Chronic Exposure to Cigarette Smoke Leads to Activation of p21 (RAC1)-activated Kinase 6 (PAK6) in Non-Small Cell Lung Cancer Cells

Oncotarget. 2016 Sep 20;7(38):61229-61245. 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.

Keywords: NSCLC; mass spectrometry; p21 (RAC1)-activated kinase 6; smoking.

MeSH terms

  • Animals
  • Carcinoma, Non-Small-Cell Lung / drug therapy
  • Carcinoma, Non-Small-Cell Lung / metabolism*
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Survival
  • ErbB Receptors / metabolism
  • Gene Silencing
  • Humans
  • Lung Neoplasms / drug therapy
  • Lung Neoplasms / metabolism*
  • Male
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Neoplasm Transplantation
  • Phosphorylation
  • Proteome
  • Pyrazoles / pharmacology
  • Pyrroles / pharmacology
  • RNA, Small Interfering / metabolism
  • Signal Transduction
  • Smoke / adverse effects*
  • Tobacco Products
  • p21-Activated Kinases / metabolism*
  • rac1 GTP-Binding Protein / metabolism

Substances

  • PF 3758309
  • Proteome
  • Pyrazoles
  • Pyrroles
  • RAC1 protein, human
  • RNA, Small Interfering
  • Smoke
  • EGFR protein, human
  • ErbB Receptors
  • PAK6 protein, human
  • p21-Activated Kinases
  • rac1 GTP-Binding Protein