Regulation of mTOR expression by Casein Kinase II (CK2) signaling pathway in leukemia
Authors: payne jonathan , Song Chunhua , Gowda Chandrika , Ding Yali , Iyer Soumya , Raju Pavan Kumar Dhanyam , Payne Kimberly , Dovat Sinisa 
Published: June 2021

The mammalian target of rapamycin(mTOR) is a kinase encoded by the MTOR gene. mTOR is a critical component of PI3K/mTOR/AKT signaling pathway that positively regulates proliferation of leukemia cells. Targeting mTOR and PI3K/mTOR/AKT pathway has been used to treat T‐cell acute lymphoblastic leukemia (T‐ALL). However, little is known about mechanisms that regulate transcription and expression of mTOR gene in T‐ALL. Here, we present the evidence that expression of mTOR in T‐ALL is regulated at transcriptional level by oncogenic Casein Kinase II (CK2) via direct phosphorylation of the Ikaros, a transcription factor and a tumor suppressor protein. Global chromatin immunoprecipitation coupled with the next‐generation sequencing (ChIP‐seq) studies in primary human T‐ALL, demonstrated that Ikaros binds of the promoter of mTOR gene. Ikaros binding to mTOR promoter was confirmed by quantitative chromatin immunoprecipitation (qChIP) in primary T‐ALL cells. The role of Ikaros in regulation of mTOR transcription in T‐ALL was tested using gain‐of‐function and loss‐of‐function experiments. Ikaros knock‐down with shRNA, results in increased transcription of mTOR in T‐ALL. Overexpression of Ikaros in human T‐ALL was associated with strongly reduced transcription of mTOR. In mice, T‐ALL cells that are derived from Ikaros‐knockout mice express high level of mTOR. Transduction of these cells with Ikaros‐containing retrovirus, results in sharp reduction of mTOR expression. Since Ikaros function in T‐ALL is negatively regulated by pro‐oncogenic Casein Kinase II (CK2), we tested whether CK2 can regulate expression of mTOR in T‐ALL. Overexpression of CK2 via retroviral transduction resulted in increased transcription of the MTOR gene, as well as increased overall expression of mTOR, as measured by Western blot. Increased expression of CK2 was associated with loss of Ikaros binding to the promoter of the MTOR gene. Molecular inhibition of CK2 using shRNA, as well as pharmacological inhibition with a specific CK2 inhibitor resulted in reduced expression of mTOR in primary T‐ALL. Inhibition of CK2 was associated with increased Ikaros binding at promoter of mTOR. Ikaros knock‐down restored high expression of mTOR in T‐ALL cells that are treated with CK2 inhibitors. These data showed that CK2 and Ikaros are major transcriptional regulators of mTOR transcription in T‐ALL and that CK2 inhibition represses mTOR transcription via Ikaros‐mediated repression. CK2 inhibition, along with an increased Ikaros binding was associated with reduced histone H3K9ac and H3K4me3 marks at mTOR promoter suggesting that CK2 and Ikaros regulate mTOR transcription via chromatin remodeling. In conclusion, results presented the evidence that expression of mTOR oncogene is regulated by CK2 signaling pathway that involves Ikaros activity in T‐ALL. Results provide the rationale for the use of CK2 inhibitors in T‐ALL to target PI3K/mTOR/AKT pathway.Support or Funding InformationR01CA209829‐02 (SD and KP) and R01CA213912‐01A1 (SD)St. Baldrick's foundation ( SD and CG) and Hyundai Hope on wheels (SD and CG)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.