Relevance of 3' untranslated region (3'UTR) for regulation of expression of b1 integrin mRNAs

ALBANA GATTELLI; JONATHAN LAMARRE; EDITH KORDON

Bariloche, Argentina

Congreso; Gene expression and RNA processing; 2007

International Centre for genetic Engineering and Biotechnology (ICGEB); FCEN, UBA; IFIBYNE-CONICET; ANPCYT

Integrins belong to a superfamily of cell surface adhesion receptors that play a critical role in tumor progression as well as in a number of physiological processes. Particularly in mammary gland, the relevance of different expression patterns of b 1 integrin for normal and tumor development has become evident. Based on numerous studies implicating 3?UTR sequences in the regulation of mRNA levels, we have examined gene products of b 1 integrin in normal and neoplastic mammary glands by 3?RACE-PCR. Cloning and sequencing these reaction products we have found a new b 1 integrin RNA species, 578bp shorter (S) than the previously reported (L). By sequence analysis we have determined that this different species arise from the use of alternative polyadenylation sites. Our analysis also revealed the presence of two AU-rich element (ARE) sequences, localized between those sites and, therefore, absent in the S mRNA. We then studied the levels of expression and ratio between the S and L b 1 integrin mRNA species during mammary development and in mammary tumors. We found that although both S and L b 1 integrin mRNA species have been detected in tumors and normal mammary glands, L levels are always higher. However, each stage of mammary gland development corresponds to a specific L/S ratio. In addition, working with HC11 normal epithelial mammary cells and mammary glands from different developmental stages we have found that estrogen levels influence this ratio. We have subcloned the different 3?UTRs coming from the L and S forms into a reporter vector downstream of a CMV driven luciferase gene. In addition, we introduced a point mutation in the first construct that abolishes the first PolyA signal and only produces the L form. Results from these studies suggest that these mutations also alter transcription and/or translation of the L form. Taken together, these data suggest that the use of alternative polyadenilation sites at the b1-integrin 3?UTR provides another regulatory strategy to control b1-integrin abundance in different physiological contexts.