Differentiation Of Retinoblastoma Cells Research Articles

The N-myc gene product in primary retinoblastomas.

The N-myc gene product in retinoblastomas was examined using the antisera against the N-myc gene product, which was produced as a fusion protein by Escherichia coli. The N-myc gene product was detected not only in the retinoblastoma cell line Y79 but also in primary retinoblastomas as a pair of bands of approximately 62 kilodaltons (KD) by immunoblotting. Immunohistochemical analysis showed positively stained cells with the antibody against the N-myc gene product in a few rosettes or fleuretts containing area of the tumor. The nuclei of the cells were positively stained. The N-myc gene product was not detected in the normal part of the retina or in other parts of the eye. The results suggested that the level of the N-myc gene product may be inversely correlated with the differentiation of retinoblastoma cells and that the detection of the N-myc gene product may be useful in the diagnosis of retinoblastoma. Because the undifferentiated form of retinoblastoma carries a worse prognosis than the differentiated forms, the level of the N-myc gene product may be related to the aggressiveness of the tumor cells. It remains to be seen whether metastatic retinoblastoma has a higher concentration of the N-myc gene product.

Retinoblastoma cell differentiation in culture.

Human retinoblastoma cells were grown in tissue culture and their differentiation into Flexner-Wintersteiner rosettes was investigated. This process of photoreceptor cell differentiation was only observed in primary cultures and subsequent cell passages of tumors which showed these structures in vivo. Rosettes formed spontaneously within 5-9 d after plating of the tumor cells. Under optimal conditions in certain tumor cell strains, up to 80% of the cultured cell aggregates contained one or more differentiated Flexner-Wintersteiner rosettes. Exposure of retinoblastoma cells to RA or dcAMP did not alter the number of rosettes in culture. Retinoblastoma cells within rosettes continued to synthesize DNA, and mitotic figures were frequently observed in histological sections. Ultrastructural analysis of rosettes formed in vitro showed many of the characteristics described in those found in vivo including a polarized shape, established cell junctions (Zonula adherens), extensive accumulation of mitochondria and microtubules in the apical part of the cells, numerous basal bodies and centrioles as well as cilia typical of the mature photoreceptor cell. Lamellated stacks of membranes were also found and their nature is discussed.

Alteration in gene expression at the onset of human Y-79 retinoblastoma cell differentiation

We have tested the hypothesis that differentiation and growth arrest of Y-79 human retinoblastoma cells in culture is associated with a modification of gene expression. We first examined proteins translated from mRNAs isolated from Y-79 cells growing in suspension and in attachment cultures in serum-containing medium and found them to be markedly different. This suggests that membrane-substrate interactions are of major consequence in the biochemical differentiation of these cells. Secondly, we examined the patterns of proteins translated from attached cells which had been induced to morphologically differentiate into neuronal-like and glial-like cells by serum-withdrawal and dibutyryl cAMP treatment respectively. The in vitro translatable proteins of mRNAs isolated from these cultures were found to be markedly different from those of the suspension and attachment cultures. Thirdly, we found that treatment of cells growing in attachment culture in serum-containing medium supplemented with 8-bromo cAMP, butyrate and retinoic acid as well as dibutyryl cAMP resulted in discreet alterations in proteins translated in vitro from extracted mRNAs. Although all these substances inhibit the growth of Y-79 cells, only dibutyryl cAMP and butyrate result in morphological differentiation of cells. Our results suggest that (1) attachment and morphological differentiation of Y-79 cells are both related to specific alterations in gene expression and (2) differentiation and inhibition of cell growth by various agents can be correlated with changes in translatable mRNA species although all agents do not act in the same mode.