Effect of rare coding variants of charged amino acid residues on the function of human organic anion transporting polypeptide 1B3 (SLCO1B3)

Human organic anion transporting polypeptide 1B3 (OATP1B3) is more heavily N-glycosylated than OATP1B1 in extracellular loops 2 and 5

Human organic anion transporting polypeptide 1B3 (OATP1B3) and 1B1 are two liver-specific and highly homologous uptake transporters, whose structures consist of 12 transmembrane domains. The present study showed that OATP1B3 is more heavily N-glycosylated than OATP1B1 in extracellular loop 2 (EL2) and EL5. OATP1B3 has six N-glycosylation sites, namely N134, N145, N151, N445, N503, and N516, which is twice of that of OATP1B1. Single removal of individual N-glycans seems to have minimal influence on the surface expression and function of OATP1B3. However, simultaneous removal of all N-glycans will lead to OATP1B3's large retention in the endoplasmic reticulum and cellular degradation and thus significantly disrupts its surface expression. While N-glycosylation plays a crucial role in the surface expression of OATP1B3, it also has some effect on the transport function of OATP1B3 per se, which is not due to a decrease of substrate binding affinity but due to a reduced transporter's turnover number. Taken together, N-glycosylation is essential for normal surface expression and function of OATP1B3. Its disruption by some liver diseases such as NASH might alter the pharmacokinetic/pharmacodynamic properties of OATP1B3's substrate drugs.

Reconstructing the ancestral gene pool to uncover the origins and genetic links of Hmong-Mien speakers

BACKGROUND

Hmong-Mien (HM) speakers are linguistically related and live primarily in China, but little is known about their ancestral origins or the evolutionary mechanism shaping their genomic diversity. In particular, the lack of whole-genome sequencing data on the Yao population has prevented a full investigation of the origins and evolutionary history of HM speakers. As such, their origins are debatable.

RESULTS

Here, we made a deep sequencing effort of 80 Yao genomes, and our analysis together with 28 East Asian populations and 968 ancient Asian genomes suggested that there is a strong genetic basis for the formation of the HM language family. We estimated that the most recent common ancestor dates to 5800 years ago, while the genetic divergence between the HM and Tai-Kadai speakers was estimated to be 8200 years ago. We proposed that HM speakers originated from the Yangtze River Basin and spread with agricultural civilization. We identified highly differentiated variants between HM and Han Chinese, in particular, a deafness-related missense variant (rs72474224) in the GJB2 gene is in a higher frequency in HM speakers than in others.

CONCLUSIONS

Our results indicated complex gene flow and medically relevant variants involved in the HM speakers' evolution history.

The Importance of Val386 in Transmembrane Domain 8 for the Activation of OATP1B3 by Epigallocatechin Gallate

Estrone-3-sulfate (E3S) uptake mediated by organic anion transporting polypeptide 1B3 (OATP1B3) can be activated by epigallocatechin gallate (EGCG). In this study, by using chimeric transporters and site-directed mutagenesis, we found that Val386 in transmembrane domain 8 (TM8) is essential for OATP1B3's activation by EGCG. Kinetic studies showed that the loss of activation of 1B3-TM8 and 1B3-V386F in the presence of EGCG is due to their decreased substrate binding affinity and reduced maximal transport rate. The overall transport efficiencies of OATP1B3, 1B3-TM8, and 1B3-V386F in the absence and presence of EGCG are 8.6 ± 0.7 vs 15.9 ± 1.4 (p < 0.05), 11.2 ± 2.1 vs 2.7 ± 0.3 (p < 0.05), and 10.2 ± 1.0 vs 2.5 ± 0.3 (p < 0.05), respectively. While 1B3-V386F cannot be activated by EGCG, its transport activity for EGCG is also diminished. OATP1B3's activation by EGCG is substrate-dependent as EGCG inhibits OATP1B3-mediated pravastatin uptake. Furthermore, the activation of OATP1B3-mediated E3S uptake by quercetin 3-O-α-l-arabinopyranosyl(1 → 2)-α-l-rhamnopyranoside is not affected by TM8 and V386F. Taken together, the activation of OATP1B3 by small molecules is substrate- and modulator-dependent, and V386 in TM8 plays a critical role in the activation of OATP1B3-mediated E3S uptake by EGCG.

Human Organic Anion Transporting Polypeptides 1B1, 1B3, and 2B1 Are Involved in the Hepatic Uptake of Phenolsulfonphthalein

Phenolsulfonphthalein (PSP or phenol red), a sulfonphthalein dye, has been used as a diagnostic agent and a pH indicator in cell culture medium. After administered into the body, PSP is excreted into urine and bile. The urinary excretion of PSP is mediated by organic anion transporter 1/3 (OAT1/3) and multidrug resistance protein 2 (MRP2). In biliary excretion, PSP is effluxed from hepatocytes into the bile via MRP2. However, so far, the molecular mechanism for PSP transport from the blood into hepatocytes is unclear. In the present study, six human major hepatic uptake transporters expressed on the basolateral membrane of hepatocytes, namely, organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, OATP2B1, Na+/taurocholate cotransporting polypeptide (NTCP), organic cation transporter 1 (OCT1), and OAT2, have been investigated to see whether they are involved in the hepatic uptake of PSP. An in vitro cell-based study demonstrated that PSP is a substrate for OATP1B1, OATP1B3, and OATP2B1, with OATP1B3 showing the highest transport efficiency. The K m values for OATP1B1-, OATP1B3-, and OATP2B1-mediated PSP uptake were 11.3 ± 1.5, 7.0 ± 1.5, and 5.1 ± 1.0 μM, respectively. PSP interacts with known OATP substrates/inhibitors. However, the presence of PSP in cell culture medium has no significant effect on OATP's function. In vivo pharmacokinetic study in wild-type and Oatp1b2-knockout mice showed that Oatp1b2-knockout led to elevated plasma concentration and decreased liver accumulation of PSP. Taken together, the present study showed that in the liver, OATP1B1, OATP1B3, and OATP2B1 are involved in the uptake of PSP from the blood into hepatocytes, which, along with MRP2-mediated efflux of PSP from hepatocytes into the bile, constitute the vectorial transport of PSP from the blood to the bile and may play a critical role in the biliary excretion of PSP.