Background: Polo-like kinase 1 (PLK1) is an important molecule in proliferation of many human cancers. The aim of study is to clarify the expression patterns and potential function of PLK1 in colorectal cancers.

Material/methods: Fifty-six colorectal cancers samples were collected and arranged onto a tissue array and the expression of PLK1 were detected by immunohistochemistry and correlated with clinico-pathological characteristics and expression of PCNA. Expression of PLK1 in 9 colorectal cancer cells lines was investigated by RT-PCR and Western blot, then SW1116 cells lines were treated with PLK1 siRNA and the efficiency was examined by Western blot. Transwell test was applied to detect the migration and invasion capability of cancer cells by counting the number of cells passing through the membranes. Cell proliferation and apoptosis were examined by Cell Counting Kit-8 (CCK-8) and Annexin-V Kit.

Results: PLK1 was positively expressed in 73.2% (41/56) of colorectal cancers tissues, but in only 3.6% (2/56) of normal tissues, and was associated with Duke's stage (P<0.01), tumor size (P<0.01), invasion extent (P<0.05) and lymphatic metastasis (P<0.01). The expression of PLK1 was correlated with expression of PCNA (R=0.553, P<0.01). PLK1 was inhibited in SW1116 cells by treating with PLK1 siRNA oligos, which resulted in a decreased number of cells passing through the membrane as compared with control groups (P<0.01) at 24 hours after transfection. Cell proliferation was inhibited from 48 hours after transfection, while cells apoptosis was induced from 72 hours after transfection.

Conclusions: PLK1 could be a progression marker for colorectal cancer patients and PLK1 depletion can inhibit migration and invasion capability of colorectal cancer cells SW1116, suggesting that PLK1 might be involved in metastasis and invasion of colorectal cancer. Therapeutic strategies targeting PLK1 may be a new approach to colorectal cancer.