Importin β1 regulates cell growth and survival during adult T cell leukemia/lymphoma therapy

ML385, a selective inhibitor of Nrf2, demonstrates efficacy in the treatment of adult T-cell leukemia

Nrf2 plays a critical role in regulating cytoprotective transcriptional responses and glucose metabolism while also preventing inflammation-induced carcinogenesis. However, Nrf2 can paradoxically promote carcinogenesis. Here, we aimed to elucidate the role of Nrf2 in ATL associated with HTLV-1. HTLV-1-infected T-cell lines exhibited nuclear accumulation of Nrf2. Nrf2 knockdown along with the inhibition of its activity using ML385, decreased cell proliferation and survival. Furthermore, ML385-induced G1 arrest by enhancing γH2AX and p53 expression while downregulating CDK4/6, cyclin D2/E, and c-Myc. Additionally, ML385 triggered caspase-mediated apoptosis by downregulating the expression of anti-apoptotic proteins while upregulating pro-apoptotic proteins. The compound also induced necroptosis, promoted JNK phosphorylation, and inhibited the NF-κB, AP-1, and STAT3/5 signaling. Moreover, ML385 was found to reduce the expression of LDHA, glucose uptake, and the levels of lactate derived from glycolysis. Overall, these results suggest that Nrf2 functions as an oncogene in ATL and may represent a promising therapeutic target.

A New Strategy for Adult T-Cell Leukemia Treatment Targeting Glycogen Synthase Kinase-3β

OBJECTIVES

The role of glycogen synthase kinase (GSK)-3β in adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type 1 (HTLV-1) is paradoxical and enigmatic. Here, we investigated the role of GSK-3β and its potential as a therapeutic target for ATL.

METHODS

Cell proliferation/survival, cell cycle, apoptosis, and reactive oxygen species (ROS) generation were examined using the WST-8 assay, flow cytometry, and Hoechst 33342 staining, respectively. Expression of GSK-3β and cell cycle/death-related proteins, and survival signals was analyzed using RT-PCR, immunofluorescence staining, and immunoblotting.

RESULTS

HTLV-1-infected T-cell lines showed nuclear accumulation of GSK-3β. GSK-3β knockdown and its inhibition with 9-ING-41 and LY2090314 suppressed cell proliferation/survival. 9-ING-41 induced G2/M arrest by enhancing the expression of γH2AX, p53, p21, and p27, and suppressing the expression of CDK1, cyclin A/B, and c-Myc. It induced caspase-mediated apoptosis by decreasing the expression of Bcl-xL, Mcl-1, XIAP, c-IAP1/2, and survivin, and increasing the expression of Bak and Bax. 9-ING-41 also induced ferroptosis and necroptosis, promoted JNK phosphorylation, and suppressed IKKγ and JunB expression. It inhibited the phosphorylation of IκBα, Akt, and STAT3/5, induced ROS production, and reduced glycolysis-derived lactate levels.

CONCLUSION

GSK-3β functions as an oncogene in ATL and could be a potential therapeutic target.

Inhibitory effect of a neddylation blockade on HTLV-1-infected T cells via modulation of NF-κB, AP-1, and Akt signaling

Adult T-cell leukemia (ATL), caused by HTLV-1, is the most lethal hematological malignancy. NEDD8-activating enzyme (NAE) is a component of the NEDD8 conjunction pathway that regulates cullin-RING ubiquitin ligase (CRL) activity. HTLV-1-infected T cells expressed higher levels of NAE catalytic subunit UBA3 than normal peripheral blood mononuclear cells. NAE1 knockdown inhibited proliferation of HTLV-1-infected T cells. The NAE1 inhibitor MLN4924 suppressed neddylation of cullin and inhibited the CRL-mediated turnover of tumor suppressor proteins. MLN4924 inhibited proliferation of HTLV-1-infected T cells by inducing DNA damage, leading to S phase arrest and caspase-dependent apoptosis. S phase arrest was associated with CDK2 and cyclin A downregulation. MLN4924-induced apoptosis was mediated by the upregulation of pro-apoptotic and downregulation of anti-apoptotic proteins. Furthermore, MLN4924 inhibited NF-κB, AP-1, and Akt signaling pathways and activated JNK. Therefore, neddylation inhibition is an attractive strategy for ATL therapy. Our findings support the use of MLN4924 in ATL clinical trials.

Pivotal role of dihydroorotate dehydrogenase as a therapeutic target in adult T-cell leukemia

OBJECTIVES

We aimed to determine the role of dihydroorotate dehydrogenase (DHODH) in pathogenesis of adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type 1 (HTLV-1) and the effects of its inhibition on the de novo pyrimidine biosynthesis pathway.

METHODS

Cell proliferation, viability, cycle, and apoptosis were analyzed using WST-8 assays, flow cytometry, and Hoechst 33342 staining. To elucidate the molecular mechanisms involved in the anti-ATL effects of DHODH knockdown and inhibition, RT-PCR and immunoblotting were conducted.

