The role of 17βHSDs in breast tissue and breast cancers

Structural basis of lipid-droplet localization of 17-beta-hydroxysteroid dehydrogenase 13

Hydroxysteroid 17-beta-dehydrogenase 13 (HSD17B13) is a hepatic lipid droplet-associated enzyme that is upregulated in patients with non-alcoholic fatty liver disease. Recently, there have been several reports that predicted loss of function variants in HSD17B13 protect against the progression of steatosis to non-alcoholic steatohepatitis with fibrosis and hepatocellular carcinoma. Here we report crystal structures of full length HSD17B13 in complex with its NAD+ cofactor, and with lipid/detergent molecules and small molecule inhibitors from two distinct series in the ligand binding pocket. These structures provide insights into a mechanism for lipid droplet-associated proteins anchoring to membranes as well as a basis for HSD17B13 variants disrupting function. Two series of inhibitors interact with the active site residues and the bound cofactor similarly, yet they occupy different paths leading to the active site. These structures provide ideas for structure-based design of inhibitors that may be used in the treatment of liver disease.

Aldo-Keto Reductases and Cancer Drug Resistance

Human aldo-keto reductases (AKRs) catalyze the NADPH-dependent reduction of carbonyl groups to alcohols for conjugation reactions to proceed. They are implicated in resistance to cancer chemotherapeutic agents either because they are directly involved in their metabolism or help eradicate the cellular stress created by these agents (e.g., reactive oxygen species and lipid peroxides). Furthermore, this cellular stress activates the Nuclear factor-erythroid 2 p45-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 pathway. As many human AKR genes are upregulated by the NRF2 transcription factor, this leads to a feed-forward mechanism to enhance drug resistance. Resistance to major classes of chemotherapeutic agents (anthracyclines, mitomycin, cis-platin, antitubulin agents, vinca alkaloids, and cyclophosphamide) occurs by this mechanism. Human AKRs also catalyze the synthesis of androgens and estrogens and the elimination of progestogens and are involved in hormonal-dependent malignancies. They are upregulated by antihormonal therapy providing a second mechanism for cancer drug resistance. Inhibitors of the NRF2 system or pan-AKR1C inhibitors offer promise to surmount cancer drug resistance and/or synergize the effects of existing drugs. SIGNIFICANCE STATEMENT: Aldo-keto  reductases (AKRs) are overexpressed in a large number of human tumors and mediate resistance to cancer chemotherapeutics and antihormonal therapies. Existing drugs and new agents in development may surmount this resistance by acting as specific AKR isoforms or AKR pan-inhibitors to improve clinical outcome.

Evaluation of 17β-hydroxysteroid dehydrogenase activity using androgen receptor-mediated transactivation

17β-Hydroxysteroid dehydrogenases (17β-HSDs) catalyze the reduction of 17-ketosteroids and the oxidation of 17β-hydroxysteroids to regulate the production of androgens and estrogens. Among them, 17β-HSD type 3 (HSD17B3) is expressed almost exclusively in testicular Leydig cells and contributes to development of male sexual characteristics by converting androstenedione (A4) to testosterone (T). Mutations of HSD17B3 genes cause a 46,XY disorder of sexual development (46,XY DSD) as a result of low T production. Therefore, the evaluation of 17β-HSD3 enzymatic activity is important for understanding and diagnosing this disorder. We adapted a method that easily evaluates enzymatic activity of 17β-HSD3 by quantifying the conversion from A4 to T using androgen receptor (AR)-mediated transactivation. HEK293 cells were transduced to express human HSD17B3, and incubated medium containing A4. Depending on the incubation time with HSD17B3-expressing cells, the culture media progressively increased luciferase activities in CV-1 cells, transfected with the AR expression vector and androgen-responsive reporter. Culture medium from HSD17B1 and HSD17B5-expressing cells also increased the luciferase activities. This system is also applicable to detect the conversion of 11-ketoandrostenedione to 11-ketotestosterone by HSD17B3. Establishment of HEK293 cells expressing various missense mutations in the HSD17B3 gene associated with 46,XY DSD revealed that this system is effective to evaluate the enzymatic activities of mutant proteins.