Promoter Haplotypes of the ABCB1 Gene Encoding the P-Glycoprotein Differentially Affect Its Promoter Activity by Altering Transcription Factor Binding

Regulation of P-Glycoprotein during Oxidative Stress

P-glycoprotein (Pgp, ABCB1, MDR1) is an efflux transporter protein that removes molecules from the cells (outflow) into the extracellular space. Pgp plays an important role in pharmacokinetics, ensuring the absorption, distribution, and excretion of drugs and its substrates, as well as in the transport of endogenous molecules (steroid and thyroid hormones). It also contributes to tumor cell resistance to chemotherapy. In this review, we summarize the mechanisms of Pgp regulation during oxidative stress. The currently available data suggest that Pgp has a complex variety of regulatory mechanisms under oxidative stress, involving many transcription factors, the main ones being Nrf2 and Nf-kB. These factors often overlap, and some can be activated under certain conditions, such as the deposition of oxidation products, depending on the severity of oxidative stress. In most cases, the expression of Pgp increases due to increased transcription and translation, but under severe oxidative stress, it can also decrease due to the oxidation of amino acids in its molecule. At the same time, Pgp acts as a protector against oxidative stress, eliminating the causative factors and removing its by-products, as well as participating in signaling pathways.

Effect of polymorphisms in the 5’-flanking sequence of MC1R on feather color in Taihang chickens

MC1R plays an important role in the regulation of the formation, transfer, and deposition of melanin in animals and is important for determining coat color. Many studies have reported on single nucleotide polymorphisms (SNPs) in the coding sequence of MC1R. However, few studies have investigated the polymorphisms in the 5’-flanking sequence of MC1R. In this study, we sequenced 2000 bp of the 5’-flanking sequence of MC1R in 300 Taihang chickens with brown feathers (MTH) and 300 Taihang chickens with black feathers (HTH). The sequencing results showed that 4 SNPs (MC1R g.18838722 G > C, g.18838624 T > C, g.18838694 G > A, and g.18838624 C > T) were located in the 5’-flanking sequence of MC1R between the MTH and HTH groups. Association analysis showed that there was a significant correlation between the 4 SNPs and feather color in Taihang chickens. The correlation between MC1R g.18838624 T >C and feather color of Taihang chicken was 100%, of which the CC (E1) genotype is MTH and the TT (E2) genotype is HTH. Furthermore, there was a significant correlation between MC1R g.18838624 T > C and egg production at 302 d. E1 (184.14 ± 0.674) was significantly higher than that in E2 (181.75 ± 0.577) (P < 0.05). Luciferase reporter assays were used to detect the transcriptional activity of MC1R with different SNP genotypes. The results showed that the luciferase activity of E2 was significantly higher than that of E1 (P < 0.05). In addition, transcription factor-binding site predictions showed that E2 creates a new binding site for ZEB1. RT‒qPCR results revealed that the expression of MC1R in E2 was significantly lower than that in E1 (P < 0.05), and the expression of ZEB1 in E2 was significantly higher than that in E1 (P < 0.05). Overexpression and shRNA experiments demonstrated that ZEB1 regulates the expression of MC1R in DF1 cells. ZEB1 has a negative regulatory effect on the transcriptional activity of MC1R; it inhibits the expression of MC1R and affects the feather color of Taihang chickens. This study provides new insight into the molecular mechanism of feather color formation and the transcriptional regulation of MC1R in Taihang chickens.

Phytochemicals reverse P-glycoprotein mediated multidrug resistance via signal transduction pathways

P-glycoprotein, encoded by ATP-binding cassette transporters B1 gene (ABCB1), renders multidrug resistance (MDR) during cancer chemotherapy. Several synthetic small molecule inhibitors affect P-glycoprotein (P-gp) transport function in MDR tumor cells. However, inhibition of P-gp transport function adversely accumulates chemotherapeutic drugs in non-target normal tissues. Moreover, most small-molecule P-gp inhibitors failed in the clinical trials due to the low therapeutic window at the maximum tolerated dose. Therefore, downregulation of ABCB1-gene expression (P-gp) in tumor tissues seems to be a novel approach rather than inhibiting its transport function for the reversal of multidrug resistance (MDR). Several plant-derived phytochemicals modulate various signal transduction pathways and inhibit translocation of transcription factors, thereby reverses P-gp mediated MDR in tumor cells. Therefore, phytochemicals may be considered an alternative to synthetic small molecule P-gp inhibitors for the reversal of MDR in cancer cells. This review discussed the role of natural phytochemicals that modulate ABCB1 expression through various signal transduction pathways in MDR cancer cells. Therefore, modulating the cell signaling pathways by phytochemicals might play crucial roles in modulating ABCB1 gene expression and the reversal of MDR.

Genetic Association of Solute Carrier Transporter Gene Variants with Metformin Response

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by elevated blood glucose levels and is influenced by both genetic and environmental factors. It is treated with various classes of oral antidiabetic drugs, however, response to treatment is highly variable with patients failing to achieve adequate glycemic control. Treatment response variability has been associated with single nucleotide polymorphisms (SNPs) which influence the pharma-cokinetics and pharmacodynamics of drug(s). The aim of this study was to evaluate the genetic association of 17 SNPs and the response to metformin therapy in patients diagnosed with diabetes from the indigenous Nguni population of South Africa. One hundred and forty indigenous African patients diagnosed with T2DM were recruited and genotyped using the MassARRAY® system. Therapeutic response of patients was ascertained by a change in Hb A1c. Two SNPs (rs1801282 and rs6265) were monomorphic. All other variants were within the Hardy-Weinberg equilibrium (HWE). The T allele of the SLC variant rs316009 [odds ratio (OR) = 0.25, 95% confidence interval (95% CI) = 0.01-0.09, p value = 0.044] and the CT genotype of the PCK1 variant rs4810083 (OR = 2.80, 95% CI = 1.01-7.79, p value = 0.049) were associated with an improved response to treatment after adjustment. No association was observed with post Bonferroni correction. Moreover, this study provides important additional data regarding possible associations between genetic variants and metformin therapy outcomes. In addition, this is one of the first studies providing genetic data from the understudied indigenous sub-Saharan African populations.

A T > G Mutation in the NR5A2 Gene Is Associated With Litter Size in Hu Sheep Through Upregulation of Promoter Activity by Transcription Factor MTF-1

Nuclear receptor subfamily 5 group A member 2 (NR5A2), also referred to as LRH-1 or FTF, is an orphan nuclear hormone receptor that is involved in regulating embryonic development, ovarian granulosa cell differentiation, gonadal sex differentiation, and steroidogenesis in mammals. However, little is known about how NR5A2 regulates reproduction in sheep. In this study, we amplified the promoter sequence of NR5A2 and determined that its core promoter region ranged from -721 nt to -281 nt. A T > G polymorphism at -700 nt was detected in the core promoter region. Association analysis found that the litter sizes of Hu ewes at their second and average parities with genotype GG (2.20 ± 0.20 and 1.97 ± 0.06, respectively) were significantly higher than those of ewes with genotype TG (1.68 ± 0.10 and 1.74 ± 0.05, respectively) (p < 0.05) and TT (1.67 ± 0.10 and 1.62 ± 0.06, respectively) (p < 0.05). The litter size of Hu ewes at their third parity with genotype GG (2.10 ± 0.10) was significantly higher than that of ewes with genotype TT (1.56 ± 0.12) (p < 0.05). A luciferase assay showed that the -700G allele increased the luciferase activity relative to the -700T allele. Furthermore, the -700T > G polymorphism created a novel binding site for metal-regulatory transcription factor 1 (MTF-1). A competitive electrophoretic mobility shift assay confirmed that MTF-1 specifically bound with the G-type promoter of NR5A2. An overexpression experiment demonstrated that MTF-1 was involved in the alteration of NR5A2 transcription activity and further increased NR5A2 gene mRNA expression. Our findings revealed that the -700T > G polymorphism promoted NR5A2 expression due to the positive effects on NR5A2 gene transcription activity by MTF-1 and thereby increased fecundity in Hu sheep.