Impact of Rapamycin on Genome Organization

mTOR(definition)-inhibiting drug studied for extending healthspan and lifespan." style="text-decoration:underline dotted; text-underline-offset:2px; cursor:help;">Rapamycin(definition), a putative anti-aging drug, has been shown to extend the lifespan of several model organisms. Rapamycin’s core effect is to inhibit a major nutrient sensing pathway of the cell, mechanistic Target of Rapamycin Complex 1 (mTORC1). This inhibition was previously thought to induce similar beneficial effects that parallel caloric restriction(definition) – the restriction of calories in an organism without causing malnutrition. Previous work has shown that Rapamycin induces significant changes in gene expression of normal human dermal fibroblasts, as well as inducing repositioning of chromosome within the nuclear volume. However, questions remained on how other chromosomes repositioned and if changes were occurring at sub-chromosomal levels. By utilizing fluorescence in situ hybridization (FISH) and Chromosome Conformation Capture (3C), we analyzed genome organization under several different growth conditions including Rapamycin treatment. Despite significantly altering the transcript levels of several CXCL (chemokine C-X-C motif ligand) genes during treatment with Rapamycin, we observed only minimal movement of chromosome 4 which contains these genes. However, when we analyzed the sub-chromosomal organization of the locus containing these genes, we discovered altered topology in response to both Rapamycin treatment and reversible growth arrest through induction of quiescence. We also observed that interactions occurred between LIF (Leukemia inhibitory factor) and two putative enhancers. Furthermore, we investigated a locus containing several KRTAP (keratin associated proteins) on chromosome 17 and discovered they also altered local genome topology in response to our treatments.