Surfactant protein-C Promoter Research Articles

TRANSGENIC MOUSE MODELS FOR LUNG CANCER

Transgenic technology allows the ability to target regulatory genes to the lungs in a cell-specific fashion. Using this technology, we have generated a model to investigate the phenotypic consequences of targeting oncogenes to particular cell types in the lungs and are developing a second model for the regulated expression of oncogenes in the lung. The transgenic model involves the constitutive expression of simian virus 40 large T antigen in the Clara cells of mouse lungs. This model has been used to investigate changes in expression of cell cycle regulatory genes in the Clara cells during the transformation process, as well as the expression of the transcription factors regulating the expression of Clara cell differentiation markers. The second model we are developing investigates the regulated expression of the genes in the lungs. This system is based on the establishment of two types of transgenic lines. The regulator line consists of a chimeric transcriptional factor placed under the control of a lung-specific SPC (surfactant protein C) promoter. This chimeric regulator is composed of a transcription activation domain, the GAL4 DNA-binding domain, and a truncated progesterone receptor that is responsive to RU 486, but not to endogenous progesterone. The second transgenic mouse line contains the silent target transgene under the control of a minimal promoter with upstream activating sequences (UAS) that are recognized by the regulator transgene. Upon breeding these two lines, the resulting bitransgenic mice can then be induced to express the target transgene only with the administration of RU 486. Two generations of regulators have been evaluated on their ability to regulate the expression of a growth hormone reporter gene. This system demonstrated the inducible expression of the reporter genes in the distal airways of the lungs.

Nuclear Factor I Family Members Regulate the Transcription of Surfactant Protein-C

Transcription of the surfactant protein-C (SP-C) gene is restricted to Type II epithelial cells in the adult lung. We have shown previously that the 0.32-kilobase pair (kb) mouse SP-C promoter is functional in transient transfection assays of the lung epithelial cell-derived cell line, MLE-15, and that thyroid transcription factor 1 (TTF-1) transactivates promoter activity. The 0.32-kb SP-C promoter can be separated into a proximal promoter region (-230 to +18) and an enhancer region (-318 to -230). Three DNase I footprints were mapped in the promoter region (C1 through C3) and two in the enhancer region (C4 and C5). We now show that nuclear factor I (NFI) family members bind to both individual NFI half-sites in footprints C1, C3, and C5, and to a composite site in footprint C4 by competition gel retardation and antibody supershift analyses. Mutational analysis of the 0.32-kb mouse SP-C promoter and transient transfection of MLE-15 cells demonstrated that the NFI binding sites are required for promoter activity in this cell type. Site-specific mutation of the proximal or distal NFI sites drastically reduced transactivation by a co-transfected NFI-A expression vector in HeLa cells. These data indicate that NFI family member(s), binding to sites in both the promoter and enhancer regions, regulate SP-C gene expression in a process independent of TTF-1.

Expression of transgenic carcinoembryonic antigen (CEA) in tumor‐prone mice: An animal model for CEA‐directed tumor immunotherapy

Carcinoembryonic antigen (CEA) is a tumor marker for the most common forms of adenocarcinomas. We have previously described C57BL/6 mice transgenic for the complete human CEA gene. Compared with humans, these mice reveal a conserved spatiotemporal CEA expression pattern. To establish animal models for CEA-targeted tumor immunotherapy, we have crossed CEA transgenic mice with mice that are genetically predisposed to tumor development. These immunocompetent animals should allow optimization of immunotherapy strategies for maximal destruction of tumor tissues with minimal damage to CEA-expressing normal tissues. To develop a breast tumor model, CEA transgenic mice were cross-bred with mice transgenic for the rat neu protooncogene controlled by the mouse mammary tumor virus long terminal repeat. Female offspring developed poorly differentiated breast tumors, none of which, however, expressed CEA. As a model for colorectal tumors, mice bearing a mutation in the Apc gene (Min mice) and the CEA transgene developed multiple intestinal adenomas with strong CEA expression in all tumor cells. CEA expression had no significant effect on tumor growth. Occasional, well-differentiated breast adenocarcinomas in female offspring expressed CEA focally in tumor cells lining pseudolumina. Cross-breeding ApcMin/+ mice with neu transgenic mice did not reveal a synergistic effect on the kinetics of breast tumor formation. Finally, CEA transgenic mice crossbred with mice transgenic for the SV40 large T antigen regulated by the surfactant protein-C promoter, developed multiple lung adenocarcinomas that revealed a mosaic CEA expression pattern. Int. J. Cancer 72:197–202, 1997. © 1997 Wiley-Liss Inc.

Expression of transgenic carcinoembryonic antigen (CEA) in tumor-prone mice: an animal model for CEA-directed tumor immunotherapy.

