High-mobility group A1a protein regulates Ras/ERK signaling in MCF-7 human breast cancer cells

Abstract

High-mobility group (HMG) A1 proteins are gene regulatory factors whose overexpression is frequently observed in naturally occurring human cancers. The overexpression of transgenic HMGA1 proteins in cells results in neoplastic transformation and promotes progression to malignant cellular phenotypes. To understand the underlying molecular and biological events involved in these phenomena, we used oligonucleotide microarray analyses to generate an HMGA1a-induced expression profile for approximately 22 000 genes. This gene expression profile was generated using a well-characterized transgenic human MCF-7 mammary adenocarcinoma cell line in which overexpression of transgenic HMGA1 promotes a transition to a more malignant and metastatic phenotype. Microarray expression analyses, together with independent quantitative real-time reverse transcriptase polymerase chain reaction results, indicate that HMGA1a regulates genes involved in the Ras-extracellular signalrelated kinase (Ras/ERK) mitogenic signaling pathway, including KIT ligand and caveolins 1 and 2. We also found that many cholesterol biosynthesis genes were decreased in cells overexpressing HMGA1a. Cholesterol depletion, decreased caveolin, and increased KIT ligand expression, are all independently associated with the activation of Ras/ERK signaling. Upon further analysis, we found that sensitivity to epidermal growth factor activation of ERK phosphorylation was significantly higher, and that cholesterol was significantly depleted, in cells overexpressing HMGA1a. The cumulative evidence indicates that one likely mechanism by which the HMGA1a protein promotes malignant changes in cells is through increased sensitivity to the activation of the Ras/ERK signaling pathway.

Human KIT ligand promoter is positively regulated by HMGA1 in breast and ovarian cancer cells

“…KL promoter activity was 4.670.8-fold more active in cells overexpressing HMGA1a (Figure 1b). This value is very close to the reported 4.270.3-fold change in KL transcription in MCF-7 cells overexpressing HMGA1a, as determined by oligonucleotide microarray analysis (Treff et al, 2004). This indicates that the effects of HMGA1a on KL expression are at the transcriptional level.…”

“…Also supporting this conclusion is the fact that many previous reports characterizing the role of KL in cancer biology are consistent with observations of the influence of HMGA1 on cancer cells. For example, HMGA1 overexpression in MCF-7 breast cancer cells results in increased sensitivity to EGF activation of Ras/ERK signaling (Treff et al, 2004). A similar observation (e.g.…”

“…Results from these ChIP assays with HMGA1a-ON cells demonstrate that HMGA1a does, in fact, bind to KL promoter DNA in vivo (Figure 3d) and supports the in vitro observations of HMGA1a protein binding to the KL promoter obtained by EMSA analyses (Figure 3a). The results also demonstrate that in these same cells the promoter region of HPRT1, a gene that is not regulated by HMGA1 Treff et al, 2004) and therefore serves as a negative control, does not bind HMGA1a in vivo (Figure 3d). …”

“…We recently discovered that increased levels of the high-mobility group (HMG)A1a protein (formerly called HMG-I(Y); Bustin, 2001) are correlated with increased transcription of the KL gene in MCF-7 human breast cancer cells (Treff et al, 2004). HMGA1a has already been shown to regulate negatively the expression of BRCA1, which may account for reduced BRCA1 expression in sporadic breast cancer (Baldassarre et al, 2003).…”

Differential regulation of the insulin‐like growth factor II mRNA‐binding protein genes by architectural transcription factor HMGA2

“…One way to address this issue is to search for genes of which the expression is regulated by this architectural transcription factor, such as recently described for the structurally related HMGA1 gene [17]. We have performed expression profiling experiments using embryos of the spontaneous pg/pg mouse mutant, which is HMGA2-deficient, and corresponding wild-type mouse embryos, and report on the differential impact of HMGA2 on the expression of the genes encoding the various members of the insulin-like growth factor II (IGF-II) mRNAbinding protein (IMP) family.…”