Abnormal expression of REST/NRSF and Myc in neural stem/progenitor cells causes cerebellar tumors by blocking neuronal differentiation.

Medulloblastoma, one of the most malignant brain tumors in children, is thought to arise from undifferentiated neural stem/progenitor cells (NSCs) present in the external granule layer of the cerebellum. However, the mechanism of tumorigenesis remains unknown for the majority of medulloblastomas. In this study, we found that many human medulloblastomas express significantly elevated levels of both myc oncogenes, regulators of neural progenitor proliferation, and REST/NRSF, a transcriptional repressor of neuronal differentiation genes. Previous studies have shown that neither c-Myc nor REST/NRSF alone could cause tumor formation. To determine whether c-Myc and REST/NRSF act together to cause medulloblastomas, we used a previously established cell line derived from external granule layer stem cells transduced with activated c-myc (NSC-M). These immortalized NSCs were able to differentiate into neurons in vitro. In contrast, when the cells were engineered to express a doxycycline-regulated REST/NRSF transgene (NSC-M-R), they no longer underwent terminal neuronal differentiation in vitro. When injected into intracranial locations in mice, the NSC-M cells did not form tumors either in the cerebellum or in the cerebral cortex. In contrast, the NSC-M-R cells did produce tumors in the cerebellum, the site of human medulloblastoma formation, but not when injected into the cerebral cortex. Furthermore, the NSC-M-R tumors were blocked from terminal neuronal differentiation. In addition, countering REST/NRSF function blocked the tumorigenic potential of NSC-M-R cells. To our knowledge, this is the first study in which abnormal expression of a sequence-specific DNA-binding transcriptional repressor has been shown to contribute directly to brain tumor formation. Our findings indicate that abnormal expression of REST/NRSF and Myc in NSCs causes cerebellum-specific tumors by blocking neuronal differentiation and thus maintaining the "stemness" of these cells. Furthermore, these results suggest that such a mechanism plays a role in the formation of human medulloblastoma.

The surgical treatment of tumors of the fourth ventricle: a single-institution experience.

OBJECTIVE Fourth ventricle tumors are rare, and surgical series are typically small, comprising a single pathology, or focused exclusively on pediatric populations. This study investigated surgical outcome and complications following fourth ventricle tumor resection in a diverse patient population. This is the largest cohort of fourth ventricle tumors described in the literature to date. METHODS This is an 18-year (1993-2010) retrospective review of 55 cases involving patients undergoing surgery for tumors of the fourth ventricle. Data included patient demographic characteristics, pathological and radiographic tumor characteristics, and surgical factors (approach, surgical adjuncts, extent of resection, etc.). The neurological and medical complications following resection were collected and outcomes at 30 days, 90 days, 6 months, and 1 year were reviewed to determine patient recovery. Patient, tumor, and surgical factors were analyzed to determine factors associated with the frequently encountered postoperative neurological complications. RESULTS There were no postoperative deaths. Gross-total resection was achieved in 75% of cases. Forty-five percent of patients experienced at least 1 major neurological complication, while 31% had minor complications only. New or worsening gait/focal motor disturbance (56%), speech/swallowing deficits (38%), and cranial nerve deficits (31%) were the most common neurological deficits in the immediate postoperative period. Of these, cranial nerve deficits were the least likely to resolve at follow-up. Multivariate analysis showed that patients undergoing a transvermian approach had a higher incidence of postoperative cranial nerve deficits, gait disturbance, and speech/swallowing deficits than those treated with a telovelar approach. The use of surgical adjuncts (intraoperative navigation, neurophysiological monitoring) did not significantly affect neurological outcome. Twenty-two percent of patients required postoperative CSF diversion following tumor resection. Patients who required intraoperative ventriculostomy, those undergoing a transvermian approach, and pediatric patients (< 18 years old) were all more likely to require postoperative CSF diversion. Twenty percent of patients suffered at least 1 medical complication following tumor resection. Most complications were respiratory, with the most common being postoperative respiratory failure (14%), followed by pneumonia (13%). CONCLUSIONS The occurrence of complications after fourth ventricle tumor surgery is not rare. Postoperative neurological sequelae were frequent, but a substantial number of patients had neurological improvement at long-term followup. Of the neurological complications analyzed, postoperative cranial nerve deficits were the least likely to completely resolve at follow-up. Of all the patient, tumor, and surgical variables included in the analysis, surgical approach had the most significant impact on neurological morbidity, with the telovelar approach being associated with less morbidity.

Inhibition of radiation-induced nuclear factor-kappaB activation by an anti-Ras single-chain antibody fragment: lack of involvement in radiosensitization.

We have shown previously that the transduction of a number of human tumor cell lines with an adenovirus (AV1Y28) expressing a single-chain antibody fragment (scFv) directed against Ras proteins results in radiosensitization. Because Ras is involved in the regulation of a number of transcription factors, we have determined the effects of this adenovirus on the activation of nuclear factor-kappaB (NF-kappaB), a radiation-responsive transcription factor associated with cell survival. In U251 human glioma cells, radiation-induced NF-kappaB was significantly attenuated by prior transduction of the anti-Ras scFv adenovirus. This effect appeared to involve an inhibition of IkappaB kinase activity and IkappaBalpha phosphorylation. Inhibitors to the Ras effectors mitogen-activated protein kinase kinase, phosphatidylinositol 3-kinase, and p38, however, did not reduce radiation-induced NF-kappaB. Whereas AV1Y28 inhibited NF-kappaB activation by hydrogen peroxide and ferricyanide, it had no effect of tumor necrosis factor-alpha-induced NF-kappaB activation. These results are consistent with a novel Ras-dependent, oxidant-specific signaling pathway mediating the activation of NF-kappaB. In additional cell lines radiosensitized by AV1Y28, radiation-induced NF-kappaB activation was also inhibited by the anti-Ras scFv, whereas in cell lines not radiosensitized, radiation did not activate NF-kappaB. This correlation suggested that AV1Y28-mediated radiosensitization involved the inhibition of radiation-induced NF-kappaB activation. However, inhibition of NF-kappaB activation via the expression of a dominant-negative form of IkappaBalpha in U251 cells had no effect on radiation-induced cell killing and did not influence AV1Y28-mediated radiosensitization. Therefore, whereas AV1Y28 inhibits radiation-induced NF-kappaB activation, this process does not appear to play a direct role in its radiosensitizing actions.