Alternative splicing in human tumour viruses: a therapeutic target?

Hernandez-Lopez, Hegel; Graham, Sheila V.

doi:10.1042/bj20120413

Cited by 23 publications

(21 citation statements)

References 139 publications

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“…This suggests it could be a valid target for therapeutic inhibition in cervical tumors. SR protein function is regulated by phosphorylation, and drugs that regulate SR kinases have been used successfully to inhibit the replication of HIV and hepatitis C virus (34). Development of small-molecule inhibitors against SR kinases could have the potential to abrogate HPV oncoprotein expression in the early stages of cervical cancer progression.…”

Section: Discussionmentioning

confidence: 99%

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Human Papillomavirus 16 Oncoprotein Expression Is Controlled by the Cellular Splicing Factor SRSF2 (SC35)

McFarlane

MacDonald

Stevenson

et al. 2015

J Virol

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High-risk human papillomaviruses (HR-HPV) cause anogenital cancers, including cervical cancer, and head and neck cancers. Human papillomavirus 16 (HPV16) is the most prevalent HR-HPV. HPV oncogenesis is driven by two viral oncoproteins, E6 and E7, which are expressed through alternative splicing of a polycistronic RNA to yield four major splice isoforms (E6 full length, E6*I, E6*II, E6*X). The production of multiple mRNA isoforms from a single gene is controlled by serine/arginine-rich splicing factors (SRSFs), and HPV16 infection induces overexpression of a subset of these, SRSFs 1, 2, and 3. In this study, we examined whether these proteins could control HPV16 oncoprotein expression. Small interfering RNA (siRNA) depletion experiments revealed that SRSF1 did not affect oncoprotein RNA levels. While SRSF3 knockdown caused some reduction in E6E7 expression, depletion of SRSF2 resulted in a significant loss of E6E7 RNAs, resulting in reduced levels of the E6-regulated p53 proteins and E7 oncoprotein itself. SRSF2 contributed to the tumor phenotype of HPV16-positive cervical cancer cells, as its depletion resulted in decreased cell proliferation, reduced colony formation, and increased apoptosis. SRSF2 did not affect transcription from the P 97 promoter that controls viral oncoprotein expression. Rather, RNA decay experiments showed that SRSF2 is required to maintain stability of E6E7 mRNAs. These data show that SRSF2 is a key regulator of HPV16 oncoprotein expression and cervical tumor maintenance. H uman papillomaviruses (HPV) infect mucosal and cutaneous epithelia. At least 13 so-called "high-risk" HPV (HR-HPV) infect the anogenital epithelium and can cause persistent lesions that may progress to cancer (1). For example, around 500,000 women worldwide experience anogenital HPV infection, and nearly 300,000 die per annum from cervical cancer. Increasingly, HPV infection is also being linked to oropharyngeal cancer, whereby incidence of this disease is increasing rapidly (2). HPV16 is the most prevalent HR-HPV. HPV-associated tumorigenesis is driven by increased expression of the HPV E6 and E7 oncoproteins (3). E6 promotes ubiquitin-mediated degradation of p53 to inhibit apoptosis, modulates transcription of cell cycle-related genes, induces telomerase activity, controls cell shape and polarity, and activates cap-dependent translation (4). E7 binds and degrades Rb to promote S phase entry and cell division, controls transcription of cell cycle-related genes, and acts as a mitotic mutator (4). IMPORTANCE Expression of the HPV16 oncoproteins E7 and E6 drives HPV-associated tumor formation. Although increased transcription may yield increased levels of E6E7 mRNAs, it is known that theHPV E6 and E7 oncoproteins are expressed from a polycistronic transcript that for HPV16 can potentially produce four different alternatively spliced mRNAs (E6 full length [E6fl], E6*I, E6*II, and E6*X [also called E6*III]) (5, 6). The putative E6* proteins all share the first 44 amino acids of full-length E6 with C-terminal trun...

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Section: Discussionmentioning

confidence: 99%

“…These data suggest that SRSF2 is a key cellular factor controlling HPV16 oncoprotein expression by protecting the RNAs encoding them from decay. Since SR protein activity is a proven relevant antiviral drug target (34), these findings provide insight into new therapeutic avenues against HPV-associated oncogenesis.…”

mentioning

confidence: 99%

Human Papillomavirus 16 Oncoprotein Expression Is Controlled by the Cellular Splicing Factor SRSF2 (SC35)

McFarlane

MacDonald

Stevenson

et al. 2015

J Virol

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“…Small-molecule inhibitors of SR protein kinases that modulate the functions of SR proteins are available. Since they have been shown to be effective in inhibiting replication of HIV, hepatitis C virus, and Sindbis virus (14), they may also be effective against HPV replication. However, it will also be important also to understand any potential effects of these therapies on the switch from the viral replicative cycle to persistent or latent infection that underlies tumor progression.…”

Section: Discussionmentioning

confidence: 99%

“…Alternative splicing is a mechanism used by mammalian and viral genomes to maximize coding potential (13,14). A gene is transcribed to give a single primary transcript, but from this precursor RNA (pre-mRNA) different mature mRNA isoforms are produced by differential inclusion or exclusion of exons and introns.…”

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confidence: 99%

Human Papillomavirus E2 Regulates SRSF3 (SRp20) To Promote Capsid Protein Expression in Infected Differentiated Keratinocytes

