Abstract LB-101: A novel role of semaphorin4a (sema4a) in genotoxin-induced DNA damage response in human lung fibroblasts

Abstract

Abstract Dysregulation of DNA repair signaling after genotoxin exposure contributes to genomic instability and carcinogenesis. Hexavalent chromium [Cr(VI)] is a genotoxin of occupational and environmental concern. Protein tyrosine phosphatase (PTP) inhibitors (i.e., sodium orthovanadate (SOV)) activate key survival pathways. We reported that SOV enhances clonogenic survival after Cr(VI) exposure by overriding Cr-induced growth arrest in human lung fibroblasts (HLFs). PTP inhibition with SOV increased expression of DNA damage/repair genes as determined by microarray analysis. Kinetic analysis of DNA double-strand breaks (DSBs) by comet assay showed equal DSB formation 15 min after Cr(VI) exposure in the absence and presence of SOV. However, PTP inhibition significantly decreased DSBs 0.5-24 hr after Cr(VI) treatment. Aim of the present study was to determine the molecular mechanism(s) by which PTP inhibition affects DNA damage response during genotoxic stress. Gene expression was examined by DNA Damage Signaling Pathway PCR Array after 1 μM Cr(VI) treatment for 24 hr in the absence or presence of SOV. The PTP inhibitor reversed Cr-mediated changes in expression of several unique genes. Interestingly, the sema4a gene, known to be involved in T cell activation and endothelial cell proliferation and migration, was strongly induced by co-treatment of SOV and Cr(VI). Gene expression correlated with increased sema4a protein expression after co-treatment of SOV and Cr(VI). A potential role of sema4a in Cr-induced DNA DSB formation/repair in the absence or presence of SOV was assessed after sema4a siRNA transfection. Silencing of sema4a did not alter the effect of SOV on Cr-induced DSBs. However, sema4a silencing completely blocked Cr-induced DSBs 4 hr after exposure. These results suggest a novel role of sema4a in DNA DSB formation/repair in normal HLFs. Taken together, these data shed light on the emerging role of semaphorins as mediators of cell survival as well as potential therapeutic targets in carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-101.