Research Article: Pleiotropic Effect of a High Resolution Mapped Blood Pressure QTL on Tumorigenesis

Date Published: April 13, 2016

Publisher: Public Library of Science

Author(s): Xi Cheng, Harshal Waghulde, Blair Mell, Kathryn Smedlund, Guillermo Vazquez, Bina Joe, Michael Bader.

http://doi.org/10.1371/journal.pone.0153519

Abstract

This study is focused on a translationally significant, genome-wide-association-study (GWAS) locus for cardiovascular disease (QT-interval) on human chromosome 17. We have previously validated and high resolution mapped the homologous genomic segment of this human locus to <42.5 kb on rat chromosome 10. This <42.5 kb segment in rats regulates both QT-interval and blood pressure and contains a single protein-coding gene, rififylin (Rffl). The expression of Rffl in the hearts and kidneys is differential between Dahl S and S.LEW congenic rats, which are the strains used for mapping this locus. Our previous study points to altered rate of endocytic recycling as the underlying mechanism, through which Rffl operates to control both QT-interval and blood pressure. Interestingly, Rffl also contributes to tumorigenesis by repressing caspases and tumor suppressor genes. Moreover, the expression of Methyl-CpG Binding Domain Protein 2 (Mbd2) in the hearts and kidneys is also higher in the S.LEW congenic strain than the background (control) Dahl S strain. Mbd2 can repress methylated tumor suppressor genes. These data suggest that the S.LEW congenic strain could be more susceptible to tumorigenesis. To test this hypothesis, the S and S.LEW strains were compared for susceptibility to azoxymethane-induced colon tumors. The number of colon tumors was significantly higher in the S.LEW congenic strain compared with the S rat. Transcriptomic analysis confirmed that the chemical carcinogenesis pathway was significantly up-regulated in the congenic strain. These studies provide evidence for a GWAS-validated genomic segment on rat chromosome 10 as being important for the regulation of cardiovascular function and tumorigenesis.

Partial Text

This study is focused on a genome-wide-association-study (GWAS) locus for QT-intervals on human chromosome 17 [1]. In our previous study, we have already validated and high resolution mapped the homologous genomic segment of this human locus to <42.5 kb on rat chromosome 10. This was done by generating and characterizing S.LEW congenic rats with chromosomal segments from the normotensive Lewis (LEW) rat introgressed onto the genetic background of the hypertensive Dahl salt-sensitive (S) rat [2–7]. The locus in rats regulates both QT-interval and blood pressure and contains a single protein-coding gene, rififylin (Rffl) [7]. While there are no exonic variants, the expression of Rffl in the hearts and kidneys is differential between Dahl S and S.LEW congenic rats, which are the strains used for mapping this locus [7, 8]. Our study points to the altered rate of endocytic recycling as the underlying mechanism, through which Rffl operates to control both cardiac QT-intervals and blood pressure [7]. The congenic rat models have been widely used as valuable genetic tools to explore the underlying mechanism of the origin and development of different diseases, including cancer and hypertension. For example, Schaffer BS, et al generated a panel of congenic rat strains to precisely map Emca8, a QTL located on rat chromosome 5, as genetic determinants of breast cancer susceptibility [17]. To identify blood pressure quantitative trait loci (BP QTLs) on the rat genome, our laboratory has generated several S.LEW congenic strains by transferring chromosomal segments from the normotensive Lewis (LEW) rat onto the genetic background of the hypertensive Dahl S rat. In one of the S.LEW congenic strains, which contains LEW alleles within the <42.5 kb BP QTL region, blood pressure was significantly increased and QT-intervals were significantly shorter compared with the S rat [7]. This BP QTL in rats contains only a single protein-coding gene, rififylin (Rffl). The expression of Rffl was significantly higher in the hearts and kidneys of the S.LEW congenic strain compared with S and the overexpression of Rffl is known to delay endocytic recycling, which has been functionally linked to hypertension [7, 8]. Intriguingly, Rffl plays an important role in the regulation of tumorigenesis by mediating tumor suppressor genes and regulating the tumor cell migration [9–11]. Further, the previous microarray study showed that Methyl-CpG Binding Domain Protein 2 (Mbd2), which functions as a transcription repressor of tumor suppressor genes, was expressed higher in the hearts (Table 2 in Reference [7]) and kidneys (Table A1 in Reference [8]) of the S.LEW congenic strain compared with S. The overexpression of these two tumor-related genes suggests that the S.LEW congenic strain could be more susceptible to tumorigenesis. After receiving the chemical carcinogen azoxymethane (AOM) to induce colorectal carcinogenesis, the number of colon tumors was significantly higher in the S.LEW congenic strain compared with S (Fig 1B). Using the colon tissues from these tumor rats, the microarray and real-time PCR results both showed that colon Mbd2 was expressed higher in the S.LEW congenic strain compared with S (Fig 3). Consistently, the S.LEW congenic strain, which had more colon tumors, had lower apoptotic level in the colon (Fig 2). All of these results demonstrate the pleiotropic effects of this <42.5 kb genomic segment on both cardiovascular regulation and tumorigenesis.   Source: http://doi.org/10.1371/journal.pone.0153519