Clear cell renal cell carcinoma (ccRCC) is the most common and aggressive subtype of renal cancer. STAT3 pathway is altered in these tumors and p-STAT3 Ser727 is an independent prognostic factor for ccRCC. Protein kinase CK2 is altered in different types of tumors and overexpression of CK2α is considered predictive of bad prognosis and metastatic risk. CK2 subunits analyses in ccRCC samples showed increased CK2α/α’ nuclear content in all cases, but decreased cytosolic CK2β (CK2βcyt) levels in the more advanced tumors. Stable downregulation of CK2β in renal proximal tubular (HK-2) and clear cell adenocarcinoma (786-O) cells triggered changes in E-cadherin, vimentin and Snail1 protein levels indicative of epithelial-to-mesenchymal transition (EMT), and increased HIF-α. Moreover, CK2β was required in order to observe STAT3 Ser727 phosphorylation in HK-2 but not in 786-O cells.We also observed that CK2β improved the prognostic value of p-STAT3 Ser727, as CK2βcyt>41 (median value) discriminates patients free of disease for a period of 10 years upon surgery, from those with CK2βcyt<41, when p-STAT3 Ser727levels are low.We conclude that CK2β down-regulation might represent a mechanism to support EMT and angiogenesis and that CK2βcyt levels are instrumental to refine prognosis of ccRCC patients with low p-STAT3 Ser727 levels.
The PI3K/Akt pathway is interconnected to protein kinase CK2, which directly phosphorylates Akt1 at S129. We have previously found that, in HK-2 renal cells, downregulation of the CK2 regulatory subunit β (shCK2β cells) reduces S129 Akt phosphorylation. Here, we investigated in more details how the different CK2 isoforms impact on Akt and other signaling pathways.We found that all CK2 isoforms phosphorylate S129 in vitro, independently of CK2β. However, in HK-2 cells the dependence on CK2β was confirmed by rescue experiments (CK2β re-expression in shCK2β HK-2 cells), suggesting the presence of additional components that drive Akt recognition by CK2 in cells. We also found that CK2β downregulation altered the phosphorylation ratio between the two canonical Akt activation sites (pT308 strongly reduced, pS473 slightly increased) in HK-2 cells. Similar results were found in other cell lines where CK2β was stably knocked out by CRISPR-Cas9 technology. The phosphorylation of rpS6 S235/S236, a downstream effector of Akt, was strongly reduced in shCK2β HK-2 cells, while the phosphorylation of two Akt direct targets, PRAS40 T246 and GSK3β S9, was increased. Differently to what observed in response to CK2β down-regulation, the chemical inhibition of CK2 activity by cell treatment with the specific inhibitor CX-4945 reduced both the Akt canonical sites, pT308 and pS473. In CX-4945-treated cells, the changes in rpS6 pS235/S236 and GSK3β pS9 mirrored those induced by CK2β knockdown (reduction and slight increase, respectively); on the contrary, the effect on PRAS40 pT246 phosphorylation was sharply different, being strongly reduced by CK2 inhibition; this suggests that this Akt target might be dependent on Akt pS473 status in HK-2 cells.Since PI3K/Akt and ERK1/2/p90rsk pathways are known to be interconnected and both modulated by CK2, with GSK3β pS9 representing a convergent point, we investigated if ERK1/2/p90rsk signaling was affected by CK2β knock-down and CX-4945 treatment in HK-PLOS ONE | https://doi.
With this translational perspective in mind, we have studied the CK2 expression level Manuscript Click here to download Manuscript: Manuscript (3).docx A u t h o r ' s a c c e p t e d m a n u s c r i p t
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