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.