Dysregulation of the tumor suppressor Menin and its target Bach2 in HTLV-1 infection.

Background: The tumor suppressor Menin, prone to mutations in both hereditary and sporadic endocrine tumors, along with its direct target Bach2, plays a crucial role in preventing autoimmunity by regulating CD4 + T cell senescence and maintaining cytokine homeostasis. Since human T-cell leukemia virus type 1 (HTLV-1) primarily infects CD4 + T cells, and its dysregulation contributes to both the hematological malignancy of adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), we examined the involvement of the Menin-Bach2 pathway in HTLV-1 infection.

Methods: The mRNA expression of menin and bach2 in HTLV-1-infected and uninfected human T-cell lines, peripheral blood mononuclear cells (PBMCs) from patients with ATL, HAM/TSP, and asymptomatic carriers were analyzed. Additionally, interactions between Menin or Bach2 and the Tax or HBZ; the subcellular localization of these proteins; the effect of knockdown of menin, tax, and HBZ genes; and the effects of interaction inhibitors between menin and its cofactor, mixed lineage leukemia (MLL), on the proliferation of HTLV-1-infected T cells were evaluated.

Results: The findings were as follows: (1) In all eight HTLV-1-infected T-cell lines tested, Menin protein was expressed, whereas Bach2 expression was absent in five of them; (2) the mRNA levels of both menin and bach2 significantly decreased in PBMCs from patients with HAM/TSP and ATL; (3) Tax and HBZ each physically interacted with both Menin and Bach2; (4) knockdown of tax, but not HBZ, downregulated Bach2, but not Menin expression in HTLV-1-transformed T-cell lines MT-2 and SLB-1; (5) knockdown of menin downregulated Bach2 expression in MT-2 but not in SLB-1; (6) A Menin-MLL interaction inhibitor suppressed cell growth of MT-2 but not in SLB-1; (7) HBZ and Menin exhibited different subcellular localization between MT-2 and SLB-1.

Conclusions: HTLV-1 infection alters the regulation of the Menin-Bach2 pathway, which controls cell proliferation. The Menin-MLL interaction inhibitor loses its effectiveness in suppressing cell proliferation when Menin loses control over Bach2 expression. Dysregulation of the Menin-Bach2 pathway may contribute to HTLV-1-associated disease pathogenesis.