A central role for TRPS1 in the control of cell cycle and cancer development

The eukaryotic cell cycle is controlled by a complex regulatory network, which is still poorly understood. Here we demonstrate that TRPS1, an atypical GATA factor, modulates cell proliferation and controls cell cycle progression. Silencing TRPS1 had a differential effect on the expression of nine key cell cycle-related genes. Eight of these genes are known to be involved in the regulation of the G2 phase and the G2/M transition of the cell cycle. Using cell synchronization studies, we confirmed that TRPS1 plays an important role in the control of cells in these phases of the cell cycle. We also show that silencing TRPS1 controls the expression of 53BP1, but not TP53. TRPS1 silencing also decreases the expression of two histone deacetylases, HDAC2 and HDAC4, as well as the overall HDAC activity in the cells, and leads to the subsequent increase in the acetylation of histone4 K16 but not of histone3 K9 or K18. Finally, we demonstrate that TRPS1 expression is elevated in luminal breast cancer cells and luminal breast cancer tissues as compared with other breast cancer subtypes. Overall, our study proposes that TRPS1 acts as a central hub in the control of cell cycle and proliferation during cancer development.

Graded levels of GATA-1 expression modulate survival, proliferation, and differentiation of erythroid progenitors

Transcription factor GATA-1 plays an important role in gene regulation during the development of erythroid cells. Several reports suggest that GATA-1 plays multiple roles in survival, proliferation, and differentiation of erythroid cells. However, little is known about the relationship between the level of GATA-1 expression and its nature of multifunction to affect erythroid cell fate. To address this issue, we developed in vitro embryonic stem (ES) culture system by using OP9 stromal cells (OP9/ES cell co-culture system), and cultured the mutant (GATA-1.05 and GATA-1-null) and wild type (WT)ES cells, respectively. By using this OP9/ES cell co-culture system, primitive and definitive erythroid cells were developed individually, and we examined how expression level of GATA-1 affects the development of erythroid cells. GATA-1.05 ES-derived definitive erythroid cells were immature with the appearance of proerythroblasts, and highly proliferated, compared with WT and GATA-1-null ES-derived erythroid cells. Extensive studies of cell cycle kinetics revealed that the GATA-1.05 proerythroblasts accumulated in S phase and expressed lower levels of p16(INK4A) than WT ES cell-derived proerythroblasts. We concluded that GATA-1 must achieve a critical threshold activity to achieve selective activation of specific target genes, thereby influencing the developmental decision of an erythroid progenitor cell to undergo apoptosis, proliferation, or terminal differentiation.

Reduction of DNA binding activity of the GATA-1 transcription factor in the apoptotic process induced by overexpression of PU.1 in murine erythroleukemia cells

Previously we have shown that overexpression of PU.1, an Ets family transcription factor, in murine erythroleukemia (MEL) cells results in apoptotic cell death in the presence of the differentiation-inducing reagent dimethyl sulfoxide (DMSO). In this study, we examined the dynamics of GATA-1 and NF-E2 hematopoietic transcription factors during the induction of apoptosis, because GATA-1 has been shown to be implicated in survival of erythroid cells. Formation of the GATA-1-DNA complex as judged by EMSA was markedly reduced when apoptosis was induced, although subcellular localization of the GATA-1 protein and expression levels of the GATA-1 mRNA and protein were not changed during the apoptotic process. Complex formation was not reduced when apoptosis was avoided by adding 30% serum in culture medium and when mutant PU.1 proteins with the deletion of the DNA-binding (Ets) or transactivation domain were expressed. Complex formation in nuclear extracts of parental MEL cells was reduced when they were mixed with those of apoptotic cells, suggesting that apoptotic cells may contain a factor(s) preventing GATA-1 from binding to DNA. In contrast to GATA-1, formation of the NF-E2-DNA complex was not changed during the process of apoptosis, although the expression level of the NF-E2 p45 gene was reduced in the process. These results suggest that reduction of the DNA-binding activity of GATA-1 may partly account for PU.1-mediated apoptosis in MEL cells.