ABSTRACT
Heterokonts, Alveolata protists, green algae from Charophyta and Chlorophyta divisions, and all Embryophyta plants possess an aldehyde dehydrogenase (ALDH) gene named ALDH12. Here, we provide a biochemical characterization of two ALDH12 family members from the lower plant Physcomitrella patens and higher plant Zea mays. We show that ALDH12 encodes an NAD+-dependent glutamate γ-semialdehyde dehydrogenase (GSALDH), which irreversibly converts glutamate γ-semialdehyde (GSAL), a mitochondrial intermediate of the proline and arginine catabolism, to glutamate. Sedimentation equilibrium and small-angle X-ray scattering analyses reveal that in solution both plant GSALDHs exist as equilibrium between a domain-swapped dimer and the dimer-of-dimers tetramer. Plant GSALDHs share very low-sequence identity with bacterial, fungal, and animal GSALDHs (classified as ALDH4), which are the closest related ALDH superfamily members. Nevertheless, the crystal structure of ZmALDH12 at 2.2-Šresolution⯠shows that nearly all key residues involved in the recognition of GSAL are identical to those in ALDH4, indicating a close functional relationship with ALDH4. Phylogenetic analysis suggests that the transition from ALDH4 to ALDH12 occurred during the evolution of the endosymbiotic plant ancestor, prior to the evolution of green algae and land plants. Finally, ALDH12 expression in maize and moss is downregulated in response to salt and drought stresses, possibly to maintain proline levels. Taken together, these results provide molecular insight into the biological roles of the plant ALDH12 family.
Subject(s)
Aldehyde Dehydrogenase/chemistry , Plants/chemistry , Proline/chemistry , Crystallography, X-Ray/methods , Phylogeny , Substrate SpecificityABSTRACT
Purpose: To determine expression levels of CD44 and ALDH1/2, known cancer stem cell (CSC) markers, in stomach adenocarcinomas and assess relationships with clinicopathologic parameters and prognosis. Methods: Eighty patients diagnosed with gastric cancer between the years 2011-2015 were included in this study of clinicopathologic characteristics, postoperative prognostic indexes and stem cell marker CD44 and ALDH1/2 expression in paraffin-embedded tumour sections analyzed immunohistochemically. Clinicopathologic parameters were evaluated using the chi-square test and t-test. Survival analyses were conducted using Kaplan-Meier statistics. Results: We observed positive CD44 and ALDH1/2 staining in 45.0 % and 67.5% of tumour tissues, respectively, but not in normal gastric mucosa. Recurrence-free survival (RFS) was found to be shorter in cases with high levels of CD44 expression (p=0.004). Similarly, short RFS was observed in patients with high levels of CD44 and ALDH1/2 co-expression (p=0.004). Furthermore, tumour invasion depth was found to correlate with high CD44 and ALDH1/2 co-expression (p=0.028). Conclusion: The cancer stem cell markers CD44 and ALDH1/2 may indicate poor patient prognosis and play a role in tumour development and invasion.