4-(N,N-dipropylamino)benzaldehyde inhibits the oxidation of all-trans retinal to all-trans retinoic acid by ALDH1A1, but not the differentiation of HL-60 promyelocytic leukemia cells exposed to all-trans retinal.
The signal transduction pathways mediated by retinoic acid play a critical role in the regulation of cell growth and differentiation during embryogenesis and hematopoiesis as well as in a variety of tumor cell lines in culture. Following the reports that two members of the superfamily of aldehyde dehydrogenase (ALDH) enzymes, ALDH1A1 and ALDH1A2, were capable of catalyzing the oxidation of all-trans retinal to all-trans retinoic acid with submicromolar Km values, we initiated an investigation of the ability of 4-(N,N-dipropylamino)benzaldehyde (DPAB) to inhibit the oxidation of retinal by purified mouse and human ALDH1A1. Our results show that DPAB potently inhibits retinal oxidation, with IC50 values of 0.11 and 0.13 microM for purified mouse and human ALDH1A1, respectively. Since the HL-60 human myeloid leukemic cell line has been used extensively to study the retinoic acid induced differentiation of HL-60 cells to granulocytes, and ALDH1A1 activity had previously been reported in HL-60 cells, we investigated the ability of DPAB to block differentiation of HL-60 promyelocytic leukemia cells exposed to retinal in culture. In HL-60 cells coincubated with 1 microM retinal and 50 microM DPAB for 144 hours, cell differentiation was inhibited only 30%. Furthermore, the NAD-dependent oxidation of propanal or retinal was less than 0.05 nmoles NADH formed/min-10(7) cells in spectrophotometric assays using HL-60 cell extracts. Although ALDH1A1 may be the major catalytic activity for retinal oxidation in some retinoid-dependent mouse and Xenopus embryonic tissues and in adult human and mouse hematopoietic stem cells, another catalytic activity appears to synthesize the retinoic acid ligand necessary to stimulate the differentiation of HL-60 cells to end stage granulocytes.
PubMed ID: 11872149
PMC ID: PMC65698
Article link: BMC Pharmacol.
Genes referenced: aldh1a1 aldh1a2
Article Images: [+] show captions
|Figure 1. Chemical structures for ALDH1A1 substrate and inhibitor. (A) substrate: all-trans retinal. (B) inhibitor: 4-(N,N-dipropylamino)benzaldehyde (DPAB).|
|Figure 2. Differentiation response of HL-60 cells to retinoids and ALDH inhibitors. Retinoid concentrations were 1 μM for all-trans retinal (Ral) and all-trans retinoic acid (RA). Inhibitor concentrations were 50 μM for 4-(N,N-dipropylamino)benzaldehyde (DPAB) and 4-(N,N-diethylamino)benzaldehyde (DEAB). Control (black squares). Ral (red diamonds). RA (green circles). Ral + DPAB (dark blue triangles). RA + DPAB (hatched light blue squares). Ral + DEAB (hatched dark red diamonds).|
|Figure 3. A schematic depicting the potential roles of different oxidative enzymes in retinoic acid biosynthesis and the differentiation vs. self-renewal response to the retinoic acid ligand at different stages of hematopoiesis. Hematopoietic stem cell (HSC). All-trans retinal (Ral). All-trans retinoic acid (RA).|