hnRNP K Is a Novel Internal Ribosomal Entry Site-Transacting Factor That Negatively Regulates Foot-and-Mouth Disease Virus Translation and Replication and Is Antagonized by Viral 3C Protease

Abstract

Cap-independent translation initiation on picornavirus mRNAs is mediated by an internal ribosomal entry site (IRES) in the 5′ untranslated region. Regulation of internal initiation requires the interaction of IRES-transacting factors (ITAFs) with the IRES. In this study, we identified a novel ITAF, heterogeneous nuclear ribonucleoprotein K (hnRNP K), which negatively regulates foot-and-mouth disease virus (FMDV) translation and viral replication. Further investigation revealed that the KH2 and KH3 domains of hnRNP K directly bind to domains II, III and IV of the FMDV IRES, resulting in the inhibition of IRES-mediated translation by interfering with the recognition of another positive ITAF, polypyrimidine tract-binding protein (PTB). Conversely, hnRNP K-mediated inhibition is antagonized by the viral 3C protease through cleavage of hnRNP K at the Glu-364 residue during FMDV infection. Interestingly, the N-terminal cleavage product, hnRNP K1-364, retains partial inhibitory effects on IRES activity, whereas the C-terminal cleavage product hnRNP K364-465 becomes a positive regulator of FMDV replication. Our findings expand the current understanding of virus-host interactions concerning viral recruitment and modulation of ITAFs, providing new insights into translational control during viral infection. IMPORTANCE The translation of picornaviral genome RNA mediated by the internal ribosomal entry site (IRES) is a crucial step for virus infections. Virus-host interactions play a critical role in the regulation of IRES-dependent translation, but the regulatory mechanism remains largely unknown. In this study, we identified an ITAF, hnRNP K, that negatively regulates FMDV replication by inhibiting viral IRES-mediated translation. In addition, we describe a novel translational regulation mechanism involving proteolytic cleavage of hnRNP K by FMDV protease 3C. The cleavage of hnRNP K yields two cleavage products with opposite functions: the cleavage product hnRNP K1-364 retains a partial inhibitory effect on IRES activity, and the cleavage product hnRNP K364-465 becomes a positive regulator of FMDV replication. Our findings shed light on the effect of a novel ITAF on the translational regulation of picornavirus, and provide new insights into translational control during viral infection.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

“…In the context of viral infections, the recruitment of RBPs that function as ITAFs, controlling the activity of viral and cellular IRESs, and the sequestration of RBPs regulating the expression of cytokine and stress response mRNAs may have a direct impact on the antiviral response [384]. Among canonical and non-canonical ITAFs (see for reviews [384,385]), G3BP1 [69,386], heterogeneous nuclear ribonucleoprotein (hnRNP) A1 [278,387], poly(rC) binding protein 2 (PCBP2), [279,388,389], receptor for activated C kinase 1 (RACK1) [292,390], PTB [280,391], RNA-binding motif protein 4 (RBM4) [282], Hu Antigen R (HuR) [392,393], and hnRNPK [283,394] localize in SGs. Interestingly, the anti-apoptotic Bcl-xL mRNA was found to be sequestered together with its inhibitory ITAFs in SGs, which prevents its translation during osmotic stress [395].…”

The DDX23 Negatively Regulates Translation and Replication of Foot-and-Mouth Disease Virus and Is Degraded by 3C Proteinase

“…The IRES of FMDV strongly dependent on cellular helicases and IRES transacting factors (ITAFs). ITAFs such as PCBP2, PTB, ERBB3-binding protein 1, FBP2, FBP1, hnRNPA1, G3BP1, and CSDE1, ARF5, Rab1b, Gemin5, Sam68, hnRNPK, [14][15][16][17][18][19][20][21][22] may have IRES-promoting or repressing activity [23]. For example, polypyrimidine tract-binding protein (PTB) is the component of the 80S and 48S ribosomal initiation complex formed when FMDV internal ribosome entry site RNA recruits the ribosome.…”

“…Pull-down assay revealed that Gemin5 forms two complexes, eIF4E containing IRES-independent complex and ribonucleoprotein-IRES complex, which play critical roles in translation regulatory activity [20]. Recently, it was identified that novel ITAF, heterogeneous nuclear ribonucleoprotein (hnRNPK), a negative regulator of FMDV IRES translation, interacted with the FMDV IRES II, III and IV domains via KH2 and KH3 domain sites and inhibited the viral replication [22]. To this end, the virus-host interplay is a crucial step in viral replication.…”

Ribosomal Protein L13 Participates in Innate Immune Response Induced by Foot-and-Mouth Disease Virus

“…During its long-term evolution, FMDV has acquired a series of mechanisms with which to antagonize the antiviral activity of the host. Studies have shown that to block the activation of the innate immune system, FMDV inhibits, cleaves, or blocks some nodal molecules in the immune response signaling pathways mediated by PRRs with its own proteins, especially the FMDV nonstructural proteins L pro and 3C pro (28)(29)(30). Both L pro and 3C pro have protease activity and participate in the cleavage of FMDV polymer precursor proteins to form mature viral proteins.…”