Abstract C19: Molecular biology of lung cancer in Puerto Ricans
Authors: Santiago-Cardona Pedro G. , Engel Brienne E. , González-Flores Jonathan , Cruz-Cosme Ruth , Muñoz-Antonia Teresita , Cress W. Douglas 
Published: May 2015

Lung cancer is a leading cancer killer, lung adenocarcinoma (AC) being its most common type. Several studies suggest that the frequency or nature of genetic events driving AC differ among ethnic populations. These differences impact treatment decisions as targeted agents are under development for a number of genes that drive lung cancer. For example, mutations in the epidermal growth factor receptor (EGFR) represent a driving event in a substantial number of AC patients that can be targeted with tyrosine kinase inhibitors. With the funding of a U54 Partnership grant between the Ponce School of Medicine in Ponce, PR and the Moffitt Cancer Center in Tampa, Florida we are constructing a molecular database for Puerto Rican Lung Cancer patients. Sample collection includes acquisition of fresh frozen and paraffin-embedded tissues via the U54-funded Puerto Rico tissue bank. DNA analysis of these tissues includes ancestry markers and exome sequencing of genes commonly altered in AC, including KRAS, TP53, EGFR, STK11, CDKN1C and RB1. Initial results suggest that the frequency of KRAS mutations in this population are significantly lower than those seen in a white mainland cohort, whereas the rate of EGFR and STK11 mutations is elevated. Since both EFGR and STK11 are potentially targetable mutations these data suggest that Puerto Rican AC patients would greatly benefit from genetic screening. Our U54 project also probes the role of the retinoblastoma protein (Rb) in lung cancer. Rb was the first tumor suppressor to be discovered, and yet its potency as a tumor suppressor remains only partially explained. We are interested in characterizing how Rb loss contributes to the aggressiveness of small cell lung carcinomas (SCLC). SCLC are poorly differentiated tumors with early proclivity for metastasis. Prognosis is poor with only 10-20% of patients achieving long-term disease-free intervals. Still, SCLC aggressivity remains to be molecularly explained. Interestingly, SCLC show high rates of Rb inactivation, which led us to hypothesize that in SCLC, Rb loss during early tumorigenesis facilitates both over-proliferation and early metastasis. Supporting our hypothesis, we found that the Rb-deficient SCLC cell line H187 lacks expression of E-cadherin while overexpressing N-cadherin, relative to Rb-expressing non-small cell lung carcinoma cell lines H1666 and H1650. We confirmed the Rb-positive status of H1666 and H1650 and the Rb-negative status of H187 by immunoblot. These results suggest that Rb loss in lung cancer cell lines provokes a cadherin switch indicative of an epithelial-to-mesenchymal transition. Consistently, we found overexpression of the mesenchymal marker vimentin in H187 relative to H1666 and H1650. When compared to H1666 and H1650, H187 lacked expression of the adherens junction component α-catenin and of the cytoskeletal adapter Eplin. Furthermore, H187 cells show up-regulated levels of Pak1, a Rac1 and Cdc42 effector whose up-regulation is associated to adherens junction disruption. Tiam-1, a Rac1 and Cdc42 activator, is also up-regulated in H187 relative to H1666 and H1650. Together, our data in lung cell lines suggests that Rb loss results in adherens junction alterations possibly due to transcriptional alteration of cell adhesion genes, aberrant regulation of the Rho GTPases Rac1 and Cdc42, and disruption of the cortical cytoskeleton. Based on our data, we propose that Rb loss in SCLC, not only leads to an increased proliferative capacity during early tumorigenesis, but also exacerbates early tumor aggressiveness by perturbing cellular adhesion, which facilitates tumor cell detachment and metastasis. Our ultimate goal is to link the genetic alterations we found in Puerto Ricans to Rb function, cell adhesion, and tumor aggressivity.

Citation Format: Pedro G. Santiago-Cardona, Brienne E. Engel, Jonathan González-Flores, Ruth Cruz-Cosme, Teresita Muñoz-Antonia, W. Douglas Cress. Molecular biology of lung cancer in Puerto Ricans. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C19. doi:10.1158/1538-7755.DISP13-C19