RATIONALE: Tetraspanins are cell membrane-spanning proteins that transduce extracellular signals and control cell adhesion via interactions with multiple molecules, including the protein immunoglobulin superfamily, member 3 (IGSF3). Exhibiting a large extracellular domain, and anchored in tetraspanin-enriched microdomains within the plasma membrane, the function of IGSF3 is unknown. OBJECTIVES: Building on our finding that IGSF3 knockdown in lung epithelial cells increases glucosylceramides, sphingolipids that are known to enhance the stability of tetraspanin complexes, we hypothesized that IGSF3 is critical for cell adhesion. Further, because we found that IGSF3 expression was consistently decreased after cigarette smoke exposure we investigated whether genomic alterations (single-nucleotide polymorphisms [SNPs]) within IGSF3 are present in chronic obstructive pulmonary disease (COPD). METHODS: To knock down IGSF3, human bronchial epithelial cells (Beas2b) were stably transfected with lentiviral IGSF3-shRNA or control short hairpin RNA and then compared, with respect to cell adhesion, with fibronectin and migration in a scratch wound assay. The role of glucosylceramides in IGSF3 function was tested with GENZ-123346, a pharmacological inhibitor of glucosylceramide synthase. IGSF3 SNPs were evaluated in COPDGene data sets. RESULTS: Cells with IGSF3 knockdown did not exhibit increased cell death; on the contrary, they had increased rates of proliferation. However, inhibition of IGSF3 expression markedly increased cell adhesion (>twofold; P < 0.01). This was associated with significantly decreased cell migration (P < 0.01) that was restored on glucosylceramide synthase inhibition. Of the 11 IGSF3 SNPs identified to associate with COPD, rs6703791, in the exon 11 coding region, consisting of a missense A-G mutation, may regulate IGSF3 expression. CONCLUSIONS: IGSF3 may be required for lung structural cell adhesion and motility by controlling the synthesis of glycosphingolipids. Loss of IGSF3, either through exposure to cigarette smoking, or through mutations, may impair functions that require cell migration, such as lung tissue repair.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine