Human leukocyte antigen class-I variation is associated with atopic dermatitis: A case-control study.

Atopic dermatitis (AD) is a common immune-medicated skin disease. Previous studies have explored the relationship between Human Leukocyte Antigen (HLA) allelic variation and AD with conflicting results. The aim was to examine HLA Class I genetic variation, specifically peptide binding groove variation, and associations with AD. A case-control study was designed to evaluate HLA class I allelic variation and binding pocket polymorphisms, using next generation sequencing on 464 subjects with AD and 388 without AD. Logistic regression was used to evaluate associations with AD by estimating odds ratios (95% confidence intervals). Significant associations were noted with susceptibility to AD (B*53:01) and protection from AD (A*01:01, A*02:01, B*07:02 and C*07:02). Evaluation of polymorphic residues in Class I binding pockets revealed six amino acid residues conferring protection against AD: A9F (HLA-A, position 9, phenylalanine) [pocket B/C], A97I [pocket C/E], A152V [pocket E], A156R [pocket D/E], B163E [pocket A] and C116S [pocket F]. These findings demonstrate that specific HLA class I components are associated with susceptibility or protection from AD. Individual amino acid residues are relevant to protection from AD and set the foundation for evaluating potential HLA Class I molecules in complex with peptides/antigens that may initiate or interfere with T-cell responses.

beta-Carotene production and its role in sclerotial differentiation of Sclerotium rolfsii.

The fungus Sclerotium rolfsii produces beta-carotene, the main detected carotenoid, in levels dependent upon oxidative growth conditions and upon differentiation. beta-Carotene accumulation is 5-, 6.5-, and 6.7-fold higher in undifferentiated mycelia, sclerotia, and differentiated mycelia, respectively, at high than at low oxidative stress. It accumulates more in older than in younger mycelia and is 2-fold higher in differentiated than in undifferentiated mycelia. We propose that beta-carotene is formed possibly to help the fungus reduce oxidative stress that develops during growth. This is supported by the finding that exogenous beta-carotene at non-growth-inhibiting concentrations causes a concentration-dependent reduction of oxidative stress (lipid peroxidation) of undifferentiated mycelia, which results in an equally proportional reduction of sclerotial differentiation. The data of this study support our hypothesis that sclerotial differentiation is induced by oxidative stress.

Alteration in the retinoid specificity of retinoic acid receptor-beta by site-directed mutagenesis of Arg269 and Lys220.

Retinoic acid receptor-beta (RAR-beta) specifically binds retinoic acid (RA) and functions as a RA-inducible transcriptional regulatory factor. Simultaneous mutation of Arg269 and Lys220 of RAR-beta to Ala results in a dramatic reduction in both transactivation and affinity for RA along with creating a RA concentration-dependent dominant negative mutant. In this report, we found that mutation of these two amino acid residues singly and simultaneously to Gln results in mutant RAR-beta s, each displaying a more dramatic reduction in transactivation and affinity for RA than their corresponding Ala mutant, with the R269Q more profoundly affected than K220Q. Furthermore, we examined both the Ala and Gln mutants for their ability to transactivate and bind two other retinoids with different functional end groups (all-trans-retinol and all-trans-retinal). Mutation of Lys220 to either an Ala or a Gln favors transactivation and binding of retinal, while mutation of either Lys220 or Arg269 to Gln favors retinol transactivation and binding. Taken together, these results suggest that Arg269 and Lys220 lie within the ligand binding pocket of RAR-beta and Lys220 lie within the ligand binding pocket of RAR-beta and that these two amino acid residues play an important role in determining retinoid specificity most likely by directly interacting with the carboxylate group of RA.

Arg269 and Lys220 of retinoic acid receptor-beta are important for the binding of retinoic acid.

Retinoic acid receptors, RARs, are retinoic acid (RA)-inducible transcriptional regulatory proteins which transduce the RA signal at the level of gene expression via a retinoic acid response element. Three subtypes of RARs have been described termed RAR-alpha, RAR-beta, and RAR-gamma. RARs, like other members of the steroid/thyroid hormone receptor family, are composed of six structurally distinct domains, one of which is responsible for binding RA. No structural information is available concerning the nature of the amino acids which are responsible for binding of RA within the ligand binding domain of any RAR. In this report, the role of 2 positively charged amino acids of RAR-beta for binding of RA, Arg269 and Lys220, was examined using site-directed mutagenesis. When compared with wild type RAR-beta, mutation of either Arg269 or Lys220 singly to the small neutral amino acid Ala had only a small effect on both the EC50 value in all-trans-RA and 9-cis-RA transactivation assays and the apparent Kd for all-trans-RA. However, mutation of both of these positively charged amino acids simultaneously to Ala caused a 500- and 100-fold elevation in the EC50 for all-trans-RA and 9-cis-RA, respectively, compared with that of wild type RAR-beta. Similarly, the apparent Kd for all-trans-RA was increased 580-fold when that of the double mutant was compared with that of the wild type RAR-beta. Furthermore, this double mutant RAR-beta acted as a dominant negative mutant when transfected with wild type RAR-alpha, -beta, or -gamma in a RA concentration-dependent fashion. Taken together these data demonstrate the importance of both Arg269 and Lys220 of RAR-beta for the binding of RA, possibly by interacting with the negatively charged carboxyl group of RA.

Induction of RAR-beta 2 gene expression in embryos and RAR-beta 2 transactivation by the synthetic retinoid Ro 13-6307 correlates with its high teratogenic potency.

Vitamin A (retinol), its metabolite all-trans retinoic acid (RA), and many synthetic analogs (retinoids) express variable potencies as teratogens. Although biological activities of retinoids are mediated by nuclear RA receptors (RARs) and retinoid X receptors (RXRs), it is not known if any of these receptors mediate teratogenicity, and if the potency also depends on the nature of the ligand-receptor interactions. Previous evidence has implicated that one specific isoform, RAR-beta 2, does play a role in mediating retinoid teratogenicity. Here, we employed an aromatic retinoid with a triene side chain, Ro 13-6307, to study its interactions with RAR-beta 2 since its teratogenicity is much higher and its accessibility to the embryo is much lower than RA. A fully teratogenic dose of Ro 13-6307 (10 mg-kg) given to pregnant mice preferentially elevated the level of RAR-beta 2 mRNA in susceptible embryonic regions (maximal induction, 10- to 12-fold above control in limb buds) in a manner comparable to a fully teratogenic dose of all-trans RA (100 mg-kg). Using the RAR-beta 2 promoter linked to a reporter gene in cotransfection experiments, the efficacy of Ro 13-6307 and RAR-beta 2 in transcription transactivation was found to be 30-40 times greater than all-trans RA. Since the teratogenic potency of Ro 13-6307 is estimated from a previous study to be 44-fold greater than all-trans RA, we suggest that the teratogenicity of this synthetic retinoid is generally proportional to its ability to enhance receptor function.