RESULTS

HTLV-1-infected T-cell lines aberrantly expressed DHODH. Viral infection and the oncoprotein, Tax, enhanced DHODH expression, while knockdown of DHODH decreased HTLV-1-infected T-cell growth. In addition, BAY2402234, a DHODH inhibitor, exerted an anti-proliferative effect, which was reversed by uridine supplementation. BAY2402234 induced DNA damage and S phase arrest by downregulating c-Myc, CDK2, and cyclin A and upregulating p53 and cyclin E. It also induced caspase-mediated apoptosis by the upregulation of pro-apoptotic and downregulation of anti-apoptotic proteins. Furthermore, BAY2402234 induced caspase-independent ferroptosis and necroptosis. It decreased phosphorylation of IKK, IκBα, PTEN, Akt, and its downstream targets, suggesting that inhibition of NF-κB and Akt signaling is involved in its anti-ATL action.

CONCLUSION

These findings highlight DHODH as a potential therapeutic target for treating ATL.

Mouse Models for HTLV-1 Infection and Adult T Cell Leukemia

Adult T cell leukemia (ATL) is an aggressive hematologic disease caused by human T cell leukemia virus type 1 (HTLV-1) infection. Various animal models of HTLV-1 infection/ATL have been established to elucidate the pathogenesis of ATL and develop appropriate treatments. For analyses employing murine models, transgenic and immunodeficient mice are used because of the low infectivity of HTLV-1 in mice. Each mouse model has different characteristics that must be considered before use for different HTLV-1 research purposes. HTLV-1 Tax and HBZ transgenic mice spontaneously develop tumors, and the roles of both Tax and HBZ in cell transformation and tumor growth have been established. Severely immunodeficient mice were able to be engrafted with ATL cell lines and have been used in preclinical studies of candidate molecules for the treatment of ATL. HTLV-1-infected humanized mice with an established human immune system are a suitable model to characterize cells in the early stages of HTLV-1 infection. This review outlines the characteristics of mouse models of HTLV-1 infection/ATL and describes progress made in elucidating the pathogenesis of ATL and developing related therapies using these mice.

Heat shock factor 1 is a promising therapeutic target against adult T-cell leukemia

Patients with adult T-cell leukemia (ATL), which is caused by human T-cell leukemia virus type 1 (HTLV-1), show poor prognosis because of drug resistance. Heat shock protein (HSP) 90 is reportedly essential for ATL cell survival as it regulates important signaling pathways, thereby making HSP90 inhibitors new therapeutic candidates for ATL. However, HSP90 inhibition increases the expression of other HSPs, suggesting that HSPs may contribute to drug resistance. The heat shock factor 1 (HSF1) transcription factor is the primary regulator of the expression of HSPs. Furthermore, targeting HSF1 disrupts the HSP90 chaperone function. Herein, we demonstrated that HSF1 is overexpressed in HTLV-1-infected T cells. HSF1 knockdown inhibited the proliferation of HTLV-1-infected T cells. HSF1 inhibitor KRIBB11 reduced the expression and phosphorylation of HSF1, downregulated HSP70 and HSP27 expression, and suppressed Akt, nuclear factor-κB, and AP-1 signals. KRIBB11 treatment induced DNA damage, upregulated p53 and p21, and reduced the expression of cyclin D2/E, CDK2/4, c-Myc, MDM2, and β-catenin, thereby preventing retinoblastoma protein phosphorylation and inhibiting G1-S cell cycle progression. KRIBB11 also induced caspase-mediated apoptosis concomitant with the suppression of Bcl-xL, Mcl-1, XIAP, c-IAP1/2, and survivin expression. KRIBB11 inhibited HSP70 and HSP90 upregulation through treatment with AUY922, an HSP90 inhibitor, and enhanced the cytotoxic effect of AUY922, suggesting a salvage role of HSF1-dependent HSP induction in response to drug treatment. Finally, treatment of mice with KRIBB11 reduced ATL tumor growth. Therefore, this study provides a strong rationale to target HSF1 and validates the anti-ATL activity of KRIBB11.

Exportin-1 is critical for cell proliferation and survival in adult T cell leukemia

Since treatment options for adult T cell leukemia (ATL) associated with human T cell leukemia virus type 1 (HTLV-1) fail to obtain long-term response, novel therapies targeting ATL-dysregulated pathways are necessary. Dysregulated nuclear import and export machinery is common in malignancies. This study aimed to investigate the potential of exportin-1 (XPO1), which mediates nuclear export of cargos, as a target in ATL. RT-PCR and western blotting were performed to determine XPO1 expression. We evaluated XPO1's effects on cell proliferation and viability through WST-8 assays, cell cycle and apoptosis via Hoechst 33342 staining and flow cytometry, and intracellular signaling cascades using western blotting. XPO1 expression was upregulated in HTLV-1-infected T cells. XPO1 knockdown reduced cell proliferation. XPO1 inhibitor KPT-330 also reduced proliferation, increased DNA damage, and induced G1 cell cycle arrest and caspase-dependent apoptosis. KPT-330 downregulated cell cycle regulators (CDK2/4/6, cyclin D2, c-Myc and phosphorylated pRb) and anti-apoptotic proteins (XIAP, c-IAP1/2, survivin and Mcl-1), and upregulated p53, p21 and Bak. KPT-330 suppressed XPO1 and increased the nuclear localization of cargos (NF-κB RelA and its negative regulator IκBα, protein phosphatase 2A and its inhibitor SET, p53 and its negative regulator MDM2, p21, p27, FOXO1 and pRb). KPT-330 treatment resulted in the abrogation of aberrant pathways (NF-κB, Akt and STAT3/5) simultaneously through the activation of tumor suppressor proteins and inhibition of oncogenes and proliferative/survival factors. These findings encourage investigating the use of KPT-330 in clinical trials targeting ATL.