Identification of tumorigenic retinal stem‐like cells in human solid retinoblastomas

Abstract

Retinoblastoma (RB) is the most common malignant tumor of the retina in human children. Although it has been hypothesized for a long time that RB derives from multipotent retinal stem cells (RSCs) or retinoblasts, the direct evidence that the presence of tumorigenic RSCs in RB tumors is still lacking. Some studies indicate that malignant tumors contain tumor stem cells similar to their normal tissue stem cell counterparts. With in vitro culture and differentiation method we demonstrate that tumorigenic retinal stem-like cells (RSLCs) indeed exist in RB lesions and that RB tumor-derived cultures encompass undifferentiated cells capable of extensive proliferation as clonal nonadherent neurospheres and can differentiate into different retinal cells in vitro. Interestingly, cultured cells expressed retinal development related genes including nestin, CD133, pax6, chx10 and Rx, and overexpressed Bmi-1, a gene required for self-renewal and proliferation of stem cells. Significantly, when these cultured cells were intraocularly transplanted into SCID mice, they gave rise to new tumors with histomorphological features and immunophenotypes similar to their parental primary RBs. The results show that RBs contain tumorigenic RSLCs that contribute to tumorigenesis. This study provides a new insight to investigate the histogenesis of RBs and establishes a model for other RB research. ' 2007 Wiley-Liss, Inc.Key words: retinoblastoma; tumor stem cell; retinal stem cell; tumorigenesis Retinoblastom (RB) is the most common malignant tumor of the retina in children and has become an excellent study model for cancer biology and molecular mechanism. [1][2][3][4][5][6] It is categorized into differentiated and undifferentiated types by the World Health Organization (WHO) classification according to the presence of rosettes and the degree of atypia. 2 Most of previous studies have been focusing on the cellular and molecular analysis of the bulk tumor mass to search cell origin of RB tumor and RB gene mutation. Although the origin of RB cells has been somewhat controversial, it has been generally agreed that RB cells originate from the multipotent primitive retinoblasts or retinal stem cells (RSCs). 3,[7][8][9][10][11][12][13][14][15][16] Up to date, there is no direct evidence to support that tumorigenic RSCs exist in RBs. In recent years, brain tumor stem cells (BTSCs) have been isolated from human brain malignant tumor samples and cultured then transplanted into experimental animals to form new tumors, providing strong evidence that these BTSCs are the origin of the brain tumor. [17][18][19] In 2005, Siegal et al. demonstrated that mouse and human RB cells contained a small subpopulation of cells exhibiting a cancer stem cell-like phenotype. 20 Recently, our research group successfully cultured stemlike cells from human RB lesions using the methods culturing BTSCs and RSCs. 19,21 Our previous data showed that these stemlike cells exhibited RSC properties in vitro including extensive proliferation, self-renewal and multipotency. 22 H...

PAX6 Is Expressed in Pancreatic Cancer and Actively Participates in Cancer Progression through Activation of the MET Tyrosine Kinase Receptor Gene

“…In other tissue types, PAX6 is correlated with an oncogenic phenotype. PAX6 is expressed in retinoblastoma and in tumors of the pancreas and the intestine (24,43,44). Very little is known about the expression of the PAX6(5a) variant in tumors.…”

Nestin expression in human tumors and tumor cell lines.

“…Similarly, strong nestin expression was also found in tumor cells of anaplastic oligodendrogliomas (grade III-IV), whereas only minimal expression was detected in oligodendrogliomas (grade II) [32,38,39]. Furthermore, nestin expression was confirmed in embryonic tumors that arise from undifferentiated precursors in various locations within the nervous system: in medulloblastomas [32,35,36], neuroblastomas [40,41], and retinoblastomas [42]. …”

“…The existence of the "side population" has been confirmed both in adult SCs and CSCs [73,74]. CSCs have been found in acute myeloid leukemia [51,75], multiple myeloma [76], as well as in solid tumors of breast [77], CNS [42,78], prostate [79], pancreas [80], head and neck [81], intestine [82], and in melanomas [83].…”

Pax6 Regulates the Expression of Dkk3 in Murine and Human Cell Lines, and Altered Responses to Wnt Signaling Are Shown in FlpIn-3T3 Cells Stably Expressing Either the Pax6 or the Pax6(5a) Isoform

“…Around 1000 of these were occupied in two tissues, and 131 in all three tissues [10]. In addition to its important role in embryo development, Pax6 is expressed in several tumors of the brain, pancreas and eye [11]–[13]. A link between the Wnt pathway and Pax6 is reported both in the brain [14], in the lens [15] and in the cornea [16].…”