Daniela Haase1, Tiantian Cui1, Linlin Yang1, Yunxia Ma1, Hongyu Liu2, Bernhard Theis1, Iver Petersen1, Yuan Chen3. 1. Section Pathology of the Institute of Forensic Medicine, University Hospital Jena, Friedrich Schiller University Jena, Am Klinikum 1, 07747 Jena, Germany. 2. Hematology, Oncology and Tumorimmunology, Charité Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany. 3. Section Pathology of the Institute of Forensic Medicine, University Hospital Jena, Friedrich Schiller University Jena, Am Klinikum 1, 07747 Jena, Germany. Electronic address: Yuan.Chen@med.uni-jena.de.
Abstract
BACKGROUND: Plakophilin 1 (PKP1) is an important plaque component of desmosomes, major intercellular adhesive junctions that act as anchorage points for intermediate filaments. Abnormal expression of PKP1 was observed in various types of cancer, however so far its function in lung cancer has not yet been elucidated. METHODS: The expression of PKP1 was analyzed by RT-PCR and western blotting in lung cancer cell lines. The protein expression of PKP1 was evaluated by immunohistochemistry in tissue microarray. The epigenetic mechanism of PKP1 was explored by demethylation test, bisulfite sequencing and Methylation-Specific-PCR. The function of PKP1 was investigated by stable transfection with an expression vector. RESULTS: We found that PKP1 was downregulated in 6 out of 8 lung cancer cell lines, and downregulation of PKP1 was associated with DNA hypermethylation. In advanced primary lung tumor samples, higher expression of PKP1 was significantly associated with favorable clinical outcome (p = .003). Ectopic expression of PKP1 inhibited cell proliferation, colony formation, migration/invasion and enhanced apoptosis. These phenomena are accompanied by increased caspase 3/7 activities and cleaved PARP-1 as well as decreased extracellular signal-regulated kinase (ERK) activity. CONCLUSION: Taken together, our data suggest that PKP1 is a novel tumor suppressor and its protein expression might be a potential prognostic marker for patients with advanced lung cancer.
BACKGROUND:Plakophilin 1 (PKP1) is an important plaque component of desmosomes, major intercellular adhesive junctions that act as anchorage points for intermediate filaments. Abnormal expression of PKP1 was observed in various types of cancer, however so far its function in lung cancer has not yet been elucidated. METHODS: The expression of PKP1 was analyzed by RT-PCR and western blotting in lung cancer cell lines. The protein expression of PKP1 was evaluated by immunohistochemistry in tissue microarray. The epigenetic mechanism of PKP1 was explored by demethylation test, bisulfite sequencing and Methylation-Specific-PCR. The function of PKP1 was investigated by stable transfection with an expression vector. RESULTS: We found that PKP1 was downregulated in 6 out of 8 lung cancer cell lines, and downregulation of PKP1 was associated with DNA hypermethylation. In advanced primary lung tumor samples, higher expression of PKP1 was significantly associated with favorable clinical outcome (p = .003). Ectopic expression of PKP1 inhibited cell proliferation, colony formation, migration/invasion and enhanced apoptosis. These phenomena are accompanied by increased caspase 3/7 activities and cleaved PARP-1 as well as decreased extracellular signal-regulated kinase (ERK) activity. CONCLUSION: Taken together, our data suggest that PKP1 is a novel tumor suppressor and its protein expression might be a potential prognostic marker for patients with advanced lung cancer.