title: Targeting the effector domain of the myristoylated alanine rich C-kinase substrate enhances lung cancer radiation sensitivity.
abstract: Lung cancer is the leading cause of cancer related deaths. Common molecular drivers of lung cancer are mutations in receptor tyrosine kinases (RTKs) leading to activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pro-growth, pro-survival signaling pathways. Myristoylated alanine rich C-kinase substrate (MARCKS) is a protein that has the ability to mitigate this signaling cascade by sequestering the target of PI3K, phosphatidylinositol (4,5)-bisphosphate (PIP2). As such, MARCKS has been implicated as a tumor suppressor, though there is some evidence that MARCKS may be tumor promoting in certain cancer types. Since the MARCKS function depends on its phosphorylation status, which impacts its subcellular location, MARCKS role in cancer may depend highly on the signaling context. Currently, the importance of MARCKS in lung cancer biology is limited. Thus, we investigated MARCKS in both clinical specimens and cell culture models. Immunohistochemistry scoring of MARCKS protein expression in a diverse lung tumor tissue array revealed that the majority of squamous cell carcinomas stained positive for MARCKS while other histologies, such as adenocarcinomas, had lower levels. To study the importance of MARCKS in lung cancer biology, we used inducible overexpression of wild-type (WT) and non-phosphorylatable (NP)-MARCKS in A549 lung cancer cells that had a low level of endogenous MARCKS. We found that NP-MARCKS expression, but not WT-MARCKS, enhanced the radiosensitivity of A549 cells in part by inhibiting DNA repair as evidenced by prolonged radiation-induced DNA double strand breaks. We confirmed the importance of MARCKS phosphorylation status by treating several lung cancer cell lines with a peptide mimetic of the phosphorylation domain, the effector domain (ED), which effectively attenuated cell growth as measured by cell index. Thus, the MARCKS ED appears to be an important target for lung cancer therapeutic development.
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Rohrbach
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Jarboe
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Anderson
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Hoa Q
authors.initials: HQ
authors.lastname: Trummell
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Patricia H
authors.initials: PH
authors.lastname: Hicks
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Alice N
authors.initials: AN
authors.lastname: Weaver
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Eddy S
authors.initials: ES
authors.lastname: Yang
authors.affiliation: Division of Preventive Medicine, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Oster
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Jessy S
authors.initials: JS
authors.lastname: Deshane
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Chad
authors.initials: C
authors.lastname: Steele
authors.affiliation: Department of Pathology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Gene P
authors.initials: GP
authors.lastname: Siegal
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Bonner
authors.affiliation: Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Willey
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology; D000077192:Adenocarcinoma of Lung; D000595:Amino Acid Sequence; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000378:metabolism* / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D018716:Molecular Mimicry; D008969:Molecular Sequence Data; D058990:Molecular Targeted Therapy / Q000379:methods; D009154:Mutation; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D046888:Tissue Array Analysis
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; C000619710:MARCKS protein, human; D008565:Membrane Proteins; D010446:Peptide Fragments; D000076250:Myristoylated Alanine-Rich C Kinase Substrate