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

Abstract

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.

Nuclear Jak2 and Transcription Factor NF1-C2: a Novel Mechanism of Prolactin Signaling in Mammary Epithelial Cells

“…p53 is a central component in the protection of the mammary epithelium against tumor progression, and transcriptional control of p53 expression participates in the generation of appropriate levels of active p53 in response to mitogenic stimulation. We have previously provided data showing that NF1-C2 is one of the factors responsible for stimulating p53 gene expression in the mouse mammary gland (14). In the present paper, we extend this information by showing that nuclear Jak2 is important for the expression of p53.…”

“…We showed by using promoter studies and the in vivo methods chromatin immunoprecipitation and oligonucleotide decoy that binding of NF-C2 to the mouse p53 promoter is important for the expression of p53 at midpregnancy. Furthermore, we have shown that during the development of the mouse mammary epithelial cells, NF1-C2 activates the CEL and whey acidic protein gene promoters (14,16). Since we had shown by siRNA experiments and several other methods that there is a correlation between nuclear Jak2 and the level of NF1-C2, we wanted to investigate if the decrease of Jak2/NF1-C2 had any effect on the expression of the p53 gene and the CEL gene.…”

“…We have previously identified the transcription factor nuclear factor 1-C2 (NF1-C2) as an important activator of milk genes as well as the p53 tumor suppressor gene in the mouse mammary gland during pregnancy (14,16). This activity indicates that NF1-C2 might participate both in the establishment of a functional gland and in the protection of the gland against tumorigenesis during proliferation.…”

“…The proteasome pathway in particular plays an important role in the degradation of a number of cellular proteins (26,31). Earlier studies have shown that proteasome inhibitors prolong the activity of the Jak-Stat signaling pathway by protecting tyrosine-phosphorylated Jak2 proteins from degradation (33, 38).We have previously identified the transcription factor nuclear factor 1-C2 (NF1-C2) as an important activator of milk genes as well as the p53 tumor suppressor gene in the mouse mammary gland during pregnancy (14,16). This activity indicates that NF1-C2 might participate both in the establishment of a functional gland and in the protection of the gland against tumorigenesis during proliferation.…”

Nuclear Janus-Activated Kinase 2/Nuclear Factor 1-C2 Suppresses Tumorigenesis and Epithelial-to-Mesenchymal Transition by Repressing Forkhead Box F1

“…The mechanism by which Jak2 increases the amount of active NF1-C2 is independent of the signal transducers and activators of transcription (Stat) pathway, relies on direct interaction between Jak2 and NF1-C2, and involves tyrosine phosphorylation of NF1-C2 and protection against proteasomal degradation (14). The known function for NF1-C2 is to activate p53 and participate in the establishment of expression of milk protein genes during pregnancy (15,16).…”