Both Tumor Cell and Mature Tumor Vascular Endothelium of the Orthotopic Transplantation Model of Retinoblastoma Shows Nuclear Accumulation of p53 Protein

Abstract

 

Purpose:

 

Functional inactivation of p53 tumor suppressor has been suggested as an important pathogenic mechanism of retinoblastoma. Here, we investigated the expression pattern of p53 protein in the tumor cell and mature tumor vascular endothelium of the orthotopic transplantation model of retinoblastoma.

 

Methods:

 

Two kinds of established retinoblastoma cell lines (Y-79 and SNUOT Rb-1) were injected into the intravitreal cavity of BALB-c nude mice for inducing orthotopic transplantation model of retinoblastoma. Four weeks after injection the eyes were enucleated and sectioned for immunofluorescence staining. Double immunofluorescence stain with anti-von Willebrand factor and anti-p53antibodies and DAPI nuclear counterstain were performed to identify the presence of mature tumor vascular endothelium which shows immunoreactivityagainst anti-p53 antibody. To estimate the proportion of p53 positive endothelium among total mature tumor vascular endothelium, two blinded investigators counted at least 10 randomly selected high power fields.

 

Results:

 

In the orthotopic transplantation model, most tumor cells showed nuclear accumulation of p53 protein. A small fraction of mature tumor endothelium also demonstrated nuclear p53 accumulation, whereas pre-existing retinal vessels supplying uninvolved retina didn’t contain any p53 positive endothelial cell. The estimated ratio of p53 positive endothelium to total tumor vascular endothelial cell was 9.3%.

 

Conclusions:

 

Some proportion of mature tumor vascular endothelium showed nuclear accumulation of p53, the phenomenon of which resembles that of tumor cells. These data suggest that an endothelial differentiation of retinoblastoma cell might partially contribute to the tumor vascularization in the orthotopic transplantation model of retinoblastoma.  

 

Keywords: retinoblastoma • tumors • transplantation