Transcription factor NF 1 expression in involuting mammary gland

Nuclear factor I/B mediates epithelial-mesenchymal transition in human melanoma cells through ZEB1

The relationship between nuclear factor I/B (NFIB) and cancer attracts growing research interest. NFIB has diverse and specific roles in tumor progression and invasion. However, the potential effects and functions of this transcription factor in melanoma remain unclear. The present study sought to determine the distinguishing properties of NFIB in melanoma cells. Immunohistochemical examination of the tissues of 15 patients with melanoma indicated that the expression of NFIB was high in melanoma specimens, compared with the benign nevus and normal skin specimens. In addition, the relationship between high NFIB expression and low overall survival rate was assessed. Functional studies demonstrated that NFIB enhanced the malignancy of melanoma, including proliferation, migration and invasion. In addition, NFIB silencing in A375 and A875 cell lines inhibited the process of epithelial-mesenchymal transition (EMT), upregulated E-cadherin and zona occludens-1, but suppressed N-cadherin and vimentin expression. These findings may suggest a new function of NFIB in promoting the migration and invasion of melanoma cells. Therefore, the present study further evaluated the association between NFIB and zinc finger protein E-box binding homeobox-1 (ZEB1) in melanoma. Mechanistic experiments revealed that NFIB exerted its roles during EMT by regulating ZEB1. Overall, the present data indicates that NFIB promotes the malignancy of melanoma, particularly EMT, by modulating the ZEB1 axis, such as ZEB2, ATM and CHK1, which may represent a potential molecular therapeutic target in melanoma.

The convergent roles of the nuclear factor I transcription factors in development and cancer

The nuclear factor I (NFI) transcription factors play important roles during normal development and have been associated with developmental abnormalities in humans. All four family members, NFIA, NFIB, NFIC and NFIX, have a homologous DNA binding domain and function by regulating cell proliferation and differentiation via the transcriptional control of their target genes. More recently, NFI genes have also been implicated in cancer based on genomic analyses and studies of animal models in a variety of tumours across multiple organ systems. However, the association between their functions in development and in cancer is not well described. In this review, we summarise the evidence suggesting a converging role for the NFI genes in development and cancer. Our review includes all cancer types in which the NFI genes are implicated, focusing predominantly on studies demonstrating their oncogenic or tumour-suppressive potential. We conclude by presenting the challenges impeding our understanding of NFI function in cancer biology, and demonstrate how a developmental perspective may contribute towards overcoming such hurdles.

Transcriptomic analysis reveals key regulators of mammogenesis and the pregnancy-lactation cycle

An organ unique to mammals, the mammary gland develops 90% of its mass after birth and experiences the pregnancylactation-involution cycle (PL cycle) during reproduction. To understand mammogenesis at the transcriptomic level and using a ribo-minus RNA-seq protocol, we acquired greater than 50 million reads each for the mouse mammary gland during pregnancy (day 12 of pregnancy), lactation (day 14 of lactation), and involution (day 7 of involution). The pregnancy-, lactation- and involution-related sequencing reads were assembled into 17344, 10160, and 13739 protein-coding transcripts and 1803, 828, and 1288 non-coding RNAs (ncRNAs), respectively. Differentially expressed genes (DEGs) were defined in the three samples, which comprised 4843 DEGs (749 up-regulated and 4094 down-regulated) from pregnancy to lactation and 4926 DEGs (4706 up-regulated and 220 down-regulated) from lactation to involution. Besides the obvious and substantive up- and down-regulation of the DEGs, we observe that lysosomal enzymes were highly expressed and that their expression coincided with milk secretion. Further analysis of transcription factors such as Trps1, Gtf2i, Tcf7l2, Nupr1, Vdr, Rb1, and Aebp1, and ncRNAs such as mir-125b, Let7, mir-146a, and mir-15 has enabled us to identify key regulators in mammary gland development and the PL cycle.

