Chronic exposure to cigarette smoke leads to activation of p21 (RAC1)-activated kinase 6 (PAK6) in non-small cell lung cancer cells

Remya Raja,Xiaofei Chang,Nazia Syed,Nandini A Sahasrabuddhe,Niraj Babu,Santosh Renuse,Evgeny Izumchenko,Annapoorni Rangarajan,Harsha Gowda,Aneesha Radhakrishnan,Sai A Balaji,Keshava K Datta,Aditi Chatterjee,David Sidransky,Vishalakshi Nanjappa,Akhilesh Pandey,Hitendra S Solanki,T S Keshava Prasad ,Vinuth N Puttamallesh ,Arun H Patil

doi:10.18632/oncotarget.11310

Abstract

Epidemiological data clearly establishes cigarette smoking as one of the major cause for lung cancer worldwide. Recently, targeted therapy has become one of the most preferred modes of treatment for cancer. Though certain targeted therapies such as anti-EGFR are in clinical practice, they have shown limited success in lung cancer patients who are smokers. This demands discovery of alternative drug targets through systematic investigation of cigarette smoke-induced signaling mechanisms. To study the signaling events activated in response to cigarette smoke, we carried out SILAC-based phosphoproteomic analysis of H358 lung cancer cells chronically exposed to cigarette smoke. We identified 1,812 phosphosites, of which 278 phosphosites were hyperphosphorylated (≥ 3-fold) in H358 cells chronically exposed to cigarette smoke. Our data revealed hyperphosphorylation of S560 within the conserved kinase domain of PAK6. Activation of PAK6 is associated with various processes in cancer including metastasis. Mechanistic studies revealed that inhibition of PAK6 led to reduction in cell proliferation, migration and invasion of the cigarette smoke treated cells. Further, siRNA mediated silencing of PAK6 resulted in decreased invasive abilities in a panel of non-small cell lung cancer (NSCLC) cells. Consistently, mice bearing tumor xenograft showed reduced tumor growth upon treatment with PF-3758309 (group II PAK inhibitor). Immunohistochemical analysis revealed overexpression of PAK6 in 66.6% (52/78) of NSCLC cases in tissue microarrays. Taken together, our study indicates that PAK6 is a promising novel therapeutic target for NSCLC, especially in smokers.

Highlights

Lung cancer accounts for ~19% of the cancer related deaths worldwide [1]
Since inhibition of protein activated kinase 6 (PAK6) led to a decrease in the migration of lung cancer cells chronically exposed to cigarette smoke, we studied whether PAK6 has a potential role in regulating invasive potential in H358-S cells and in a panel of non-small cell lung cancer (NSCLC) cell lines established from smokers (H1299, H1650 and H1703)
Our results indicate that PAK6 is activated in lung cancer cells in response to cigarette smoke and targeting PAK6 leads to a decrease in oncogenic potential of NSCLC cells

Summary

Introduction

Lung cancer accounts for ~19% of the cancer related deaths worldwide [1]. The 5 year survival rate is only 15% for patients diagnosed with lung cancer in the advanced stage [2]. NSCLC in smokers presents distinct molecular signatures compared to lung cancer from non-smokers [6, 7]. Anti-EGFR therapy such as gefitinib and erlotinib are currently in practice for treatment of NSCLC. Though, these drugs have shown marked the efficacy in non-smokers, smokers seem to be largely resistant [7]. Dysregulation in other key signaling pathways such as PI3K/AKT/mTOR, Ras/Raf/MAPK and MET kinase have been reported as potential targets but are pending clinical validation. These observations accentuate the need for systematic investigation of alternative signaling pathways that are activated upon chronic exposure to smoke

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Results

Conclusion