Linking VHL and SETD2 in a common oncogenic pathway that converges on the mitotic spindle

Background: Loss of chromosome 3p is a landmark event in clear cell renal cell carcinoma (ccRCC) that results in mono-allelic loss of VHL ( von Hippel-Lindau ) and SETD2 ( Set-domain containing 2 ) (and other tumor suppressors co-located on 3p). Second hits in VHL inactivate this key tumor suppressor, initiating tumor progression. SETD2, a histone methyltransferase, has been previously shown to have a dual function in methylating both histones and microtubules, thereby contributing to the histone and tubulin codes. Methylation by SETD2 on microtubules occurs at the mitotic spindle and is essential for normal mitosis and cytokinesis; the loss of SETD2 acts as a strong driver of apoptosis. This raises a conundrum of how cancer cells survive the early mono-allelic loss of SETD2 , escaping cell death. Methods: Using biochemical kinase assays and mass spectrometry, we have identified SETD2 as a substrate for AURKA. Additionally, we have employed immunoblotting and immunofluorescence assays to investigate the phosphorylation of SETD2 and its effects on both chromatin and cytoskeleton targets. Results: We have identified the mitotic kinase, Aurora kinase A (AURKA), as a regulator of SETD2. Our data uncover SETD2 as a unique substrate for phosphorylation by AURKA, with mass spectrometry identifying serine 2080 (S2080) as the site of phosphorylation on SETD2. We found that phosphorylation of SETD2 by AURKA at S2080 contributes to its methyltransferase (i.e., enzymatic) activity on microtubules but does not impact chromatin methylation at H3K36, which remains unchanged. We demonstrate that VHL regulates SETD2 through AURKA, and the loss of phosphorylation on SETD2 leads to mitotic defects and genomic instability. Importantly, we demonstrate that inhibition of AURKA is synthetic lethal in the setting of VHL and SETD2 deficiency. Conclusions: AURKA expression levels are high in VHL -null cells, resulting from an inability of VHL to target AURKA for degradation, and our data now highlight a direct link between VHL and SETD2, two tumor suppressors believed to drive RCC pathogenesis independently. In summary, our data reveal a tumor-specific vulnerability linked to mitotic fragility that can be precisely targeted to drive mitotic catastrophe ultimately. *Presenting and primary author.