The formation of new blood vessels, angiogenesis, is an essential process during development and disease. Angiogenesis is well known as a crucial step in tumor growth and progression. Angiogenesis is induced by hypoxic conditions and regulated by the hypoxia-inducible factor 1 (HIF-1). The expression of HIF-1 correlates with hypoxia-induced angiogenesis as a result of the induction of the major HIF-1 target gene, vascular endothelial cell growth factor (VEGF). In this review, a brief overview of the mechanism of angiogenesis is discussed, focusing on the regulatory processes of the HIF-1 transcription factor. HIF-1 consists of a constitutively expressed HIF-1 beta (HIF-1beta) subunit and an oxygen-regulated HIF-1 alpha (HIF-1a) subunit. The stability and activity of HIF-1alpha are regulated by the interaction with various proteins, such as pVHL, p53, and p300/CBP as well as by post-translational modifications, hydroxylation, acetylation, and phosphorylation. It was recently reported that HIF-1alpha binds a co-activator of the AP-1 transcription factor, Jab-1, which inhibits the p53-dependent degradation of HIF-1 and enhances the transcriptional activity of HIF-1 and the subsequent VEGF expression under hypoxic conditions. ARD1 acetylates HIF-1alpha and stimulates pVHL-mediated ubiquitination of HIF-1alpha. With a growing knowledge of the molecular mechanisms in this field, novel strategies to prevent tumor angiogenesis can be developed, and from these, new anticancer therapies may arise.

Hepatocellular carcinoma is a typical hypervascular tumor. Generally, hepatocellular carcinoma is developed through liver cirrhosis induced by chronic liver injury. This chronic injury leads to changes in the cellular property of the liver and subsequently causes fibrogenesis to demolish normal liver blood system. The catastrophe of the normal liver blood system leads to the shortage of blood circulation in the liver and causes hypoxia. Moreover, the increased cellularity due to highly proliferative tumor cells also induces local hypoxia inside hepatocellular carcinoma. Hypoxia can stimulate angiogenesis to support tumor growth by induction of angiogenic factors. Thus hypoxia may be a major cause of hypervasculature of hepatocellular carcinoma. Recently it has been reported that several hypoxia-regulatory factors are closely involved in angiogenesis of hepatocellular carcinoma. The stability and function of these factors can be regulated by interaction with other protein factors and consequently modulate the expression of angiogenic factors depending on oxygen tension. Therefore induction mechanism of hypoxia and the role of hypoxia-regulatory factors could provide new insights into hepatocarcinogenesis and the treatment of hepatocellular carcinoma.

Metastasis-associated protein 1 (MTA1) is highly upregulated in cancer cells with metastatic potential; however, the molecular mechanism by which MTA1 increases the metastatic potential of cancer cells is unknown. We characterized the functional consequences of MTA1 overexpression in cancer cells with an emphasis on its potential role as a deacetylator of hypoxia-inducible factor-1• (HIF-1•). MTA1 increased the expression of HIF-1• protein, but did not increase the expression of its mRNA. Glutathione S-transferase pulldown and coimmunoprecipitation assays demonstrated direct interaction of MTA1 with HIF-1• both in vitro and in vivo. Immunoprecipitation and acetylation assays also showed that MTA1 has deacetylation activity on HIF-1• in vivo. Moreover, MTA1 increased the transcriptional activity of HIF-1• and enhanced the expression of vascular endothelial growth factor, a target molecule of HIF-1•. Conditioned medium collected from MTA1 transfectants also increased angiogenesis in vitro and in vivo, probably through enhanced HIF-1• stabilization. These results indicate that MTA1 enhances angiogenesis by stabilization of the HIF-1• protein, which is closely related to the increased metastatic potential of cancer cells with high MTA1 expression.

Abstract. Metastasis-associated protein 1 (MTA1) is highly upregulated in cancer cells with metastatic potential; however, the molecular mechanism by which MTA1 increases the metastatic potential of cancer cells is far from clear. We characterized the functional consequences of MTA1 overexpression on p53-induced apoptosis of cancer cells. MTA1 was associated with p53 in a co-immunoprecipitation assay. MTA1 also had deacetylation activity on p53 in human non-small cell lung cancer cells H1299 and human hepatoma cells SK-Hep1. MTA1 attenuated the transactivation and p21 induction by p53. Moreover, MTA1 expression decreased p53-mediated apoptosis. These results indicate that MTA1 inhibits p53-induced apoptosis by deacetylation of p53, which might be related to the increased metastatic potential of cancer cells with high MTA1 expression. IntroductionMTA1 was originally isolated by differential expression screening of metastatic cell lines with high and low metastatic potentials (1). In vitro studies have shown that MTA1 increases invasiveness and migration (2,3) and suggest that MTA1 may be involved in the regulation of gene expression by covalent modification of histone proteins (4). Consistent with this notion, MTA proteins are physically associated with histone deacetylases (HDAC1/2) and play a role in histone deacetylation and modulation of transcriptional activity as components of the nucleosome remodeling histone deacetylation (NuRD) complex (5). Recent reports have shown that MTA1 enhances angiogenesis by deacetylation and the stabilization of HIF-1α (6,7), providing an important clue in understanding the mechanism of the increased metastatic potential of the cancer cells with high MTA1 expression.Because MTA1 has deacetylating activity, MTA1 may affect the function of other proteins related to cancer progression whose activity is determined by acetylation status. In fact, MTA2, a homologue of MTA1, has been reported to modulate acetylation status and transcriptional activity of p53, while MTA2 has not been linked to metastasis or cancer progression in contrast to MTA1 (8). In response to DNA damage and other types of stress, p53 stabilizes and induces apoptosis, cell-cycle arrest, senescence and differentiation (9,10). Overexpression of p53 activates a number of target genes involved in those processes such as p21CIP1/WAF1, MDM2, GADD45, Cyclin G, Noxa, Bax and PUMA (11-16) through binding to p53 consensus sequences. Therefore, the investigations of the effects of MTA1 on p53 may provide an important clue in understanding the mechanism of the increased metastasis of cancer cells with high MTA1 expression. In this study, we found that MTA1 decreases the transcriptional activity of p53 and inhibits apoptosis through deacetylation of p53. Materials and methodsReagents and antibodies. G418 was purchased from Invitrogen (Carlsbad, CA, USA). Protein G-agarose, protease inhibitor cocktail and FuGENE 6 Reagent were from Roche (Mannheim, Germany). Antibodies to p21, ß-actin and acetylated p53 (Ac-p53) (Lys373, Lys382...