Polimorfismo do gene TAX e seus elementos responsivos no genoma proviral do vírus t-linfotrópico humano do tipo 1 (HTLV-1): análise em portadores assintomáticos e sintomáticos do Estado do Maranhão

Abstract

Human T-lymphotropic virus type 1 (HTLV-1) is an oncogenic retrovirus that can lead to the development of adult T-cell leukemia/lymphoma (ATLL) and neurodegenerative diseases such as HTLV-1-associated myelopathy (HAM). HTLV-1 is endemic in certain countries, including Brazil, where prevalence rates in Maranhão range between 0.1%-0.99%. The HTLV-1 genome contains promoter sites in its 5’LTR region, such as Tax-responsive elements (TRE), and encodes the Tax protein, whose function and genetic polymorphisms are associated with infection pathogenesis and the clinical outcomes of carriers. Moreover, the interaction between Tax and TRE activates the transcription of viral elements. Thus, this study aims to analyze the promoter and coding regions of the proviral genome, LTR sequences and the tax gene, to identify circulating variants in the region and their possible association with disease in individuals living with HTLV. Using a convenience sampling approach, nine HTLV-1-positive individuals were included in this study: seven asymptomatic carriers and two with HAM. Infection confirmation was performed through ELISA and Western Blot serological tests. Extracted proviral DNA was used for nested PCR amplification of the LTR region and conventional PCR for tax, followed by Sanger sequencing. The obtained sequences were aligned with each other and with the ATK1 reference sequence to assess the presence of polymorphisms, and the tax sequences were also used for phylogenetic tree construction. Alignment of the promoter region of the nine LTR sequences identified the presence of polymorphisms A125G (7/9 samples) and G174A (7/9 samples) in the first and second TRE repeats, respectively. Alignment of the seven partial tax sequences revealed the presence of polymorphisms C7897T, C7959T, and G8208A (7/7 samples); T7891C (5/7); and C7930T (1/7). The nucleotide substitutions C7959T and G8208A resulted in nonsynonymous mutations leading to amino acid changes A→V and S→N, occurring in the NF-κB pathway activation and CREB protein domains of the Tax protein, respectively. The presence of these polymorphisms was associated with the transcontinental cosmopolitan taxA genotype, as revealed by phylogenetic analysis. When comparing the occurrence of polymorphisms between asymptomatic carriers and individuals with HAM, no statistically significant difference was observed. Evaluating polymorphism frequencies in both studied regions, A125G and G174A were more frequent in samples that also carried polymorphisms in tax. The analysis of LTR and tax regions demonstrated the presence of polymorphisms that may influence the activation dynamics of the proviral genome promoter region, as well as interfere with pathways leading to HTLV-related diseases. Furthermore, the identified tax polymorphisms are characteristic of Brazil, a pattern shaped by the introduction of the virus into the country, primarily through the transatlantic slave trade from Africa, which is reflected in the observed genotype. The identification of these polymorphisms contributes to the limited molecular data available in the literature, enhancing the understanding of viral diversity and its epidemiological and clinical implications.