Showing papers by "Saraswati Sukumar published in 2007"

DNA methylation regulates MicroRNA expression.

Abstract: MicroRNAs (miRNAs), an important class of small regulatory molecules for gene expression, are transcribed by RNA polymerase II. But little is known about the mechanisms that control miRNA expression. Comparing miRNA expression profiles between colon cancer cell line HCT 116 and its derivative, DNA methyltransferase 1 and 3b (DNMT1 and DNMT3b) double knockout cell line, we found that the expression of about 10% miRNAs was regulated by DNA methylation. In addition, neither 5-aza-2′-deoxycytidine treatment nor deletion of DNMT1 alone recapitulated miRNA expression profile seen in double knockout cell line, suggesting that miRNA expression was tightly controlled by DNA methylation and partial methylation reduction was not sufficient for miRNA re-expression. We also found that HOXA3 and HOXD10 were putative targets of mir-10a, one of the differentially expressed miRNAs that is located in HOX gene cluster.

A role for the HOXB7 homeodomain protein in DNA repair

Abstract: Homeobox genes encode transcription factors which function in body axis patterning in the developing embryo. Recent evidence suggests that the maintenance of specific HOX expression patterns is necessary for regulating the homeostasis of adult tissues as well. In this study, HOXB7 transformed human mammary epithelial cells, MCF10A, to grow in minimally supplemented medium, to form colonies in Matrigel, and display resistance to ionizing radiation. Searching for protein partners of HOXB7 that might contribute to resistance to ionizing radiation, we identified four HOXB7-binding proteins by GST pull-down/affinity chromatography and confirmed their interactions by coimmunoprecipitation in vivo. Interestingly, all four HOXB7-binding proteins shared functions as genomic caretakers and included members of the DNA-dependent protein kinase holoenzyme (Ku70, Ku80, DNA-PK(cs)) responsible for DNA double-strand break repair by nonhomologous end joining pathway and poly(ADP) ribose polymerase. Exogenous and endogenous expression of HOXB7 enhanced nonhomologous end joining and DNA repair functions in vitro and in vivo, which were reversed by silencing HOXB7. This is the first mechanistic study providing definitive evidence for the involvement of any HOX protein in DNA double-strand break repair.

Clostridium perfringens enterotoxin as a novel-targeted therapeutic for brain metastasis.

Abstract: Brain metastasis is the most commonly occurring intracranial tumor whose incidence seems to be increasing. With standard therapy, the average survival time of patients is approximately 8 months, and treatment often leads to neurologic dysfunction in long-term survivors, emphasizing the need for novel therapeutics. Clostridium perfringens enterotoxin (CPE) has recently been shown to rapidly and specifically destroy cancer cells expressing CPE receptors claudin-3 and claudin-4. Unfortunately, the utility of CPE is precluded by systemic toxicity because its receptors are expressed in numerous organs. Here, we provide the first preclinical evidence that CPE may be uniquely suited to the local treatment of brain metastasis. By immunohistochemical analysis, claudin-3 and claudin-4 were expressed frequently in metastases from breast (15 of 18), lung (15 of 20), and colon (12 of 14) carcinoma, and infrequently in metastases from renal cell carcinoma (2 of 16) and melanoma (2 of 16). In contrast, expression of claudin-3 and claudin-4 was absent in adjacent normal brain tissue. Further examination of the central nervous system (CNS) revealed low or undetectable levels of claudin-3 and claudin-4 in all regions tested by Western and immunohistochemical analysis. Treatment of breast cancer cell lines (MCF-7, MDA-MB-468, NT2.5-luc) and normal human astrocytes with CPE in vitro resulted in rapid and dose-dependent cytolysis exclusively in breast cancer cells, correlating with claudin-3 and claudin-4 expression. Moreover, intracranial CPE treatment significantly inhibited tumor growth and increased survival in two murine models of breast cancer brain metastasis, without any apparent local or systemic toxicity. These data suggest that CPE therapy may have efficacy against a wide variety of brain metastases without CNS toxicity.

HOXA5 Acts Directly Downstream of Retinoic Acid Receptor β and Contributes to Retinoic Acid–Induced Apoptosis and Growth Inhibition

