DA-Raf-dependent inhibition of the Ras-ERK signaling pathway in type 2 alveolar epithelial cells controls alveolar formation.
Alveolar formation is coupled to the spatiotemporally regulated differentiation of alveolar myofibroblasts (AMYFs), which contribute to the morphological changes of interalveolar walls. Although the Ras-ERK signaling pathway is one of the key regulators for alveolar formation in developing lungs, the intrinsic molecular and cellular mechanisms underlying its role remain largely unknown. By analyzing the Ras-ERK signaling pathway during postnatal development of lungs, we have identified a critical role of DA-Raf1 (DA-Raf)-a dominant-negative antagonist for the Ras-ERK signaling pathway-in alveolar formation. DA-Raf-deficient mice displayed alveolar dysgenesis as a result of the blockade of AMYF differentiation. DA-Raf is predominantly expressed in type 2 alveolar epithelial cells (AEC2s) in developing lungs, and DA-Raf-dependent MEK1/2 inhibition in AEC2s suppresses expression of tissue inhibitor of matalloprotienase 4 (TIMP4), which prevents a subsequent proteolytic cascade matrix metalloproteinase (MMP)14-MMP2. Furthermore, MMP14-MMP2 proteolytic cascade regulates AMYF differentiation and alveolar formation. Therefore, DA-Raf-dependent inhibition of the Ras-ERK signaling pathway in AEC2s is required for alveolar formation via triggering MMP2 activation followed by AMYF differentiation. These findings reveal a pivotal role of the Ras-ERK signaling pathway in the dynamic regulation of alveolar development.
Departments of Biomedical Science andDepartment of Biology, Graduate School of Science andJapan Society for the Promotion of Science, Chiyoda-ku, Tokyo 102-0083, Japan; and.
Haruko
H
Watanabe-Takano
Department of Biology, Graduate School of Science andGraduate School of Advanced Integration Science, Chiba University, Yayoicho, Inage-ku, Chiba 263-8522, Japan;
Kazunori
K
Takano
Developmental Genetics, Graduate School of Medicine, Chiba University, Inohana, Chuo-ku, Chiba 260-8670, Japan;
Akemi
A
Sakamoto
Department of Allergy and Immunology, National Research Institute for Child Health and Development, Setagaya-ku, Tokyo 157-8535, Japan.
Kenji
K
Matsumoto
Developmental Genetics, Graduate School of Medicine, Chiba University, Inohana, Chuo-ku, Chiba 260-8670, Japan;
Takeshi
T
Tokuhisa
Department of Biology, Graduate School of Science andGraduate School of Advanced Integration Science, Chiba University, Yayoicho, Inage-ku, Chiba 263-8522, Japan; t.endo@faculty.chiba-u.jp hatanom@faculty.chiba-u.jp.
Takeshi
T
Endo
Departments of Biomedical Science and t.endo@faculty.chiba-u.jp hatanom@faculty.chiba-u.jp.
Masahiko
M
Hatano
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D055879:Gene Knock-In Techniques; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D053511:Matrix Metalloproteinase 14 / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D048491:Proto-Oncogene Proteins A-raf / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D019714:Tissue Inhibitor of Metalloproteinases / Q000235:genetics / Q000378:metabolism; D000097792:Tissue Inhibitor of Metalloproteinase-4
D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D053511:Matrix Metalloproteinase 14; D020778:Matrix Metalloproteinase 2; D048491:Proto-Oncogene Proteins A-raf; D019908:Proto-Oncogene Proteins c-raf; D019714:Tissue Inhibitor of Metalloproteinases; D000097792:Tissue Inhibitor of Metalloproteinase-4; C507096:Mmp14 protein, mouse; C521643:DA-Raf1 protein, mouse; C482127:Map2k1 protein, mouse; C482129:Map2k2 protein, mouse; C522362:Mmp2 protein, mouse