Succinate dehydrogenase (SDH) and
fumarate hydratase (FH) are
tricarboxylic acid (TCA) cycle
enzymes and
tumor suppressors. Loss-of-function mutations give rise to hereditary
paragangliomas/
pheochromocytomas and hereditary
leiomyomatosis and
renal cell carcinoma. Inactivation of SDH and FH results in an abnormal accumulation of their substrates
succinate and
fumarate, leading to inhibition of numerous α-ketoglutarate dependent
dioxygenases, including
histone demethylases and the ten-eleven-translocation (TET) family of
5-methylcytosine (5 mC)
hydroxylases. To evaluate the distribution of
DNA and
histone methylation, we used immunohistochemistry to analyze the expression of 5 mC,
5-hydroxymethylcytosine (5 hmC), TET1,
H3K4me3, H3K9me3, and H3K27me3 on tissue microarrays containing
paragangliomas/
pheochromocytomas (n = 134) and hereditary and sporadic
smooth muscle tumors (n = 56) in comparison to their normal counterparts. Our results demonstrate distinct loss of 5 hmC in
tumor cells in SDH- and FH-deficient
tumors. Loss of 5 hmC in SDH-deficient
tumors was associated with nuclear exclusion of TET1, a known regulator of 5 hmC levels. Moreover, increased methylation of H3K9me3 occurred predominantly in the chief cell component of SDH mutant
tumors, while no changes were seen in
H3K4me3 and H3K27me3, data supported by in vitro knockdown of SDH genes. We also show for the first time that FH-deficient
smooth muscle tumors exhibit increased H3K9me3 methylation compared to wildtype
tumors. Our findings reveal broadly similar patterns of epigenetic deregulation in both FH- and SDH-deficient
tumors, suggesting that defects in genes of the TCA cycle result in common mechanisms of inhibition of
histone and
DNA demethylases.