Abstract: The promise of retinoids as chemopreventive agents in breast cancer is based on the differentiation and apoptosis induced upon their binding to the retinoic acid (RA) receptor β (RARβ). We have previously shown that HOXA5 induces apoptosis in breast cancer cells. In this study, we investigated whether RA/RARβ and HOXA5 actions intersect to induce apoptosis and differentiation in breast cancer cells. We found that HOXA5 expression can be induced by RA only in RARβ-positive breast cancer cells. We have, for the first time, identified the RA response element in HOXA5, which was found to be located in the 3′ end of the gene. Chromatin immunoprecipitation assays showed that RARβ binds directly to this region in vivo . Overexpression of RARβ strongly enhances RA responsiveness, and knocking down RARβ expression abolishes RA-mediated induction of HOXA5 expression in breast cancer cells. In addition, there is coordinated loss of both HOXA5 and RARβ expression during neoplastic transformation and progression in the breast epithelial cell model, MCF10A. Knockdown of HOXA5 expression partially abrogates retinoid-induced apoptosis and promotes cell survival upon RA treatment. These results strongly suggest that HOXA5 acts directly downstream of RARβ and may contribute to retinoid-induced anticancer and chemopreventive effects. [Cancer Res 2007;67(17):8007–13]

HOXA1-stimulated oncogenicity is mediated by selective upregulation of components of the p44/42 MAP kinase pathway in human mammary carcinoma cells

Abstract: Expression of homeobox A1 (HOXA1) results in oncogenic transformation of immortalized human mammary epithelial cells with aggressive tumor formation in vivo. However, the mechanisms by which HOXA1 mediates oncogenic transformation is not well defined. To identify molecules that could potentially be involved in HOXA1-mediated oncogenic transformation, microarray analysis was utilized to characterize and compare the gene expression pattern in response to forced expression or depletion of HOXA1 in human mammary carcinoma cells. Gene expression profiling identified that genes involved in the p44/42 mitogen-activated protein (MAP) kinase activation pathway (GRB2, MAP kinase kinase (MEK1) and SDFR1) or p44/42 MAP kinase-regulated genes (IER3, EPAS1, PCNA and catalase) are downstream expression targets of HOXA1. Forced expression of HOXA1 increased GRB2 and MEK1 mRNA and protein expression and increased p44/42 MAP kinase phosphorylation, activity and Elk-1-mediated transcription. Use of a MEK1 inhibitor demonstrated that increased p44/42 MAP kinase activity is required for the HOXA1-mediated increase in cell proliferation, survival, oncogenicity and oncogenic transformation. Thus, modulation of the p44/42 MAP kinase pathway is one mechanism by which HOXA1 mediates oncogenic transformation of the human mammary epithelial cell.

A comparative study of Korean with Caucasian breast cancer reveals frequency of methylation in multiple genes correlates with breast cancer in young, ER, PR-negative breast cancer in Korean women.

Abstract: To test whether promoter hypermethylation in breast cancer provides a basis for the interethnic difference in breast cancer incidence and distribution, we compared the methylation profiles of tumors arising in native Korean women with Caucasian women in the United States. Methylation-specific PCR analysis of seven genes frequently methylated in breast cancer (HIN-1, Twist, Cyclin D2, RARbeta, GSTP1, RASSF1A and CDH1) was performed on DNA from 67 Korean and 50 Caucasian invasive ductal breast cancers which were categorized into four subgroups by ER status and age. Methylation frequencies for individual genes were similar between the two races. However, tumors in Korean women of age ( 50). Furthermore, methylation of multiple genes (four or more genes per case) was associated with younger age at diagnosis (OR = 3.2; 95% CI = 1.2-8.7; p = 0.03). In contrast, there was no association between promoter hypermethylation and age at diagnosis in Caucasian women. A significantly higher frequency of methylation, for all seven genes and in multiple genes, was observed in ER-/PR breast carcinomas in Korean women of age 50 had a significantly higher frequency of methylation in three of seven genes. Our data suggest that promoter hypermethylation is a prevalent phenomenon in breast cancer of young Korean women. By analyzing the methylation patterns in tumors stratified by race, ER/PR status, and age, dissimilarities in promoter hypermethylation profiles, particularly in the ER-/PR- tumors arising in young women, were revealed that characterize tumors of one ethnicity from the other.

Hox compositions and methods

Abstract: The present invention relates to compositions to treat HOXB7 related disorders. The invention also relates to methods treating HOXB7 related disorders. The invention further relates to kits for treating HOXB7 related disorders in a subject. The invention further relates to methods of identifying novel treatments for treating HOXB7 related disorders in a subject.

Heyl as a therapeutic target and a diagnostic marker for neoplasia and uses therefor

Abstract: The invention generally features compositions and methods that are useful for treating or diagnosing a neoplasia, in particular breast neoplasia. The invention is based in part on the observation that the basic helix loop helix transcription factor HEYL was found to be overexpressed in breast cancer cells. Accordingly, the invention provides therapeutic compositions and methods for altering the levels and expression of HEYL of the invention, thereby treating a neoplasia, as well as compositions and methods for diagnosing a neoplasia.

ETS genes in breast cancer: A step in the right direction

Abstract: Commentary to:Profile of Ets Gene Expression in Human Breast CarcinomaJin He, Yong Pan, Jianhua Hu, Constance Albarracin, Yun Wu and Jia Le Dai