The oncogeneTrop2regulates fetal lung cell proliferation

Abstract

The factors regulating growth of the developing lung are poorly understood, although the degree of fetal lung expansion is critical. The oncogene Trop2 (trophoblast antigen 2) is upregulated during accelerated fetal lung growth, and we hypothesized that it may regulate normal fetal lung growth. We investigated Trop2 expression in the fetal and neonatal sheep lung during accelerated and delayed lung growth induced by alterations in fetal lung expansion, as well as in response to glucocorticoids. Trop2 expression was measured using real-time PCR and localized spatially using in situ hybridization and immunofluorescence. During normal lung development, Trop2 expression was higher at 90 days gestational age (GA; 4.0 ± 0.8) than at 128 days GA (1.0 ± 0.1), decreased to 0.5 ± 0.1 at 142 days GA (full term ∼147 days GA), and was positively correlated to lung cell proliferation rates (r = 0.953, P < 0.005). Trop2 expression was regulated by fetal lung expansion, but not by glucocorticoids. It was increased nearly threefold by 36 h of increased fetal lung expansion (P < 0.05) and was reduced to ∼55% of control levels by reduced fetal lung expansion (P < 0.05). Trop2 expression was associated with lung cell proliferation during normal and altered lung growth, and the TROP2 protein colocalized with Ki-67-positive cells in the fetal lung. TROP2 was predominantly localized to fibroblasts and type II alveolar epithelial cells. Trop2 small interfering RNA decreased Trop2 expression by ∼75% in cultured fetal rat lung fibroblasts and decreased their proliferation by ∼50%. Cell viability was not affected. This study demonstrates that TROP2 regulates lung cell proliferation during development.

Intrauterine Growth Restriction Alters the Postnatal Development of the Rat Cerebellum

“…We have shown that Trop2 regulates the migration of fetal lung cells [37,58] , which suggests a previously unrecognized role of Trop2 during lung development. In this study, we showed, for the first time, that TROP2 protein is localized in granule cells in all layers of the developing cerebellum, but particularly to the postmitotic, migrating granule cells.…”

Trop2: From development to disease

“…This suggests that Trop2 may play a role in late gestation fetal lung development, which is distinct from that of Epcam . This is supported by the observation that TROP2 is localized to airway and alveolar epithelium, endothelium, smooth muscle cells, and myofibroblasts during normal fetal lung development in rats and sheep (McDougall et al, ). In contrast, EpCAM localization is limited to bronchiolar epithelial cells throughout the embryonic, pseudoglandular, canalicular, and alveolar stages of lung development as well as a subset of alveolar epithelial cells (AECs), likely to be surfactant‐producing type II AECs during the alveolar stage of human lung development (Kasper et al, ).…”

“…Trop2 expression levels are very high during the canalicular stage in both fetal rats and fetal sheep, when cell proliferation rates are high. However, Trop2 levels increase in fetal rats from the canalicular to the saccular stage of development, but decrease in fetal sheep from the mid‐canalicular through to the alveolar stage of lung development (McDougall et al, ). This may be due to the differences in the development of the lungs and the timing of cellular events in these two species.…”

“…During fetal life, the lungs are filled with lung liquid, which is secreted by the lungs and which maintains the fetal lungs in an expanded state, which is critical for promoting lung growth and development (Wallace et al, ). Trop2 mRNA levels are increased during accelerated fetal lung growth induced by an increase in lung expansion in fetal sheep, when there is a ∼5‐fold increase in cell proliferation (McDougall et al, ). In contrast, Trop2 mRNA levels are reduced by lung liquid drainage, which causes lung growth to cease (Nardo et al, ; McDougall et al, ).…”

“…Trop2 mRNA levels are increased during accelerated fetal lung growth induced by an increase in lung expansion in fetal sheep, when there is a ∼5‐fold increase in cell proliferation (McDougall et al, ). In contrast, Trop2 mRNA levels are reduced by lung liquid drainage, which causes lung growth to cease (Nardo et al, ; McDougall et al, ). This suggests that Trop2 expression is mechanically regulated, an observation supported by the presence of a putative stretch‐sensitive, sheer‐stress response element Sp1 in the Trop2 promoter (Linnenbach et al, ; Lin et al, ).…”