PBRM1 acts as a p53 lysine-acetylation reader to suppress renal tumor growth.

p53 acetylation is indispensable for its transcriptional activity and tumor suppressive function. However, the identity of reader protein(s) for p53 acetylation remains elusive. PBRM1, the second most highly mutated tumor suppressor gene in kidney cancer, encodes PBRM1. Here, we identify PBRM1 as a reader for p53 acetylation on lysine 382 (K382Ac) through its bromodomain 4 (BD4). Notably, mutations on key residues of BD4 disrupt recognition of p53 K382Ac. The mutation in BD4 also reduces p53 binding to promoters of target genes such as CDKN1A (p21). Consequently, the PBRM1 BD4 mutant fails to fully support p53 transcriptional activity and is defective as a tumor suppressor. We also find that expressions of PBRM1 and p21 correlate with each other in human kidney cancer samples. Our findings uncover a tumor suppressive mechanism of PBRM1 in kidney cancer and provide a mechanistic insight into the crosstalk between p53 and SWI/SNF complexes

Multiple tumor suppressors regulate a HIF-dependent negative feedback loop via ISGF3 in human clear cell renal cancer.

Whereas VHL inactivation is a primary event in clear cell renal cell carcinoma (ccRCC), the precise mechanism(s) of how this interacts with the secondary mutations in tumor suppressor genes, including PBRM1, KDM5C/JARID1C, SETD2, and/or BAP1, remains unclear. Gene expression analyses reveal that VHL, PBRM1, or KDM5C share a common regulation of interferon response expression signature. Loss of HIF2α, PBRM1, or KDM5C in VHL-/-cells reduces the expression of interferon stimulated gene factor 3 (ISGF3), a transcription factor that regulates the interferon signature. Moreover, loss of SETD2 or BAP1 also reduces the ISGF3 level. Finally, ISGF3 is strongly tumor-suppressive in a xenograft model as its loss significantly enhances tumor growth. Conversely, reactivation of ISGF3 retards tumor growth by PBRM1-deficient ccRCC cells. Thus after VHL inactivation, HIF induces ISGF3, which is reversed by the loss of secondary tumor suppressors, suggesting that this is a key negative feedback loop in ccRCC. © 2018, Liao et al

Data Supporting the Roles of BAP1, Sting, and IFN-β in ISGF3 Activation in ccRCC

The data presented in this article are companion materials to our manuscript titled BAP1 maintains HIF-dependent interferon beta induction to suppress tumor growth in clear cell renal cell carcinoma (Langbein et al., 2022), where we investigated the downstream effects of BAP1 (BRCA1-associated protein 1) expression in clear cell renal cell carcinoma (ccRCC) cell lines and mouse xenograft models. In the manuscript, we showed that BAP1 upregulates STING (stimulator of interferon genes) expression and activity in ccRCC cells, leading to IFN-β transcription and activation of interferon stimulated gene factor 3 (ISGF3), the transcription factor that mediates the effects of type I interferons (IFNs). Here, we suppressed additional components of the type I IFN pathway, including IRF9 (a component of ISGF3), IFNAR1 (the type I IFN receptor), and STING (a stimulator of IFN production) by shRNA to investigate their involvement in BAP1-mediated upregulation of ISGF3 activity. We also inhibited extracellular IFN-β via neutralizing antibody treatment in BAP1-expressing cells to ascertain the role of the secreted cytokine in this pathway. ISGF3 activity was assessed by western blot analysis and qPCR measurement of its transcriptional targets. To examine the relevance of our observations in another model system, we characterized primary kidney cells from WT and Bap1 fl/fl mice by cytokeratin 8 immunohistochemistry and examined the effect of Bap1 knockout on Sting protein expression. Finally, we treated mice bearing BAP1 knockdown xenografted tumors with diABZI, a STING agonist, and measured immune cell recruitment via CD45 immunohistochemistry. These data can serve as a starting point for further investigation on the roles of BAP1 and other tumor suppressor genes in interferon pathway regulation

BAP1 Maintains Hif-Dependent Interferon Beta Induction to Suppress Tumor Growth in Clear Cell Renal Cell Carcinoma.

BRCA1-associated protein 1 (BAP1) is a deubiquitinase that is mutated in 10-15% of clear cell renal cell carcinomas (ccRCC). Despite the association between BAP1 loss and poor clinical outcome, the critical tumor suppressor function(s) of BAP1 in ccRCC remains unclear. Previously, we found that hypoxia-inducible factor 2α (HIF2α) and BAP1 activate interferon-stimulated gene factor 3 (ISGF3), a transcription factor activated by type I interferons and a tumor suppressor in ccRCC xenograft models. Here, we aimed to determine the mechanism(s) through which HIF and BAP1 regulate ISGF3. We found that in ccRCC cells, loss of the von Hippel-Lindau tumor suppressor (VHL) activated interferon beta (IFN-β) expression in a HIF2α-dependent manner. IFN-β was required for ISGF3 activation and suppressed the growth of Ren-02 tumors in xenografts. BAP1 enhanced the expression of IFN-β and stimulator of interferon genes (STING), both of which activate ISGF3. Both ISGF3 overexpression and STING agonist treatment increased ISGF3 activity and suppressed BAP1-deficient tumor growth in Ren-02 xenografts. Our results indicate that BAP1 loss reduces type I interferon signaling, and reactivating this pathway may be a novel therapeutic strategy for treating ccRCC