In this study we investigated for the first time the transcriptional regulation of pig Gal beta 1,3GalNAc alpha 2,3-sialyltransferase (pST3Gal I) in response to TGF-beta 1 in porcine kidney PK-15 cells. The pST3Gal I gene was found to span about 90 kb and to be composed of 8 exons including 2 exons in the 5'-untranslated region. RT-PCR analysis indicated that the induction of pST3Gal I by TGF-beta 1 is regulated at the transcriptional level. Functional analysis of the 5'-flanking region of the pST3Gal I gene revealed the -1257 to -976 region functions as the TGF-beta 1-inducible promoter and that the Smad-binding site at -01020 is crucial for TGF-beta 1-induced expression of pST3Gal I in PK-15 cells. In addition, the transcriptional activity of pST3Gal I induced by TGF-beta 1 in PK-15 cells was strongly inhibited by SIS3, which is a specific Smad-3 inhibitor. In summary, our results identified the core promoter region in the pST3Gal I promoter and demonstrated that Smad-3 binding to the Samd-3 binding site at -1020 is essential for transcriptional activation of pST3Gal I in TGF-beta 1-induced PK-15 cells. (C) 2011 Elsevier Inc. All rights reserved.