Enzymatic conversion of retinaldehyde to retinoic acid by cloned murine cytosolic and mitochondrial aldehyde dehydrogenases.
Academic Article
Overview
abstract
It has previously been reported that retinaldehyde can be converted to retinoic acid by cytosolic aldehyde dehydrogenase (AHD-2) in liver extracts [Biochem. Pharmacol. 42: 1279-1285 (1991)]. To determine which enzyme(s) carried out this reaction in murine embryonic stem cells, two aldehyde dehydrogenases were cloned; the AHD-2 gene was cloned from a liver cDNA library, and a closely related gene, AHD-M1, was cloned from an embryonic F9 cell cDNA library by conserved oligonucleotide sequence screening. AHD-M1 contained an open reading frame of 1554 base pairs, which encoded 517 amino acids. The AHD-M1 gene encoded a protein with a putative amino acid sequence that was 94% and 97% identical to the mitochondrial aldehyde dehydrogenases of human and rat, respectively, and thus we have cloned the murine cDNA for this enzyme for the first time. The AHD-M1 cDNA was only 64% identical to AHD-2. Northern analysis showed that AHD-M1 mRNA was constitutively expressed in F9 and P19 embryonic teratocarcinoma stem cells and in AB1 embryonic stem cells. There was a 3-5-fold retinoic acid-associated increase in the amount of this mRNA during the differentiation of F9 cells into parietal endoderm. In contrast, we could not detect the expression of AHD-2 mRNA in AB1, P19, or F9 cells, even though the F9 cells could convert retinaldehyde to retinoic acid. When the AHD-M1 and AHD-2 cDNAs were inserted into the expression vector pSG5 and transfected into cultured COS cells, 3-5-fold and 100-fold increases, respectively, in the conversion of [3H]retinaldehyde to [3H]retinoic acid could be detected by high performance liquid chromatographic assay. We conclude that both enzymes are capable of converting retinaldehyde to retinoic acid in intact COS cells. AHD-2 is more active than AHD-M1 in this conversion, but AHD-2 is not the enzyme responsible for this conversion in F9 embryonic stem cells.
