CRL4B E3 ligase recruited by PRPF19 inhibits SARS-CoV-2 infection by targeting ORF6 for ubiquitin-dependent degradation

The accessory protein ORF6 of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a key interferon (IFN) antagonist that strongly suppresses the production of primary IFN as well as the expression of IFN-stimulated genes. However, how host cells respond to ORF6 remains largely unknown. Our research of ORF6-binding proteins by pulldown revealed that E3 ligase components such as Cullin 4B (CUL4B), DDB1, and RBX1 are potential ORF6-interacting proteins. Further study found that the substrate recognition receptor PRPF19 interacts with CUL4B, DDB1, and RBX1 to form a CRL4B-based E3 ligase, which catalyzes ORF6 ubiquitination and subsequent degradation. Overexpression of PRPF19 promotes ORF6 degradation, releasing ORF6-mediated IFN inhibition, which inhibits SARS-CoV-2 replication. Moreover, we found that activation of CUL4B by the neddylation inducer etoposide alleviates lung lesions in a SARS-CoV-2 mouse infection model. Therefore, targeting ORF6 for degradation may be an effective therapeutic strategy against SARS-CoV-2 infection.IMPORTANCEThe cellular biological function of the ubiquitin-proteasome pathway as an important modulator for the regulation of many fundamental cellular processes has been greatly appreciated. The critical role of the ubiquitin-proteasome pathway in viral pathogenesis has become increasingly apparent. It is a powerful tool that host cells use to defend against viral infection. Some cellular proteins can function as restriction factors to limit viral infection by ubiquitin-dependent degradation. In this research, we identificated of CUL4B-DDB1-PRPF19 E3 Ubiquitin Ligase Complex can mediate proteasomal degradation of ORF6, leading to inhibition of viral replication. Moreover, the CUL4B activator etoposide alleviates disease development in a mouse infection model, suggesting that this agent or its derivatives may be used to treat infections caused by SARS-CoV-2. We believe that these results will be extremely useful for the scientific and clinic communities in their search for cues and preventive measures to combat the COVID-19 pandemic.

PRPF19 functions in DNA damage repair and gemcitabine sensitivity via regulating DDB1 in bladder cancer cells

PRPF19 seems to play either tumor-promoting or anti-tumor roles depending on cancer types. This study aimed to clarify the potential role and mechanism of PRPF19 in bladder cancer. PRPF19 expression and its correlation with patients' overall survival were analyzed in bladder cancer. The effects of PRPF19 on the viability, apoptosis, DNA damage repair, and gemcitabine sensitivity in human bladder cancer cells (T24 and 5637) were analyzed through loss- or gain-of-function methods. Moreover, the influences of DDB1 small interfering RNA on these indexes were evaluated in bladder cancer cells. At last, rescue experiment using DDB1 overexpression was carried out to confirm whether PRPF19 functioned via regulating DDB1. PRPF19 was highly expressed in bladder cancer tissues and cells. Elevated PRPF19 expression was related to shorter overall survival of bladder cancer patients. Downregulation of PRPF19 inhibited cell proliferation, promoted cell apoptosis, increased the number of γ-H2AX-positive cells, and reduced the mRNA and protein levels of DDB1 and BRCA1. Meanwhile, knockdown of PRPF19 decreased the IC50 of gemcitabine and promoted gemcitabine-induced cell apoptosis. Whereas, PRPF19 overexpression significantly decreased gemcitabine-induced apoptosis in bladder cancer cells. DDB1 downregulation suppressed cell proliferation and BRCA1 expression, but elevated the number of γ-H2AX-positive cells and gemcitabine sensitivity. Upregulation of DDB1 attenuated γ-H2AX-positive cell number, BRCA1 expression and IC50 of gemcitabine that were affected by PRPF19 silencing. In conclusion, PRPF19 expression was upregulated in bladder cancer. It promoted cell growth and DNA damage repair, and decreased gemcitabine sensitivity via positively regulating DDB1 expression.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00599-7.

