Carcinoembryonic cell adhesion molecule 6 in human lung: regulated expression of a multifunctional type II cell protein

Abstract

It binds gram-negative bacteria and is overexpressed in cancers, where it is antiapoptotic and promotes metastases. To characterize CEACAM6 expression in developing lung, we cultured human fetal lung epithelial cells and examined responses to differentiation-promoting hormones, adenovirus expressing thyroid transcription factor-1 (TTF-1), and silencing of TTF-1 with small inhibitory RNA. Glucocorticoid and cAMP had additive stimulatory effects on CEACAM6 content, and combined treatment maximally increased transcription rate, mRNA, and protein ϳ10-fold. Knockdown of TTF-1 reduced hormone induction of CEACAM6 by 80%, and expression of recombinant TTF-1 increased CEACAM6 in a dosedependent fashion. CEACAM6 content of lung tissue increased during the third trimester and postnatally. By immunostaining, CEACAM6 was present in fetal type II cells, but not mesenchymal cells, and localized to both the plasma membrane and within surfactant-containing lamellar bodies. CEACAM6 was secreted from cultured type II cells and was present in both surfactant and supernatant fractions of infant tracheal aspirates. In functional studies, CEACAM6 reduced inhibition of surfactant surface properties by proteins in vitro and blocked apoptosis of electroporated cultured cells. We conclude that CEACAM6 in fetal lung epithelial cells is developmentally and hormonally regulated and a target protein for TTF-1. Because CEACAM6 acts as an antiapoptotic factor and stabilizes surfactant function, in addition to a putative role in innate defense against bacteria, we propose that it is a multifunctional alveolar protein.alveolar type II cells; thyroid transcription factor-1; glucocorticoid; adenosine 3Ј,5Ј-cyclic monophosphate; apoptosis; surfactant THE IGCAM SUPERFAMILY is a diverse group of adhesive receptor glycoproteins that contain an amino-terminal N domain, which is homologous to the Ig variable domain, and different numbers of domains homologous to the Ig constant domain. In the human, the carcinoembryonic antigen (CEA) gene family is an IgCAM subset consisting of 29 related genes and pseudogenes clustered at q13.2 on chromosome 19 (22). CEA proteins function as intercellular homophilic and heterophilic adhesion molecules and have signaling properties.Carcinoembryonic cell adhesion molecule (CEACAM)6 (also called NCA, NCA-50/90, and CD66c) and CEACAM5 (originally called CEA and also designated CD66e) share ϳ90% homology of the N domain but differ in the number of IgC2-like domains (A and B domains). Both proteins contain a glycosylphosphatidylinositol (GPI) membrane anchor (28) and are targeted to lipid rafts in apical membranes of polarized epithelial cells (32). CEACAM5/6 bind a variety of gramnegative bacteria and mediate internalization/phagocytosis, participating in innate immune defense in the intestine (10). The two genes are not found in rodents, and they may represent pathogen-host coevolution, providing different protein structures with selective bacterial binding properties.Expression of CEACAM5/6 is deregulated and overexpresse...

Distribution and surfactant association of carcinoembryonic cell adhesion molecule 6 in human lung

“…CEACAM6/CEA immunoreactivity has been reported for al- veolar epithelium of adult human lung (30,32), and previously we found that fetal human type II cells in monolayer culture expressed CEACAM6 (24). Fig.…”

“…Results of our laboratory's previous studies (2,24) plus the data of Fig. 5, Be and Bg, establish the expression of CEACAM6 in type II cells of the alveolus.…”

“…In our laboratory's previous publication (24), we reported the presence of CEACAM6 in TAF from intubated premature infants. To further characterize this finding, we now describe CEACAM6 content in lung epithelium and lavage fluid at different postnatal ages, the content of different isoforms, influence of lung injury and infection, and studies of CEACAM6 affinity for surfactant.…”

“…We also found that CEACAM6 is a target protein of thyroid transcription factor-1 (product of Nkx2.1), which is required for differentiation of type II cells and expression of surfactant-associated proteins (SP) (25). In additional recent studies with cultured fetal type II cells, we presented evidence that CEACAM6 is associated with surfactant-containing lamellar bodies, is found in lung fluid of infants, and protects surfactant from inhibition by extraneous proteins in vitro (24). Based on these observations, we hypothesized that CEACAM6 in human lung is a SP.…”

“…Five-micrometer cryosections were cut using a Microm HM560 cryostat (Walldorf). Sections were permeabilized and stained as previously described (16,24). All antibodies were applied successively.…”