SIRT1 Regulates RNA Stability to Promote Breast Cancer - Project Summary Breast cancer is responsible for the deaths of more than 600,000 women each year. Thus, there is an over- riding need to better understand the mechanisms that promote breast cancer, as this information can potentially lead to new strategies to treat the disease. Recently, the Cerione lab discovered a mechanism through which highly aggressive forms of breast cancer cells produce a secretome containing factors that promote cancer cell survival and metastatic spread. Specifically, the researchers showed that the decreased expression of the NAD+- dependent deacetylase Sirtuin 1 (SIRT1) increases the formation and release of exosomes, a specific class of extracellular vesicles (EVs) that are derived from multi-vesicular bodies (MVBs) within the endocytic/lysosomal trafficking pathway. This effect was due to the increased acetylation of the RNA binding protein, IGF2BP2, that binds to the 3' untranslated region of the transcript encoding ATP6V1A, a major catalytic subunit of the vacuolar ATPase (v-ATPase) that maintains the proper pH and activity of lysosomes. Acetylated IGF2BP2 recruits an exonuclease, XRN2, which degrades the ATP6V1A transcript, resulting in impaired lysosomal activity. Thus, MVBs that would otherwise be targeted and degraded in lysosomes are instead directed to the cell surface where they fuse with the plasma membrane and release their contents, i.e., exosomes enriched in unique cargo and soluble hydrolases, into the extracellular space. These components of the secretome were shown to work together to strongly promote the invasiveness of breast cancer cells. Whether there were additional transcripts that were regulated similarly to the ATP6V1A transcripts by SIRT1 and IGF2BP2 were then determined. Based on a comprehensive RNA sequencing analysis performed, fourteen transcripts were identified; four of which encode proteins that potentially play important roles in breast cancer progression and/or exosome biogenesis. For the F99 phase of this application, I plan to establish that the stability of these transcripts is indeed regulated by SIRT1 and IGF2BP2, and to investigate how changes in their levels impact breast cancer progression (Aim 1). In addition to the tumor suppressor role played by SIRT1 in breast cancer, reductions in its expression have also been heavily implicated in aging, a major risk factor for developing cancer, as well as other diseases. In the K00 phase of this proposal, I would like to investigate the interplay between aging and cancer. It has been recently shown that the accumulation of aged/senescent cells results in the production of a secretome that can increase the growth of cancer cells. My plan as a Post-doctoral trainee will be to determine whether the EVs from aged/senescent cells contribute to this effect. Furthermore, I am also interested in exploring whether the EVs secreted from cancer cells enable cells to evade undergoing senescence (Aim 2). Ultimately, the goal of this study is to understand the relationship between aging and cancer to help identify potential therapeutic treatment for patients.
