Abstract A30: Characterizing the non-linear dependency of the CDK5-Rb axis in non-small cell lung cancer
Authors: Jaileene Perez-Morales, Mauricio Cabrera-Rios, Jonathan Gonzalez-Flores, Pedro Santiago-Cardona
Journal: Cancer Research (2017)

Abstract In spite of recent therapeutics advances and early detection, lung cancer is still the leading cause of cancer-associated deaths worldwide. The five-year survival rates for its two major subtypes, small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) are estimated to be 6% and 18%, respectively. This high mortality is due to its aggressive nature even when detected at an early stage. Besides its aggressive nature and tendency for early metastasis, another feature of lung cancer is the inactivation of the retinoblastoma protein (Rb) that is observed in both lung cancer subtypes. NSCLC exhibits Rb inactivation by hyper-phosphorylation. Rb is phosphorylated by cyclin dependent kinases (CDKs) and their cyclin regulatory partners. CDK5 is a unique CDK because its regulatory partners, p35 and p39, are not cyclins, hence its function is not cell cycle related. This work aims to employ empirical modeling and statistical experimental design techniques to gain a comprehensive mechanistic understanding of metastasis. Previous mass spectroscopy experiments performed in our laboratory on a panel of NSCLC cell lines identified five-residues (S249, S612, S807, S811, and T821) whose phosphorylation is associated with lack of E-cadherin expression, and therefore may be associated with metastasis. Our hypothesis is that Rb inactivation via phosphorylation due to CDK5 leads to the acquisition of the epithelial-to-mesenchymal transition (EMT) phenotype and the disruption of cell-cell adhesion that characterizes metastatic cells. As a first step to establish a mathematical model the dependency of the controllable variables, Rb residues and CDK5 expression was assessed. To this end, we used siRNA to knockdown CDK5 expression, which caused a decrease in phosphorylation of Rb in the five residues mentioned above and a subsequent decrease in E-cadherin expression. These data suggest that Rb phosphorylation in the five residues is dependent on CDK5 expression. This dependency in our controllable variables points to a nested experimental design. Our next step is to perform invasion assays and lung acini formation to quantify the invasion capacity and the malignant transformation. In the long term, at a clinical setting, a lung cancer tumor may be extracted from a biopsy and immunohistochemistry staining will be performed with antibodies of interest such as Rb phosphorylation residues, E-cadherin, and CDK5/p35 or CDK5/p39. This mathematical model would help provide a prognosis about the invasion capacity and a malignancy prediction of the lung tumor. Citation Format: Jaileene Perez-Morales, Mauricio Cabrera-Rios, Jonathan Gonzalez-Flores, Pedro Santiago-Cardona. Characterizing the non-linear dependency of the CDK5-Rb axis in non-small cell lung cancer. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A30.