Co-dependence of HTLV-1 p12 and p8 Functions in Virus Persistence

Abstract

HTLV-1 orf-I is linked to immune evasion, viral replication and persistence. Examining the orf-I sequence of 160 HTLV-1-infected individuals; we found polymorphism of orf-I that alters the relative amounts of p12 and its cleavage product p8. Three groups were identified on the basis of p12 and p8 expression: predominantly p12, predominantly p8 and balanced expression of p12 and p8. We found a significant association between balanced expression of p12 and p8 with high viral DNA loads, a correlate of disease development. To determine the individual roles of p12 and p8 in viral persistence, we constructed infectious molecular clones expressing p12 and p8 (D26), predominantly p12 (G29S) or predominantly p8 (N26). As we previously showed, cells expressing N26 had a higher level of virus transmission in vitro. However, when inoculated into Rhesus macaques, cells producing N26 virus caused only a partial seroconversion in 3 of 4 animals and only 1 of those animals was HTLV-1 DNA positive by PCR. None of the animals exposed to G29S virus seroconverted or had detectable viral DNA. In contrast, 3 of 4 animals exposed to D26 virus seroconverted and were HTLV-1 positive by PCR. In vitro studies in THP-1 cells suggested that expression of p8 was sufficient for productive infection of monocytes. Since orf-I plays a role in T-cell activation and recognition; we compared the CTL response elicited by CD4+ T-cells infected with the different HTLV-1 clones. Although supernatant p19 levels and viral DNA loads for all four infected lines were similar, a significant difference in Tax-specific HLA.A2-restricted killing was observed. Cells infected with Orf-I-knockout virus (12KO), G29S or N26 were killed by CTLs, whereas cells infected with D26 virus were resistant to CTL killing. These results indicate that efficient viral persistence and spread require the combined functions of p12 and p8.

Human T Cell Leukemia Virus Type 1 Infection of the Three Monocyte Subsets Contributes to Viral Burden in Humans

“…Monocytes can be infected in vitro and in vivo by HTLV-1 (26,29,30,(33)(34)(35)(36)(37)(38)(39)(40). Furthermore, studies with nonhuman primates indicate that monocyte infection, which depends on the expression of the viral orf-I-encoded p8 and p12 proteins and the viral p30 protein, is pivotal for viral infectivity and persistence in vivo (38,40,41). However, recent in vitro studies by others demonstrated that infection of primary monocytes is abortive due to the expression of the sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1) restriction factor and that, by hydrolyzing endogenous deoxynucleoside triphosphates, it inhibits reverse transcription (RT) (42), calling into question the role of monocytes in viral persistence.…”

Expression of Alternatively Spliced Human T-Cell Leukemia Virus Type 1 mRNAs Is Influenced by Mitosis and by a Novel cis -Acting Regulatory Sequence

“…To identify a possible association between sequence variation of the 3= CRS and the proviral load or clinical outcome of HTLV-1-infected individuals, we aligned the nucleotide sequence of the region in proviruses identified in a cohort of 86 patients with clinical manifestations and 34 healthy carriers (36) (Fig. 6A).…”

First report of HTLV-1 truncated p12 protein in Brazil

“…22 In a very interesting study, ORF-I sequences of 160 HTLV-1 infected individuals from different areas of the world (including Brazil) were cloned and none of 1600 obtained sequences had a premature stop codon either. 3 In Japan, the prevalence of truncated p12 protein was 4% (n D 10) among HTLV-1 infected individuals. 20 An in vitro study demonstrated that strains producing a truncated p12 protein (without the amino acids 87-99) presented a dramatic reduction of NFAT activation.…”

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15] Previous studies demonstrated that mutations in p12 may influence the HTLV-1 infection outcome. 3,5,8,16,17 Here, we identified, at the first time, a HTLV-1 strain with a premature stop codon in p12 infecting an individual from Brazil, presenting a very low proviral load. We hypothesize if this mutation would have a protective role against HTLV-1 replication.…”

“…Interestingly, all described truncated proteins presented alleles that were previously associated with an increased expression of p12 (F3L, S23P, F34L/ F61L, S63P). 3 A transfection study, as performed by Pise-Masison et al (2014) to evaluate the expression profile of both proteins would be interesting.…”