Showing papers by "Suresh K. Rayala published in 2010"

Metastasis-associated protein 1 and its short form variant stimulates Wnt1 transcription through promoting its derepression from Six3 corepressor

Abstract: Although Wnt1 downstream signaling components have been well studied and activated in human cancer, the pathways that regulate Wnt1 itself have not been explored in depth. Here, we provide gain-of-function, loss-of function, and molecular evidence supporting functional interactions between metastasis-associated protein 1 short-form (MTA1s), metastasis-associated protein 1 (MTA1), and Wnt1 signaling components during mammary gland development and tumorigenesis. Using multiple model systems involving overexpression or knockdown of MTA1s or MTA1, we discovered that MTA1s and MTA1 hyperactivate the Wnt1 pathway due to increased expression of Wnt1 transcription. MTA1s and MTA1 physically interact with Six3 chromatin, a protein product of which is a direct histone deacetylase inhibitor–dependent repressor of Wnt1 transcription. Deletion of the MTA1s and MTA1 allele in murine embryonic fibroblasts resulted in the upregulation of Six3 and downregulation of Wnt signaling. In addition, mammary glands from the MTA1s/MTA1−/− mice exhibited increased recruitment of Six3 corepressor complex to the Wnt1 promoter and inhibition of Wnt1 pathway in mammary glands. These findings identify MTA1s and MTA1 as important upstream modifiers of the Wnt1 transcription, and consequently its functions, by directly inhibiting the transcription of Six3, allowing derepression of Wnt1 transcription. Cancer Res; 70(16); 6649–58. ©2010 AACR.

Acetylation-dependent oncogenic activity of metastasis-associated protein 1 co-regulator.

Abstract: High expression of metastasis-associated protein 1 co-regulator (MTA1), a component of the nuclear remodelling and histone deacetylase complex, has been associated with human tumours. However, the precise role of MTA1 in tumorigenesis remains unknown. In this study, we show that induced levels of MTA1 are sufficient to transform Rat1 fibroblasts and that the transforming potential of MTA1 is dependent on its acetylation at Lys626. Underlying mechanisms of MTA1-mediated transformation include activation of the Ras-Raf pathway by MTA1 but not by acetylation-inactive MTA1; this was due to the repression of Galphai2 transcription, which negatively influences Ras activation. We observed that acetylated MTA1-histone deacetylase (HDAC) interaction was required for the recruitment of the MTA1-HDAC complex to the Galphai2 regulatory element and consequently for the repression of Galphai2 transcription and expression leading to activation of the Ras-Raf pathway. The findings presented in this study provide for the first time--to the best of our knowledge--evidence of acetylation-dependent oncogenic activity of a cancer-relevant gene product.

Metastasis associated protein 1 short-form stimulates Wnt1 pathway in mammary epithelial and cancer cells

Abstract: Although Wnt1 downstream signaling components as well as cytoplasmic level of metastatic tumor antigen 1 short form (MTA1s) are elevated in human breast cancer, it remains unknown whether a regulatory cross-talk exists between these two pathways. Here, we provide evidence of a remarkable correlation between the levels of MTA1s and stimulation of the Wnt1 signaling components, leading to increased stabilization of β-catenin and stimulation of Wnt1 target genes in the murine mammary epithelial and human breast cancer cells. We found that MTA1s influences Wnt1 pathway through extracellular signal-regulated kinase (ERK) signaling as selective silencing of the endogenous MTA1s or ERK, or its target glycogen synthase kinase 3β resulted in a substantial decrease in β-catenin expression, leading to the inhibition of Wnt1 target genes. Furthermore, downregulation of β-catenin in cells with elevated MTA1s level was accompanied by a corresponding decrease in the expression of Wnt1 target genes, establishing a mechanistic role for the ERK/glycogen synthase kinase 3β/β-catenin pathway in the stimulation of the Wnt1 target genes by MTA1s in mammary epithelial cells. In addition, mammary glands from the virgin MTA1s transgenic mice mimicked the phenotypic changes found in the Wnt1 transgenic mice and exhibited an overall hyperactivation of the Wnt1 signaling pathway, leading to increased stabilization and nuclear accumulation of β-catenin. Mammary glands from the virgin MTA1s-TG mice revealed ductal hyperplasia and ductal carcinoma in situ, and low incidence of palpable tumors. These findings reveal a previously unrecognized role for MTA1s as an important modifier of the Wnt1 signaling in mammary epithelial and cancer cells. Cancer Res; 70(16); 6598–608. ©2010 AACR.

Identification of a Novel Estrogen Receptor-α Variant and Its Upstream Splicing Regulator

Abstract: Alternative splicing of precursor mRNA is a fundamental mechanism to generate multiple proteins from a single gene. Although constitutive and alternative mRNA splicing is temporally and spatially regulated, deregulation of mRNA splicing could cause development, progression, and metastasis of tumors. Through yeast two-hybrid screening of a human breast cDNA library using estrogen receptor-alpha (ERalpha) as bait, we identified a novel nuclear receptor box containing full-length protein, nuclear protein E3-3 (NPE3-3). Our results revealed that NPE3-3 associates with not only ERalpha but also with splicing factors, serine/arginine-rich protein (SRp)-30c, SRp40, and splicing factor SC-35, suggesting that NPE3-3 is likely to be involved in regulation of mRNA splicing. Accordingly, transient expression of NPE3-3 in cells resulted in expected splicing of the CD44 control minigene. We also discovered that NPE3-3-overexpressing clones produced a novel, previously unrecognized, alternatively spliced variant of ERalpha (termed ERalphaV), which had a molecular size of 37 kDa composed of only exons 1, 2, 7, and 8. ERalphaV was expressed and sequestered in the cytoplasm in MCF-7 cells stably overexpressing NPE3-3, suggesting its involvement in nongenomic hormone signaling. NPE3-3 clones exhibited up-regulation of ERK1/2 signaling, cyclin D1, and cathepsin D and enhanced tumor cell proliferation, migration, and tumorigenicity. Moreover, direct expression of the ERalphaV in breast cancer cells stimulated ERK1/2 up-regulation and cyclin D1 expression. We found that ERalphaV physically interacted with MAPK kinase (MEK)-1/2, and thus, an ERalphaV and MEK1/2 complex could lead to the activation of the ERK1/2 pathway. Interestingly, NPE3-3 was up-regulated in human breast tumors. These findings revealed a role for NPE3-3 in alternative splicing and suggest that ERalpha is a physiological target of NPE3-3, leading to a constitutive nongenomic signaling pathway in breast cancer cells.

Integrative Functional Genomics in Cancer Research and Its Clinical Implications

Abstract: Many cancer predisposition and causative genes have been identified in the past few decades and have been extensively evaluated in primary tumors. The complex and highly heterogeneous nature of tumors requires more clinically useful candidate genes as prognostic, diagnostic, and therapeutic biomarkers for different subtypes of tumors and for predicting therapeutic response. Although genomics platforms have revealed the complex nature of tumors, integrative functional genomics approaches have the potential to provide a holistic understanding of the molecular genomic processes of carcinogenesis. While integration of the data gathered from genome and transcriptome is the simplest approach in integrative genomics, these approaches are also extended to analyze different levels of information, different cancer model systems, and multiple studies. Recent studies have revealed that integrative genomics has the potential to revolutionize the diagnosis and management of cancer by offering an unprecedented comprehensive understanding of cancer through unbiased experimental approaches.