Generation of a Primitive Erythroid Cell Line and Promotion of Its Growth by Basic Fibroblast Growth Factor

Oncogenic potential of the DNA replication licensing protein CDT1

The expression of a gene, designated as Retroviral insertion site (Ris)2, was activated by retroviral DNA integration in an immortalized primitive erythroid cell line, EB-PE. Ris2 was also expressed at high levels in all human tumor cell lines analysed. Consistently, NIH3T3 fibroblasts overexpressing Ris2 formed tumors in Rag2 -/- mice when injected subcutaneously. The putative RIS2 protein shows a high sequence similarity to Xenopus CDT1, Drosophila DUP, and human CDT1, a newly identified DNA replication licensing protein, suggesting that Ris2 is a mouse homologue of CDT1. Cells overexpressing Ris2/Cdt1 exhibited a quicker entry into S phase when released from serum starvation compared to controls. Our results suggest that CDT1, an essential licensing protein for DNA replication, can function as an oncogene in mammals.

The fibroblast growth factor receptor FGFR-4 acts as a ligand dependent modulator of erythroid cell proliferation

Receptor and non-receptor tyrosine kinases constitute a large family of proteins that play a pivotal role in hematopoiesis. Here we conducted a comprehensive survey of tyrosine kinase gene expression in primary erythroid progenitor cells from bone marrow by employing a PCR-based strategy that targets the conserved kinase encoding region. We demonstrate that erythroid progenitor cells express several receptor and non-receptor tyrosine kinases, like c-kit, Jak1, Ryk, FAK, Syk, Arg, Csk and members of the insulin receptor family. Specific changes in the expression profile of tyrosine kinases were observed following differentiation induction. We also report on the identification of a new ligand dependent modulator of erythropoiesis, fibroblast growth factor receptor-4 (FGFR-4). FGFR-4 is effectively expressed in erythroid progenitors and downregulated when cells differentiate. Furthermore, the FGFR-4 ligand, basic fibroblast growth factor (bFGF), enhanced erythroid cell proliferation induced by SCF or insulin, and thus modulated both erythroid proliferation and differentiation in vitro.