Abstract
It is still not clear whether the p53 pathway is altered in retinoblastoma development. We assessed the expression of the p53 pathway genes p14 ARF , mouse double minute 2 ( MDM2), and mouse double minute 4 ( MDM4) in human retinoblastoma compared to normal retina. Primary human retinoblastomas, retinoblastoma cell lines and normal retinas were assessed for p14 ARF and MDM4 mRNA by quantitative RT-PCR. p14 ARF, MDM2, and MDM4 protein were measured by immunoblot and immunohistochemistry. Compared to retina, p14 ARF mRNA expression was notably increased in retinoblastoma but p14 ARF protein was undetectable. MDM2 and MDM4 proteins were expressed in 22/22 retinoblastomas. MDM2 was expressed in 3/10 retinas tested, and MDM4 in 10/10 retinas. The expression level of MDM2 protein in retinoblastomas and retina was comparable, while MDM4 protein was overexpressed in one retinoblastoma cell line Y79 and two primary retinoblastomas. We observe that overexpression of MDM2 and MDM4 is not a necessary step in retinoblastoma development. However, loss of detectable p14 ARF protein and resultant lack of functional inactivation of these p53 inhibitors may contribute to retinoblastoma development by constitutive inhibition of p53.
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