Abstract 576: Transforming growth factor-beta (TGF-β) inhibits growth of human myeloid leukemia cells and downregulates the expression of CDK inhibitor, p18INK4C.

Abstract

Abstract The cell cycle progression controlled by cyclin-dependent kinases (CDKs) is counterbalanced by CDK inhibitors (CKIs). The CKIs have two families: CIP/KIP and INK. The CIP/KIP members are composed of p21WAF1/CIP1, p27KIP1 and p57KIP2, which bind to and inhibit both cyclin D-CDK4/6 kinases and cyclin-E/A-CDK2. The INK members consist of p15INK4B, p16INK4A, p18INK4C and p19INK4D. The members in this family only bind to and inhibit G1CDKs (CDK4 and CDK6). We have previously reported that p27KIP1 plays both a positive and a negative role in human myeloid leukemia cells. In this study, we investigated whether p18INK4C plays any role in TGF-β-mediated cell cycle control of human myeloid leukemia cells. TGF-β significantly inhibited proliferation of MV4-11 and TF-1 cells, with upregulation of p27KIP1and downregulation of multiple CDKs and cyclins. Surprisingly, TGF-β significantly inhibited the expression of p18INK4C, a traditional G1 CDK inhibitor. The inhibitory effect of TGFβ on p18INK4C was time dependent. The time course showed that early inhibition of p18INK4C occurred at 3h after initiating TGFβ treatment in the cells with a maximal inhibition of 70% being observed at 72h incubation with TGF-β. The control cells treated with the solvent for TGFβ did not show any significant changes in the levels of p18INK4C. As a sample loading control, the cells treated with or without TGF-β expressed about the same levels of actin.TGFβ-induced p18INK4C inhibition is also dose dependent with a maximal inhibition being detected by Western blot when 30ng/ml of TGFβ was added to the culture. Low concentrations (5ng/ml or less) did not markedly affect the expression of p18INK4C. The association of p18INK4C with CDK4 was also decreased in response to TGF-β treatment detected by immunoprecipitation. Our data also showed that the two cell lines tested barely expresses p15INK4B, p16INK4A, p19INK4D, and p21WAF1/CIP1 and these inhibitors do not appear to play an important role, either positively or negatively, in the cell cycle control of the leukemia cells. Our data suggest that p18INK4C may be required for cell cycle progression in human myeloid leukemia cells tested. Whether such a positive role of p18INK4C is caused by a possible gene mutation(s) and thereby contributes to leoplasia of the leukemia cells is currently under investigation (supported by NIH-NIGMS MBRS RISE: R25 GM059244, Barry University). . Citation Format: Talia Guardia, Reshma Badaloo, Valentina Serrano, Alejandra Toro, Xiaotang Hu. Transforming growth factor-beta (TGF-β) inhibits growth of human myeloid leukemia cells and downregulates the expression of CDK inhibitor, p18INK4C. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 576. doi:10.1158/1538-7445.AM2013-576