Combined Analyses of the VHL and Hypoxia Signaling Axes in an Isogenic Pairing of Renal Clear Cell Carcinoma Cells

The
loss of function of the Von Hippel–Lindau (VHL) tumor
suppressor leads to the development of hypervascular tumors, exemplified
by clear-cell-type renal cell carcinoma (RCC). VHL governs the adaptive
responses to fluctuation of oxygen levels largely through the regulated
suppression of hypoxia inducible factors (HIFs). Here, we combine
proteome and phospho-proteomic analysis of isogenic 786-O RCC (±VHL)
cells to compare signatures that reflect hypoxia and/or loss of VHL.
VHL-independent hypoxic responses, notably include up-regulation of
phosphorylation at Ser232 on the pyruvate dehydrogenase α subunit
that is known to promote glycolysis. Hypoxic responses governed by
VHL include up-regulation of known biomarkers of RCC (e.g., GLUT1,
NDRG1) and the signaling adaptor molecule IRS-2. Notably, we also
observe down-regulation of linked-components associated with the Jacobs–Stewart
cycle, including the intracellular carbonic anhydrase II (CA2), which
governs cellular response to CO2 fluctuations that often
accompany hypoxia in tumors. Further studies indicate an unusual mechanism
of control for CA2 expression that, at least in part, reflects enhanced
activity of the NFκB pathway, which is associated with loss
of VHL.