Human proteins curing yeast prions

Recognition that common human amyloidoses are prion diseases makes the use of the Saccharomyces cerevisiae prion model systems to screen for possible anti-prion components of increasing importance. [PSI+] and [URE3] are amyloid-based prions of Sup35p and Ure2p, respectively. Yeast has at least six anti-prion systems that together cure nearly all [PSI+] and [URE3] prions arising in their absence. We made a GAL-promoted bank of 14,913 human open reading frames in a yeast shuttle plasmid and isolated 20 genes whose expression cures [PSI+] or [URE3]. PRPF19 is an E3 ubiquitin ligase that cures [URE3] if its U-box is intact. DNAJA1 is a J protein that cures [PSI+] unless its interaction with Hsp70s is defective. Human Bag5 efficiently cures [URE3] and [PSI+]. Bag family proteins share a 110 to 130 residue "BAG domain"; Bag 1, 2, 3, 4, and 6 each have one BAG domain while Bag5 has five BAG domains. Two BAG domains are necessary for curing [PSI+], but one can suffice to cure [URE3]. Although most Bag proteins affect autophagy in mammalian cells, mutations blocking autophagy in yeast do not affect Bag5 curing of [PSI+] or [URE3]. Curing by Bag proteins depends on their interaction with Hsp70s, impairing their role, with Hsp104 and Sis1, in the amyloid filament cleavage necessary for prion propagation. Since Bag5 curing is reduced by overproduction of Sis1, we propose that Bag5 cures prions by blocking Sis1 access to Hsp70s in its role with Hsp104 in filament cleavage.

PRPF19 promotes the proliferation, migration, and inhibits autophagy in prostate cancer by suppressing SLC40A1

Prostate cancer (PCa) is a common cancer and the leading cause of cancer-related death in men. To investigate the role of pre-mRNA processing factor 19 (PRPF19) in proliferation, migration of PCa, and evaluate the potential ability of PRPF19 as a therapeutic target. PRPF19 expression was analyzed from The Cancer Genome Atlas and GEPIA databank. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to evaluate the transcription of PRPF9 and solute carrier family 40 member 1 (SLC40A1). Immunohistochemistry (IHC) was used to test PRPF9 expression in PCa tissues. The cell viability and 5-ethynyl-2'-deoxyuridine incorporation analysis were performed to assess cell proliferation. Transwell assay was performed to investigate the migration and invasion of cancer cells. Western blot was used to measure the expression level of PRPF9, E-cadherin, Vimentin and α-smooth muscle actin (α-SMA), SLC40A1, LC3, Beclin-1 and ATG7. Immunofluorescence assay was performed to measure LC3 expression in PCa cells. The bioinformatic analysis revealed PRPF19 was highly expressed in PCa which was certified by qRT-PCR, western blot and IHC detection in PCa tissues. The proliferation of PCa cells could be promoted by PRPF19 overexpression and suppressed by PRPF19 knockdown. Moreover, the migration and invasion of PCa cells could be positively regulated by PRPF19 which promoted the expression of E-cadherin, Vimentin, and α-SMA. Furthermore, the expression of LC3, Beclin-1, and ATG7 was negatively regulated by PRPF19, indicating that PRPF19 inhibited autophagy in PCa cells. In the double knockdown of PRPF19 and SLC40A1, PRPF19 repressed the mRNA and reduced protein level of SLC40A1, and SLC40A1 antagonized effects of PRPF19 on proliferation, migration and autophagy of PCa cells. PRPF19 promoted proliferation and migration, and inhibited autophagy in PCa by attenuating SLC40A1 expression, indicating PRPF19 was a potential therapeutic target for PCa treatment.

