The Over-expression Of Polo-like Kinase 1 (PLK1) In Bronchoscopic Bioptic Specimens Of Lung Cancer

ObjectivePrimary lung cancer is one of the most frequent male malignant disease. PLK 1 (polo-like kinase 1), the human counterpart of polo in Drosophila melanogaster and of CDC5 in Saccharomyces cerevisiae, belongs to a family of serine/threonine kinases. It is intimately involved in spindle formation and chromosome segregation during mitosis. Now, the over-expression of PLK 1 (or PLK) has been found in various primary carcinomata, and indicated the probability of PLK 1 as a new tumor marker. The purpose of this study is to determine whether PLK1 mRNA is over-expressed in bronchoscopic bioptic specimens of primary lung cancer as compared with pulmonary benign disease and to assess its relations to TNM staging and pathological classification.MethodsIn the present study, fluorescent real-time quantitative PCR(FQ-PCR) was performed for PLK1 mRNA expression levels in 69 primary lung cancer specimens as well as 28 pulmonary Benign disease specimens . In FQ-PCR experiment, the extracted RNA samples were first reversely transcribed to cDNA prior to assay, and standard reference housekeeping GAPDH gene and PLK1 gene were analyzed. For each sample, the determination of the Ct (Cycle threshold value) of PLK1 and GADPH gene was reported. The value of 2CtGAPDH-CtPLK1 indicated expression level of PLK1 . The Clinico -pathological characteristics of the cases were applied. Pathological TNM staging was performed according to UICC1997 protocol. The Mann -Whitney U test was applied to examine associations of PLK1 expression between primary lung cancer and pulmonary Benign disease , and SPSS 12.0 For Windows Software was used to analyze Statistical dataResultsThe detected PLK1 mRNA level was 0.124±0.194 in primary lung cancer specimens, and 0.037±0.042 in pulmonary benign disease specimens. The expression level elevation in the malignant group was satistically significant compared with that of the benign group(P=0.03, Mann-Whitney U test).Classifying patients by the pathological classifications, we found thatPLK1 mRNA expression level was 0.098±0.146 in squamous cell specimens, 0.107±0.170 in adenocarcinoma specimens, 0.191±0.275 in small cell lung cancer specimens. Although no statistical significance was found between them(P>0.05, Mann-Whitney U test). But in the trendgram, elevated expression of PLKl mRNA level was found in small cell lung cancer specimens compared with that of non-small cell lung cancer specimens.According to TNM staging, we divided these patients into two groups. One consisted of patients from stage I to stage Ob, and the other from stage IIIb to stage IV. The PLKl mRNA expression level was 0.1367±0.2212 in the former group and 0.1070±0.1534 in the latter group. No statistical significance was found between these two groups (u=0.484, P=0.555,Mann Whitney U test) .The PLKl mRNA expression level in primary lung cancer patients had no statistical correlation with age or pack year of smoking.Conclusion1 the over-expressed PLKl mRNA level in primary lung cancer specimens, compared with that of pulmonary benign disease specimens, indicated that PLKl might have a potential to be a new tumor marker for lung cancer.2 the higher PLK1 mRNA expression level in small cell lung cancerspecimens, compared with that of non-small cell lung cancer, might have correlation with the mitotic activity of cells.3 No statistical significance was found between the PLK1 mRNA expression levels of two groups according to TNM pathological classifications.4 No statistical correlation was found between the PLK1 mRNA expression level and age, or smoking.