Role of Rac1-regulated signaling in medulloblastoma invasion

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Medulloblastomas are the most common malignant brain tumors in children. These tumors are highly invasive, and patients harboring these lesions are frequently diagnosed with distant spread. In this study, the authors investigated the role of Rac1, a member of the Rho family of small guanosine triphosphatases, in medulloblastoma invasion.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Three established medulloblastoma cell lines were used: DAOY, UW-228, and ONS-76. Specific depletion of Rac1 protein was accomplished by transient transfection of small interfering RNA. Cell invasion through extracellular matrix (Matrigel) was quantified using a transwell migration assay. Mitogen activated protein kinase activation was determined using phospho-MAP kinase–specific antibodies, and inhibition of MAP kinase pathways was achieved by specific small molecule inhibitors. Localization of Rac1 and its expression levels were determined by immunohistochemical analysis using a Rac1-specific antibody, and Rac1 activation was qualitatively assessed by Rac1 plasma membrane association.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Small interfering RNA–mediated depletion of Rac1 strongly inhibited medulloblastoma cell invasion. Although depletion of Rac1 inhibited the proliferation of UW-228 cells, and of ONS-76 cells to a lesser extent, it stimulated the proliferation of DAOY cells. Depletion of Rac1 also inhibited the activation of the ERK and JNK MAP kinase pathways, and inhibition of either pathway diminished invasion and proliferation. Immunohistochemical analysis demonstrated that the Rac1 protein was overexpressed in all medulloblastoma tumors examined, and indicated that Rac1 was hyperactive in 6 of 25 tumors.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The authors' data show that Rac1 is necessary for the invasive behavior of medulloblastoma cells in vitro, and plays a variable role in medulloblastoma cell proliferation. In addition, these results indicate that Rac1 stimulates medulloblastoma invasion by activating the ERK and JNK pathways. The authors suggest that Rac1 and signaling elements controlled by this guanosine triphosphatase may serve as novel targets for therapeutic intervention in malignant medulloblastomas.</jats:p></jats:sec>

The Tumor Suppressor Role of miR-124 in Osteosarcoma

“…Rac1 activation is correlated with the progression of many types of cancer such as pancreatic cancer, gastric cancer, and breast cancer [29]–[33]. More investigations have revealed that Rac-dependent cell signaling activation can promote cell adhesion, migration, invasion and metastasis in a variety of cancers, such as prostate cancer, breast cancer, hepatocellular carcinoma, colon carcinoma and renal carcinoma, suggesting that Rac1 plays an important role in tumorigenesis and carcinoma progression [31], [34], [35]. In this study, we confirmed that Rac1 is overexpressed in osteosarcoma.…”

Secreted meningeal chemokines, but not VEGFA, modulate the migratory properties of medulloblastoma cells

“…The overexpression of RAC1, a member of the RHO protein super-family, has been previously shown in DAOY cells and in medulloblastoma tumors and RAC1 activity is known to functionally regulate DAOY cell migration [21,22]. Our result shows significant activation of RAC1 when DAOY cells are stimulated with BMEN1 CM and to a lesser degree with DAOY CM (Fig.…”

The Ser/Thr kinase MAP4K4 drives c-Met-induced motility and invasiveness in a cell-based model of SHH medulloblastoma

“…However, we found that 24 h ARQ197 pretreatment was necessary to block acute, HGF-induced c-Met signaling (Figure 2 C). c-Met can activate the c-Jun N-terminal kinase (JNK) (Rodrigues et al 1997 ), which controls growth and invasion of MB cells (Zavarella et al 2009 ). Consistently, we detected PHA-665752-sensitive phosphorylation of mainly the p46 isoform of JNK within five to ten minutes of HGF stimulation (Figure 2 D).…”