The ESCRT-0 Protein HRS Interacts with the Human T Cell Leukemia Virus Type 2 Antisense Protein APH-2 and Suppresses Viral Replication

Abstract

The divergent clinical outcomes of human T cell leukemia virus type 1 (HTLV-1) and HTLV-2 infections have been attributed to functional differences in their antisense proteins. In contrast to HTLV-1 bZIP factor (HBZ), the role of the antisense protein of HTLV-2 (APH-2) in HTLV-2 infection is poorly understood. In previous studies, we identified the endosomal sorting complex required for transport 0 (ESCRT-0) subunit HRS as a novel interaction partner of APH-2 but not HBZ. HRS is a master regulator of endosomal protein sorting for lysosomal degradation and is hijacked by many viruses to promote replication. However, no studies to date have shown a link between HTLVs and HRS. In this study, we sought to characterize the interaction between HRS and APH-2 and to investigate the impact of HRS on the life cycle of HTLV-2. We confirmed a direct specific interaction between APH-2 and HRS and showed that the CC2 domain of HRS and the N-terminal domain of APH-2 mediate their interaction. We demonstrated that HRS recruits APH-2 to early endosomes, possibly furnishing an entry route into the endosomal/lysosomal pathway. We demonstrated that inhibition of this pathway using either bafilomycin or HRS overexpression substantially extends the half-life of APH-2 and stabilizes Tax2B expression levels. We found that HRS enhances Tax2B-mediated long terminal repeat (LTR) activation, while depletion of HRS enhances HTLV-2 production and release, indicating that HRS may have a negative impact on HTLV-2 replication. Overall, our study provides important new insights into the role of the ESCRT-0 HRS protein, and by extension the ESCRT machinery and the endosomal/lysosomal pathway, in HTLV-2 infection. IMPORTANCE While APH-2 is the only viral protein consistently expressed in infected carriers, its role in HTLV-2 infection is poorly understood. In this study, we characterized the interaction between the ESCRT-0 component HRS and APH-2 and explored the role of HRS in HTLV-2 replication. HRS is a master regulator of protein sorting for lysosomal degradation, a feature that is manipulated by several viruses to promote replication. Unexpectedly, we found that HRS targets APH-2 and possibly Tax2B for lysosomal degradation and has an overall negative impact on HTLV-2 replication and release. The negative impact of interactions between HTLV-2 regulatory proteins and HRS, and by extension the ESCRT machinery, may represent an important strategy used by HTLV-2 to limit virus production and to promote persistence, features that may contribute to the limited pathogenic potential of this infection.

HTLV-2 Encoded Antisense Protein APH-2 Suppresses HIV-1 Replication

“…Our findings highlight the functional involvement of the IXXLL motif. These results highlighting the importance of the N-terminal region of APH-2 and are compatible with the study by Martini et al, which identified a similar domain of APH-2 for the interaction with the PSAP domain of HRS [ 27 ]. Although the Tat-mediated transcription was affected in the presence of APH-2, we did not find a specific association between APH-2 and Tat, indicating that HTLV-2 APH-2 may not directly engage HIV-1 Tat to impose its inhibitory effect.…”

“…The negative regulator APH-2 crucially controls HTLV-2 replication by influencing transcription [ 6 , 7 ]. Recent studies also explored its role in managing viral release and budding [ 27 ]. Considering the common aspects between HIV-1 and HTLV-2 such as lineage, mode of transcription, replication and the clinical impact of co-infection over the disease progression of HIV-1, there might be a possible intervening effect of viral regulators on replication of one another.…”

“…This could be attributed to the functional differences between HBZ and APH-2 [ 12 ], leading to contradictory effects on HIV-1 transcription. A recent study by Martini et al highlighted the association of APH-2 with a component of the host endosomal-sorting complex required for transport (ESCRT) [ 27 ]. ESCRT-0 hepatocyte growth factor regulated tyrosine kinase substrate (HRS) recruits ESCRT-I by interacting with TSG 101, followed by recruitment of complex II and III sequentially to promote budding and release of vesicles.…”

Virion Secretion of Hepatitis B Virus Naturally Occurring Core Antigen Variants

“…In addition to an effect on HBV transcription, HGS can diminish the pool size of intracellular nucleocapsids with ongoing genome maturation, probably in part by promoting the secretion of naked capsids. Recently, HGS was also found to be important in the life cycle of RNA viruses, such as chikungunya virus [65] and HTLV-2 [66]. Table 1.…”

HBV enveloped particle secretion is positively regulated by GRP78 through direct interaction with preS1

“…The copyright holder for this this version posted December 10, 2021. ; https://doi.org/10.1101/2021.12.08.471876 doi: bioRxiv preprint HBV-particle secretion. Vps4 and the molecular endosomal sorting complexes required for transport (ESCRT) machinery could cooperate in the secretion of the HBV virion (10,11). Cellular kinases can regulate virion formation and promote intracellular capsid accumulation by modifying capsid phosphorylation (12)(13)(14).…”