Newly established human retinoblastoma cell lines exhibit an “immortalized” but not an invasive phenotype in vitro

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Abstract
Retinoblastoma (RB), an intraocular childhood tumor occurring in a hereditary (mostly bilateral) or non‐hereditary (unilateral) form, is associated with the inactivation of both alleles of a putative tumor suppressor gene (RB‐I) located on chromosome 13q14. Both the process of RB development and the biological characteristics of RB cells are as yet poorly understood. We have established 7 new RBL lines (RBL13, RBL14, RBL18 and RBL30, derived from unilateral RB; and RBL7, RBL15 and RBL20, derived from bilateral RB). Southern blot analyses of restriction fragment length polymorphisms in DNA samples from 6 cell lines revealed loss of constitutional heterozygosity at one or several polymorphic locion chromosome 13 in 4 cases. Gross deletions involving the RB‐1 locus and amplification of the N‐myc gene were not detected in any of the RBL lines. The phenotypic properties of the RBL lines were analyzed in comparison with cells from the original RB tumors, with 4 RB lines established by others (RB383, RB355, RB247C3 and Y79) and with the adenovirus‐EIA‐transformed human retinoblast line HER‐Xhol ‐CC2. It was found that RB tumors consist of phenotypically heterogeneous cell subpopulations with varying nutrient requirements and differentiation potential in vitro. All cell lines showed the typical characteristics of established (immortalized) cells. In some cases, cells from original RB tumors or cell lines were able to form colonies when cell aggregates of 2‐10 cells were suspended in semi‐solid agar medium; however, anchorage‐independent colonies never developed from single cells. Cell lines RBL13, RBL18, RB247C3, RB355, RB383 and Y79 were tested for invasion into embryonic chick heart fragments in vitro and found to be non‐invasive. None of the RBL or RB lines were tumorigenic in nu/nu (T‐) mice. Y79 cells (propagated in culture for many years) exhibited properties distinctly different from those of the other cell lines, and thus cannot be considered phenotypically representative of RB cells.
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