Two chromatin remodeling activities cooperate during activation of hormone responsive promoters

Steroid hormones regulate gene expression by interaction of their receptors with hormone responsive elements (HREs) and recruitment of kinases, chromatin remodeling complexes, and coregulators to their target promoters. Here we show that in breast cancer cells the BAF, but not the closely related PBAF complex, is required for progesterone induction of several target genes including MMTV, where it catalyzes localized displacement of histones H2A and H2B and subsequent NF1 binding. PCAF is also needed for induction of progesterone target genes and acetylates histone H3 at K14, an epigenetic mark that interacts with the BAF subunits by anchoring the complex to chromatin. In the absence of PCAF, full loading of target promoters with hormone receptors and BAF is precluded, and induction is compromised. Thus, activation of hormone-responsive promoters requires cooperation of at least two chromatin remodeling activities, BAF and PCAF.

In order to adapt its gene expression program to the needs of the environment, the cell must access the information stored in the DNA sequence that is tightly packaged into chromatin in the cell nucleus. How the cell manages to do it in a selective maner is still unclear. Here we show that, in breast cancer cells treated with the ovarian hormone progesterone, the hormone receptor recruits to the regulated genes two chromatin remodeling complexes that cooperate in opening the chromatin structure. One of the complexes puts a mark in a chromatin protein that anchors the other complex, enabling full gene activation. The present discovery highlights the importance of the concerted order of events for access to genomic information during activation of gene expression and reveals the intricacies of hormonal gene regulation.

The C-terminal domain of the nuclear factor I-B2 isoform is glycosylated and transactivates the WAP gene in the JEG-3 cells

The transcription factor nuclear factor I (NFI) has been shown previously both in vivo and in vitro to be involved in the cooperative regulation of whey acidic protein (WAP) gene transcription along with the glucocorticoid receptor and STAT5. In addition, one of the specific NFI isoforms, NFI-B2, was demonstrated in transient co-transfection experiments in JEG cells, which lack endogenous NFI, to be preferentially involved in the cooperative regulation of WAP gene expression. A comparison of the DNA-binding specificities of the different NFI isoforms only partially explained their differential ability to activate the WAP gene transcription. Here, we analyzed the transactivation regions of two NFI isoforms by making chimeric proteins between the NFI-A and B isoforms. Though, their DNA-binding specificities were not altered as compared to the corresponding wild-type transcription factors, the C-terminal region of the NFI-B isoform was shown to preferentially activate WAP gene transcription in cooperation with GR and STAT5 in transient co-transfection assays in JEG-3 cells. Furthermore, determination of serine and threonine-specific glycosylation (O-linked N-acetylglucosamine) of the C-terminus of the NFI-B isoform suggested that the secondary modification by O-GlcNAc might play a role in the cooperative regulation of WAP gene transcription by NFI-B2 and STAT5.

Chromatin-dependent cooperativity between site-specific transcription factors in vivo

Accessing binding sites in DNA wrapped around histones in condensed chromatin is an obstacle that transcription factors must overcome to regulate gene expression. Here we demonstrate cooperativity between two transcription factors, the glucocorticoid receptor (GR) and nuclear factor 1 (NF1) to bind the mouse mammary tumor virus promoter organized as regular chromatin in vivo. This cooperativity is not observed when the promoter is introduced transiently into cells. Using RNA interference to deplete NF1 protein levels in the cells, we confirmed that NF1 promotes binding of GR to the promoter. Furthermore, we observed a similar synergism between GR and NF1 binding on the endogenous 11beta-hydroxysteroid dehydrogenase promoter, also regulated by GR and NF1. Our results suggest that the chromatin architecture of the promoters does not permit strong association of GR in the absence of NF1. Therefore we propose that cooperativity among DNA binding factors in binding to their cognate recognition sites in chromatin may be an important feature in the regulation of gene expression.

