Reply to the comment of Ana I. Alvarez and Gracia Merino regarding “Assessment of ABCG2-mediated transport of xenobiotics across the blood-milk barrier of dairy animals using a new MDCKII in vitro model” by Wassermann et al. 2013

Abstract

June 2009) and GQ141082 (oABCG2: submitted on 3 July 2009). These generated ABCG2 full-length clones consist of the open reading frame (ORF) sequence as well as an 5′ untranslated region (5′-UTR) where regulatory elements are located. In this context, we identified besides other regulatory elements such as SP-1 and AP-1 aryl hydrocarbon receptor response elements (AhRE) in the bovine as well as the caprine ABCG2 5′-UTR (Wassermann et al. 2013). In further mechanistic studies, we showed that the functional expression of ABCG2 was induced due to binding of ligand-activated AhR to AhRE sequences in the ABCG2 5′-UTR (Halwachs et al. 2012). Merino and coworkers (Merino et al. 2009) as well as Real and coworkers (Real et al. 2011) did not provide NCBI accession numbers for the hepatocellular ABCG2 cDNA sequences in their publications. To our knowledge, the NCBI database entry (NM_001037478) from Real et al. was first published and accessible in June 2012. Since then, it was not possible to perform sequence analysis to determine cDNA sequence homology between the bovine hepatocellular and mammary ABCG2 clones. In addition, we did not only generate a full-length bovine mammary ABCG2 cDNA sequence but also caprine and ovine mammary ABCG2 sequences. In this context, differences between the three species occurred regarding the ABCG2 cDNA as well as protein sequences (Wassermann et al. 2013). Former studies (Wassermann et al. 2013) as well as the present publication additionally revealed species-dependent differences regarding the substrate specificity of the generated MDCKII-ABCG2 cell lines. However, the aim of our research was to generate tissue-specific full-length ABCG2 cDNA clones to investigate the influence of xenobiotics on the tissue-specific expression of ABCG2. In this context, the generated MDCKII cell lines stably expressing bABCG2, cABCG2 or oABCG2 represent a new in vitro model. “However, to the best of our knowledge, there is no report of any difference in the ABCG2 cDNA sequence due to the tissue source used for cloning. Thus, an in vitro model to study ABCG2-mediated transport across a physiologically normal barrier was firstly generated by Real et al.” Earlier studies in our research group provided insights into tissue-specific differences in the expression of membranous transporters such as the uptake transporter Rfc-1 (Slc19a1) (Kneuer et al. 2004; Schrader et al. 2006). However, in context with ABC transporter, data on tissue-specific expression are sparse (Brayden et al. 2010). So far, only species-dependent differences in the functional activity and inhibitory potency have been reported for ABC transporter such as ABCB1 (Schrickx and Fink-Gremmels 2008). In the present study, we used an MDCKII in vitro model stably expressing mammary ABCG2 to investigate tissuespecific ABCG2-mediated transport processes. Therefore, the bovine (bABCG2), caprine (cABCG2) or ovine (oABCG2) ABCG2 was isolated from the lactating mammary gland (Wassermann et al. 2013). In this context, we generated full-length bABCG2, cABCG2 or oABCG2 mRNA-derived cDNA sequences as described recently and published the respective sequences at the NCBI database (http://www.ncbi.nlm.nih.gov/) under the following accession numbers: EU570105 (bABCG2: submitted on 14 April 2008), GQ241418 (cABCG2: submitted on 3

DOI: 10.1007/s00204-013-1126-1

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@article{Wassermann2013ReplyTT, title={Reply to the comment of Ana I. Alvarez and Gracia Merino regarding “Assessment of ABCG2-mediated transport of xenobiotics across the blood-milk barrier of dairy animals using a new MDCKII in vitro model” by Wassermann et al. 2013}, author={Louise Wassermann and Sandra Halwachs and Daniela Baumann and Ingo Sch{\"a}fer and Peter Seibel and Walther Honscha}, journal={Archives of Toxicology}, year={2013}, volume={87}, pages={1865-1867} }