ABSTRACT
Glioblastoma is the most common malignant primary brain tumor. Temozolomide (TMZ) is the standard chemotherapeutic agent for this disease. However, intrinsic and acquired TMZ-resistance represents a major obstacle for this therapy. In order to identify factors involved in TMZ-resistance, we engineered different TMZ-resistant glioblastoma cell lines. Gene expression analysis demonstrated that EFEMP1, an extracellular matrix protein, is associated with TMZ-resistant phenotype. Silencing of EFEMP1 in glioblastoma cells resulted in decreased cell survival following TMZ treatment, whereas overexpression caused TMZ-resistance. EFEMP1 acts via multiple signaling pathways, including γ-secretase-mediated activation of the Notch pathway. We show that inhibition of γ-secretase by RO4929097 causes at least partial sensitization of glioblastoma cells to temozolomide in vitro and in vivo. In addition, we show that EFEMP1 expression levels correlate with survival in TMZ-treated glioblastoma patients. Altogether our results suggest EFEMP1 as a potential therapeutic target to overcome TMZ-resistance in glioblastoma.
Subject(s)
Amyloid Precursor Protein Secretases/metabolism , Antineoplastic Agents, Alkylating/pharmacology , Brain Neoplasms/drug therapy , Dacarbazine/analogs & derivatives , Extracellular Matrix Proteins/metabolism , Glioblastoma/drug therapy , Receptors, Notch/metabolism , Animals , Antineoplastic Combined Chemotherapy Protocols/pharmacology , Benzazepines/administration & dosage , Benzazepines/pharmacology , Brain Neoplasms/genetics , Brain Neoplasms/metabolism , Brain Neoplasms/pathology , Cell Line, Tumor , Dacarbazine/administration & dosage , Dacarbazine/pharmacology , Drug Resistance, Neoplasm , Extracellular Matrix Proteins/biosynthesis , Extracellular Matrix Proteins/genetics , Female , Gene Expression , Glioblastoma/genetics , Glioblastoma/metabolism , Glioblastoma/pathology , Humans , Mice , Receptors, Notch/genetics , Signal Transduction , Temozolomide , TransfectionABSTRACT
At least 5% of individuals with hypertension have adrenal aldosterone-producing adenomas (APAs). Gain-of-function mutations in KCNJ5 and apparent loss-of-function mutations in ATP1A1 and ATP2A3 were reported to occur in APAs. We find that KCNJ5 mutations are common in APAs resembling cortisol-secreting cells of the adrenal zona fasciculata but are absent in a subset of APAs resembling the aldosterone-secreting cells of the adrenal zona glomerulosa. We performed exome sequencing of ten zona glomerulosa-like APAs and identified nine with somatic mutations in either ATP1A1, encoding the Na(+)/K(+) ATPase α1 subunit, or CACNA1D, encoding Cav1.3. The ATP1A1 mutations all caused inward leak currents under physiological conditions, and the CACNA1D mutations induced a shift of voltage-dependent gating to more negative voltages, suppressed inactivation or increased currents. Many APAs with these mutations were <1 cm in diameter and had been overlooked on conventional adrenal imaging. Recognition of the distinct genotype and phenotype for this subset of APAs could facilitate diagnosis.
