Jae Heun Chung1, Dae Hyun Kim2, Yun Seong Kim1, Bong Soo Son3, Dohyung Kim3, Chungsu Hwang4, Donghoon Shin4, Sang Gyun Noh2, Jun Hee Han5, Dae Kyung Kim6, Jae Ho Kim6, Ja Seok Koo7, Hae Young Chung2, Seong Hoon Yoon1. 1. Department of Internal Medicine, Pusan National University Yangsan Hospital, Yangsan, Republic of Korea. 2. Molecular Inflammation Research Center for Aging intervention (MRCA), College of Pharmacy, Pusan National University, Busan, Republic of Korea. 3. Department of Thoracic and Cardiovascular Surgery, Pusan National University Yangsan Hospital, Yangsan, Republic of Korea. 4. Department of Pathology, Pusan National University Yangsan Hospital, Yangsan, Republic of Korea. 5. Department of Statistics, Hallym University, Chuncheon, Republic of Korea. 6. Department of Physiology, School of Medicine, Pusan National University, Yangsan, Republic of Korea. 7. Section of Medical Oncology, Department of Internal Medicine, Yale Comprehensive Cancer Center, Yale School of Medicine, New Haven, Connecticut, USA.
Abstract
BACKGROUND/AIMS: p21-activated Ser/Thr kinase 1 (PAK1) is essential for the genesis and development of many cancers. The purpose of this study was to investigate the role of the PAK1-cyclic AMP response element-binding (CREB) axis in non-small cell lung cancer (NSCLC) tumorigenesis and its related mechanisms. METHODS: Western blot assay and immunohistochemical staining were employed to investigate the PAK1 and CREB expression in the tissue microarray of human squamous NSCLC. Co-immunoprecipitation and immunofluorescence confocal assays were performed to determine the link between PAK1 and CREB. NSCLC xenograft models were used to study oncogenic function of PAK1 in vivo. RESULTS: We observed that PAK1 and CREB expression levels were significantly elevated in human squamous NSCLC-tissue specimens, compared with those in adjacent normal bronchial or bronchiolar epithelial-tissue specimens, as well as their phosphorylated forms, based on western blotting. We showed in vitro that PAK1 knockdown by small-interfering RNA (siRNA) blocked CREB phosphorylation, whereas plasmid-based PAK1 overexpression resulted in CREB phosphorylation at Ser133, based on western blotting. In addition, PAK1 interacted with CREB in co-immunoprecipitation assays. Additionally, our in vitro findings detected by flow cytometry revealed that PAK1 silencing attenuated cell cycle progression, inducing apoptosis. Inhibition of PAK1 expression reduced tumor sizes and masses by modulating CREB expression and activation in xenograft models. CONCLUSION: These results suggest a novel mechanism whereby the PAK1-CREB axis drives carcinogenesis of squamous-cell carcinomas, and have important implications in the development of targeted therapeutics for squamous-cell lung cancer.
BACKGROUND/AIMS: p21-activated Ser/Thr kinase 1 (PAK1) is essential for the genesis and development of many cancers. The purpose of this study was to investigate the role of the PAK1-cyclic AMP response element-binding (CREB) axis in non-small cell lung cancer (NSCLC) tumorigenesis and its related mechanisms. METHODS: Western blot assay and immunohistochemical staining were employed to investigate the PAK1 and CREB expression in the tissue microarray of human squamous NSCLC. Co-immunoprecipitation and immunofluorescence confocal assays were performed to determine the link between PAK1 and CREB. NSCLC xenograft models were used to study oncogenic function of PAK1 in vivo. RESULTS: We observed that PAK1 and CREB expression levels were significantly elevated in human squamous NSCLC-tissue specimens, compared with those in adjacent normal bronchial or bronchiolar epithelial-tissue specimens, as well as their phosphorylated forms, based on western blotting. We showed in vitro that PAK1 knockdown by small-interfering RNA (siRNA) blocked CREB phosphorylation, whereas plasmid-based PAK1 overexpression resulted in CREB phosphorylation at Ser133, based on western blotting. In addition, PAK1 interacted with CREB in co-immunoprecipitation assays. Additionally, our in vitro findings detected by flow cytometry revealed that PAK1 silencing attenuated cell cycle progression, inducing apoptosis. Inhibition of PAK1 expression reduced tumor sizes and masses by modulating CREB expression and activation in xenograft models. CONCLUSION: These results suggest a novel mechanism whereby the PAK1-CREB axis drives carcinogenesis of squamous-cell carcinomas, and have important implications in the development of targeted therapeutics for squamous-cell lung cancer.