Tax and Semaphorin 4D Released from Lymphocytes Infected with Human Lymphotropic Virus Type 1 and Their Effect on Neurite Growth

Abstract

Human lymphotropic virus type 1 (HTLV-1) is a retrovirus causing HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurodegenerative central nervous system (CNS) axonopathy. This virus mainly infects CD4 + T lymphocytes without evidence of neuronal infection. Viral Tax, secreted from infected lymphocytes infiltrated in the CNS, is proposed to alter intracellular pathways related to axonal cytoskeleton dynamics, producing neurological damage. Previous reports showed a higher proteolytic release of soluble Semaphorin 4D (sSEMA-4D) from CD4 + T cells infected with HTLV-1. Soluble SEMA-4D binds to its receptor Plexin-B1, activating axonal growth collapse pathways in the CNS. In the current study, an increase was found in both SEMA-4D in CD4+ T cells and sSEMA-4D released to the culture medium of peripheral blood mononuclear cells (PBMCs) from HAM/TSP patients compared to asymptomatic carriers and healthy donors. After a 16-h culture, infected PBMCs showed significantly higher levels of CRMP-2 phosphorylated at Ser 522 . The effect was blocked either with anti-Tax or anti-SEMA-4D antibodies. The interaction of Tax and sSEMA-4D was found in secreted medium of PBMCs in patients, which might be associated with a leading role of Tax with the SEMA-4D-Plexin-B1 signaling pathway. In infected PBMCs, the migratory response after transwell assay showed that sSEMA-4D responding cells were CD4 + Tax + T cells with a high CRMP-2 pSer 522 content. In the present study, the participation of Tax-sSEMA-4D in the reduction in neurite growth in PC12 cells produced by MT2 (HTLV-1-infected cell line) culture medium was observed. These results lead to the participation of plexins in the reported effects of infected lymphocytes on neuronal cells.

Roles of Semaphorins in Neurodegenerative Diseases

“…To test the effect of Tax and Sema4D (or the Tax/Sema4D complex) in neuronal cells, culture media from infected lymphocytes were added to PC12 cells during their differentiation to neuronal type, finding decreased neurite length as a result. The effect of HTLV-1-infected PBMC culture media was blocked by both anti-Sema4D and anti-Tax antibodies, suggesting neurite length reduction by a Tax/Sema4D complex [142]. In the same report, it was shown that infected lymphocytes strongly migrate in response to Sema4D using a trans-well system.…”

“…In the same report, it was shown that infected lymphocytes strongly migrate in response to Sema4D using a trans-well system. It was found that in the population of migrated lymphocytes, the levels of CRMP-2 phosphorylation at Ser522 were increased [142]. A change in Sema4Dmediated phosphorylation of CRMP-2 could be responsible for the increased motility.…”

“…Using in vitro culture of PBMCs from HAM/TSP patients, it has been recently found that the levels of secreted Sema4D were increased compared to healthy subjects [142]. Elevated Sema4D could be explained as a result of increased levels of MT1-MMP-the enzyme responsible for generating soluble Sema4D (Sema4D) from the transmembrane Sema4D-found in PBMCs from HAM/TSP patients.…”

“…A change in Sema4Dmediated phosphorylation of CRMP-2 could be responsible for the increased motility. Authors proposed that infected lymphocytes have an increased migratory response toward Sema4D, making them able to cross the BBB [142]. Once in the CNS, infected lymphocytes secrete Tax and Sema4D, attracting more HTLV-1-infected lymphocytes at the same time that these proteins could mediate pathological disturbances on neuronal cells.…”

CRMP4-mediated fornix development involves Semaphorin-3E signaling pathway

“…Eluted fractions were analyzed by mass spectrometry to identify MAP6 partners. Interestingly, proteins in the CRMP family, members of which are known to play critical roles during semaphorin signaling ( Arbeille et al, 2015 ; Goshima et al, 1995 ; Niisato et al, 2012 ; Quintremil et al, 2016 ; Uchida et al, 2009 ; Yamashita et al, 2007 ), were identified as MAP6 partners. More precisely, we identified twelve specific peptides belonging to CRMP2, three specific peptides from CRMP4, two specific peptides from CRMP1, and six peptides shared by two or three of these CRMP proteins ( Supplementary file 1 ).…”