Estrogen-triggered delays in mammary gland gene expression during the estrous cycle: evidence for a novel timing system

Abstract

During the estrous cycle and beginning in estrus, the mammary gland undergoes pregnancy-like development that depends on transcriptional regulation by the estrogen and progesterone receptors (ER, PR) and Pax-2 as well as the action of the growth factors Wnt-4 and RANKL. In this report, we first describe the decay and delayed expression of ERa, PR, and Pax-2 proteins as well as depression of Wnt-4 and RANKL mRNA coincident with the strong estrogen surge in proestrus. In time-course studies using ovariectomized mice, a single estrogen injection replicated these delays and caused an 18 h delay in Wnt-4 expression. Molecular time-delay systems are at the core of cellular cycles, most notably the circadian clock, and depend on proteasome degradation of transcriptional regulators that exhibit dedicated timing functions. The cytoplasmic dynamics of these regulators govern delay duration through negative transcription/translation feedback loops. A proteasome inhibitor, PS-341, blocked estrogen-stimulated ERa, PR, and Pax-2 decay and proteasome chymotryptic activity, assayed using a fluorogenic substrate, was elevated in proestrus correlating with the depletion of the transcription factors. The 18-h delay in Wnt-4 induction corresponded to the turnover time of Pax-2 protein in the cytoplasm and was eliminated in Pax-2 knockout mammary tissue, demonstrating that Pax-2 has a unique timing function. The patterns of estrogen-triggered ERa, PR, and Pax-2 turnover were consistent with a negative transcriptional feedback. Retarding the expression of ERa, PR, and Pax-2 may optimize preparations for pregnancy by coordinating expression of critical receptors and transcription factors with rising estrogen and progesterone levels in estrus. The estrogen surge in proestrus has no defined mammotropic function. This study provides the first evidence that it is a synchronizing signal triggering proteasome-dependent turnover of mammary gland ERa, PR, and Pax-2. We hypothesize that the delays reflect a previously unrecognized timing system, which is present in all ovarian target tissues.

Wnt Signaling in Mammary Glands: Plastic Cell Fates and Combinatorial Signaling

“…Thus, recent reports describe a dynamic twofold expansion and retraction of the stem cell activity during the 4-d estrus cycle (Joshi et al 2010), and an 11-fold difference in activity in estrogen/progesterone positive/negative mammary environments . These hormonal dynamics closely resemble the expression of Wnt4 mRNA and protein expression in luminal mammary epithelial cells (Table 1) (Silberstein et al 2006).…”

Regulation of Genes of the Circadian Clock in Human Colon Cancer: Reduced Period-1 and Dihydropyrimidine Dehydrogenase Transcription Correlates in High-Grade Tumors

“…2). Although nothing is known of the gender-specific regulation of the FEO, mammary gland and endometrium gene expression are estrogen triggered during the estrous cycle reminiscent of the circadian clock (39). Although the colon cannot be considered a sex hormone-dependent organ like the mammary gland and the uterus, it should, however, be recognized that the colon is also positive for estrogen receptor-h (ER-h) and ER-ain both men and women (see, e.g., ref.…”

R-spondin1 is a novel hormone mediator for mammary stem cell self-renewal

“…Wnt4 and RANKL share many similar traits, including their expression in luminal cells, expression fluctuation during estrous cycle (Silberstein et al 2006), up-regulation during pregnancy (Fata et al 2000;Brisken et al 2002), and essential functions in alveologenesis (Brisken et al 2000). We attempted to maintain the MaSC properties in vitro using recombinant RANKL.…”