Modulation of retinoblastoma gene in normal adult hematopoiesis: peak expression and functional role in advanced erythroid differentiation.

Abstract

The retinoblastoma (RB) gene specifies a nuclear phosphoprotein (pRb 105), which is a prototype tumor suppressor inactivated in a variety of human tumors. Recent studies suggest that RB is also involved in embryonic development of murine central nervous and hematopoietic systems. We have investigated RB expression and function in human adult hematopoiesis-i.e., in liquid suspension culture of purified quiescent hematopoietic progenitor cells (HPCs) induced by growth factor stimulus to proliferation and unilineage differentiation/maturation through the erythroid or granulocytic lineage. In the initial HPC differentiation stages, the RB gene is gradually induced at the mRNA and protein level in both erythroid and granulopoietic cultures. In late HPC differentiation and then precursor maturation, RB gene expression is sustained in the erythroid lineage, whereas it is sharply downmodulated in the granulocytic series. Functional studies were performed by treatment of HPC differentiation culture with phosphorothioate antisense oligomer targeting Rb mRNA; coherent with the expression pattern, oligomer treatment of late HPCs causes a dose-dependent and selective inhibition of erythroid colony formation. These observations suggest that the RB gene plays an erythroid-and stagespecific functional role in normal adult hematopoiesis, particularly at the level of late erythroid HPCs.

Expression and role of PML gene in normal adult hematopoiesis: functional interaction between PML and Rb proteins in erythropoiesis

“…Cells were collected for RNA extraction at day 7 and day 9 from the culture Expression and role of PML and Rb proteins in erythropoiesis C Labbaye et al extensive self-renewal and feed into lineage-committed HPCs. We have developed methodology for normal HPC/HSC puri®cation (Gabbianelli et al, 1990;Labbaye et al, 1994) and unilineage di erentiation/ maturation in liquid-phase suspension culture: this allows a step-by-step analysis of hematopoietic di erentiation/maturation through a single lineage at both cellular and molecular levels (Labbaye et al, 1994(Labbaye et al, , 1995Giampaolo et al, 1994;Condorelli et al, 1995).…”

“…We have exploited this model system to investigate the pattern of expression and the possible role of several transcription factors in hematopoietic differentiation (Labbaye et al, 1994(Labbaye et al, , 1995Giampaolo et al, 1994;Condorelli et al, 1995). The relevance of PML in the physiology of the hematopoietic system is indirectly suggested by its involvement in the pathogenesis of APL as a partner of RARa in the PML/RARa fusion protein (Warrell et al, 1993;Grignani et al, 1994;de TheÁ et al, 1991) and is also directly supported by the phenotypic analysis of PML 7/7 mice (Wang et al, 1998).…”

p300 functions as a transcriptional coactivator for the TAL1/SCL oncoprotein

“…Further, expression of a full length TAL1 cDNA potentiated erythroid di erentiation of a human leukemia cell line (Hoang et al, 1996) and increased erythroid colony formation by normal human bone marrow cells (Elwood et al, 1998). In contrast, treatment of human hematopoietic progenitors with a TAL1 antisense oligonucleotide led to a reduction in the number of erythroid colonies (Condorelli et al, 1995). Finally, two growth factors important in erythropoiesis, erythropoietin and stem cell factor, were both found to induce TAL1 expression (Miller et al, 1994;Prasad et al, 1995).…”

Tumor suppressor genes in normal and malignant hematopoiesis

“…Surprisingly, heterozygous Rb +/7 mice are not prone to retinoblastomas, but have a high incidence of pituitary adenocarcinomas. Rb expression increases during erythroid di erentiation of hematopoietic progenitor cells, and antisense treatment results in a dose-dependent decline of erythroid colony numbers (Condorelli et al, 1995). Rb interacts with the transcription factor PU.1 (Hagemeier et al, 1993).…”