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Regulatory role of HTm4 gene in hematopoietic cell cycle

Li Jin, Xie Chao, Xie Xiaoyan, Wang Dongmei, Pei Xuetao

Department of Stem Cell Biology, Beijing Institute of Transfusion Medicine.Beijing 100850

Abstract

Cell cycle progression is tightly regulated in hematopoietic stem cells. The cycle state decides cells'fates, which include self-renewal, proliferation and differentiation. Proper cell cycle regulation is a pivotal element for the maintenance of hematopoiesis homeostasis. Htm4 is a newly identified specific cell cycle regulator of the hematopoietic cell. Through interacting with KAP-CDK2 complex, it arrests cells in G(0)/G_(1) phase. K562 is a human chronic myelogenous leukemia cell; it could be induced to megakaryoblast by PMA. Such differentiation must associate with cell cycle change. To further clarify Htm4's function in hematopoietic cell cycle regulation, K562 cells were treated with PMA. Cell cycle change was analysed using flow cytometric system. And during the induction process gene expression of HTm4 as well as CycleE and CDK2, which are responsible for G_(1) to S transition, were analysed using semi-quantitative RT-PCR. The C-terminal domain of HTm4 protein has been shown to be important for HTm4's binding with KAP-CDK2 complex. To determine its impact on HTm4's function, HTm4 and C-terminal truncated HTm4 (HTm4-ct) were transfected into K562 cells using Tet-Off regulation expression system. Their influence on cell cycle was observed. Results showed that PMA induced both expansion and differentiation of K562 cells as measured by cell number count and NBT staining respectively. During PMA treatment, G(0)/G_(1) cell proportion and HTm4 expression displayed coordinated change, which suggested that HTm4 might drive K562 cells out of cell cycle but was not involved in the quiescence maintenance. Additionally, transfection of HTm4 caused G(0)/G_(1) arrest in K562 cells, while transfection of HTm4-ct did not. .It is therefore suggested that the C-terminal domain is important for the function of HTm4 in cell cycle regulation.

Key words: Cell cycle;HTm4 gene;K562 cells

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Citing This Article：

Li Jin, Xie Chao, Xie Xiaoyan, Wang Dongmei, Pei Xuetao. Regulatory role of HTm4 gene in hematopoietic cell cycle. Acta Physiol Sin 2005; 57 (2): (in Chinese with English abstract).