Regulation of Small GTPase Rab20 by Ikaros in B-Cell Acute Lymphoblastic Leukemia

• Main Authors: Jonathon L Payne, Chunhua Song, Yali Ding, Pavan Kumar Dhanyamraju, Yevgeniya Bamme, Joseph W Schramm, Dhimant Desai, Arati Sharma, Chandrika Gowda, Sinisa Dovat
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: International Journal of Molecular Sciences
• Subjects: ikaros; ck2; pp1; rab20; b-all
• Online Access: https://www.mdpi.com/1422-0067/21/5/1718

Ikaros is a DNA-binding protein that regulates gene expression and functions as a tumor suppressor in B-cell acute lymphoblastic leukemia (B-ALL). The full cohort of Ikaros target genes have yet to be identified. Here, we demonstrate that Ikaros directly regulates expression of the small GTPase, Rab20. Using ChIP-seq and qChIP we assessed Ikaros binding and the epigenetic signature at the RAB20 promoter. Expression of Ikaros, CK2, and <i>RAB20</i> was determined by qRT-PCR. Overexpression of Ikaros was achieved by retroviral transduction, whereas shRNA was used to knockdown Ikaros and CK2. Regulation of transcription from the <i>RAB20</i> promoter was analyzed by luciferase reporter assay. The results showed that Ikaros binds the <i>RAB20</i> promoter in B-ALL. Gain-of-function and loss-of-function experiments demonstrated that Ikaros represses <i>RAB20</i> transcription via chromatin remodeling. Phosphorylation by CK2 kinase reduces Ikaros&#8217; affinity toward the <i>RAB20</i> promoter and abolishes its ability to repress <i>RAB20</i> transcription. Dephosphorylation by PP1 phosphatase enhances both Ikaros&#8217; DNA-binding affinity toward the <i>RAB20</i> promoter and <i>RAB20</i> repression. In conclusion, the results demonstrated opposing effects of CK2 and PP1 on expression of Rab20 via control of Ikaros&#8217; activity as a transcriptional regulator. A novel regulatory signaling network in B-cell leukemia that involves CK2, PP1, Ikaros, and Rab20 is identified.