Abstract:Spliceostatin A, meayamycin, and pladienolide B are small molecules that target the SF3b subunit of the spliceosomal U2 small nuclear ribonucleoprotein (snRNP). These compounds are attracting much attention as tools to manipulate splicing and for use as potential anticancer drugs. We investigated the effects of these inhibitors on mRNA transport and stability in human cells. Upon splicing inhibition, unspliced pre-mRNAs accumulated in the nucleus, particularly within enlarged nuclear speckles. However, a small… Show more
“…Supporting the idea that apigenin and luteolin affect splicing rather than export, the apigenin- and luteolin-derived nuclear speckle-associated poly(A) + RNA accumulation pattern was similar to that observed in cells depleted of SF3B1, a component of U2 snRNP (Figure S2A), and was distinguishable from the uniform poly(A) + RNA accumulation throughout the nucleus observed in cells depleted of TAP (also known as NXF1), an mRNA exporter (Figure S2B) (Wang et al., 2018). The subnuclear localization of accumulated poly(A) + RNA observed in apigenin- and luteolin-treated cells was also reminiscent of a phenotype exhibited by cells treated with spliceostatin A, a well-known splicing inhibitor, also implicating the mRNA splicing process as a cellular target of these flavonoids (Figure 2D) (Carvalho et al., 2017, Kaida et al., 2007). Figure 3The Effect on Splicing of Some Genes and Identification of Apigenin- and Luteolin-Targeted Proteins(A) Schematic of β-globin construct containing the CMV promoter and BGH poly(A) site is presented.…”
SummaryCancer cells often exhibit extreme sensitivity to splicing inhibitors. We identified food-derived flavonoids, apigenin and luteolin, as compounds that modulate mRNA splicing at the genome-wide level, followed by proliferation inhibition. They bind to mRNA splicing-related proteins to induce a widespread change of splicing patterns in treated cells. Their inhibitory activity on splicing is relatively moderate, and introns with weak splice sites tend to be sensitive to them. Such introns remain unspliced, and the resulting intron-containing mRNAs are retained in the nucleus, resulting in the nuclear accumulation of poly(A)+ RNAs in these flavonoid-treated cells. Tumorigenic cells are more susceptible to these flavonoids than nontumorigenic cells, both for the nuclear poly(A)+ RNA-accumulating phenotype and cell viability. This study illustrates the possible mechanism of these flavonoids to suppress tumor progression in vivo that were demonstrated by previous studies and provides the potential of daily intake of moderate splicing inhibitors to prevent cancer development.
“…Supporting the idea that apigenin and luteolin affect splicing rather than export, the apigenin- and luteolin-derived nuclear speckle-associated poly(A) + RNA accumulation pattern was similar to that observed in cells depleted of SF3B1, a component of U2 snRNP (Figure S2A), and was distinguishable from the uniform poly(A) + RNA accumulation throughout the nucleus observed in cells depleted of TAP (also known as NXF1), an mRNA exporter (Figure S2B) (Wang et al., 2018). The subnuclear localization of accumulated poly(A) + RNA observed in apigenin- and luteolin-treated cells was also reminiscent of a phenotype exhibited by cells treated with spliceostatin A, a well-known splicing inhibitor, also implicating the mRNA splicing process as a cellular target of these flavonoids (Figure 2D) (Carvalho et al., 2017, Kaida et al., 2007). Figure 3The Effect on Splicing of Some Genes and Identification of Apigenin- and Luteolin-Targeted Proteins(A) Schematic of β-globin construct containing the CMV promoter and BGH poly(A) site is presented.…”
SummaryCancer cells often exhibit extreme sensitivity to splicing inhibitors. We identified food-derived flavonoids, apigenin and luteolin, as compounds that modulate mRNA splicing at the genome-wide level, followed by proliferation inhibition. They bind to mRNA splicing-related proteins to induce a widespread change of splicing patterns in treated cells. Their inhibitory activity on splicing is relatively moderate, and introns with weak splice sites tend to be sensitive to them. Such introns remain unspliced, and the resulting intron-containing mRNAs are retained in the nucleus, resulting in the nuclear accumulation of poly(A)+ RNAs in these flavonoid-treated cells. Tumorigenic cells are more susceptible to these flavonoids than nontumorigenic cells, both for the nuclear poly(A)+ RNA-accumulating phenotype and cell viability. This study illustrates the possible mechanism of these flavonoids to suppress tumor progression in vivo that were demonstrated by previous studies and provides the potential of daily intake of moderate splicing inhibitors to prevent cancer development.
