Colonic transcriptional response to 1α,25(OH) 2 vitamin D 3 in African- and European-Americans

Abstract

Colorectal cancer (CRC) is a significant health burden especially among African Americans (AA). Epidemiological studies have correlated low serum vitamin D with CRC risk, and, while hypovitaminosis D is more common and more severe in AA, the mechanisms by which vitamin D modulates CRC risk and how these differ by race are not well understood. Active vitamin D (1α,25(OH)2D3) has chemoprotective effects primarily through transcriptional regulation of target genes in the colon. We hypothesized that transcriptional response to 1α,25(OH)2D3 differs between AA and European Americans (EA) irrespective of serum vitamin D and that regulatory variants could impact transcriptional response. We treated ex vivo colon cultures from 34 healthy subjects (16 AA and 18 EA) with 0.1 µM 1α,25(OH)2D3 or vehicle control for 6 hours and performed genome-wide transcriptional profiling. We found 8 genes with significant differences in transcriptional response to 1α,25(OH)2D3 between AA and EA with definitive replication of inter-ethnic differences for uridine phosphorylase 1 (UPP1) and zinc finger-SWIM containing 4 (ZSWIM4). We performed expression quantitative trait loci (eQTL) mapping and identified response cis-eQTLs for ZSWIM4 as well as for histone deacetylase 3 (HDAC3), the latter of which showed a trend toward significant inter-ethnic differences in transcriptional response. Allele frequency differences of eQTLs for ZSWIM4 and HDAC3 accounted for observed transcriptional differences between populations. Taken together, our results demonstrate that transcriptional response to 1α,25(OH)2D3 differs between AA and EA independent of serum 25(OH)D levels . We provide evidence in support of a genetic regulatory mechanism underlying transcriptional differences between populations for ZSWIM4 and HDAC3. Further work is needed to elucidate how response eQTLs modify vitamin D response and whether genotype and/or transcriptional response correlate with chemopreventive effects. Relevant biomarkers, such as tissue-specific 1α,25(OH)2D3 transcriptional response, could identify individuals likely to benefit from vitamin D for CRC prevention as well as elucidate basic mechanisms underlying CRC disparities.

Vitamin D Regulation of the Uridine Phosphorylase 1 Gene and Uridine-Induced DNA Damage in Colon in African Americans and European Americans

“…We used organoids derived from healthy individuals undergoing screening colonoscopies to study 1a,25(OH) 2 D 3 treatment on UPP1 mRNA and protein expression as well as uridine homeostasis. Similar to results from ex vivo colon cultures 12 and cell lines, 1 α ,25(OH) 2 D 3 up-regulated UPP1 3.5-fold in colonic organoids (Figure 5A). Consistent with results from cell lines, human colonic organoids also showed higher of expression of UPP1 protein after 24 hours of treatment with 1 α ,25(OH) 2 D 3 (Figure 4C and 5B).…”

“…Based on results of UPP1 messenger RNA (mRNA) up-regulation in response to 1 α ,25(OH) 2 D 3 in ex vivo primary human colon cultures previously published by our group, 12 we sought to further characterize 1a,25(OH) 2 D 3 regulation of UPP1 using murine and human colonic epithelial cells. Consistent with our results in primary human colon cultures, both murine colonocytes and human colon cancer cells showed UPP1 up-regulation in response to 1 α ,25(OH) 2 D 3 .…”

“…Specifically, European Americans showed consistent up-regulation of UPP1 in response to 1 α ,25(OH) 2 D 3 treatment at 6 hours, whereas African Americans showed little to no induction of UPP1 in response to the same amount of 1 α ,25(OH) 2 D 3 . 12 To validate these interethnic differences in response to 1 α ,25(OH) 2 D 3 , human colonic organoids derived from 5 African Americans and 5 European Americans were examined for UPP1 mRNA and protein expression. We noted significantly increased UPP1 mRNA and protein induction in organoids from European Americans compared with African Americans (Figure 6A and B).…”

“…For organoids, 100 nmol/L 1 α ,25(OH) 2 D 3 was used based on our previous experiments in primary ex vivo colon cultures. 12 The vehicle control for 1 α ,25(OH) 2 D 3 was ethanol.…”

“…To better characterize interethnic differences in host– vitamin D interactions in the colon, we previously used an ex vivo culture model of primary human colon, the target tissue for CRC development and chemoprevention, to identify differences in transcriptome-wide responses to 1 α ,25(OH) 2 D 3 between self-identified African and European Americans. 12 Uridine phosphorylase 1 ( UPP1 ) showed the most significant difference in gene induction in response to 1a,25(OH) 2 D 3 between populations that was validated subsequently in an independent cohort. Specifically, European Americans showed consistent up-regulation of UPP1 in response to 1 α ,25(OH) 2 D 3 , whereas African Americans showed little induction of UPP1 with the same concentration of 1 α ,25(OH) 2 D 3 .…”