A novel role of cdc-family gene PFTK1 in the control of liver cancer cell motility

Abstract

Cancer metastasis remains a major cause of cancer morbidity and mortality in individuals diagnosed with hepatocellular carcinoma (HCC). We previously reported on regional chromosome 7q21-q22 gains in close association with HCC progression, and discerned a candidate proto-oncogene PFTK1 within this region by array-based CGH mapping. The PFTK1 protein, PFTAIRE protein kinase 1, is a novel member of the Cdc2-related serine/threonine protein kinases. Our earlier investigations by ectopic expression and gene knockdown of PFTK1 confirmed a functional role for the PFTAIRE protein kinase in the motile phenotype of HCC cells, yet the biological basis remained to be determined. The aims of this study are therefore to establish the clinicopathologic significance of PFTK1 in HCC, and to define the PFTK1-modulated mechanisms in the control of HCC cell motility. Recent Tissue Microarray Analysis (TMA) on 180 paired primary HCC and their adjacent non-tumoral liver suggested common up-regulated PFTK1 compared to non-malignant counterpart (76.1%; p<0.0001). Correlative analysis further indicated PFTK1 over-expression in association with advanced tumor grading (P<0.0001) and the presence of microvascular invasion (P=0.05). By 2D-PAGE coupled with mass spectrometry, comparative proteomic profiling for phosphorylated proteins in PFTK1-suppressed HCC cells highlighted 5 differentially down-regulated spots, which included β-actin (ACTB), transgelin2 (TAGLN2), heat shock protein 70, mitochondrial aldehyde dehydrogenase and 14-3-3 gamma protein. Western blot analysis further verified a consistent reduction on ACTB phosphorylation and the serine phosphorylation of the TAGLN2 protein in the absence of PFTK1 protein kinase. Immunofluorescence analysis for cytoskeletal organizations indicated marked reduction on the actin stress fibers in PFTK1 knockdown cells. In conclusion, our results suggested that PFTK1 can affect the actin cytoskeletal organization and thus a motile phenotype in HCC cells through phosphorylation of ACTB and TAGLN2.