Dataset Information

PBRM1 loss in kidney cancer unbalances the proximal tubule master transcription factor hub to repress proximal tubule differentiation.

ABSTRACT: PBRM1, a subunit of the PBAF coactivator complex that transcription factors use to activate target genes, is genetically inactivated in almost all clear cell renal cell cancers (RCCs). Using unbiased proteomic analyses, we find that PAX8, a master transcription factor driver of proximal tubule epithelial fates, recruits PBRM1/PBAF. Reverse analyses of the PAX8 interactome confirm recruitment specifically of PBRM1/PBAF and not functionally similar BAF. More conspicuous in the PAX8 hub in RCC cells, however, are corepressors, which functionally oppose coactivators. Accordingly, key PAX8 target genes are repressed in RCC versus normal kidneys, with the loss of histone lysine-27 acetylation, but intact lysine-4 trimethylation, activation marks. Re-introduction of PBRM1, or depletion of opposing corepressors using siRNA or drugs, redress coregulator imbalance and release RCC cells to terminal epithelial fates. These mechanisms thus explain RCC resemblance to the proximal tubule lineage but with suppression of the late-epithelial program that normally terminates lineage-precursor proliferation.

SUBMITTER: Gu X

PROVIDER: S-EPMC8561673 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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PBRM1 loss in kidney cancer unbalances the proximal tubule master transcription factor hub to repress proximal tubule differentiation.

Gu Xiaorong X Enane Francis F Tohme Rita R Schuerger Caroline C Radivoyevitch Tomas T Parker Yvonne Y Zuberi Eric E Przychodzen Bartlomiej B Jha Babal Kant BK Lindner Daniel D Rini Brian B Saunthararajah Yogen Y

Cell reports 20210901 12

PBRM1, a subunit of the PBAF coactivator complex that transcription factors use to activate target genes, is genetically inactivated in almost all clear cell renal cell cancers (RCCs). Using unbiased proteomic analyses, we find that PAX8, a master transcription factor driver of proximal tubule epithelial fates, recruits PBRM1/PBAF. Reverse analyses of the PAX8 interactome confirm recruitment specifically of PBRM1/PBAF and not functionally similar BAF. More conspicuous in the PAX8 hub in RCC cell ...[more]

PMID: 34551289

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Project description:PBRM1 is the 2nd-most frequently inactivated gene in clear cell renal cell cancer (RCC) but the oncogenic mechanisms, and hence methods for correction, are unclear. PBRM1 is a subunit of the PBAF coactivator complex that transcription factors use to reposition nucleosomes (‘open chromatin’) for gene activation. We therefore looked for transcription factors that recruit endogenous PBRM1 in kidney lineage/RCC cells, as a waypoint to identifying pathways impacted by PBRM1 loss. Unbiased immunoprecipitation/mass-spectrometry analyses of the endogenous PBRM1 interactome in kidney lineage cells revealed PAX8, a master transcription factor essential for proximal tubule epithelial fates, as the major transcription factor recruiting PBRM1/PBAF. The reverse analyses of the PAX8 interactome confirmed recruitment specifically of PBRM1/PBAF, and not the functionally similar BAF coactivator complex. More conspicuous in the PAX8 hub in RCC cells, however, were several corepressors, e.g. DNMT1, which oppose coactivators to repress instead of activate genes. Accordingly, key PAX8 target genes, e.g., GATA3, LHX1, WT1, and ~1000 other downstream kidney epithelial genes, but not PAX8 or PAX2, demonstrated loss of the histone lysine 27 acetylation (H3K27ac) activation mark, increase in CpG methylation repression marks, and lower expression in RCC vs normal kidney cortex, with the greatest repression in cases with bi-allelic PBRM1 inactivation. PBRM1 re-introduction into RCC cells, or depletion of the corepressor DNMT1 using siRNA or a clinical drug decitabine, rebalanced composition and function of the PAX8 transcription factor hub to coactivators, to thereby activate terminal epithelial-fates in vitro and in vivo. In sum, PBRM1 loss in RCC cells skews coregulator composition of the PAX8 master transcription factor hub toward corepressors and repression instead of activation of the downstream terminal epithelial-program; this oncogenic action could be reversed by pharmacologic corepressor depletion/inhibition.

Project description:The multiligand receptors megalin (Lrp2) and cubilin (Cubn) and their endocytic adaptor protein Dab2 (Dab2) play essential roles in maintaining the integrity of the apical endocytic pathway of proximal tubule (PT) cells and have complex and poorly understood roles in the development of chronic kidney disease. Here, we used RNA-sequencing and CRISPR/Cas9 knockout (KO) technology in a well-differentiated cell culture model to identify PT-specific transcriptional changes that are directly consequent to the loss of megalin, cubilin, or Dab2 expression. KO of Lrp2 had the greatest transcriptional effect, and nearly all genes whose expression was affected in Cubn KO and Dab2 KO cells were also changed in Lrp2 KO cells. Pathway analysis and more granular inspection of the altered gene profiles suggested changes in pathways with immunomodulatory functions that might trigger the pathological changes observed in KO mice and patients with Donnai-Barrow syndrome. In addition, differences in transcription patterns between Lrp2 and Dab2 KO cells suggested the possibility that altered spatial signaling by aberrantly localized receptors contributes to transcriptional changes upon the disruption of PT endocytic function. A reduction in transcripts encoding sodium-glucose cotransporter isoform 2 was confirmed in Lrp2 KO mouse kidney lysates by quantitative PCR analysis. Our results highlight the role of megalin as a master regulator and coordinator of ion transport, metabolism, and endocytosis in the PT. Compared with the studies in animal models, this approach provides a means to identify PT-specific transcriptional changes that are directly consequent to the loss of these target genes.NEW & NOTEWORTHY Megalin and cubilin receptors together with their adaptor protein Dab2 represent major components of the endocytic machinery responsible for efficient uptake of filtered proteins by the proximal tubule (PT). Dab2 and megalin expression have been implicated as both positive and negative modulators of kidney disease. We used RNA sequencing to knock out CRISPR/Cas9 cubilin, megalin, and Dab2 in highly differentiated PT cells to identify PT-specific changes that are directly consequent to knockout of each component.

Dataset Information

PBRM1 loss in kidney cancer unbalances the proximal tubule master transcription factor hub to repress proximal tubule differentiation.

Publications

PBRM1 loss in kidney cancer unbalances the proximal tubule master transcription factor hub to repress proximal tubule differentiation.

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