Transforming growth factor-beta (TGF-beta) is a multifunctional polypeptide that is the prototypical member of a large family of cytokines that regulate many aspects of cellular function, including proliferation, differentiation, adhesion, and migration. TGF-beta plays a major role in adult physiology, as well as in the control of differentiation and morphogenesis in embryonic development. The tissue distribution pattern of the TGF-betas, which include TGF-betas 1, 2, and 3 in mammals, has possible significance for signaling roles in epithelial-mesenchymal interactions during embryogenesis, as well as in cancer and carcinogenesis. TGF-beta is secreted by a variety of normal and malignant cells. The TGF-betas function through a set of cell surface protein receptors that includes TGF-beta type I (RI) and type II (RII). TGF-beta RII can bind TGF-beta directly to form a complex, which then is able to bind TGF-beta RI, and TGF-beta RII is then able to phosphorylate TGF-beta RI, which is necessary for signal transduction. The TGF-beta signaling system has been implicated as a tumor suppressor pathway in several organ systems. Loss of functional TGF-beta RI or RII contributes to loss of TGF-beta responsiveness, resulting in tumor progression. The most recent efforts have investigated the role of the TGF-beta ligands and receptors receptors in epithelial-mesenchymal interactions in normal mouse embryogenesis. An-depth comparison of the patterns of expression of TGF-beta RI and RII proteins and mRNAs in the developing mouse embryo was made. Immunohistochemical and in situ hybridization analyses were performed on formalin-fixed paraffin-embedded sections of developing embryonic mouse tissues using specific antibodies and cRNA probes for TGF-beta RI and RII. Although widespread expression of both TGF-beta receptors was detected throughout the embryonic development period, TGF-beta RI was expressed in a well-defined, non-uniform pattern that was different in many respects from that of TGF-beta RII. The heart was the first organ that showed expression of TGF-beta RI and RII during embryogenesis, with TGF-beta RI predominanting. Whereas higher levels of TGF-beta RI compared to TGF-beta RII were detected in some tissues of the embryo at the beginning of organogenesis, the level of TGF-beta RII increased more dramatically than that of TGF-beta RI during late organogenesis; this was especially true in many neural structures where TGF-beta RI and RII were comparable by day 16. The lung, kidney and intestine, in which epithelial-mesenchymal interactions occur, showed a complex pattern of TGF-beta RI and RII expression. Additionally, northern blot hybridization and reverse transcription-polymerase chain reaction (RT-PCR) amplification showed non-uniform expression of the transcripts for TGF-beta RI and RII in embryonic and adult mouse and rat tissues. Regulation of TGF-beta 1 RI and RII occurs concurrently, but distinctly, in a spatial and temporal manner in rodent embryogenesis. Concurrent, but distinct, expression of TGF-beta RI and RII in rodent embryogenesis may allow control of signal transduction of TGF-beta during development. Future efforts will be directed at investigating the role of TGF-beta and its receptors in epitheial-mesenchymal interactions in lung carcinogenesis using a mouse model system in which one allele of the TGF-beta 1 gene has been deleted.A study was also made of the participation of adrenomedullin (AM), another growth modulator that is secreted by a variety of normal and malignant cells, in epithelial-mesenchymal interactions with TGF-beta in mouse embryogenesis. Immunohistochemical and in situ hybridization analyses were performed on formalin-fixed paraffin-embedded sections of developing embryonic tissues using specific antibodies and cRNA probes for TGF-beta 1 and AM. The early placenta, including the giant trophoblastic cells, showed high levels of staining and hybridization for TGF-beta 1 and AM proteins and mRNAs. The heart was the first organ that showed expression of TGF-beta 1 and AM during embryogenesis. The spatio-temporal patterns of expression of TGF-beta 1 and AM in cardiovascular, neural, and skeletal-forming tissues showed striking similarities. The lung, kidney, and intestine, in which epithelial-mesenchymal interactions occur, showed similar patterns of TGF-beta 1 and AM expression. Colocailzation of TGF-beta 1 and AM occur in specific cell types associated with several tissues in the developing mouse exmbryo. Additionally, RT-PCR amplification and northern blot hybridization showed expression of TGF-beta 1 and AM mRNAs in all embryonic and adult mouse and rat tissues examined. The expression of TGF-beta 1 and AM is regulated in a spatial and temporal manner such that overlapping patterns of expression of TGF-beta 1 and AM occur in several tissues at the same stage of development and in the same cellular location in rodent embryogenesis. Future efforts will be aimed at studying the interaction of TGF-beta 1 and AM during embryogenesis in mice in which either the TGF-beta 1 gene or the AM gene has been deleted.In addition to examining the localization of TGF-beta and its receptors in epithelial-mesenchymal interactions during mouse embryogenesis, the role of TGF-beta in pediatric pulmonary hypoplasia was also studied. Pulmonary hypoplasia has been found in the human neonatal autopsy population and has been attributed to an alteration in epithelial-mesenchymal interactions during development of the lung. Pulmonary acinar aplasia is a very rare and severe form of pulmonary hypoplasia. TGF-beta and its receptors were investigated in the lungs of a term female infant diagnosed with pulmonary acinar aplasia whose autopsy revealed extremely hypoplastic lungs with complete absence of alveolar ducts and alveoli. Immunostaining for TGF-beta 1 and TGF-beta 2 and TGF-beta RI and RII was significantly lower in the bronchial epithelium and muscle of the hypoplastic lungs than in normal lungs, while no difference was detected in staining for other proteins including adrenomedullin, Clara cell 10 kd protein, and hepatocyte growth factor/scatter factor and its receptor, Met in the hypoplastic and normal lungs or in the liver and kidneys of this infant compared to normal liver and kidney. In addition, in situ hybidization showed that TGF-beta 1 and TGF-beta RI transcripts were considerably reduced in the bronchial epithelium of the hypoplastic lung compared to normal lung. There is a selective reduction of TGF-beta in pulmonary acinar aplasia and suggest that the signaling action of TGF-beta in epithelial-mesenchymal interactions in the lungs of this developmental condition may be compromised.The significance of this project is to determine the role of TGF-beta in cancer and the manner in which the signaling pathway of TGF-beta is altered from the normal condition. The identification of other important growth factors with which TGF-beta interacts in normal cells will be important in defining and determining how this interaction may be altered in cancer and carcinogenesis.
Showing the most recent 10 out of 13 publications
