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.

Polybromo‐1 ( PBRM 1) is an important tumor suppressor in kidney cancer. It contains six tandem bromodomains ( BD s), which are specialized structures that recognize acetyl‐lysine residues. While BD 2 has been found to bind acetylated histone H3 lysine 14 (H3K14ac), it is not known whether other BD s collaborate with BD 2 to generate strong binding to H3K14ac, and the importance of H3K14ac recognition for the molecular and tumor suppressor function of PBRM 1 is also unknown. We discovered that full‐length PBRM 1, but not its individual BD s, strongly binds H3K14ac. BD s 2, 4, and 5 were found to collaborate to facilitate strong binding to H3K14ac. Quantitative measurement of the interactions between purified BD proteins and H3K14ac or nonacetylated peptides confirmed the tight and specific association of the former. Interestingly, while the structural integrity of BD 4 was found to be required for H3K14ac recognition, the conserved acetyl‐lysine binding site of BD 4 was not. Furthermore, simultaneous point mutations in BD s 2, 4, and 5 prevented recognition of H3K14ac, altered promoter binding and gene expression, and caused PBRM 1 to relocalize to the cytoplasm. In contrast, tumor‐derived point mutations in BD 2 alone lowered PBRM 1's affinity to H3K14ac and also disrupted promoter binding and gene expression without altering cellular localization. Finally, overexpression of PBRM 1 variants containing point mutations in BD s 2, 4, and 5 or BD 2 alone failed to suppress tumor growth in a xenograft model. Taken together, our study demonstrates that BD s 2, 4, and 5 of PBRM 1 collaborate to generate high affinity to H3K14ac and tether PBRM 1 to chromatin. Mutations in BD 2 alone weaken these interactions, and this is sufficient to abolish its molecular and tumor suppressor functions.

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.

No abstract

Eukaryotic chromosome segregation requires a protein complex known as the kinetochore that mediates attachment between mitotic spindle microtubules and centromere-specific nucleosomes composed of the widely conserved histone variant CENP-A. Mutations in kinetochore proteins of the fission yeast lead to chromosome missegregation such that daughter cells emerge from mitosis with unequal DNA content. We find that multiple copies of Msc1-a fission yeast homolog of the KDM5 family of proteins-suppresses the temperature-sensitive growth defect of several kinetochore mutants, including and , as well as, , and, components of the Constitutive Centromere Associated Network (CCAN). On the other hand, deletion of exacerbates both the growth defect and chromosome missegregation phenotype of each of these mutants. The C-terminal PHD domains of Msc1, previously shown to associate with a histone deacetylase activity, are necessary for Msc1 function when kinetochore mutants are compromised. We also demonstrate that, in the absence of Msc1, the frequency of localization to the kinetochore of Mis16 and Mis15 is altered from wild-type cells. As we show here for, others have shown that elevating levels acts similarly to promote survival of the CCAN mutants. The rescue of and by is, however, independent of Thus, Msc1 appears to contribute to the chromatin environment at the centromere: the absence of Msc1 sensitizes cells to perturbations in kinetochore function, while elevating Msc1 overcomes loss of function of critical components of the kinetochore and centromere.