Mammary gland factor activated by prolactin on mammary epithelial cells and acute-phase response factor activated by interleukin-6 in liver cells share DNA binding and transactivation potential.

Abstract

We have studied transcription factors that are coupled to the activation of cytokine receptors in liver and in mammary epithelial cells. Interleukin-6 (IL-6) causes the rapid activation of the acute-phase response factor (APRF) in the liver of animals during acute inflammation and in cultured human hepatoma cells (HepG2) and induces the transcription of the acute-phase protein genes, e.g. alpha 2-macroglobulin (alpha 2-M). In the mammary gland and in cultured HC11 mammary epithelial cells, milk protein genes, e.g. beta-casein, are induced by the lactogenic hormones, insulin, glucocorticoids, and PRL. The induction of the beta-casein gene promoter is preceded by the activation of the mammary gland factor (MGF). We have compared the DNA binding sequences of APRF and MGF, 5'-CTTCTT/GGGAATT-3', and have found that they coincide in 11 of 12 positions. Bandshift experiments and oligonucleotide competition experiments showed that both factors, MGF and APRF, are able to bind to the IL-6 response element of the alpha 2-M gene promoter and to the lactogenic hormone response element of the beta-casein gene promoter with very similar specificities. Partial proteolytic digestion of APRF and MGF DNA complexes yielded similar clipping patterns. The UV cross-linked DNA complexes of both transcription factors were of the same apparent molecular mass. IL-6 activation of APRF in HepG2 cells can be observed within minutes. MGF induction by PRL in HC11 cells occurs with similar kinetics. The synergistic action of glucocorticoids and PRL is necessary for the induction of the beta-casein gene, but PRL is sufficient for MGF activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of STAT Factors by Prolactin, Interferon-γ, Growth Hormones, and a Tyrosine Phosphatase Inhibitor in Rabbit Primary Mammary Epithelial Cells

“…As our studies were being completed, our observation of a very rapid activation of MGF in HC11 cells was independently corroborated (40,41). HC11 cells, derived from COMMA-1D cell line, have been used for studies on the transcriptional regulation of ␤-casein gene expression.…”

“…Furthermore, the induction of MGF by PRL must be accompanied by additional hormonal stimulation by glucocorticoids and insulin at confluence to activate ␤-casein gene expression (61,63). Additionally, it was observed that the activation of MGF in HC11 cells is not sufficient to stimulate the transcription from the promoter composed of multimeric MGF sites, whereas the same promoter is activated by IL-6 in HepG2 cells (40). Moreover, all studies on this cell line were conducted in the presence of serum.…”

Stat5a is mandatory for adult mammary gland development and lactogenesis.

“…It has been established in tissue culture cells that mammary gland-specific factors (MGF) (now StatSa and StatSb) activate the (i-casein gene promoter that contains a GAS site (Schmitt-Ney et al 1991;Gouilleux et al 1994a;Standke et al 1994;Liu et al 1995;Moriggl et al 1996). Support for an in vivo role of STATs in milk protein gene expression comes from experiments with WAP (Li and Rosen 1995) and BLG (Burdon et al 1994) transgenes in which the GAS sites had been inactivated.…”

Colony‐stimulating factors and interferon‐γ activate a protein related to MGF‐Stat 5 to cause formation of the differentiation‐induced factor in myeloid cells

“…The common denominator of these elements is their ability to bind a dimer of Stat 1, the gamma-interferon activation factor (GAF), [11]. However, GAS-like elements differ slightly in their DNA sequence and are thus capable of specific association with other different Stat proteins [12][13][14][15][16][17][18]. One of these GAS-like elements has originally been found in the promoters of genes that encode milk proteins and that are induced upon prolactin stimulation of mammary gland cells during lactation [19].…”