Two new RCC subtypes were defined by distinct epigenetic and metabolic pathway expression patterns, the hypermethylated CpG island methylator phenotype-associated (CIMP) RCCs and metabolically divergent chRCCs, and new biomarkers of poor patient outcome were identified, including PBRM1 mutation in type 1 pRCC and CDKN2A loss in chRCC.
PBRM1 nuclear staining of the 124-immunostained metastases of ccRCC specimens showed that 98 (79.0%) had negative expression and 26 (21.0%) positive expression of PBRM1.
As an application of this resource, we discovered RCC GCN edges and modules that were associated with genetic lesions in known RCC driver genes, including VHL, a common initiating clear cell RCC (ccRCC) genetic lesion, and PBRM1 and BAP1 which are early genetic lesions in the Braided Cancer River Model (BCRM).
The evolution patterns of ccRCC have great inter-patient heterogeneities, with del(3p) being regarded as the common earliest event followed by three early departure points: VHL and PBRM1 mutations, del(14q) and other somatic copy number alterations (SCNAs) including amp(7), del(1p) and del(6q).
Genomic evaluation in this case was characterized in part by a PBRM1 variant, similar to the only other described case of RCC with rhabdoid features obtaining a complete response to nivolumab.
Taken together, our biochemical and mutational analyses have identified BD4 as being critically important for maintaining proper PBRM1 function and demonstrate that BD4 mutations increase ccRCC cell growth.
The human polybromo-1 protein (BAF180) is a known driver mutation in clear cell renal cell carcinoma, where it is mutated in approximately 40% of cases.
Recurrent secondary molecular alterations in clear cell RCC (BAP1, SETD2, PBRM1, and TP53) and papillary RCC (CDKN2A) may be associated with poor prognosis; however, intratumoral genomic heterogeneity may limit the clinical utility of these molecular biomarkers in renal mass biopsies.
This results in concurrent one-copy loss of four tumor suppressor genes that are also mutated individually at high frequency in ccRCC (ie, VHL, 80%; PBRM1, 29% to 46%; BAP1, 6% to 19%; and SETD2, 8% to 30%).
Polybromo1 (PBRM1), a subunit of the Polybromo-associated BRG1- or hBRM-associated factors (PBAF) chromatin remodeler, contains six tandem BDs and is frequently mutated in clear cell renal cell carcinoma (ccRCC).
Of the remaining, 6 had other clear cell renal cell carcinoma-associated gene alterations (PBRM1, SMARCA4, BAP1, SETD2), leaving 11 specimens, including 2 high-grade or sarcomatoid renal cell carcinomas and 2 with prominent fibromuscular stroma (not TCEB1 mutant).
Our study reports a physiological preclinical ccRCC mouse model that recapitulates somatic mutations in human ccRCC and provides mechanistic and therapeutic insights into PBRM1 mutated subtypes of human ccRCC.
Similarly, seven of the ten patients that demonstrated discordant PBRM1 expression showed loss of PBRM1 expression during progression to metastatic ccRCC.
To investigate the intratumoral heterogeneity of BAP1 and PBRM1 expression at the primary site and metastatic sites and to evaluate whether BAP1 and PBRM1 expression in metastatic sites of clear cell renal cell carcinoma (ccRCC) has prognostic value.
Thus, our studies reveal that BAF180 function in ccRCC is context dependent, and that mutation of PBRM1/BAF180 serves as an alternative strategy for ccRCC tumors to reduce HIF1 tumor-suppressive activity in H1H2 ccRCC tumors.
PBRM1 was expressed at high levels in RCC ACHN cells and lentivirus-mediated PBRM1 knockdown in these cells caused an increase in the proportion of cells in S phase of the cell cycle and promoted in vitro proliferation and migration.
Compared to patients with PBRM1+ BAP1+ tumors those with PBRM1- BAP1+ lesions were more likely to die of renal cell carcinoma (HR 1.39, p = 0.035), followed by those with PBRM1+ BAP1- and PBRM1- BAP1- tumors (HR 3.25 and 5.2, respectively, each p <0.001).