Inactivation of SDH and FH cause loss of 5hmC and increased H3K9me3 in paraganglioma/pheochromocytoma and smooth muscle tumors.

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.

Expression of matrix metalloproteinases in patients with uterine smooth muscle tumors: an immunohistochemical analysis of MMP-1 and MMP-2 protein expression in leiomyoma, uterine smooth muscle tumor of uncertain malignant potential, and leiomyosarcoma.

OBJECTIVE: Matrix metalloproteinases (MMPs) have been suggested to play an important role in tumor invasion and metastasis. We compared the expression of MMP-1 and MMP-2 protein in patients with leiomyoma, uterine smooth muscle tumor of uncertain malignant potential (STUMP), and leiomyosarcoma (LMS). METHODS: MMP-1 and MMP-2 expression was investigated by immunohistochemistry from paraffin-embedded tissue in 26 patients with leiomyoma, in 24 patients with STUMP, and in 21 patients with LMS. RESULTS: MMP-1 was expressed in 92% of leiomyomas, in 83% of STUMP, and in 86% of LMS, whereas MMP-2 was expressed in 12% of leiomyomas, in 17% of STUMP, and in 48% of LMS. A statistically significant difference regarding the frequency of MMP-2 expression was observed between LMS and STUMP (P =.025) as well as between LMS and leiomyoma (P =.006), but not between STUMP and leiomyoma (P >.05). Likewise, the staining intensity did significantly differ between LMS and leiomyoma (P =.025), but no statistical significant difference was observed between LMS and STUMP (P >.05) and between STUMP and leiomyoma (P >.05). CONCLUSION: The stronger MMP-2 expression in patients with LMS compared with STUMP and leiomyoma indicates that this protein might be a marker for tumor invasion or metastasis in patients with uterine LMS. Furthermore, MMP-2 seems to be a useful immunohistochemical parameter to distinguish cases of smooth muscle tumors in which histologic features are ambiguous or borderline. Further studies including larger numbers of patients are necessary to establish MMP-2 as a routine marker for tumor invasion and progression.