“…It is known that mRNAs can pass through nuclear speckles at diffusion rates that are similar to the nucleoplasm but normally mRNAs do not amass within nuclear speckles (61–64). The accumulation of export-deficient mRNAs in nuclear speckles has been demonstrated in several studies (25,54,55,65–67), but notably, this was observed for unspliced intron-containing pre-mRNAs. Also, it was shown that EJC proteins are not recruited to transcription sites of splicing defective mRNAs (53).…”
Eukaryotic cells contain sub-cellular compartments that are not membrane bound. Some structures are always present, such as nuclear speckles that contain RNA-binding proteins (RBPs) and poly(A)+ RNAs. Others, like cytoplasmic stress granules (SGs) that harbor mRNAs and RBPs, are induced upon stress. When we examined the formation and composition of nuclear speckles during stress induction with tubercidin, an adenosine analogue previously shown to affect nuclear speckle composition, we unexpectedly found that it also led to the formation of SGs and to the inhibition of several crucial steps of RNA metabolism in cells, thereby serving as a potent inhibitor of the gene expression pathway. Although transcription and splicing persisted under this stress, RBPs and mRNAs were mislocalized in the nucleus and cytoplasm. Specifically, lncRNA and RBP localization to nuclear speckles was disrupted, exon junction complex (EJC) recruitment to mRNA was reduced, mRNA export was obstructed, and cytoplasmic poly(A)+ RNAs localized in SGs. Furthermore, nuclear proteins that participate in mRNA export, such as nucleoporins and mRNA export adaptors, were mislocalized to SGs. This study reveals structural aspects of granule assembly in cells, and describes how the flow of RNA from the nucleus to the cytoplasm is severed under stress.
“…( Figure S2A), and was distinguishable from the uniform poly(A) + RNA accumulation throughout the nucleus observed in cells depleted of TAP (also known as NXF1), an mRNA exporter ( Figure S2B) (Wang et al, 2018). The subnuclear localization of accumulated poly(A) + RNA observed in apigenin-and luteolin-treated cells was also reminiscent of a phenotype exhibited by cells treated with spliceostatin A, a well-known splicing inhibitor, also implicating the mRNA splicing process as a cellular target of these flavonoids ( Figure 2D) (Carvalho et al, 2017;Kaida et al, 2007).…”
Section: Mrna Splicing Is a Candidate For The Cellular Target Of Apigmentioning
confidence: 80%
“…Such enrichment of RNA processing factors, especially of mRNA splicing, was also observed in the genes that we identified to harbor introns whose retention was induced by apigenin and luteolin. It has been reported that unspliced mRNAs resulting from the global inhibition of splicing by spliceostatin A treatment manifest as a robust accumulation of bulk poly(A) + RNAs at the nuclear speckles (Carvalho et al, 2017;Kaida et al, 2007). Similarly, we observed that apigenin and luteolin treatment induced the accumulation of bulk poly(A) + RNA, as well as the retention of intron-containing transcripts from target mini genes, in the nuclear speckles, implying that these flavonoids affect a broad range of mRNA splicing events.…”
Cancer cells often exhibit extreme sensitivity to splicing inhibitors. We identified food-derived flavonoids, apigenin and luteolin, as compounds that modulate mRNA splicing at the genome-wide level, followed by proliferation inhibition. They bind to mRNA splicing-related proteins to induce a widespread change of splicing patterns in treated cells. Their inhibitory activity on splicing is relatively moderate, and introns with weak splice sites tend to be sensitive to them. Such introns remain unspliced, and the resulting intron-containing mRNAs are retained in the nucleus, resulting in the nuclear accumulation of poly(A) + RNAs in these flavonoid-treated cells. Tumorigenic cells are more susceptible to these flavonoids than nontumorigenic cells, both for the nuclear poly(A) + RNA-accumulating phenotype and cell viability. This study illustrates the possible mechanism of these flavonoids to suppress tumor progression in vivo that were demonstrated by previous studies and provides the potential of daily intake of moderate splicing inhibitors to prevent cancer development.
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