Ahmed_Shireman Brain 2021 ChIPSeq

Glioblastoma is a primary brain cancer with a near 100% recurrence rate. Upon recurrence, the tumor is resistant to all conventional therapies, and because of this, 5-year survival is dismal. One of the major drivers of this high recurrence rate is the ability of GBM cells to adapt to complex changes within the tumor microenvironment. To elucidate the molecular mechanisms of this adaptation, specifically during chemotherapy, we employed ChIP-Sequencing and gene expression analysis. We identified a molecular circuit in which the expression of ciliary protein ALR13B is epigenetically regulated to promote adaptation to chemotherapy. Immuno-precipitation combined with Liquid Chromatography-Mass Spectrometry binding partner analysis revealed that that ARL13B interacts with the purine biosynthetic enzyme IMPDH2. Further, radioisotope tracing revealed that this interaction function as a negative regulator for purine salvaging. Inhibition of ARL13B-IMPDH2 interaction enhances temozolomide (TMZ)-induced DNA damage by forcing GBM cells to rely on the purine salvage pathway. Targeting the ARLI3B-IMPDH2 circuit can be achieved by using an FDA-approved drug, Mycophenolate Mofetil, that can block the IMPDH2 activity and enhance the therapeutic efficacy of TMZ. Our results suggest and support clinical evaluation of MMF in combination with TMZ treatment in glioma patients. Comparison of H3K27me3 marks in glioblastoma cells (proneural GBM 43) after 4 days of either DMSO or TMZ treatment