The Effects of the LINE-1 Protein ORF1p on MAPK p38 Pathways
ABSTRACT THE EFFECTS OF THE LINE-1 PROTEIN ORF1P ON MAPK P38 PATHWAYS By BRIAN EZELL Under the direction of PAMELA COOK, Ph.D. Transposable elements make up approximately 50% of the human genome and include endogenous retroviruses, retrotransposons, and remnants of inactive transposons. LINE-1 is the only currently active autonomous retrotransposon in humans and replicates via a “copy-and-paste” mechanism termed retrotransposition. This process is highly mutagenic to genomic DNA. In addition, LINE-1 encodes two proteins, ORF1p and ORF2p, that can also perturb cellular function. LINE-1 is repressed in most somatic cells, but approximately 80 – 100 of the > 500,000 genomic copies of LINE-1 are capable of re-activation in epithelial precancerous and malignant cells and by exposures to environmental toxicants. Previous studies have shown that LINE-1 retrotransposition depends on activation of the mitogen activated protein kinase (MAPK) p38. Prior data in our lab showed that p38 phosphorylates the LINE-1 protein ORF1p on motifs whose phosphorylation is required for LINE-1 function, supporting a possible mechanistic role for p38 in LINE-1 activation. The experiments outlined in this thesis test our hypothesis that ORF1 exerts reciprocal effects on p38 by measuring p38 mRNA and protein expression in the presence or absence of transfected ORF1. In addition, we determined the effect of ORF1p on the phosphorylation of p38 on Thr180/Tyr182, which is required for p38 kinase activity. Phosphorylation of p38 induces biological responses such as inflammation, apoptosis, growth, or cell differentiation via activation of multiple, complex downstream pathways. Deregulation of p38 is implicated in the pathologies of many diseases, including cancer. Identification of crosstalk between LINE-1 and p38 will therefore inform our understanding of how LINE-1 contributes to tumorigenesis, tumor progression, and cellular responses during environmental exposures.