PRPF19 modulates morphology and growth behavior in a cell culture model of human skin

The skin provides one of the most visual aging transformations in humans, and premature aging as a consequence of oxidative stress and DNA damage is a frequently seen effect. Cells of the human skin are continuously exposed to endogenous and exogenous DNA damaging factors, which can cause DNA damage in all phases of the cell cycle. Increased levels of DNA damage and/or defective DNA repair can, therefore, accelerate the aging process and/or lead to age-related diseases like cancer. It is not yet clear if enhanced activity of DNA repair factors could increase the life or health span of human skin cells. In previous studies, we identified and characterized the human senescence evasion factor (SNEV)/pre-mRNA-processing factor (PRPF) 19 as a multitalented protein involved in mRNA splicing, DNA repair pathways and lifespan regulation. Here, we show that overexpression of PRPF19 in human dermal fibroblasts leads to a morphological change, reminiscent of juvenile, papillary fibroblasts, despite simultaneous expression of senescence markers. Moreover, conditioned media of this subpopulation showed a positive effect on keratinocyte repopulation of wounded areas. Taken together, these findings indicate that PRPF19 promotes cell viability and slows down the aging process in human skin.

PRPF19 Limits Porcine Epidemic Diarrhea Virus Replication through Targeting and Degrading Viral Capsid Protein

Porcine epidemic diarrhea (PED) indicates the disease of the acute and highly contagious intestinal infection due to porcine epidemic diarrhea virus (PEDV), with the characteristics of watery diarrhea, vomiting, and dehydration. One of the reasons for diarrhea and death of piglets is PEDV, which leads to 100% mortality in neonatal piglets. Therefore, it is necessary to explore the interaction between virus and host to prevent and control PEDV. This study indicated that the host protein, pre-mRNA processing factor 19 (PRPF19), could be controlled by the signal transducer as well as activator of transcription 1 (STAT1). Thus, PEDV replication could be hindered through selective autophagy. Moreover, PRPF19 was found to recruit the E3 ubiquitin ligase MARCH8 to the N protein for ubiquitination. For the purpose of degradation, the ubiquitin N protein is acknowledged by the cargo receptor NDP52 and transported to autolysosomes, thus inhibiting virus proliferation. To conclude, a unique antiviral mechanism of PRPF19-mediated virus restriction was shown. Moreover, a view of the innate immune response and protein degradation against PEDV replication was provided in this study. IMPORTANCE The highly virulent porcine epidemic diarrhea virus (PEDV) emerged in 2010, and causes high mortality rates in newborn pigs. There are no effective and safe vaccines against the highly virulent PEDV. This virus has caused devastating economic losses in the pork industry worldwide. Studying the relationship between virus and host antiviral factors is important to develop the new antiviral strategies. This study identified the pre-mRNA processing factor 19 (PRPF19) as a novel antiviral protein in PEDV replication and revealed its viral restriction mechanisms for the first time. PRPF19 recruited the E3 ubiquitin ligase MARCH8 to the PEDV N protein for ubiquitination, and the ubiquitin N protein was acknowledged by the cargo receptor NDP52 and transported to autolysosomes for degradation. Our findings provide new insights in host antiviral factors PRPF19 that regulate the selective autophagy protein degradation pathway to inhibit PEDV replication.

PRPF19 promotes tongue cancer growth and chemoradiotherapy resistance

Pre-mRNA processing factor 19 (PRPF19) is a multifaceted protein and participates in DNA damage response and pre-mRNA processing. The role of PRPF19 in cancer is unclear. Here, we report that the expression of PRPF19 in human tongue cancer is associated with unfavorable prognosis. Overexpression of PRPF19 promotes while knockdown of PRPF19 inhibits tongue cancer cell migration, proliferation, and tumor growth. Overexpression of PRPF19 increases the resistance of tongue cancer cells to radiation and cisplatin treatment. Furthermore, PRPF19 regulates the expression of solute carrier family 40 member 1 (SLC40A1) and mono-ADP ribosylhydrolase 2 (MACROD2), knockdown of SLC40A1 or MACROD2 decreases the sensitivity of tongue cancer cells to radiation and cisplatin treatment. Thus, our results establish a key role of PRPF19 in tongue cancer growth and chemoradiotherapy resistance, targeting PRPF19 would be an effective therapeutic strategy for tongue cancer, especially for those resistant to chemoradiotherapy.