Discrete genetic effects of VHL and PBRM1 inactivation co-operate to disrupt epithelial homeostasis and promote ccRCC

Inactivation of VHL is a truncal alteration in clear cell renal cell carcinoma, but additional events are required for oncogenesis, most commonly PBRM1 inactivation. To better understand this co-operation, we used an oncogenic cell-tagging strategy to analyze the earliest transcriptional and cellular consequences of Vhl and/or Pbrm1 inactivation in the renal tubular epithelium, in vivo, at single-cell resolution. Pbrm1 inactivation did not globally alter HIF-dependent transcription or increase early tubular proliferation induced by Vhl inactivation. Instead, it had independent effects on epithelial organization. Combined genetic and morphological analyses suggested that Pbrm1 inactivation allows cells to sustain Vhl/HIF-dependent proliferation by disrupting tubular architectures that ordinarily restrain this proliferation, resulting in extra-tubular cell accumulation, multilayered epithelia, and tumor formation. Our findings frame a new model for the VHL-PBRM1 interaction that explains loss of epithelial homeostasis through an interaction between discrete effects that drive proliferation and remove structural tissue restraints on that proliferation. Statement of SignificanceVHL and PBRM1 are frequently co-inactivated in ccRCC. Combining transcriptomic and histological analyses of Vhl and/or Pbrm1-inactivated renal cells in vivo, this study highlights independent effects on transcription and epithelial organization that converge to promote sustained proliferation and dysplasia. The work illuminates how tissue homeostasis is disrupted by oncogenic co-operation.