Carcinoembryonic antigen (CEA)-related cell adhesion molecules are co-expressed in the human lung and their expression can be modulated in bronchial epithelial cells by non-typable Haemophilus influenzae, Moraxella catarrhalis, TLR3, and type I and II interferons

Klaile, Esther; Klassert, Tilman E; Scheffrahn, Inka; Müller, Mario M; Heinrich, Annina; Heyl, Kerstin A; Dienemann, Hendrik; Grünewald, Christiane; Bals, Robert; Singer, Bernhard B; Slevogt, Hortense

In NHBE cells, CEACAM1 mRNA and protein levels were also increased by IFNα, IFNβ, IFNγ and the TLR3 agonist poly I:C ( Figure 3B ). All membrane-bound CEACAM1 isoforms examined here were basically coregulated under all conditions that affected their expression level (Figures 3 and 5) . However, some differences were found for the differential up-regulation of the CEACAM1 isoforms. Type I interferons (IFNα and IFNβ) favored the two short isoforms while the type II interferon IFNγ favored the long isoforms, and poly I:C favored the long and the short isoforms bearing 4 extracellular domains. Especially the former differences, even though not significant, are interesting with regard to the fact that in order to interfere with TLR signaling or with T-cell activation, binding of the Shp-1 phosphatase to the immunoreceptor tyrosine-based inhibitory motif (ITIM) within the cytoplasmic domain of the long CEACAM1 isoform was necessary [15, 16, 19] . The two tyrosine residues that are part of the ITIM can bind to protein tyrosine kinases (e.g. c-Src) as well as protein tyrosine phosphatases (e.g. Shp-2) -leading to the stimulation or the inhibition of cell-signaling pathways, respectively. Long and short CEACAM1 isoforms can appear as monomers, dimers and oligomeric microclusters in the membrane [26, 28] . Trans-homophilic binding between different CEACAM1 molecules increases cis-dimerization in the plane of the membrane via an allostery-based mechanism. Binding of CEACAM1-L to Shp-1 or c-Src is dependent on the balance between the oligomeric states as well as the ratio of long and short isoforms [26, 28] . Interestingly, no cytoplasmic domain is necessary for the CEACAM1-mediated internalization of H. influenzae, M. catarrhalis and N. gonorrhea [27] . But bacterial engagement of CEACAM1 might, in addition to procuring adherence, also influence the cis-dimerization and subsequent inhibitory or activatory signaling of CEACAM1, either supporting pathogen colonization or host response. For example, the interaction of CEACAM1 with M. catarrhalis and N. meningitidis proteins resulted in reduced Tolllike receptor (TLR) 2-initiated inflammatory responses (the major mediator of M. catarrhalis-induced immune responses) of NHBE cells [16, 61, 62] . Part of the host response to microbial infection is the production of cytokines [63] . Type I interferons IFNα and IFNβ can be produced by most cell types and are the major effector cytokines of the host immune response against viral infections. However, the production of type I interferons is also induced in response to bacterial infections [64] . The type II interferon IFNγ plays an important role during the immune response to bacterial pathogens, but is also induced upon infection with viruses. It is produced predominantly by natural killer (NK) cells and natural killer T cells as part of the innate immune response and by Th1 CD4+ and CD8+ cytotoxic T lymphocyte effector T cells once antigen-specific immunity develops [65] . In the present study CEACAM5 is up-regulated in NHBE cells by IFNγ, but not by type I interferons, and CEACAM1 is increased by type I and type II interferons (IFNβ and IFNγ, Figure 3B and D). While for CEACAM1, CEACAM5 and CEACAM6 an upregulation by IFNγ and viral infections has been described in epithelial cells [55, [66] [67] [68] [69] [70] , to our knowledge this is the first report that also type I interferons enhance CEACAM1 expression.