Carcinoembryonic antigen (CEA) is a tumor marker for the most common forms of adenocarcinomas. We have previously described C57BL/6 mice transgenic for the complete human CEA gene. Compared with humans, these mice reveal a conserved spatiotemporal CEA expression pattern. To establish animal models for CEA-targeted tumor immunotherapy, we have crossed CEA transgenic mice with mice that are genetically predisposed to tumor development. These immunocompetent animals should allow optimization of immunotherapy strategies for maximal destruction of tumor tissues with minimal damage to CEA-expressing normal tissues. To develop a breast tumor model, CEA transgenic mice were cross-bred with mice transgenic for the rat neu protooncogene controlled by the mouse mammary tumor virus long terminal repeat. Female offspring developed poorly differentiated breast tumors, none of which, however, expressed CEA. As a model for colorectal tumors, mice bearing a mutation in the Apc gene (Min mice) and the CEA transgene developed multiple intestinal adenomas with strong CEA expression in all tumor cells. CEA expression had no significant effect on tumor growth. Occasional, well-differentiated breast adenocarcinomas in female offspring expressed CEA focally in tumor cells lining pseudolumina. Cross-breeding Apc(Min/+) mice with neu transgenic mice did not reveal a synergistic effect on the kinetics of breast tumor formation. Finally, CEA transgenic mice crossbred with mice transgenic for the SV40 large T antigen regulated by the surfactant protein-C promoter, developed multiple lung adenocarcinomas that revealed a mosaic CEA expression pattern.

Reversal of lung lesions in transgenic transforming growth factor alpha mice by expression of mutant epidermal growth factor receptor.

Transgenic mice expressing transforming growth factor alpha (TGF-alpha) in type II cells under control of the lung-specific surfactant protein-C (SP-C) promoter develop pulmonary fibrosis and marked airspace hypoplasia. To identify cellular signaling mechanisms involved in lesion formation, we generated transgenic mice expressing a mutant epidermal growth factor receptor lacking a portion of the intracytoplasmic domain (EGF-R-M) under control of the human SP-C promoter. Transcripts of the SP-C-EGF-R-M transgene were detected in distal bronchiolar and type II cells by in situ hybridization. The morphology of lungs from the SP-C-EGF-R-M transgenic mice was normal. Lung fibrosis was not detectable and airspace hypoplasia was significantly corrected in bitransgenic mice derived by breeding SP-C-TGF-alpha and SP-C-EGF-R-M mice. Correction of lung pathology in the bitransgenic mice occurred without altering the level of hTGF-alpha mRNA. To further demonstrate that reversal of TGF-alpha lesions required signaling through the EGF-R, SP-C-TGF-alpha transgenic mice were bred to mice homozygous for the wa-2 mutation which encodes a mutated EGF-R. TGF-alpha-induced lesions were reversed in homozygous wa-2 mice. Amelioration of TGF-alpha-dependent pulmonary lesions in SP-C-EGF-R-M mice or wa-2/wa-2 mice supports the concept that autocrine and paracrine signaling mediate fibrosis and airspace remodeling caused by TGF-alpha.

Transcription of the Lung-specific Surfactant Protein C Gene Is Mediated by Thyroid Transcription Factor 1

Surfactant protein C (SP-C) is expressed in alveolar Type II epithelial cells of the lung. In order to determine the mechanism(s) that regulate gene transcription, we have analyzed the activation of the murine SP-C promoter in mouse lung epithelial cells (MLE cells) and in HeLa cells after co-transfection with a vector expressing rat thyroid transcription factor-1 (TTF-1). TTF-1 transactivated SP-C-chloramphenicol acetyltransferase constructs containing -13 kilobase pairs to -320 base pairs (bp) of the 5 flanking region of the SP-C gene. Essential cis-acting elements were functionally localized to between -320 and -180 bp from the start of transcription by transfection analysis. Five DNase-protected regions, indicating multiple protein-DNA interactions within the -320 bp TTF-1-responsive region of the SP-C gene, were identified by DNase footprint analysis. A 40-bp segment of SP-C DNA from -197 to -158 linked to a heterologous promoter-chloramphenicol acetyltransferase construct activated expression after co-transfection with CMV-TTF-1 in HeLa and MLE cells. The -197 to -158 segment contained two consensus TTF-1 sites, which were specifically identified as TTF-1 binding sites by gel retardation and antibody supershift with MLE cell nuclear extracts and purified TTF-1 homeodomain protein. Site-specific mutagenesis of either of the TTF-1 binding sites completely blocked activation by TTF-1, indicating both sites are required for TTF stimulation of SP-C transcription.

Tumor Necrosis Factor-α Inhibits Surfactant Protein C Gene Transcription

Pulmonary surfactant protein C (SP-C) is a 3.7-kDa, hydrophobic peptide secreted by alveolar type II epithelial cells. SP-C enhances surface tension lowering activity of surfactant phospholipids that is critical to the maintenance of alveolar volume at end expiration. The proinflammatory cytokine, tumor necrosis factor alpha (TNF-alpha), decreased SP-C mRNA within 24 h of intratracheal administration to mice. In vitro, TNF-alpha decreased SP-C mRNA in a time-and dose-dependent manner, reducing the steady state levels of SP-C mRNA by 3-5 fold. In contrast, TNF-alpha induced intercellular adhesion molecule-1 expression in both mouse lung and murine lung epithelial cell lines. Nuclear run-on analysis demonstrated that transcription of both the endogenous SP-C gene and a human SP-C promoter-driven transgene was inhibited by TNF-alpha. TNF-alpha decreased mouse SP-C chloramphenicol acetyltransferase mRNA in stably transfected murine epithelial cells. Deletion analysis of the SP-C promoter region demonstrated that TNF-alpha inhibited gene expression in constructs containing 320 base pairs 5' from the start of transcription of the mouse SP-C gene. Inhibition of surfactant protein C gene transcription by TNF-alpha may contribute to the abnormalities of surfactant homeostasis associated with pulmonary injury and infection.