Rosamaria Ruggieri

Platelet-derived growth factor and fibronectin-stimulated migration are differentially regulated by the Rac and extracellular signal-regulated kinase pathways

Directed cell migration is essential for a variety of important biological processes ranging from development and angiogenesis to metastasis. Ras plays a pivotal role in the signaling cascade that governs chemotaxis of fibroblasts toward platelet-derived growth factor-BB (PDGF-BB). Ras activates multiple downstream pathways, which include the extracellular signal-regulated kinase (ERK), Rac, and Ral signaling cascades. We therefore investigated the role of the Rac and ERK pathways in cell migration. We showed that migration of fibroblasts toward PDGF-BB is inhibited by expression of dominant negative Asn-17 Rac1. Blocking of the ERK pathway by either expression of dominant negative Ala-218/Ala-222-mitogen-activated protein kinase kinase (A218/A222-MEK1) or by a MEK-specific inhibitor did not inhibit migration toward PDGF-BB. In contrast, migration toward soluble fibronectin was suppressed by inhibition of the ERK pathway but not by Asn-17 Rac1 expression. These results indicate that directed cell migration mediated by different receptor classes in response to different ligands differentially utilizes the Rac and ERK pathways and suggest that Rac might play a critical role in pathological processes such as angiogenesis and metastasis.

Radioresistance of Brain Tumors

Radiation therapy (RT) is frequently used as part of the standard of care treatment of the majority of brain tumors. The efficacy of RT is limited by radioresistance and by normal tissue radiation tolerance. This is highlighted in pediatric brain tumors where the use of radiation is limited by the excessive toxicity to the developing brain. For these reasons, radiosensitization of tumor cells would be beneficial. In this review, we focus on radioresistance mechanisms intrinsic to tumor cells. We also evaluate existing approaches to induce radiosensitization and explore future avenues of investigation.

Microtubule-targeting agents can sensitize cancer cells to ionizing radiation by an interphase-based mechanism

Background The cytotoxic effects of microtubule-targeting agents (MTAs) are often attributed to targeted effects on mitotic cells. In clinical practice, MTAs are combined with DNA-damaging agents such as ionizing radiation (IR) with the rationale that mitotic cells are highly sensitive to DNA damage. In contrast, recent studies suggest that MTAs synergize with IR by interfering with the trafficking of DNA damage response (DDR) proteins during interphase. These studies, however, have yet to demonstrate the functional consequences of interfering with interphase microtubules in the presence of IR. To address this, we combined IR with an established MTA, mebendazole (MBZ), to treat glioma cells exclusively during interphase. Materials and methods To test whether MTAs can sensitize interphase cells to IR, we treated GL261 and GBM14 glioma cells with MBZ during 3–9 hours post IR (when the mitotic index was 0%). Cell viability was measured using a WST-1 assay, and radiosensitization was quantified using the dose enhancement factor (DEF). The effect of MBZ on the DDR was studied via Western blot analysis of H2AX phosphorylation. To examine the effects of MTAs on intracellular transport of DDR proteins, Nbs1 and Chk2, cytoplasmic and nuclear fractionation studies were conducted following treatment of glioma cells with MBZ. Results Treatment with MBZ sensitized interphase cells to the effects of IR, with a maximal DEF of 1.34 in GL261 cells and 1.69 in GBM14 cells. Treatment of interphase cells with MBZ led to more sustained γH2AX levels post IR, indicating a delay in the DDR. Exposure of glioma cells to MBZ resulted in a dose-dependent sequestration of Chk2 and Nbs1 in the cytoplasm. Conclusion This study demonstrates that MBZ can sensitize cancer cells to IR independently of the induction of mitotic arrest. In addition, evidence is provided supporting the hypothesis that MTA-induced radiosensitization is mediated by inhibiting DDR protein accumulation into the nucleus.