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Cis-acting elements in its 3' UTR mediate post-transcriptional regulation of KRAS.

ABSTRACT: Multiple RNA-binding proteins and non-coding RNAs, such as microRNAs (miRNAs), are involved in post-transcriptional gene regulation through recognition motifs in the 3' untranslated region (UTR) of their target genes. The KRAS gene encodes a key signaling protein, and its messenger RNA (mRNA) contains an exceptionally long 3' UTR; this suggests that it may be subject to a highly complex set of regulatory processes. However, 3' UTR-dependent regulation of KRAS expression has not been explored in detail. Using extensive deletion and mutational analyses combined with luciferase reporter assays, we have identified inhibitory and stabilizing cis-acting regions within the KRAS 3' UTR that may interact with miRNAs and RNA-binding proteins, such as HuR. Particularly, we have identified an AU-rich 49-nt fragment in the KRAS 3' UTR that is required for KRAS 3' UTR reporter repression. This element contains a miR-185 complementary element, and we show that overexpression of miR-185 represses endogenous KRAS mRNA and protein in vitro. In addition, we have identified another 49-nt fragment that is required to promote KRAS 3' UTR reporter expression. These findings indicate that multiple cis-regulatory motifs in the 3' UTR of KRAS finely modulate its expression, and sequence alterations within a binding motif may disrupt the precise functions of trans-regulatory factors, potentially leading to aberrant KRAS expression.

SUBMITTER: Kim M

PROVIDER: S-EPMC4914247 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Cis-acting elements in its 3' UTR mediate post-transcriptional regulation of KRAS.

Kim Minlee M Kogan Nicole N Slack Frank J FJ

Oncotarget 20160301 11

Multiple RNA-binding proteins and non-coding RNAs, such as microRNAs (miRNAs), are involved in post-transcriptional gene regulation through recognition motifs in the 3' untranslated region (UTR) of their target genes. The KRAS gene encodes a key signaling protein, and its messenger RNA (mRNA) contains an exceptionally long 3' UTR; this suggests that it may be subject to a highly complex set of regulatory processes. However, 3' UTR-dependent regulation of KRAS expression has not been explored in ...[more]

PMID: 26930719

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Project description:BackgroundPost-transcriptional gene regulation controls the amount of protein produced from an individual mRNA by altering rates of decay and translation. Many sequence elements that direct post-transcriptional regulation have been found; in mammals, most such elements are located within the 3' untranslated regions (3'UTRs). Comparative genomic studies demonstrate that mammalian 3'UTRs contain extensive conserved sequence tracts, yet only a small fraction corresponds to recognized elements, implying that many additional novel elements exist. Despite a variety of computational, molecular, and biochemical approaches, identifying functional 3'UTRs elements remains difficult.ResultsWe created a high-throughput cell-based screen that enables identification of functional post-transcriptional 3'UTR regulatory elements. Our system exploits integrated single-copy reporters, which are expressed and processed as endogenous genes. We screened many thousands of short random sequences for their regulatory potential. Control sequences with known effects were captured effectively using our approach, establishing that our methodology was robust. We found hundreds of functional sequences, which we validated in traditional reporter assays, including verifying their regulatory impact in native sequence contexts. Although 3'UTRs are typically considered repressive, most of the functional elements were activating, including ones that were preferentially conserved. Additionally, we adapted our screening approach to examine the effect of elements on RNA abundance, revealing that most elements act by altering mRNA stability.ConclusionsWe developed and used a high-throughput approach to discover hundreds of post-transcriptional cis-regulatory elements. These results imply that most human 3'UTRs contain many previously unrecognized cis-regulatory elements, many of which are activating, and that the post-transcriptional fate of an mRNA is largely due to the actions of many individual cis-regulatory elements within its 3'UTR.

Project description:BackgroundThe eukaryotic parasite Plasmodium falciparum causes millions of malarial infections annually while drug resistance to common anti-malarials is further confounding eradication efforts. Translation is an attractive therapeutic target that will benefit from a deeper mechanistic understanding. As the rate limiting step of translation, initiation is a primary driver of translational efficiency. It is a complex process regulated by both cis and trans acting factors, providing numerous potential targets. Relative to model organisms and humans, P. falciparum mRNAs feature unusual 5' untranslated regions suggesting cis-acting sequence complexity in this parasite may act to tune levels of protein synthesis through their effects on translational efficiency.MethodsHere, in vitro translation is deployed to compare the role of cis-acting regulatory sequences in P. falciparum and humans. Using parasite mRNAs with high or low translational efficiency, the presence, position, and termination status of upstream "AUG"s, in addition to the base composition of the 5' untranslated regions, were characterized.ResultsThe density of upstream "AUG"s differed significantly among the most and least efficiently translated genes in P. falciparum, as did the average "GC" content of the 5' untranslated regions. Using exemplars from highly translated and poorly translated mRNAs, multiple putative upstream elements were interrogated for impact on translational efficiency. Upstream "AUG"s were found to repress translation to varying degrees, depending on their position and context, while combinations of upstream "AUG"s had non-additive effects. The base composition of the 5' untranslated regions also impacted translation, but to a lesser degree. Surprisingly, the effects of cis-acting sequences were remarkably conserved between P. falciparum and humans.ConclusionsWhile translational regulation is inherently complex, this work contributes toward a more comprehensive understanding of parasite and human translational regulation by examining the impact of discrete cis-acting features, acting alone or in context.

Dataset Information

Cis-acting elements in its 3' UTR mediate post-transcriptional regulation of KRAS.

Publications

Cis-acting elements in its 3' UTR mediate post-transcriptional regulation of KRAS.

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