Human Papillomavirus Type 1 E1^E4 Protein Is a Potent Inhibitor of the Serine-Arginine (SR) Protein Kinase SRPK1 and Inhibits Phosphorylation of Host SR Proteins and of the Viral Transcription and Replication Regulator E2

Abstract

The serine-arginine-specific protein kinase SRPK1 is a common binding partner of the E1^E4 protein of diverse human papillomavirus types. We show here for the first time that the interaction between HPV1 E1^E4 and SRPK1 leads to potent inhibition of SRPK1 phosphorylation of host serine-arginine (SR) proteins that have critical roles in mRNA metabolism, including pre-mRNA processing, mRNA export, and translation. Furthermore, we show that SRPK1 phosphorylates serine residues of SR/RS dipeptides in the hinge region of the HPV1 E2 protein in in vitro kinase assays and that HPV1 E1^E4 inhibits this phosphorylation. After mutation of the putative phosphoacceptor serine residues, the localization of the E2 protein was altered in primary human keratinocytes; with a significant increase in the cell population showing intense E2 staining of the nucleolus. A similar effect was observed following coexpression of E2 and E1^E4 that is competent for inhibition of SRPK1 activity, suggesting that the nuclear localization of E2 is sensitive to E1^E4-mediated SRPK1 inhibition. Collectively, these data suggest that E1^E4-mediated inhibition of SRPK1 could affect the functions of host SR proteins and those of the virus transcription/replication regulator E2. We speculate that the novel E4 function identified here is involved in the regulation of E2 and SR protein function in posttranscriptional processing of viral transcripts. IMPORTANCEThe HPV life cycle is tightly linked to the epithelial terminal differentiation program, with the virion-producing phase restricted to differentiating cells. While the most abundant HPV protein expressed in this phase is the E4 protein, we do not fully understand the role of this protein. Few E4 interaction partners have been identified, but we had previously shown that E4 proteins from diverse papillomaviruses interact with the serine-arginine-specific protein kinase SRPK1, a kinase important in the replication cycles of a diverse range of DNA and RNA viruses. We show that HPV1 E4 is a potent inhibitor of this host cell kinase. We show that E4 inhibits SRPK1 phosphorylation, not only of cellular SR proteins involved in regulating alternative splicing of RNA but also the viral transcription/replication regulator E2. Our findings reveal a potential E4 function in regulation of viral late gene expression through the inhibition of a host cell kinase. H uman papillomaviruses (HPVs) cause hyperproliferative warts and papillomas of the squamous epithelium at different body sites. Infection of the anogenital tract and oropharynx can lead to benign and malignant disease. There are 13 HPV types defined as causative agents of cancers at these sites, the most common being HPV 16 (HPV16) and HPV18. Of the viruses that infect cutaneous surfaces, some, such as HPV1, cause only benign warts, while infection with others, such as HPV5 and HPV8, can, in immunocompromised individuals, cause the formation of lesions that are at risk of malignant conversion.Despite the heterogeneity in pathogenesis, HPVs show a ...

A proteomic approach to discover and compare interacting partners of papillomavirus E2 proteins from diverse phylogenetic groups

“…Prescott et al have recently shown that SRPK1 can also phosphorylate HPV1 E2 in vitro, even though it only contains three SR/RS dipeptides [56]. Furthermore, the E1ˆE4 proteins of many HPVs bind SRPK1 and inhibit its ability to phosphorylate E2 [56]. In our study, the observed interaction of the different E2 proteins with SRPK1/2 correlates somewhat with the number of SR/RS dipeptides in the hinge region (HPV8 has 28; others have 0 to 5).…”

“…SRPK1 can phosphorylate the hinge region of HPV5 and HPV8 E2 proteins in vitro [6,55]. Prescott et al have recently shown that SRPK1 can also phosphorylate HPV1 E2 in vitro, even though it only contains three SR/RS dipeptides [56]. Furthermore, the E1ˆE4 proteins of many HPVs bind SRPK1 and inhibit its ability to phosphorylate E2 [56].…”

Serine-Arginine Protein Kinase 1 Regulates Ebola Virus Transcription

“…SRPK1 and SRPK2 are cellular kinases that shuttle between the cytosol and nucleus and target proteins containing serine-arginine-rich domains (SR proteins) (for a review, see reference 34). It has been reported that SRPK1 also phosphorylates viral proteins (35)(36)(37)(38)(39). For example, SRPK1 is recruited by the E1^E4 proteins of human papillomaviruses and the ICP27 protein of herpes simplex virus 1, resulting in the downregulation of host SR protein phosphorylation (35,37).…”

Serine-arginine protein kinase 1 regulates Ebola virus transcription

“…It has been reported that SRPK1 also phosphorylates viral proteins (34-38). For example, SRPK1 is recruited by the E1^E4 proteins of human papillomaviruses and ICP27 protein of herpes simplex virus 1, resulting in downregulation of host SR protein phosphorylation (34, 36). With regard to RNA viruses, inhibition of SRPK1 by SRPIN340 suppresses hepatitis C virus and human immunodeficiency virus replication, though these effects might be caused by modulation of RNA splicing through alteration of the SR protein phosphorylation status (24, 25).…”