The p53 tumor suppressor gene is regulated in vivo by nuclear factor 1-C2 in the mouse mammary gland during pregnancy

The p53 tumor suppressor protein plays an important role in preventing cancer development by arresting or killing potential tumor cells. Downregulated p53 levels, or mutations within the p53 gene, leading to the loss of p53 activity, are found in many breast carcinomas. Here we demonstrate that the p53 gene is transcriptionally upregulated in the normal mouse mammary gland at midpregnancy. We show that the specific isoform nuclear factor 1-C2 (NF1-C2) plays an important role in this activation. Functional mutation of the NF1-binding site in the mouse p53 promoter resulted in a reduction of the gene expression to less than 30% in mammary epithelial cells. By the use of two powerful techniques, chromatin immunoprecipitation and oligonucleotide decoy, we verify the importance of NF1-C2 in p53 gene activation in vivo. These findings demonstrate a broader role for NF1-C2 in the mammary gland at midpregnancy, beyond its earlier reported activation of milk protein genes. We also demonstrate that NF1-A1 proteins are produced in the mouse mammary gland. However, due to their lower affinity to the NF1-binding site, these proteins are not involved in the transcriptional upregulation of p53 at midpregnancy. This paper constitutes the first report demonstrating the importance of NF1 proteins in the p53 gene activation in the mouse mammary gland. It is also the first time that p53 gene activation is coupled to a specific, endogenously expressed NF1 isoform.

Microarray analysis of the involution switch

Mammary epithelial cells (MEC) undergo a series of developmental decisions during a pregnancy cycle. The switches from proliferation to differentiation to secretion and then to cell death are precisely controlled. In order to identify critical changes associated with the transition from a secretory phenotype during lactation to dedifferentiation and cell death, we have undertaken a microarray analysis of mouse mammary gland development. We have focused on the involution switch and on the transcription profiles of genes that are targets of transcription factors known to influence involution and apoptosis. Our results show that both Stat3 and NF-kB target genes are induced by the involution switch while Stat5 target genes are distinct from Stat3 induced genes. Furthermore, a substantial number of genes that were specifically upregulated at the start of involution are regulators of inflammation and the acute phase response. These results provide a novel insight into the involution process and demonstrate the value of microarray analysis in defining molecular events associated with critical developmental transitions in mammary gland.

The Nuclear Factor I (NFI) gene family in mammary gland development and function

Mammary gland development and function require the coordinated spatial and temporal expression of a large fraction of the mammalian genome. A number of site-specific transcription factors are essential to achieve the appropriate growth, branching, expansion, and involution of the mammary gland throughout early postnatal development and the lactation cycle. One family of transcription factors proposed to play a major role in the mammary gland is encoded by the Nuclear Factor I (NFI) genes. The NFI gene family is found only in multicellular animals, with single genes being present in flies and worms and four genes in vertebrates. While the NFI family expanded and diversified prior to the evolution of the mammary gland, it is clear that several mammary-gland specific genes are regulated by NFI proteins. Here we address the structure and evolution of the NFI gene family and examine the role of the NFI transcription factors in the expression of mammary-gland specific proteins, including whey acidic protein and carboxyl ester lipase. We discuss current data showing that unique NFI proteins are expressed during lactation and involution and suggest that the NFI gene family likely has multiple important functions throughout mammary gland development.

Nuclear factor 1-C2 contributes to the tissue-specific activation of a milk protein gene in the differentiating mammary gland

Members of the nuclear factor 1 (NF1) transcription factor family have been postulated to be involved in the regulation of milk genes. In this work we have been able to identify the splice variant NF1-C2 as an important member of a tissue-specific activating complex that regulates the milk gene encoding carboxyl ester lipase (CEL). Mutation of the NF1-binding site in the CEL gene promoter results in a drastic reduction of the gene expression to about 15% in mammary epithelial cells. Furthermore, we demonstrate that the NF1-C2 protein interacts with a higher affinity to the NF1-binding site in the CEL gene promoter than other NF1 family members do and that NF1-C2 in the mouse mammary gland is a phosphorylated protein. During development of the mouse mammary gland, binding of NF1-C2 to the CEL gene promoter is induced at midpregnancy, in correlation with the induction of CEL gene expression. The fact that the NF1-C2 involving complex remains throughout the lactation period and decreases during the weaning period, when the CEL gene is down-regulated, supports its importance in the regulation of CEL gene expression. To our knowledge, this is the first report identifying a specific, endogenously expressed NF1 isoform to be involved in the tissue-specific activation of a gene.