Page 243 - Haematologica May 2020

IL6R-STAT3-ADAR1(P150) interplay in 1q21(amp) MM
high levels of IL6R hypersensitize the cells to IL6 binding. Consequently, activated STAT3 leads to the transcription of not only its classical target gene, thereby mediating growth and proliferation, but also ADAR1-P150, which also has oncogenic roles, thereby augmenting proliferative phenotypes.
Since ADAR1 is a well-known RNA editing enzyme, we also investigated whether our observations were related to the canonical function of this enzyme. IL6 treatment of MM cells for up to 24 h did not lead to much change in the total number of global editing events at the whole tran- scriptome level (Online Supplementary Figure S8A). A more complex picture emerged at the gene-specific level, whereby, genes of hyper-editing, hypo-editing and no- change of editing frequency appeared without distinct functional segregation among them (Online Supplementary Figure S8B). Analysis on the CoMMpass dataset revealed that the STAT3 signature, an indicator of collective STAT3 activity, was poorly correlated with the number of global editing events (r=0.115) (Online Supplementary Figure S8C). While we could not definitively conclude that the RNA editing’s role of the IL6-induced P150 was not involved in conferring growth benefits to the cells, the fact that the localization of P150 was predominantly cytoplasmic even after IL6 stimulation (Online Supplementary Figure S8D) suggests that RNA editing is not likely to be the prevailing mechanism, as this process takes place in the nucleus where double-stranded mRNA are abundant.
Instead, we opine that the oncogenic effects are likely driven by P150-induced hyperactivation of the STAT3 pathway. The close association between ADAR1 and STAT3 signature strongly indicates that high ADAR1 expression contributes to STAT3 pathway activation, cul- minating in a conducive growth-promoting environment within the bone marrow. ADAR1 has been reported before to have an editing-independent role,42-45 albeit not an extensive one, thus, our finding adds to the important pool of knowledge on the novel non-canonical function of ADAR1, specifically of its P150 isoform.
The fact that we also found a close correlation between IL6R and ADAR1, and the STAT3 signature, as well as between these and patients’ survival, gives the strong impression that there is a close interplay between these factors which drives disease prognosis. We summarize
our findings in a schematic diagram illustrating how 1q21(amp) can result in the overexpression of IL6R and ADAR1, eventually leading to more intensified oncogenic effects from the aberrantly amplified STAT3 activity (Figure 8A, B).
In conclusion, our current work highlights the complex- ity of the STAT3 pathway in MM and for the very first time we report its important association with the 1q21(amp) phenotype. It should, however, be noted that our data do not demonstrate a direct causal effect of 1q21 abnormalities, but rather a close relationship, which we showed through our detailed mechanistic study on human cell lines, supported by robust clinical data. Our data suggesting that 1q21(amp) cells are more responsive to the STAT3 inhibitor (LLL12) indicates that these cells have a close association and dependency on STAT3 path- way activity. This study further highlights the potential complex biological impact imparted by 1q21(amp), of which oncogenic phenotypes are conferred by potentially more than just CSK1B. It is plausible that a cascade of sur- vival signals, produced by the gain of other critical onco- genes within this region, and in our case, IL6R and ADAR1-P150, led to the alteration of cytokine-mediated signaling and the intrinsic cellular phenotypes. Our results could explain why targeting IL6 may not be enough BUT targeting STAT3 activity may ACTUALLY be more beneficial. This study provides a new perspec- tive on the STAT3 pathway in MM and the potential ther- apeutic means for high-risk 1q21(amp) patients.
Acknowledgment
WJC is supported by NMRC Singapore Translational Research (STaR) Investigatorship. This research is partly sup- ported by the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centers of Excellence initiative as well as the RNA Biology Center at the Cancer Science Institute of Singapore, NUS, as part of funding under the Singapore Ministry of Education’s Tier 3 grants, grant number MOE2014-T3-1-006. The computational work for this article was partially performed with resources of the National Supercomputing Center, Singapore (https://www.nscc.sg). We thank Dr Chen Leilei for providing experimental advice and vital reagents. We would also like to thank Dr Zhou Jianbiao for kind- ly contributing the STAT3 plasmids for our experiments.
References
R, Amiot M. The role of interleukin-6/interleukin-6
1. Matthes T, Manfroi B, Huard B. Revisiting IL-6 antagonism in multiple myeloma. Crit Rev Oncol hematol. 2016;105:1-4.
2. Lee C, Oh J-I, Park J, et al. TNFα mediated IL-6 secretion is regulated by JAK/STAT pathway but not by MEK phosphorylation and AKT phosphorylation in U266 multiple myeloma cells. Biomed Res Int. 2013; 2013:580135.
7. Pelliniemi TT, Irjala K, Mattila K, et al. Immunoreactive interleukin-6 and acute phase proteins as prognostic factors in mul- tiple myeloma. Finnish Leukemia Group. Blood. 1995;85(3):765-771.
3. Mondello P, Cuzzocrea S, Navarra M, Mian M. Bone marrow micro-environment is a crucial player for myelomagenesis and dis- ease progression. Oncotarget. 2017;8(12): 20394-20409.
4. Gado K, Domjan G, Hegyesi H, Falus A. Role of interleukin-6 in the pathogenesis of multiple myeloma. Cell Biol Int. 2000;24(4):195-209.
8. Song Z, Ren D, Xu X, Wang Y. Molecular cross‐talk of IL‐6 in tumors and new progress in combined therapy. Thorac Cancer. 2018;9(6):669-675.
5. Barille S, Bataille
interleukin-6 and
receptor-alpha complex in the pathogenesis of multiple myeloma. Eur Cytokine Netw. 2000;11(4):546-551.
6. Bataille R, Jourdan M, Zhang XG, Klein B. Serum levels of interleukin 6, a potent myeloma cell growth factor, as a reflect of disease severity in plasma cell dyscrasias. J Clin Invest. 1989;84(6):2008-2011.
ry signaling pathways by natural agents for the therapy of multiple myeloma. Phytochem Rev. 2014;13(1):79-106.
10. Xiong A, Yang Z, Shen Y, Zhou J, Shen Q. Transcription factor STAT3 as a novel molecular target for cancer prevention. Cancers (Basel). 2014;6(2):926-957.
11. Yu H, Lee H, Herrmann A, Buettner R, Jove R. Revisiting STAT3 signalling in cancer: new and unexpected biological functions. Nat Rev Cancer. 2014;14(11):736-746.
12. Jung YY, Lee JH, Nam D, et al. Anti-myeloma effects of Icariin are mediated through the tttenuation of JAK/STAT3-dependent signal- ing cascade. Front Pharmacol. 2018; 9:531.
13. Catlett-Falcone R, Landowski TH, Oshiro MM, et al. Constitutive activation of Stat3 signaling confers resistance to apoptosis in human U266 myeloma cells. Immunity. 1999;10(1):105-115.
14. Quintanilla-Martinez L, Kremer M, Specht
9. Sikka S, Shanmugam MK, Kannaiyan R, et al. Suppression of essential pro-inflammato-
haematologica | 2020; 105(5)
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