ALTERNATIVE RNA EXPRESSION OF B1-INTEGRIN IN THE MAMMARY GLAND

MARTÍN GARCÍA SOLÁ; JULIÁN NAIPAUER; EDITH C KORDON; OMAR A. COSO

Congreso; LXI Reunión Anual SAIC; 2016

Integrins are cell surface receptors that play a critical role innormal and tumor tissue development. We have reported that themessenger RNA (mRNA) encoding the B1-integrin subunit (Itgb1)has an alternative cleavage and polyadenylation site that rendersa mRNA isoform (Itgb1-S), 578 nucleotide shorter than the onealready reported (Itgb1-L). In its 3?UTR, Itgb1-L contains regulatorysequences, which are absent in the Itgb1-S 3?UTR. We have previouslyshown that during mammary gland development, expressionlevels of each Itgb1 mRNA isoform are determined, at least in part,by the alternative use of these signals. The cell line HC11 allowsto study, in culture, the behavior of mammary epithelium at differentdevelopmental stages. When confluent, apoptosis is inducedin these cells by starvation. However, this effect is reversed bytreatment with lactogenic hormones, which induce mammary differentiation,or by EGF that triggers cell survival pathways. Wehypothesized that regulation of Itgb1 mRNA might be relevant forthese effects. Therefore, first, we analyzed the consequences oftreating starved HC11 cells with EGF on the different Itgb1 mRNAisoforms. To this goal, we performed a time course of EGF inductionand tested by RTqPCR the expression levels of Itgb1 mRNAvariants. Our results show an increase in the amount of total Itgb1mRNA during the first 5 hours post-stimulation. Interestingly, duringthe time window between 2 and 4 hours, we observed a decreaseof Itgb1-L mRNA levels together with an increase in the amount ofItgb1-S mRNA. This data suggest that in that time frame there is achange in the selection of the cleavage and polyadenylation site thatprivileges use of the alternative (weaker) proximal site generating apeak of expression for the shorter isoform. Currently, we are analyzingthe signaling pathways triggered by EGF, which may lead to a changein the selection of the Itgb1 polyadenylation site in Itgb1 mRNA.