Polo-like kinase 1 (Plk1) is one of the serine/threonine kinases involved in various mitotic processes, such as centrosome maturation and chromosome segregation. Although Plk1 is increased in several tumor types, the effect of Plk1 in gastric cancer is not clear because of the limited patient numbers in previous studies. This study was performed to investigate the prognostic significance and the expression profiles of Plk1 in gastric carcinoma tissues from 280 Korean patients. The expression of Plk1 was analyzed by reverse transcriptional PCR and a tissue array using immunohistochemical staining method in gastric adenocarcinoma tissues. The oncogenic potential of Plk1 was analyzed by using Plk1-specific small interference RNA in gastric cancer cells. The message of Plk1 was increased in various gastric cancer cell types and in primary cancer specimens in comparison with normal tissue. The expression rate of Plk1 was 95% (268/280) in gastric carcinoma patients. Although Plk1 expression had no specific correlation in male or female patients, among the differentiation types of cancer, its expression was generally increased in gastric cancers. Plk1 expression was significantly associated with accumulation of proliferation-related genes and oncogenes, and reversely correlated with tumor suppressor genes. When Plk1 expression was blocked, cancer cell growth was inhibited and apoptotic phenotypes were detected. Overexpression of Plk1 was important in abnormal proliferation and showed oncogenic potential in gastric cancer. Plk1 might have potential as a tumor prognostic marker for gastric cancer.

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