The nuclear factor YY1 participates in repression of the beta-casein gene promoter in mammary epithelial cells and is counteracted by mammary gland factor during lactogenic hormone induction

Abstract

Expression of the beta-casein milk protein gene in the mammary epithelial cell line HC11 is primarily regulated at the transcriptional level. A 338-bp segment of promoter sequence 5' of the transcription start site is sufficient to confer inducibility by the lactogenic hormones insulin, glucocorticoid hormone, and prolactin. Positively and negatively acting promoter elements and specific DNA binding proteins have been identified. The binding of the mammary gland factor MGF to a site between -80 and -100 is indispensable for hormonal induction of transcription. Binding of MGF activity to DNA is greatly enhanced by the action of the lactogenic hormones. Repression of transcription in the uninduced state is mediated by a promoter element located adjacent to the MGF binding site at positions -110 to -150. This repressor element consists of two interacting protein binding sites. A nuclear factor that binds specifically to the proximal site between positions -110 and -120 has been characterized and found to be identical with the nuclear factor YY1 (delta, NF-E1). YY1 does not bind to the distal site. The simultaneous mutation in the proximal and the distal sites results in high, hormone-independent transcription. This finding suggests that YY1 plays a functional role in the repression and acts in conjunction with a second DNA binding protein. Comparison of YY1 DNA binding activity in uninduced and hormone-induced cells showed that relief of repression is not mediated by changes in the concentration or binding affinity of YY1. Infection of HC11 cells with a YY1-expressing recombinant retrovirus resulted in overexpression of YY1 but did not suppress hormonal induction. The addition of purified MGF decreased YY1 binding to its DNA recognition site in vitro. This finding indicates that MGF regulates the DNA binding activity of YY1 and thereby may cause the relief of transcriptional repression.

Identification of a DNA binding site for the nuclear factor YY1 in the human GM-CSF core promoter

“…Thus, these results indicated that complex A is a multiprotein complex and YY1 is one of the protein components. As no band was revealed by the UV crosslinking analysis of the B complex (data not shown), and its mobility in EMSA is similar to that of a previously reported derivative derived from protease digestion of a YYl complex [35], our data also suggests that the B complex may be a derivative of the A complex.…”

The contribution of adhesion signaling to lactogenesis

“…These CoRE units are defined as a cluster of transcription factor binding sites containing both positive and negative regulatory elements which integrate signal transduction pathways through protein‐DNA and protein‐protein interactions (Jiang and Levine 1993). The primary factors associated with activation of the β‐casein CoRE include signal transducer and activator of transcription 5 (Stat5), glucocorticoid receptor (GR), and CCAAT enhancer binding protein β (C/EBPβ), while Yin Yang‐1 (YY‐1) associates with the CoRE as a negative regulator of gene expression (Schmitt‐Ney et al 1991; Meier and Groner 1994; Raught et al 1994; Wakao et al 1994; Doppler et al 1995; Raught et al 1995; Lechner et al 1997; Seagroves et al 1998). Interestingly, none of the transcription factors associated with the β‐casein CoRE is mammary gland‐specific or even restricted to the lactation phase of development.…”

Organisation nucléaire et expression des gènes des protéines du lait

“…L'analyse des séquences des régions régulatrices utilisées dans les expériences mentionnées ci-dessus montre que ces régions ne portent pas que des éléments potentiels de fixation pour Stat5. De nombreuses autres séquences consensus susceptibles d'interagir notamment avec les diverses formes de NF1 (Li & Rosen, 1995 ;Mukhopadhyay et al, 2001) d'ets (Galang et al, 2004Mcknight et al, 1995 ;Welte et al, 1994), de C/EBP ) ou de YY1 (Meier & Groner, 1994) sont présentes et s'étendent jusque 7 kb en amont du site d'initiation de la transcription. Les régions régulatrices de ces gènes sont donc composées de nombreux éléments de réponse et ont été baptisées "Complexe responsive elements" (CoRE) (Rosen et al, 1999).…”