Abstract
Retinoblastoma is the most common intraocular malignancy of childhood. Notch plays a key role in retinal cells from which retinoblastomas arise, and we therefore studied the role of Notch signaling in promoting retinoblastoma proliferation. Moderate or strong nuclear expression of Hes1 was found in 10 of 11 human retinoblastoma samples analyzed immunohistochemically, supporting a role for Notch in retinoblastoma growth. Notch pathway components were present in WERI Rb1 and Y79 retinoblastoma lines, with Jag2 and DLL4 more highly expressed than other ligands, and Notch1 and Notch2 more abundant than Notch3. The cleaved/active form of Notch1 was detectable in both lines. Inhibition of the pathway, achieved using a γ-secretase inhibitor (GSI) or by downregulating Jag2, DLL4 or CBF1 using short hairpin RNA, potently reduced growth, proliferation and clonogenicity in both lines. Upregulation of CXCR4 and CXCR7 and downregulation of PI3KC2β were identified by microarray upon Jag2 suppression. The functional importance of PI3KC2β was confirmed using shRNA. Synergy was found by combining GSI with Melphalan at their IC50. These findings indicate that Notch pathway is active in WERI Rb1 and Y79, and in most human retinoblastoma samples, and suggest that Notch antagonists may represent a new approach to more effectively treat retinoblastoma.
Highlights
Retinoblastoma is a malignant tumor of the developing retina, and the most common intraocular cancer in children, with 80% of cases occurring before the age of 3 [1]
Jag2 mRNA and protein levels were much higher in both retinoblastoma lines as compared to Jag1, which was barely measurable by both Western blot and Quantitative real-time PCR (qPCR) (Figure 1B, 1C)
We focused on activity of Notch in promoting growth and proliferation in retinoblastoma, since this pathway is known to play a key role in the specification and survival of stem and progenitor cells during retinal development [13]
Summary
Retinoblastoma is a malignant tumor of the developing retina, and the most common intraocular cancer in children, with 80% of cases occurring before the age of 3 [1]. It is diagnosed in approximately 300 children per year in the US, with an incidence of 11.8 cases per million in children aged 0–4 years [2]. The age-adjusted incidence rate has remained stable over the last 30 years [2]. Dystrophic calcification and multiple regions of necrosis are considered microscopic hallmarks [5, 6]
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