The Effects of Human BDH2 on the Cell Cycle, Differentiation, and Apoptosis and Associations with Leukemia Transformation in Myelodysplastic Syndrome.

Iron overload is related to leukemia transformation in myelodysplastic syndrome (MDS) patients. Siderophores help to transport iron. Type 2-hydroxybutyrate dehydrogenase (BDH2) is a rate-limiting factor in the biogenesis of siderophores. Using qRT-PCR, we analyze BDH2mRNA expression in the bone marrow (BM) of 187 MDS patients, 119 de novo acute myeloid leukemia (AML) patients, and 43 lymphoma patients with normal BM. Elevated BDH2mRNA expression in BM is observed in MDS patients (n = 187 vs. 43, normal BM; P = 0.009), and this is related to ferritin levels. Patients with higher BDH2 expression show a greater risk of leukemia progression (15.25% vs. 3.77%, lower expression; P = 0.017) and shorter leukemia-free-survival (medium LFS, 9 years vs. 7 years; P = 0.024), as do patients with a ferritin level ≥350 ng/mL. Additionally, we investigate the mechanisms related to the prognostic ability of BDH2 by using BDH2-KD THP1. The cell cycle analysis, surface markers, and special stain studies indicate that BDH2-KD induces differentiation and decreases the growth rate of THP1 cells, which is associated with the retardation of the cell cycle. Moreover, many genes, including genes related to mitochondrial catabolism, oncogenes, tumor suppressor genes, and genes related to cell differentiation and proliferation influence BDH2-KD THP1 cells. Herein, we demonstrate that BDH2 is involved in cell cycle arrest and the inhibition of differentiation in malignant cells. Furthermore, the high BDH2 expression in MDS patients could be suggestive of a poor prognostic factor. This study provides a foundation for further research on the roles of BDH2 and iron metabolism in the pathogenesis of MDS.

Involvement of tyrosyl residues in the structure-function relationships of D-beta-hydroxybutyrate dehydrogenase: a phospholipid-requiring enzyme.

The involvement of tyrosyl residues in the function of D-beta-hydroxybutyrate dehydrogenase, a lipid-requiring enzyme, has been investigated by using several tyrosyl modifying reagents, i.e., N-acetylimidazole, a hydrophilic reagent, and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and tetranitromethane, two hydrophobic reagents. Modification of the tyrosyl residues highly inactivates the derived enzyme: Treatment of the enzyme with 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole leads to an absorbance at 380 nm and to an incorporation of about 1 mol of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole per polypeptide chain for complete inactivation. Inactivation by N-acetylimidazole induces a decrease in absorbance at 280 nm which can be reversed by hydroxylamine treatment. On the other hand, the ligands of the active site, such as methylmalonate, a pseudosubstrate, and NAD+ (or NADH), do not protect the enzyme against inactivation. In contrast, the presence of phospholipids strongly protects the enzyme against hydrophobic reagents. Finally, previous modification of the enzyme with N-acetylimidazole does not affect the incorporation of 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole while modification with tetranitromethane does. These results indicate the existence of two classes of tyrosyl residues which are essential for enzymatic activity, and demonstrate their location outside of the active site. One of these residues appears to be located close to the enzyme-phospholipid interacting sites. These essential residues may also be essential for maintenance of the correct active conformation.