Bromodomain and extra-terminal (BET) inhibitors regulate NK cell biology by inhibiting BRD2 mediated NK cytolytic activity and BRD2/BRD4 mediated inflammatory function

Natural killer cells are innate lymphocytes that play a pivotal role in the immune surveillance and elimination of transformed or virally infected cells. Using a combined chemico-genetic approach, we have identified that BET bromodomains BRD2 and BRD4 are central regulators of NK cell responses. We show that both BRD2 and BRD4 play a key regulatory function in controlling NK cell specific inflammatory responses. However, knockdown of BRD2 but not BRD4 impairs NK cell cytolytic response, highlighting a redundant role for BRD4 in regulating NK cell killing. We further show that the prototypic monovalent BET inhibitor impairs in vitro NK cell mediated killing of cancer target cells, while the bivalent BET bromodomain AZD5153 does not. We ascribe these differences to the preferential affinity of JQ1(+) to BRD2, while AZD5153 has a higher affinity for BRD4. Our work suggests that inhibiting BET bromodomains may be an effective therapeutic strategy for controlling inflammatory function. Given that BRD2 but not BRD4 inhibition can impair NK cell mediated killing, our findings also have clinical significance in light of the ongoing clinical application of BET bromodomains in oncology. Examination of JQ1 and AZD5153 treated NK, CD4, CD8 and monocytes from peripheral blood