Alternative RNA expression of B1-Integrin in different stages of mammary gland devolpment

JULIAN NAIPAUER; ALBANA GATTELLI; SOL DEGESE; OMAR COSO

Simposio; The Second South American Spring Symposium in Signal Transduction and Molecular Medicine SISTAM 2012; 2012

Integrins are heterodimeric cell surface adhesion receptors that play a critical role in the normal development and tumor formation of different tissues. The characterization of the full length mRNA coding for Subunit B1 (Itgb1) reveal an alternative polyA site (PA1) that produces a new Itgb1 mRNA species, 578bp shorter than the one previously reported. Existence of the two different isoforms was confirmed by 3?RACE PCR and SAGE analysis in the mammary gland and other tissues. To corroborate our analysis, we used the pRiG vector, which can generate 2 transcript variants when a proximal poly (A) site is inserted in its cloning site. As expected, PA1 showed polyadenylation activity. The short mRNA species lack two AU-rich elements implicated in regulation of mRNA stability and miRNAs target sequences that might be implicated in translation regulation. In fact, we observed that the 3?UTR corresponding to the longer variant, placed downstream of a CMV driven luciferase gene, produced a change in mRNA stability and increased luciferase expression compared to the shorter one. In the mouse, we found that different tissues and stages during mammary gland development show specific levels of each Itgb1 mRNA. For example, in this gland the longer form was up-regulated in lactation. Similarly, in the HC11 mammary cell line, in vitro differentiation specifically induced this species. On the other hand, post-lactation involution and HC11 cell stretching down-regulated this mRNA isoform. Our data identify a new regulatory instance for controlling Itgb1 expression during mammary gland development and function.