MicroRNA 21 (miR-21) promotes glioma invasion by targeting matrix metalloproteinase (MMP) regulators. The study demonstrates that miR-21 regulates genes involved in glioma cell apoptosis, migration, and invasiveness, including RECK and TIMP3, which are suppressors of malignancy and inhibitors of MMPs. Specific inhibition of miR-21 with antisense oligonucleotides leads to increased levels of RECK and TIMP3, reducing MMP activities in vitro and in a human glioma model in nude mice. Downregulation of miR-21 in glioma cells reduces their migratory and invasive abilities. The data suggest that miR-21 contributes to glioma malignancy by downregulating MMP inhibitors, activating MMPs, and promoting cancer cell invasiveness. Inhibition of miR-21 with specific antisense molecules could provide a novel therapeutic approach for modulating multiple proteins deregulated in cancer. Malignant gliomas are the most common primary brain tumors in adults and are associated with poor prognosis. Current therapies for glioblastoma (GBM) are ineffective due to rapid tumor growth, genetic heterogeneity, and limited understanding of molecular mechanisms. MicroRNAs (miRNAs) are small regulatory RNAs that regulate gene expression and have been implicated in cancer progression. miR-21 is significantly elevated in GBMs and other cancers, and its overexpression is associated with increased cell proliferation, apoptosis, and migration. The study identifies miR-21 as a key regulator of glioma progression by targeting MMP inhibitors, such as RECK and TIMP3, which are crucial for suppressing MMP activity. Inhibition of miR-21 reduces MMP activity, decreases glioma cell motility and invasiveness, and increases the expression of RECK and TIMP3. These findings suggest that miR-21 plays a critical role in glioma progression by promoting invasiveness through the regulation of MMP inhibitors. The study also highlights the potential of miR-21 as a therapeutic target for modulating cancer progression.MicroRNA 21 (miR-21) promotes glioma invasion by targeting matrix metalloproteinase (MMP) regulators. The study demonstrates that miR-21 regulates genes involved in glioma cell apoptosis, migration, and invasiveness, including RECK and TIMP3, which are suppressors of malignancy and inhibitors of MMPs. Specific inhibition of miR-21 with antisense oligonucleotides leads to increased levels of RECK and TIMP3, reducing MMP activities in vitro and in a human glioma model in nude mice. Downregulation of miR-21 in glioma cells reduces their migratory and invasive abilities. The data suggest that miR-21 contributes to glioma malignancy by downregulating MMP inhibitors, activating MMPs, and promoting cancer cell invasiveness. Inhibition of miR-21 with specific antisense molecules could provide a novel therapeutic approach for modulating multiple proteins deregulated in cancer. Malignant gliomas are the most common primary brain tumors in adults and are associated with poor prognosis. Current therapies for glioblastoma (GBM) are ineffective due to rapid tumor growth, genetic heterogeneity, and limited understanding of molecular mechanisms. MicroRNAs (miRNAs) are small regulatory RNAs that regulate gene expression and have been implicated in cancer progression. miR-21 is significantly elevated in GBMs and other cancers, and its overexpression is associated with increased cell proliferation, apoptosis, and migration. The study identifies miR-21 as a key regulator of glioma progression by targeting MMP inhibitors, such as RECK and TIMP3, which are crucial for suppressing MMP activity. Inhibition of miR-21 reduces MMP activity, decreases glioma cell motility and invasiveness, and increases the expression of RECK and TIMP3. These findings suggest that miR-21 plays a critical role in glioma progression by promoting invasiveness through the regulation of MMP inhibitors. The study also highlights the potential of miR-21 as a therapeutic target for modulating cancer progression.