Klymenko

Hernandez-Lopez

MacDonald

et al. 2016

J Virol

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The human papillomavirus (HPV) life cycle is tightly linked to differentiation of the infected epithelial cell, suggesting a sophisticated interplay between host cell metabolism and virus replication. Previously, we demonstrated in differentiated keratinocytes in vitro and in vivo that HPV type 16 (HPV16) infection caused increased levels of the cellular SR splicing factors (SRSFs) SRSF1 (ASF/SF2), SRSF2 (SC35), and SRSF3 (SRp20). Moreover, the viral E2 transcription and replication factor that is expressed at high levels in differentiating keratinocytes could bind and control activity of the SRSF1 gene promoter. Here, we show that the E2 proteins of HPV16 and HPV31 control the expression of SRSFs 1, 2, and 3 in a differentiation-dependent manner. E2 has the greatest transactivation effect on expression of SRSF3. Small interfering RNA depletion experiments in two different models of the HPV16 life cycle (W12E and NIKS16) and one model of the HPV31 life cycle (CIN612-9E) revealed that only SRSF3 contributed significantly to regulation of late events in the virus life cycle. Increased levels of SRSF3 are required for L1 mRNA and capsid protein expression. Capsid protein expression was regulated specifically by SRSF3 and appeared independent of other SRSFs. Taken together, these data suggest a significant role of the HPV E2 protein in regulating late events in the HPV life cycle through transcriptional regulation of SRSF3 expression. IMPORTANCEHuman papillomavirus replication is accomplished in concert with differentiation of the infected epithelium. Virus capsid protein expression is confined to the upper epithelial layers so as to avoid immune detection. In this study, we demonstrate that the viral E2 transcription factor activates the promoter of the cellular SRSF3 RNA processing factor. SRSF3 is required for expression of the E4^L1 mRNA and so controls expression of the HPV L1 capsid protein. Thus, we reveal a new dimension of virus-host interaction crucial for production of infectious virus. SRSF proteins are known drug targets. Therefore, this study provides an excellent basis for developing strategies to regulate capsid protein production in the infected epithelium and the production of new virions.

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“…To express a maximum number of proteins, viruses use multiple promoters, translational frame shifting, alternative open reading frames, stop codon read-through; for regulation of gene expression, viruses further use antisense transcription and virus-encoded miRNAs. Alternative splicing represents a key mechanism that is recruited by most DNA viruses, and nuclear replicating RNA viruses to generate the full repertoire of protein functions [4].RNA trans-splicing represents a special form of alternative splicing in which sequences of distinct pre-mRNA transcripts are joined in trans. Thus, like alternative cis-splicing, trans-splicing contributes to the diversification of genotypes and phenotypes.…”

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confidence: 99%

Viral RNA Trans-Splicing: Chance Event or Product of Evolution?

Patzel¹

2013

SOJ Microbiol Infect Dis

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EditorialOne year after the discovery of exons and introns in the adenoviral hexon gene by the teams of Roberts and Sharp [1,2], Walther Gilbert suggested that the employment of different exons of a single gene could lead to the generation of various mRNA isoforms [3], a process that is today known as alternative splicing. Alternative splicing implies a number of distinct mechanisms including exon skipping, intron retention, mutually exclusive exons, alternative splice site selection as well as alternative promoter usage and alternative polyadenylation. Constitutive and alternative splicing isn't mutually exclusive which solves the former problem that for a steady evolutionary process, essential genes don't need to duplicate before one version can mutate to a new gene function. Alternative splicing generates new functions by creating new exons within existing genes and can relax the negative selection pressure against evolutionary changes in functional genes. Thus, alternative splicing might open nearly neutral paths for evolutionary changes.For most viruses, economy in genome size is a common theme. To express a maximum number of proteins, viruses use multiple promoters, translational frame shifting, alternative open reading frames, stop codon read-through; for regulation of gene expression, viruses further use antisense transcription and virus-encoded miRNAs. Alternative splicing represents a key mechanism that is recruited by most DNA viruses, and nuclear replicating RNA viruses to generate the full repertoire of protein functions [4].RNA trans-splicing represents a special form of alternative splicing in which sequences of distinct pre-mRNA transcripts are joined in trans. Thus, like alternative cis-splicing, trans-splicing contributes to the diversification of genotypes and phenotypes. Naturally occurring RNA trans-splicing was first described in 1986 in trypanosomes and one year later also in the nematode Caenorhabditis elegans. In these organisms a species-specific non-coding small RNA with a singular 5' splice donor site, the socalled small leader RNA (SL RNA), is spliced to variable 3' splice acceptor sites on separate pre-mRNA molecules. SL RNA transsplicing differs from regular cis-splicing, as the U1 small nuclear ribonucleoprotein (snRNP) containing the U1 small nuclear (sn) RNA is replaced by the SL snRNP, which carries the SL RNA. SL RNA trans-splicing was also detected in other nematodes, flatworms, and in tunicates, primitive chordates. The hypothesis it might also occur in vertebrates has not been confirmed yet. In the mid-90s first experimental evidence was obtained showing that mammalian cells can combine natural pre-mRNAs to new mRNA via RNA trans-splicing [5,6]. The mammalian RNA transsplicing, however, is independent of SL RNA but instead mediated by the spliceosome of the cell. Computational analyses of cDNAs from a gene databank indicated one percent of all sequenced mRNAs to be chimeric [7], some of which might be synthesized by RNA trans-splicing. Up to date several examples of natural...

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Alternative splicing in human tumour viruses: a therapeutic target?

Cited by 23 publications

References 139 publications

Human Papillomavirus 16 Oncoprotein Expression Is Controlled by the Cellular Splicing Factor SRSF2 (SC35)

Human Papillomavirus 16 Oncoprotein Expression Is Controlled by the Cellular Splicing Factor SRSF2 (SC35)

Human Papillomavirus E2 Regulates SRSF3 (SRp20) To Promote Capsid Protein Expression in Infected Differentiated Keratinocytes

Viral RNA Trans-Splicing: Chance Event or Product of Evolution?

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