Human HTm4 is a hematopoietic cell cycle regulator
José L. Donato, … , Mohamed H. Sayegh, Chaker N. Adra
José L. Donato, … , Mohamed H. Sayegh, Chaker N. Adra
Published January 1, 2002
Citation Information: J Clin Invest. 2002;109(1):51-58. https://doi.org/10.1172/JCI14025.
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Article

Human HTm4 is a hematopoietic cell cycle regulator

Abstract

Proper control of cell cycle progression is critical for the constant self-renewal, differentiation, and homeostasis of the hematopoietic system. Cells of all types share the common cell cycle regulators. The different expression patterns of common regulators, in a broad sense, define cell-type or lineage specificity. However, there remains the possibility of hematopoietic cell cycle regulators tailored to the demands of the hematopoietic system. Here we describe a novel protein, HTm4, which serves as a hematopoietic cell cycle regulator. Our data indicate that HTm4 is expressed in hematopoietic tissues and is tightly regulated during the differentiation of hematopoietic stem cells. It binds to cyclin-dependent kinase–associated (CDK-associated) phosphatase-CDK2 (KAP-CDK2) complexes, and the three proteins demonstrate similar patterns of cellular expression in human lymphoid tissues. HTm4 stimulates the phosphatase activity of KAP, and its C-terminal region is required for binding to KAP-CDK2 complexes and the modulation of KAP activity. Overexpression of HTm4 can cause cell cycle arrest at the G0/G1 phase. Thus, HTm4 is a novel hematopoietic modulator for the G1-S cell cycle transition.

Authors

José L. Donato, Jon Ko, Jeffery L. Kutok, Tao Cheng, Taro Shirakawa, Xiao-Quan Mao, David Beach, David T. Scadden, Mohamed H. Sayegh, Chaker N. Adra

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Figure 4

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(a) HTm4 binds to KAP-CDK2 under normal physiological conditions. Sample...
(a) HTm4 binds to KAP-CDK2 under normal physiological conditions. Samples analyzed are shown on the top. The lane marked anti-CDK2 includes the samples immunoprecipitated with anti-CDK2 mAb and analyzed by Western blot technique using Ab’s as indicated on the left. (b) The C-terminal region of HTm4 is required for its binding to KAP-CDK2. HTm4-Ct, HTm4 without the last 22 amino acids. Ab’s used for the Western blot analysis, after immunoprecipitation with anti-Flag, are listed on the left. The induction of protein expression in the absence of Dox is marked as +, and no induction in the presence of Dox is marked as –. (c) The C-terminal region of HTm4 is required for the enhancement of the phosphatase activity of KAP. The descriptions for c are the same as Figure 4b, except the top panels show the immunoprecipitation with anti-Flag Ab and the bottom panels are derived from 50 μg of total lysate per sample. The upper bands in the lower panels are the dephosphorylated form of CDK2, marked as de-(P), and the lower bands are the phosphorylated (P) form. A reduction in intensity can be seen in the phosphorylated CDK2 in the presence of overexpressed Flag-HTm4. Representative figures of at least five experiments.