Neurotrophin Receptors TrkA and TrkB in Retinoblastoma Are Differentially Expressed Depending on Cellular Differentiation

Abstract

Retinoblastoma is the most common primary intraocular malignancy in children. With the progression of retinoblastoma, retinoblastoma cells lose their ability to differentiate. Regardless of many attempts to identify prognostic factors in retinoblastoma, further investigation for prognostic factors of retinoblastoma progression is still required because of the lack of sensitivity and specificity of these prognostic factors in predicting disease progression. We demonstrated that the differential expression of the neurotrophin receptors TrkA and TrkB is closely related to the differentiation of retinoblastoma cells. While retinoblastoma cells expressed TrkA as well as TrkB, their growth rates were not influenced by the addition of nerve growth factor to the culture medium. In experimental animal models of retinoblastoma, TrkA expression was primarily detected in more differentiated areas with high nm23 immunoreactivity whereas TrkB expression was apparent in more proliferative areas with high Ki67 immunoreactivity. With retinoic-acid-induced differentiation of retinoblastoma cells, TrkA expression significantly increased whereas TrkB significantly decreased. The differential expression of TrkA and TrkB with differentiation of retinoblastoma cells was mediated by extracellular-signal-regulated kinase 1/2 activation, which was confirmed by immunocytochemistry of TrkA. Therefore, our results suggest that the differential expression of TrkA and TrkB could be valuable as a therapeutic target, for instance using specific inhibitors. Copyright (C) 2009 S. Karger AG, Basel