RalA, a GTPase targeted by miR-181a, promotes transformation and progression by activating the Ras-related signaling pathway in chronic myelogenous leukemia

Abstract

BCR/ABL is a well-known activator of multiple signaling pathways. RalA, a Ras downstream signaling molecule and a small GTPase, plays an important role in Bcr-Abl-induced leukemogenesis but the exact mechanism remains elusive. Here, we show that RalA GTPase activity is commonly high in chronic myelogenous leukemia (CML) cell lines and patient samples. Overexpression of RalA results in malignant transformation and progression, and induces resistance to imatinib (IM) in BaF3 and K562 cell lines. RalA reduced survival and led to IM resistance in a xenografted mouse model. Ablation of RalA by either siRNA or miR-181a, a RalA targeting microRNA, attenuated the malignant phenotypes in K562 cells. RBC8, a selective Ral inhibitor, enhanced the inhibitory effects of IM in K562, KCL22 and BaF3-P210 cells. Interestingly, the phospho-specific protein microarray assay revealed that multiple phosphorylation signal proteins were decreased by RalA inhibition, including SAPK, JNK, SRC, VEGFR2, P38 MAPK, c-Kit, JunB, and Keratin18. Among them, P38 MAPK and SAPK/JNK are Ras downstream signaling kinases. Taken together, RalA GTPase might be an important oncogene activating the Ras-related signaling pathway in CML.

Antitumor Effects of Blocking Protein Neddylation in T315I-BCR-ABL Leukemia Cells and Leukemia Stem Cells

“…The parental BaF3 cells were cultured in RPMI1640 with IL3. The BaF3 cells stably expressing either 210-kDa WT-BCR-ABL (BaF3-BCR-ABL) or T315I-BCR-ABL (BaF3-T315I) and KCL-22 cells were generously provided by Dr. Jia Fei (Medical College of Jinan University, Guangzhou, China) and maintained in RPMI1640 with 10% FBS (20). Cells were incubated at 37 C in a humidified incubator containing 5% CO 2 .…”

Ral signaling pathway in health and cancer

“…Rals regulate tumorigenesis and cancer progression in three ways: (1) through activation of Ral effector proteins such as RalBP1 and kinase Aurora A, (2) via activation of several signaling pathways such as phosphaolipase D1, Src, JNK, NF‐kB, and cyclin D, and (3) by phosphorylation of Ral proteins . Ral activation was shown to be involved in a number of different tumor types such as lung , colorectal , melanoma , pancreatic , squamous cell carcinoma , hepatocellular carcinoma , prostate , ovarian , bladder , chronic myelogenous leukemia , peripheral nerve sheath tumors , and medulloblastoma . Studies have even been completed showing Ral‐A autoantibodies as a potentially useful serum biomarker for prostate adenocarcinoma .…”

RCC2, a regulator of the RalA signaling pathway, is identified as a novel therapeutic target in cisplatin‐resistant ovarian cancer

“…In the downstream signaling pathway, Ral small GTPases (RalA), a member of the Ras branch of the Ras superfamily (19), has been shown to be significantly activated in colorectal cancer tissues and cell lines positively regulating cell growth and proliferation in a study by Martin et al (20). RalA is also involved in multifarious cancer progression, such as cervical cancer (21), hepatocellular carcinoma (22), chronic myelogenous leukemia (23), lung cancer (24), colorectal cancer (20), breast cancer (25) etc. In addition, Ral proteins mediate their activities through multiple downstream effectors, of which Ral binding protein-1 (RalBP1) is an important downstream effector, which is expressed at higher levels in cancer cells (26,27).…”

“…(20). RalA is also involved in multifarious cancer progression, such as cervical cancer (21), hepatocellular carcinoma (22), chronic myelogenous leukemia (23), lung cancer (24), colorectal cancer (20), breast cancer (25) etc . In addition, Ral proteins mediate their activities through multiple downstream effectors, of which Ral binding protein‐1 (RalBP1) is an important downstream effector, which is expressed at higher levels in cancer cells (26, 27).…”