Sustained elevation of Snail promotes glial-mesenchymal transition after irradiation in malignant glioma.

BACKGROUND: Ionizing irradiation is an effective treatment for malignant glioma (MG); however, a higher rate of recurrence with more aggressive phenotypes is a vital issue. Although epithelial-mesenchymal transition (EMT) is involved in irradiation-induced cancer progression, the role for such phenotypic transition in MG remains unknown. METHODS: To investigate the mechanism of irradiation-dependent tumor progression in MG, we performed immunohistochemistry (IHC) and qRT-PCR using primary and recurrent MG specimens, MG cell lines, and primary culture cells of MG. siRNA technique was used for MG cell lines. RESULTS: In 22 cases of clinically recurrent MG, the expression of the mesenchymal markers vimentin and CD44 was found to be increased by IHC. In paired identical MG of 7 patients, the expression of collagen, MMPs, and YKL-40 were also elevated in the recurrent MGs, suggesting the The Cancer Genome Atlas-based mesenchymal subtype. Among EMT regulators, sustained elevation of Snail was observed in MG cells at 21 days after irradiation. Cells exhibited an upregulation of migration, invasion, numbers of focal adhesion, and MMP-2 production, and all of these mesenchymal features were abrogated by Snail knockdown. Intriguingly, phosphorylation of ERK1/2 and GSK-3ß were increased after irradiation in a Snail-dependent manner, and TGF-ß was elevated in both fibroblasts and macrophages but not in MG cells after irradiation. It was noteworthy that irradiated cells also expressed stemness features such as SOX2 expression and tumor-forming potential in vivo. CONCLUSIONS: We here propose a novel concept of glial-mesenchymal transition after irradiation in which the sustained Snail expression plays an essential role.

STAT3 inhibition overcomes temozolomide resistance in glioblastoma by downregulating MGMT expression.

Glioblastoma multiforme (GBM) is one of the most aggressive human tumors with a poor prognosis. Current standard treatment includes chemotherapy with the DNA-alkylating agent temozolomide concomitant with surgical resection and/or irradiation. However, a number of cases are resistant to temozolomide-induced DNA damage due to elevated expression of the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT). Here, we show that upregulation of both MGMT and STAT3 was accompanied with acquisition of temozolomide resistance in the GBM cell line U87. Inactivation of STAT3 by inhibitor or short hairpin RNA (shRNA) downregulated MGMT expression in GBM cell lines. MGMT upregulation was not observed by the treatment of interleukin (IL)-6 which is a strong activator of STAT3. Contrarily, forced expressed MGMT could be downregulated by STAT3 inhibitor which was partially rescued by the proteasome inhibitor, MG132, suggesting the STAT3-mediated posttranscriptional regulation of the protein levels of MGMT. Immunohistochemical analysis of 44 malignant glioma specimens showed significant positive correlation between expression levels of MGMT and phosphorylated STAT3 (p-STAT3; P < 0.001, r = 0.58). Importantly, the levels of both MGMT and p-STAT3 were increased in the recurrence compared with the primary lesion in paired identical tumors of 12 cases. Finally, we showed that STAT3 inhibitor or STAT3 knockdown potentiated temozolomide efficacy in temozolomide-resistant GBM cell lines. Therefore, STAT3 inhibitor might be one of the candidate reagents for combination therapy with temozolomide for patients with temozolomide-resistant GBM.

Expression of O6-methylguanine DNA methyltransferase (MGMT) and immunohistochemical analysis of 12 pineal parenchymal tumors.

Pineal parenchymal tumors (PPTs) are rare neoplasms which occupy less than 1% of primary CNS tumors. Because of their rare incidence, previous reports on PPTs are limited in number and the useful molecular markers for deciding histological grading and even selecting chemotherapy are undetermined. In this study, we conducted immunohistochemical analysis of 12 PPT specimens, especially for expression of O6-methylguanine DNA methyltransferase (MGMT) to assess whether temozolomide (TMZ) could serve as a possible alternative therapy for PPTs. We analyzed 12 PPTs, consisting of three pineocytomas, six PPTs of intermediate differentiation (PPTIDs), and three pineoblastomas. Immunohistochemical analysis was performed using antibodies against MGMT, synaptophysin, neurofilament protein (NF), p53, and neuronal nuclear antigen (NeuN). Immunohistochemically, 11 out of 12 cases were positive for MGMT. The mean MIB-1 labeling index was less than 1% in pineocytoma, 3.5% in PPTID, and 10.5% in pineoblastoma. All 12 cases were positive for synaptophysin and 11 cases, except one PPTID case, showed positive for NF. Nuclear staining of NeuN was negative in all cases although cytoplasmic staining of NeuN was observed in five cases. No case was positive for p53. Eleven out of 12 cases of PPTs demonstrated MGMT expression, suggesting chemoresistancy to TMZ treatment. This is the first report showing MGMT expression in PPTs. In addition, MIB-1 labeling index correlated with WHO grade, although the immunoreactivity of synaptophysin, NF, NeuN and p53 did not correlate with the histological grade.

A case of lymphoplasmacyte-rich meningioma of the jugular foramen.

Lymphoplasmacyte-rich meningioma (LPRM), the most rare variant of meningiomas, features extensive lymphoplasmacytic infiltrates. Although the jugular foramen (JF) is occasionally involved by several types of tumor, such as paragangliomas and schwannomas, meningioma in the JF is an infrequent disease. Here we present an extremely rare case of LPRM found in the JF. A 55-year-old woman complained of paresis in her right eyelid and palsy in the right side of her lip. Hoarseness and dysphagia also occurred in the following month. Radiologic examinations disclosed a mass lesion in the right JF, and the tumor was operatively removed. Microscopically, the tumor was composed of extensive lymphoplasmacytic infiltration with mild vascular proliferation and scattered sheets of epithelioid cells with plump cytoplasm. Although the obvious whorl formation or psammoma bodies were not observed, by immunochemistry the epithelioid cells were positive for epithelial membrane antigen and also progesterone receptor, indicating a meningothelial cell origin. Considering the histological and radiologic findings, we finally diagnosed the case as LPRM, making this the second reported case of LPRM in the JF.