The splicing factor kinase, SR protein kinase 1 (SRPK1) is essential for late events in the human papillomavirus life cycle.

Human papillomaviruses (HPV) infect epithelial causing benign lesions. However, the so-called "high risk" HPVs that infect the anogenital regions and the oropharynx can cause precancerous lesions that can progress to malignant tumours. Understanding the HPV life cycle is important to the discovery of novel antiviral therapies. HPV uses cellular splicing for the production of the full suite of viral mRNAs. Members of the serine/arginine rich (SR) protein family can positively regulate splicing. SR protein activity and cellular location is regulated by kinases through phosphorylation of their serine-arginine domains. SR protein kinase 1 (SRPK1) phosphorylates SR proteins to licence their nuclear entry and can promote nuclear splicing in conjunction with another SR protein kinase, Clk1. SRPIN340 is a specific SRPK1 inhibitor that has been reported to inhibit replication of HCV, Sindbis virus and HIV. Using organotypic raft cultures supporting the HPV16 life cycle, we show that SRPIN340 inhibits the expression of the viral replication and transcription factor, E2. Drug-mediated loss of E2 is specifically associated with inhibition of late gene expression since early gene expression is unaffected. RNA sequencing revealed that SRPIN340 treatment resulted in many gene expression changes opposite to those induced by HPV16 infection. In particular, the loss of epithelial barrier structure and immune function was restored. SRPIN340 treatment resulted in changes in alternative splicing of 935 RNAs and pathway analysis showed a predominance of changes to RNAs encoding proteins involved in chromatin conformation, DNA repair and RNA processing. SRPIN340 treatment was not associated with changes in proliferation or differentiation of keratinocytes. Collectively, these results provide evidence that SRPK1 is a host factor that is essential for HPV16 replication and therefore, targeting this factor, or the phosphorylation events it mediates, could be considered as a therapeutic strategy for HPV16 infection. AUTHOR SUMMARYHuman papillomavirus (HPV) can cause precancerous and cancerous tumours of the anogenital region, for example, the cervix. HPV infects epithelial cells and utilizes the host cell gene expression machinery to produce its own proteins. Splicing is a key mechanism used by HPV to synthesise messenger RNAs that encode the viral proteins. Splicing is positively controlled by SR proteins which require to be phosphorylated by SR protein kinase (SRPK) to enter the nucleus and regulate splicing. SRPIN340 is a specific inhibitor of SRPK. SRPIN340 treatment of HPV16-infected epithelial cells resulted in loss of expression of the viral replication and transcription factor, E2 and abrogation of late events in the viral life cycle. SRPIN340 treatment counteracted some gene expression changes to the epithelium known to be cause by HPV infection. These data suggest that SRPK1 is essential for the HPV life cycle and that it could be a potential anti-viral target.