). PRL-3 protein was detected in 11% of adenocarcinoma samples. The PRL-3- and PRL-1-specific mAbs were further examined on 204 human multiple cancer tissues. The differential expressions of PRL-3 and PRL-1 confirmed the mAbs' specificity. CONCLUSIONS: Using several approaches, we show that PRL-3- or PRL-1-specific mAbs react only to their respective antigen. The expression of PRL-3 in >10% of primary colorectal cancer samples indicates that PRL-3 may prime the metastatic process. These mAbs will be useful as markers in clinical diagnosis for assessing tumor aggressiveness.

PRL-3 and PRL-1 promote cell migration, invasion, and metastasis.

We demonstrate here that Chinese hamster ovary cells stably expressing PRL-3, a M(r) 20000 prenylated protein tyrosine phosphatase, or its relative, PRL-1, exhibit enhanced motility and invasive activity. A catalytically inactive PRL-3 mutant has significantly reduced migration-promoting activity. We observe that PRL-3 is associated with diverse membrane structures involved in cell movement. Furthermore, we show that PRL-3- and -1-expressing cells, but not control cells, induce metastatic tumor formation in mice. Thus, our results deliver the first evidence for a causative role of PRL-3 and -1 in promoting cell motility, invasion activity, and metastasis.

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.