Department of Radiation Oncology, The University of Alabama at Birmingham, Birmingham, AL, USA.
Division of Preventive Medicine, The University of Alabama at Birmingham, Birmingham, AL, USA.
Int J Oncol. 2015 Mar;46(3):1079-88. doi: 10.3892/ijo.2014.2799. Epub 2014 Dec 17.
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.
肺癌是癌症相关死亡的主要原因。肺癌常见的分子驱动因素是受体酪氨酸激酶（RTKs）的突变，导致磷酸肌醇 3-激酶（PI3K）/Akt 促生长、抗凋亡信号通路的激活。丝氨酸豆蔻酰化富含丙氨酸的 C 激酶底物（MARCKS）是一种能够通过隔离 PI3K 的靶标，即磷脂酰肌醇（4,5）-二磷酸（PIP2），来减轻这种信号级联反应的蛋白质。因此，MARCKS 被认为是一种肿瘤抑制因子，尽管有一些证据表明 MARCKS 在某些癌症类型中可能具有促进肿瘤的作用。由于 MARCKS 的功能取决于其磷酸化状态，这会影响其亚细胞定位，因此 MARCKS 在癌症中的作用可能高度依赖于信号背景。目前，MARCKS 在肺癌生物学中的重要性有限。因此，我们在临床标本和细胞培养模型中研究了 MARCKS。在多样化的肺癌肿瘤组织阵列中，MARCKS 蛋白表达的免疫组织化学评分显示，大多数鳞状细胞癌呈 MARCKS 阳性染色，而其他组织学类型，如腺癌，MARCKS 水平较低。为了研究 MARCKS 在肺癌生物学中的重要性，我们在 A549 肺癌细胞中诱导过表达野生型（WT）和非磷酸化（NP）-MARCKS，这些细胞中 MARCKS 的内源性水平较低。我们发现，NP-MARCKS 表达而非 WT-MARCKS 表达增强了 A549 细胞的放射敏感性，部分原因是通过抑制 DNA 修复来延长辐射诱导的 DNA 双链断裂。我们通过用磷酸化结构域的肽模拟物，即效应结构域（ED）处理几种肺癌细胞系，证实了 MARCKS 磷酸化状态的重要性，该模拟物有效地减弱了细胞指数所衡量的细胞生长。因此，MARCKS ED 似乎是肺癌治疗开发的一个重要靶点。
