The regulation of vitamin D receptor (VDR), a key mediator in the vitamin D pathway, in breast cancer etiology has long been of interest. We have shown here that the transcriptional repressor protein SLUG inhibits the expression of VDR in human breast cancer cells. To explore the possibility that SLUG regulates the VDR gene promoter, we cloned a 628 bp fragment (−613 to +15) of the human VDR gene promoter. This region contains three E2-box sequences (CAGGTG/CACCTG), the classical binding site of SLUG. SLUG specifically inhibited VDR gene promoter activity. Chromatin-immunoprecipitation (ChIP) assays revealed that SLUG is recruited on the native VDR gene promoter along with the co-repressor protein CtBP1 and the effector protein HDAC1. These data suggests that SLUG binds to the E2-box sequences of the VDR gene promoter and recruits CtBP1 and HDAC1, which results in the inhibition of VDR gene expression by chromatin remodeling. SLUG is a member of the SNAI family of C 2 H 2 -zinc finger family of transcriptional repressors [4][5][6]. It is involved in the epithelial-mesenchymal transition during development [5], acts as an inhibitor of apoptosis [7], and causes tubulogenesis during breast and kidney developments [4,5]. The genes inhibited by SLUG include E-cadherin [8], claudins [9], BRCA2 [10], and cytokeratins [11]. Our ChIP-DSL analysis of 20,000 human gene promoter array revealed that more than 150 promoters bind to SLUG at their promoters (Mittal, M.K. and Chaudhuri, G., unpublished data). VDR gene is one of the candidate SLUG-regulated genes. Here, we report that SLUG indeed binds in vivo to the VDR gene promoter in human breast cell nucleus and inhibits VDR gene expression by chromatin remodeling.

Background: High motility of aggressive breast cancer cells is associated with high SLUG and low plakoglobin levels. Results: SLUG binds to plakoglobin gene promoter and represses its expression. Conclusion: SLUG-induced increase in breast cancer cell motility is due to repression of plakoglobin by SLUG. Significance: Management of SLUG level should diminish the motility and thus aggressiveness in breast cancer cells.

Multiple myeloma (MM) is a common and largely incurable blood cancer for which new treatment options are needed, as resistance to current modalities is an issue. Additionally, because this tumor type often resides in a hypoxic niche of the bone marrow, new therapeutics that remain effective even under hypoxic conditions are sought. Because of the secretory nature of MM cells they are uniquely under proteotoxic stress, and we hypothesized that these tumor cells may alleviate this stress by upregulating the major stress-induced cytosolic form of the chaperone HSP70. In this work we test the efficacy of the HSP70 inhibitor PET-16 for MM. We show that MM cell lines express significant levels of HSP70, and further that inhibition of HSP70 causes decreased viability and apoptosis, along with proteotoxic stress, as assessed by the accumulation of poly-ubiquitylated proteins. Importantly, we show that growth of these tumor cells under hypoxic conditions has no effect on the ability of PET-16 to be cytotoxic. The HSP70 inhibitor PET-16 should thus be considered further for pre-clinical analyses of efficacy in MM.

SNAI1P, a protein coded by a retrogene, is a member of the SNAI family of E2-box binding transcriptional repressors. To evaluate whether the mode of action of SNAI1P is similar to those of the other predominant members of the SNAI family, we studied its action on human claudin 7 (CLDN7) gene promoter which has seven E2-boxes. We over-expressed FLAG-tagged SNAI1P in MCF7 and MDA-MB-468 cells. SNAI1P inhibited the expression of CLDN7 in these recombinant cells. SNAI1P also inhibited cloned CLDN7 gene promoter activity in human breast cancer cells. ChIP assays revealed that SNAI1P is recruited on the CLDN7 gene promoter along with the corepressor CtBP1 and the effector HDAC1. Treatment of the cells with trichostatin A, an inhibitor of HDAC1, abrogated the repressor activity of SNAI1P. These data suggest that SNAI1P inhibits CLDN7 gene promoter epigenetically in breast cancer cells through chromatin remodeling.

SLUG is a transcriptional repressor protein implicated to have major role in the oncogenesis and metastasis of human breast cells. We previously have shown by chromatin immunoprecipitation assay that human SLUG (hSLUG) is co-localized with the co-repressor protein CtBP1 as bound to the BRCA2 gene silencer. hSLUG was predicted to be binding directly to CtBP1 because of an apparent presence of CtBP1 binding site in its amino acid sequences. Here, we provide evidence through yeast two-hybrid and in vitro co-immunoprecipitation analyses that hSLUG does not directly interacts with hCtBP1. This observation will help in the study of the mode of action of hSLUG in human cells. KeywordsSLUG; CtBP1; Yeast 2-hybrid; Co-immunoprecipitation; Repressor; SNAG domain SLUG is a member of a superfamily of zinc-finger transcriptional repressors [1][2][3]. SLUG and its family members are involved in tumor progression [1]. SLUG is implicated to induce epithelial to mesenchymal transition in many cells [2]. The different family members are now grouped into two families: Snail and Scratch. Vertebrates have three Snail members: SNAIL (new name SNAIL1), SLUG (now named SNAIL2), and SNAIL3 (formerly SMUC) [2,3]. Human cells have two SCRATCH proteins: SCRATCH1 and SCRATCH2. Human breast cells we have studied so far do not express SCRATCH transcripts (M.K. Tripathi and G. Chaudhuri, unpublished). Human SLUG gene is located at chromosome 8q11, has 3 exons and 2 introns, is transcribed into a ~2.1-kb mRNA (Accession No.NM_003068), and encodes a C2H2-type zinc finger transcription factor protein with 268 amino acids [4]. The encoded protein acts as a transcriptional repressor that binds to E2-box motif (5′-CACCTG-3′) [4,5].Although many genes have the E2-box sequences at their promoters, only the expressions of few proteins are experimentally shown to be regulated by SLUG. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe exact mode of action of human SLUG is not known. While the C-terminal zinc-finger domains of SLUG are responsible for DNA binding, the N-terminal domain are predicted to be responsible for the recruitment of co-repressor molecules at the target gene promoter. SLUG has a domain with 20 amino acid residues at its N-terminus known as SNAG domain. The SNAG domain was originally characterized in the growth factor independence-1 (Gfi-1) oncoprotein, where it forms part of the first 20 amino acids that suffice for transcriptional repression [2,4]. Itis proposed that SLUG binds to the E2-box sequence of the DNA through its C-terminal zinc-finger domains and then recruits either CtBP1 [4,8] or a SNAG-domain binding protein (e.g., Sin3A) as a co-repressor. The co-repressor then recruits histone deacetylase (e.g., HDAC1) at the promoter to silent the target gene expression by chromatin remodeling [8]. Here we show evidence that hSLUG does not interact directly with hCtBP1.