TRISTETRAPROLIN (TTP) EXPRESSION IS REQUIRED FOR MAINTENANCE OF THE MAMMARY PROGENITOR CELL POPULATION

MICAELA STEDILE; LOURDES PEREZ CUERVO; ANA RAIMONDI; M VICTORIA GODDIO; MARIA VICTORIA MEDINA; ALBANA GATTELLI, MARIA CECILIA CIRIO, ANA QUAGLINO, CAROLINA SCHERE-LEVY, NATALIA MARTINEZ, MAR?A BINAGHI, ROBERTO P. MEISS, LUCIO H. CASTILLA, EDITH C. KORDON; INES BECKERMAN; MARTIN GARCIA SOLA; OMAR A. COSO

Washington DC

Congreso; American Society for Cell Biology- European Molecular Biology Organization meeting; 2019

ASCB-EMBO

Messenger RNA (mRNA) stability is regulated mainly by proteins that bind sequences enriched inadenine and uracil in their 3´untranslated regions, called collectively AU-binding proteins (AUBPs).Tristetraprolin (TTP) is an AUBP that promotes mRNA degradation of proteins involved in inflammation,proliferation and tumor invasiveness. We have previously reported that TTP expression is downregulatedin breast cancer compared to normal mammary gland, where TTP reaches its highest levelsduring lactation. In addition, bitransgenic females WAP-Cre x TTPfl/fl mice (named MG TTP-KO),showed that reduction of TTP levels in the lactating mammary gland resulted in premature involutionassociated to the increase of TNFα, IL-6 and LIF expression, STAT3 activation and massive cell death.Therefore, we concluded that TTP expression in the mammary epithelium is required for lactationmaintenance. Then, as it has been reported that WAP-expressing cells behave as a pregnancy-inducedmammary progenitor subpopulation and analysis of RNA-seq data indicates that TTP is up-regulated inmammary progenitor cells, our next goal was to determine whether expression of this AUBP is relevantfor the maintenance of the mammary stem cell compartment. Our results showed that upon successivepregnancies MG TTP-KO mice exhibited underdeveloped lactating glands that also presenteddecreased pre-neoplastic lesions when crossbred with WAP-Cre/RasG12D mice. Moreover, mammaryglands from total TTP-KO mice displayed underdeveloped ductal network upon transplantation intosyngeneic mammary cleared fat pads. This suggested that diminished expression of TTP in themammary progenitor compartment caused impairment of mammary gland development anddifferentiation. To verify this hypothesis, we generated TTP knockdown cells (TTP-KD) by stabletransfection of stem-like HC11 mammary epithelial cells with specific TTP-shRNA constructs.Interestingly, these cells exhibited impaired survival rates (by MTS analysis), increased apoptosis (byTUNEL), and induction of pro-apoptotic proteins (by Western blot, WB). Besides, TTP-KD cells alsodisplayed high expression of inflammatory cytokines (analyzed by RT-qPCR), increased levels of STAT3and P-STAT3 as well as p65/RelA and p38 phosphorylation, but inhibition of ERK 1/2 activation (studiedby WB and treatment with specific inhibitors). Importantly, the TTP-KD cells revealed a substantialdecreased capacity to form mammospheres in 3D culture and to repopulate cleared fat pads of virginBALB/c female mice. Taking together, our results indicate that TTP expression is required for mammaryprogenitor cell survival by preventing spontaneous pro-inflammatory and stress-associated events,which are able to induce mammary stem cell death.