Loss of oncogenic miR-155 in tumor cells promotes tumor growth by enhancing C/EBP-β-mediated MDSC infiltration

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Loss of oncogenic miR-155 in tumor cells promotes tumor growth by enhancing C/EBP-β-mediated MDSC infiltration
S Kim; Jin Hoi Song; Seok Ho Kim; P Qu; B K Martin; W S Sehareen; D C Haines; P C Lin; S K Sharan; S Chang
Bibliographic Citation
Oncotarget, vol. 7, no. 10, pp. 11094-11112
Publication Year
The oncogenic role of microRNA-155 (miR-155) in leukemia is well established but its role in other cancers, especially breast cancer, is gradually emerging. In this study we examined the effect of mir-155 loss in a well-characterized spontaneous breast cancer mouse model where Brca1 and Trp53 are deleted by K14-Cre. miR-155 is known to be up-regulated in BRCA1-deficient tumors. Surprisingly, complete loss of miR-155 (miR-155ko/ko) did not alter the tumor free survival of the mutant mice. However, we found increased infiltration of myeloid derived suppressor cells (MDSCs) in miR-155 deficient tumors. In addition, cytokine/chemokine array analysis revealed altered level of cytokines that are implicated in the recruitment of MDSCs. Mechanistically, we identified C/EBP-β, a known miR-155 target, to regulate the expression of these cytokines in the miR-155-deficient cells. Furthermore, using an allograft model, we showed that inhibition of miR-155 in cancer cells suppressed in vivo growth, which was restored by the loss of miR-155 in the microenvironment. Taken together, we have uncovered a novel tumor suppressive function of miR-155 in the tumor microenvironment, which is also dependent on miR-155 expression in the tumor cells. Because of the oncogenic as well as tumor suppressive roles of miR-155, our findings warrant caution against a systemic inhibition of miR-155 for anticancer therapy.
Breast cancerC/EBP-betaCytokineMDSCmiR-155
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