Liu D, Yi M, Smith M, Mendelson CR. TTF-1 response element is critical for temporal and spatial regulation and necessary for hormonal regulation of human surfactant protein-A2 promoter activity. Am J Physiol Lung Cell Mol Physiol 295: L264 -L271, 2008. First published May 16, 2008 doi:10.1152/ajplung.00069.2008.-Expression of the human surfactant protein-A2 (hSP-A2) gene is lung specific, occurs in type II and Clara cells, and is developmentally and hormonally regulated in fetal lung. Using transfected human fetal type II cells, we previously observed that ϳ300 bp of 5Ј-flanking DNA mediated cAMP and interleukin-1 (IL-1) stimulation and dexamethasone (Dex) inhibition of hSP-A2 promoter activity. This region contains response elements for estrogen-related receptor ␣ element (ERRE, Ϫ241 bp), thyroid transcription factor (TTF)-1/Nkx2.1 (TTFbinding protein, Ϫ171 bp), upstream stimulatory factor 1/2 (E-box, Ϫ80 bp), and stimulatory protein (Sp) 1 (G/T-box, Ϫ62 bp), which are essential for basal and cAMP induction of hSP-A2 expression. To define genomic regions necessary for developmental, hormonal, and tissue-specific regulation of hSP-A2 expression in vivo, we analyzed transgenic mice carrying hGH reporter genes comprised of 313 bp of hSP-A2 gene 5Ј-flanking DNA Ϯ mutation in the TBE or 175 bp of 5Ј-flanking DNA, containing TBE, E-box and G/T-box, but lacking ERRE. Transgenes containing 313 or 175 bp of hSP-A2 5Ј-flanking DNA were expressed in a lung cell-specific manner and developmentally regulated in concert with the endogenous mouse SP-A gene. In cultured lung explants from hSP-A Ϫ313:hGH transgenic fetal mice, cAMP and IL-1 induced and Dex inhibited transgene expression. However, the 175-bp hSP-A2 genomic region was insufficient to mediate hormonal regulation of hSP-A2 promoter activity. The finding that expression of the hSP-AϪ313TBEmut:hGH transgene was essentially undetectable in fetal lung and was not hormonally regulated in transgenic fetal lung explants underscores the critical importance of the TBE in lung cell-specific, developmental, and hormonal regulation of hSP-A2 gene expression. fetal lung; tissue specific; type II cell; adenosine 3Ј,5Ј-cyclic monophosphate; glucocorticoid PULMONARY SURFACTANT, a developmentally regulated, phospholipid-rich lipoprotein required for air breathing, is synthesized exclusively by lung alveolar type II cells. To define the basic mechanisms involved in type II cell-specific, developmental, and hormonal regulation of surfactant synthesis, we have focused on surfactant protein (SP)-A, the major surfactant protein, that is an excellent marker of fetal lung maturity. Transcription of the SP-A gene is initiated in fetal lung after ϳ80% of gestation is completed and reaches maximal levels just before birth (44). Developmental regulation of SP-A gene expression in fetal lung is more closely associated with the induction of surfactant glycerophospholipid synthesis and appearance of identifiable type II cells than is the temporal regulation of genes encoding surfactant proteins...