Tissue Transglutaminase Regulates Steroid Resistance in Acute Lymphoblastic Leukemia Via Nuclear Factor-Kappa B Related Signaling Pathways

Steroid resistance is lethal to the patients with acute lymphoblastic leukemia (ALL). To improve survival for steroid-resistant ALL patients, it is necessary to develop innovative therapeutic strategies to overcome steroid resistance. Tissue transglutaminase (TG2) is an intracellular calcium-dependent protein cross-linking enzyme reported to be over-expressed in various metastatic or chemotherapy-resistant cancer cells including lymphoma cells. Chronic expression of TG2 constitutively activates nuclear factor kappa B (NF-kappaB) and it is directed linked to NF-kappaB-related signaling networks including hypoxia-inducible factor-1 (HIF-1), Zeb, Snail, or Twist that influence drug resistance or metastasis in inflammatory or cancer cells. In the present study, we used biochemical and molecular methodologies to demonstrate that steroid resistance was associated with TG2-regulated signaling pathways including NF-kappaB and its downstream transcriptional factors in steroid-resistant ALL. We generated steroid-adapted subclones of ALL cell lines that were extremely more resistant to steroid than the parent cells. We found that steroid-resistant ALL cells expressed elevated levels of TG2 and the modification of TG2 activities altered NF-kappaB expression in this cells. TG2-related NF-kappaB activation modulated the expression of HIF-1 and NF-kappaB-targeted genes such as Zeb, Snail, and Twist in steroid-resistant ALL cells. Also, TG2 inhibition improved the cytotoxicity of steroid in steroid-resistant ALL cells. This is the first study to show the link between TG2, NF-kappaB, its downstream signaling networks, and steroid resistance in ALL. TG2 inhibition could be used as an alternative target to overcome steroid resistance in ALL. Furthermore, TG2 and HIF-1 expression could serve as new biomarkers of steroid resistance evolution or cancer recurrence in ALL.