Tumor Suppressor Capacity of Krüppel Like Factor 4 (KLF4) in NOTCH1-Induced T-Cell Acute Lymphoblastic Leukemia

Abstract 1325

Acute lymphoblastic leukemia (ALL) is the most common hematological malignancy in children, among which T-cell ALL (T-ALL) exhibits worst prognosis. Studies on genetic factors supporting T-ALL leukemogenesis will contribute to the development of alternative therapies. Previously our laboratory described that the Krüppel like factor 4 (KLF4) restricts proliferation in normal CD8+ T cells. In addition, we have found that loss of KLF4 increases self-renewal and enhances survival of normal hematopoietic stem cells, which is a feature that cancer cells acquire during transformation. There are also emerging evidences showing reduced levels of KLF4 in bone marrow of T-ALL patients compared to healthy individuals and a correlation of KLF4 expression with response of ALL patients to standard treatment. Collectively, these findings suggest a potential role of KLF4 in tumor suppression and drug resistance in hematological malignancies. To study whether KLF4 functions as a tumor suppressor in T-ALL, we used Klf4 conditional knockout mice and NOTCH1-induced T-ALL model. Bone marrow (BM) cells from control (Klf4^fl/fl) and Klf4 deleted (Klf4^fl/fl; Vav-iCre) mice injected with 5-FU were transduced with retrovirus carrying the NOTCH1-L1601P-DP mutant found in human T-ALL patients and then transplanted into irradiated recipient mice. Mice transplanted with transduced control BM cells showed lower incidence of leukemia (21.7%, n=23) with longer median latency (130 days). In contrast, mice transplanted with transduced Klf4-deleted BM cells showed significantly higher penetrance (76.5%, n=34) with shorter median latency (93 days, p<0.01). Moribund mice from both groups showed similar infiltration of leukemic cells in liver, kidney, testis, brain and spleen. Immunoblots of leukemic cells purified from BM of diseased mice showed increased levels of Cyclin D1 and phospho-Rb in Klf4-deleted cells, suggesting enhanced proliferation. In addition to increased proliferative activity, a global gene expression analysis revealed significant differences in metabolic pathways. Concomitantly, Klf4-deleted leukemic cells displayed increased levels of phosphorylated mTOR, an important signaling involved in the metabolic reprogramming of cancer cells. Collectively, our study shows that KLF4 has tumor suppressor function in a mouse model of NOTCH1-induced T-ALL, providing a novel molecular target to prevent expansion of pre-leukemic cells.