Notch Signaling in Neuroblastoma and Renal Cell Carcinoma
Abstract: The Notch signaling pathway governs cell functions essential for normal development and organogenesis. Aberrant Notch signaling has been implicated in tumorigenesis by perturbing control of proliferation, differentiation, apoptosis, migration and angiogenesis. Neuroblastoma is an embryonal tumor derived from cells of the sympathetic nervous system, arrested at an immature stage of differentiation. Notch signaling is thought to play an important role during the development of the sympathetic nervous system, and prior studies have indicated that dysregulated Notch signaling might be associated with the perturbed differentiation that characterize neuroblastoma cells. Here we show that the histone deacetylase inhibitor valproic acid induced differentiation of neuroblastoma cells, in conjunction with activation of Notch-1 signaling. In addition, we also noted that the expression of the Notch target HES-1 was primarily regulated by ERK-MAP kinase signaling in a neuroblastoma cell line. Clear cell renal cell carcinoma (CCRCC) is characterized by activation of the hypoxia inducible factor (HIF) pathway due to functional loss of the von Hippel-Lindau tumor suppressor gene. However, cooperating oncogenic events parallel to the HIF pathway remains poorly described. Our results presented here imply a growth-promoting role for Notch signaling in CCRCC cells, seemingly independent of HIF-regulated cellular events. Treatment of nude mice bearing CCRCC xenografts, with daily injections of a Notch inhibitor (?-secretase inhibitor) in cycles of 3 days followed by 4 days without treatment, retarded tumor growth and minimized the adverse effects commonly associated with ?-secretase inhibition. In addition, analysis of primary CCRCC samples revealed that Notch-1 and Jagged-1 were expressed at significantly higher levels compared to normal kidney tissue samples. Finally, we found that inhibition of Notch signaling decreased the migratory potential of CCRCC cells. This effect might be linked to a cross-talk between Notch and TGF-? signaling in CCRCC cells.
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