Exogenous cdk4 overcomes reducedcdk4 RNA and inhibition of G1 progression in hematopoietic cells expressing a dominant-negative CBF – a model for overcoming inhibition of proliferation by CBF oncoproteins

• Published in: Oncogene Vol. 19; no. 22; pp. 2695 - 2703
• Main Authors: Lou, Jianrong, Cao, Wangsen, Bernardin, Florence, Ayyanathan, Kasirajan, Rauscher, Frank J, Friedman, Alan D
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group 18.05.2000
• Subjects: AML1 protein; Cell cycle; Cell proliferation; Cyclin-dependent kinase 4; Deoxyribonucleic acid; DNA; Estrogen receptors; INK4a protein; mRNA; Oncoproteins; Overexpression; p16 Protein; Regulatory proteins
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/sj.onc.1203588

Core Binding Factor (CBF) is required for the development of definitive hematopoiesis, and the CBF oncoproteins AML1-ETO, TEL-AML1, and CBFβ-SMMHC are commonly expressed in subsets of acute leukemia. CBFβ-SMMHC slows the G1 to S cell cycle transition in hematopoietic cells, but the mechanism of this effect is uncertain. We have sought to determine whether inhibition of CBF-mediated trans-activation is sufficient to slow proliferation. We demonstrate that activation of KRAB-AML1-ER, a protein containing the AML1 DNA-binding domain, the KRAB repression domain, and the Estrogen receptor ligand binding domain, also slows G1, if its DNA-binding domain is intact. Also, exogenous AML1 overcame CBFβ-SMMHC-induced inhibition of proliferation. Representational difference analysis (RDA) identified cdk4 RNA expression as an early target of KRAB-AML1 activation. Inhibition of CBF activities by KRAB-AML1-ER or CBFβ-SMMHC rapidly reduced endogenous cdk4 mRNA levels, even in cells proliferating at or near control rates as a result of exogenous cdk4 expression. Over-expression of cdk4, especially a variant which cannot bind p16INK4a, overcame cell cycle inhibition resulting from activation of KRAB-AML1-ER, although cdk4 did not accelerate proliferation when expressed alone. These findings indicate that mutations which alter the expression of G1 regulatory proteins can overcome inhibition of proliferation by CBF oncoproteins.