title: Involvement of serum response factor isoforms in myofibroblast differentiation during bleomycin-induced lung injury.
abstract: Serum response factor (SRF) is a transcription factor essential for smooth muscle (SM) myogenesis. Its role in myofibroblast differentiation is, however, unknown. We studied the expression and the localization of SRF in bleomycin-induced pulmonary fibrosis, where myofibroblasts are abundant. We found that SRF levels were upregulated in bleomycin-exposed mouse lungs mainly due to de novo synthesis of SRFDelta5, a less myogenic SRF isoform. Before myofibroblast differentiation, SRF/SRFDelta5 was immunolocalized mostly in the cytoplasm of scattered fibroblasts at lesion sites. With the development of myofibroblasts, however, SRF/SRFDelta5 was found in myofibroblast nuclei. cDNA array analysis showed that SRFDelta5 and SRF induced expression of transforming growth factor-beta1, a critical factor in myofibroblast differentiation. This was accompanied by de novo expression of several inflammatory cell-specific mRNAs. The latter was confirmed by reverse transcriptase-polymerase chain reaction. Treatment of lung fibroblasts with tumor necrosis factor-alpha, which is produced early in the bleomycin model, induced SRFDelta5 expression and SRF/SRFDelta5 cytoplasmic accumulation, whereas addition of transforming growth factor-beta1 caused SRF/SRFDelta5 nuclear translocation followed by SM alpha-actin synthesis. Interleukin-4, another cytokine involved in myofibroblast differentiation, did not affect SRF or induce SRFDelta5 expression. Our studies therefore suggested a new mechanism whereby SRF and SRFDelta5 contribute to the emergence of myofibroblasts in lung injury and fibrosis.
authors.affiliation: Department of Pathology, Wayne State University School of Medicine, 540 E. Canfield St., Rm. 9248, Detroit, MI 48201, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Yang
authors.forename: Xiaoning
authors.initials: X
authors.lastname: Zhe
authors.forename: Sem H
authors.initials: SH
authors.lastname: Phan
authors.forename: Matt
authors.initials: M
authors.lastname: Ullenbruch
authors.forename: Lucia
authors.initials: L
authors.lastname: Schuger
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000009:adverse effects / Q000494:pharmacology*; D001761:Bleomycin / Q000009:adverse effects / Q000494:pharmacology*; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D005347:Fibroblasts / Q000502:physiology*; D008168:Lung / Q000187:drug effects*; D051379:Mice; D020033:Protein Isoforms; D026362:Serum Response Factor / Q000235:genetics* / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D020033:Protein Isoforms; D026362:Serum Response Factor; D001761:Bleomycin