RalGPS2 Is Essential for Survival and Cell Cycle Progression of Lung Cancer Cells Independently of Its Established Substrates Ral GTPases

• Published in: PloS one 2016-05, Vol.11 (5), p.e0154840-e0154840
• Main Authors: O Santos, Adriana, Parrini, Maria Carla, Camonis, Jacques
• Format: Article
• Language: English
• Subjects: Antibiotics; Apoptosis; Biology and life sciences; Biotechnology; Care and treatment; Cell Adhesion; Cell cycle; Cell Cycle - physiology; Cell Line, Tumor; Cell survival; Cell Survival - physiology; Cyclin D1; Cyclin-dependent kinase inhibitor p21; Gene Silencing; Genomes; Growth factors; GTP Phosphohydrolases - metabolism; GTP-binding protein; Guanine; Guanine nucleotide exchange factor; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - physiology; Health aspects; Health sciences; Humans; Inhibition; Kinases; Lung cancer; Lung carcinoma; Lung diseases; Lung Neoplasms - enzymology; Lung Neoplasms - pathology; Medicine and Health Sciences; Modulation; mRNA; Mutation; Non-small cell lung carcinoma; Phase transitions; Population growth; Proteins; RalA protein; Ras genes; Ras protein; Regulators; Research and Analysis Methods; Signaling; Skp2 protein; Small cell lung carcinoma; Substrate Specificity; Substrates; Survival; Ubiquitin; Ubiquitin-protein ligase
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0154840

The human genome contains six genes coding for proteins validated in vitro as specific activators of the small GTPases "Ras-related protein Ral-A" and "Ras-related protein Ral-B", generically named Ral-guanine nucleotide exchange factors (RalGEF). Ral proteins are important contributors to Ras oncogenic signaling, and RAS oncogenes are important in human Non-Small Cell Lung Carcinoma (NSCLC). Therefore in this work, RalGEF contribution to oncogenic and non-oncogenic features of human NSCLC cell lines, as anchorage-dependent and independent growth, cell survival, and proliferation, was investigated. Among all human RalGEF, silencing of RGL1 and RALGPS1 had no detectable effect. However, silencing of either RGL2, RGL3, RALGDS or, to a larger extent, RALGPS2 inhibited cell population growth in anchorage dependent and independent conditions (up to 90 and 80%, respectively). RALGPS2 silencing also caused an increase in the number of apoptotic cells, up to 45% of the cell population in transformed bronchial BZR cells. In H1299 and A549, two NSCLC cell lines, RALGPS2 silencing caused an arrest of cells in the G0/G1-phase of cell cycle. Furthermore, it was associated with the modulation of important cell cycle regulators: the E3 Ubiquitin Protein Ligase S-phase kinase-associated protein 2 (Skp2) was strongly down-regulated (both at mRNA and protein levels), and its targets, the cell cycle inhibitors p27 and p21, were up-regulated. These molecular effects were not mimicked by silencing RALA, RALB, or both. However, RALB silencing caused a modest inhibition of cell cycle progression, which in H1299 cells was associated with Cyclin D1 regulation. In conclusion, RALGPS2 is implicated in the control of cell cycle progression and survival in the in vitro growth of NSCLC cell lines. This function is largely independent of Ral GTPases and associated with modulation of Skp2, p27 and p21 cell cycle regulators.