The LIM-only factor LMO4 regulates expression of the BMP7 gene through an HDAC2-dependent mechanism, and controls cell proliferation and apoptosis of mammary epithelial cells

Abstract

The nuclear LIM-only protein 4 (LMO4) is upregulated in breast cancer, especially estrogen receptor-negative tumors, and its overexpression in mice leads to hyperplasia and tumor formation. Here, we show that deletion of LMO4 in the mammary glands of mice leads to impaired lobuloalveolar development due to decreased epithelial cell proliferation. With the goal of discovering potential LMO4-target genes, we also developed a conditional expression system in MCF-7 cells for both LMO4 and a dominant negative (DN) form of its co-regulator, cofactor of LIM domains (Clim/Ldb/Nli). We then used DNA microarrays to identify genes responsive to LMO4 and DN-Clim upregulation. One of the genes common to both data sets was bone morphogenic protein 7 (BMP7), whose expression is also significantly correlated with LMO4 transcript levels in a large dataset of human breast cancers, suggesting that BMP7 is a bona fide target gene of LMO4 in breast cancer. Inhibition of BMP7 partially blocks the effects of LMO4 on apoptosis, indicating that BMP7 mediates at least some functions of LMO4. Gene transfer studies show that LMO4 regulates the BMP7 promoter, and chromatin immunoprecipitation studies show that LMO4 and its cofactor Clim2 are recruited to the BMP7 promoter. Furthermore, we demonstrate that HDAC2 recruitment to the BMP7 promoter is inhibited by upregulation of LMO4 and that HDAC2 knockdown upregulates the promoter. These studies suggest a novel mechanism of action for LMO4: LMO4, Clim2 and HDAC2 are part of a transcriptional complex, and increased LMO4 levels can disrupt the complex, leading to decreased HDAC2 recruitment and increased promoter activity.

LIM domain only 4 protein promotes granulocyte colony-stimulating factor-induced signaling in neurons

“…LMO4 has been shown to associate with and modulate HDAC2 function [21,23]. LMO4 over-expression was reported to prevent HDAC2 recruitment to the BMP7 promoter, thereby allowing transcription activation of the BMP7 gene [23]. Here, we showed that LMO4 interacts with the C-terminal domain of HDAC, the same domain that interacts with Stat3 [10].…”

“…The finding that LMO4 promotes acetylation of Stat3 is novel but not surprising. LMO4 has been shown to associate with and modulate HDAC2 function [21,23]. LMO4 over-expression was reported to prevent HDAC2 recruitment to the BMP7 promoter, thereby allowing transcription activation of the BMP7 gene [23].…”

“…High levels of LMO4 expression associate with the development of ERα-negative phenotypes and aggressive breast cancer growth in MDA-MB-231 cells [22]. However, over-expression of LMO4 activates the BMP7 promoter and regulates mammary gland development, likely through its interaction and sequestration of HDAC2 proteins from the bone morphogenic protein 7 (BMP7) promoter [23]. It remains to be tested whether LMO4 modulates HDAC function in neurons to favor or inhibit the expression of survival genes.…”

LMO4 is a prognostic marker involved in cell migration and invasion in non-small-cell lung cancer

“…The LMO protein mainly localizes to the nucleus (1), where it mediates interactions within multiprotein complexes and DNA. This controls the expression of genes involved in regulating many important biological functions, such as cell proliferation and mammalian development.…”

LMO4 functions as a co-activator of neurogenin 2 in the developing cortex

“…LMO4 has been shown to play a role in various developmental systems, including epithelial, mammary, ear and neural development (Sugihara et al, 1998;Hahm et al, 2004;Tse et al, 2004;Lee et al, 2005;Sum et al, 2005;Wang et al, 2007;Deng et al, 2010). Loss of Lmo4 leads to embryonic lethality; a significant percentage of Lmo4-null mice exhibit exencephaly, while the rest show overall normal brain morphology (Hahm et al, 2004;Tse et al, 2004;Lee et al, 2005).…”