All ETDs from UAB

Advisory Committee Chair

Sunil Sudarshan

Advisory Committee Members

Ravi Bhatia

Robinna Lorenz

Devin Absher

Lalita Shevde-Samant

Document Type

Dissertation

Date of Award

2020

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Recent studies have identified elevated levels of a small metabolite, L-2 Hydroxyglutare (L-2HG), which curiously has no known metabolic roles. Renal tumors, hypoxia as well as larval development, specifically in Drosophila, all have been identified to have high levels of L-2HG. These broad categories suggest L-2HG has a physiological role. This work uncovers the impact of elevated levels of L-2HG in altering normal kidney and renal tumors. With structural similarity to α-Ketoglutarate (αKG), L-2HG acts as a competitive inhibitor to enzymes that utilize αKG as substrates or co-factors. L-2HG is known to be metabolized by L-2HG dehydrogenase (L2HGDH). Loss of L2HGDH leads to elevated L-2HG levels. Despite being highly expressed in the kidney; previous research has not explored L2HGDH’s role in renal metabolism. In this study, we demonstrate L-2HG both decreases TCA cycle flux and inhibits the biosynthesis of the non-essential amino acid serine. A CRISPR/Cas9 whole body L2hgdh knockout led to the discovery of L-2HG enzymatically inhibiting Krebs Cycle enzyme α-Ketoglutarate dehydrogenase, lowering succinate levels and TCA cycle flux. In addition, serine becomes an essential amino acid in renal cancer in high L-2HG states by lowering levels of Phosphoglycerate dehydrogenase (PHGDH) and its transcription factor Activating transcription factor 4 (ATF4). L-2HG transcriptionally represses PHGDH by maintaining histone repressive mark H3K9me3 through inhibiting Lysine demethylase 4C (KDM4C). Further, L-2HG inhibits ATF4 translation by maintaining methylation in ATF4’s mRNA through inhibiting N6-methyladenosine (m6A) demethylase α-Ketoglutarate-dependent dioxygenase alkB homolog 5 (ALKBH5). Methylated ATF4 mRNA is unable to be translated and does not activate PHGDH transcription. Renal cancer, therefore, is found to depend on exogenous serine to maintain proliferation and glutathione pools. Ultimately, it was identified that amino acid transporter SLC38A2 is necessary for extracellular serine uptake. Previous work has identified heterozygous loss of L2HGDH in Renal Cancer to contribute to raising levels of L-2HG. Surprisingly, there exists a large population of renal tumors with elevated L-2HG levels without chromosomal L2HGDH loss. Bioinformatically, Peroxisome proliferator-activated receptor gamma coactivator -1α was identified as an additional contributor to raising L-2HG levels in renal cancer. Ultimately, elevated L-2HG increases tumorigenicity in renal cancer, but also exposes renal cancer to possible new therapeutic strategies.

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