Abstract 4233: Mef2C enhances 1,25-dihydroxyvitamin D3-induced monocytic differentiation of human myeloid leukemia cells by regulating C/EBPβ expression

Abstract

Abstract Myogenic enhancer factors 2 (Mef2) are members of the family of MADS (MCM1-agamous-deficiens-serum response factor)-box transcription factors known to have multiple roles in morphogenesis of skeletal, cardiac and smooth muscle cells. Recently, Mef2C was found to be also involved in hematopoiesis. Bone marrow cells isolated from Mef2C knockout mice demonstrated decreased monocytic differentiation in response to cytokine stimulation, whereas constitutive expression of Mef2C promoted monopoiesis. The above findings led us to examine the role of Mef2C in 1,25-dihydroxyvitamin D3 (1,25D)-induced monocytic differentiation. Human acute myeloid leukemia (AML) cell lines, HL60 and U937, were used in this study. We found that knockdown of Mef2C with small interfering RNA (siRNA) significantly decreased the expression of the monocytic marker CD14, as well as of nonspecific esterase (NSE), suggesting that Mef2C is required for 1,25D-induced monocytic differentiation in AML cells. Our laboratory has previously demonstrated that optimal monocytic differentiation induced by 1,25D requires ERK5, and that ERK5 expression shows positive correlation with Mef2C expression. Here we show that Mef2C knockdown demonstrates similar inhibition of CD14 expression as ERK5 knockdown. CCAAT-enhancer-binding proteins (C/EBPs) α and β are two major transcription factors that can directly regulate CD14 expression. Since 1,25D has been shown to increase both C/EBPα and β expression, and these two transcription factors form heterodimers to enhance CD14 expression, we used siRNA to knock down Mef2C and found decreased expression of 1,25D-induced C/EBPβ, but not C/EBPα. Similar results were obtained using an alternative method to titrate down Mef2C with dsDNA containing its DNA binding sequence. We conclude that Mef2C is a functional downstream target of ERK5, and that 1,25D-induced CD14 and NSE expression is mediated through ERK5/Mef2C activation. (Supported by T32 CA134268 training grant and R01 CA044722 both from the National Cancer Institute, NIH, and by the American Institute for Cancer Research grant 10A049) Citation Format: Ruifang Zheng, Xuening Wang, George P. Studzinski. Mef2C enhances 1,25-dihydroxyvitamin D3-induced monocytic differentiation of human myeloid leukemia cells by regulating C/EBPβ expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4233. doi:10.1158/1538-7445.AM2014-4233