C-terminal truncation impairs glycosylation of transmembrane collagen XVII and leads to intracellular accumulation.

[junctional epidermolysis bullosa]

Collagen XVII , a type II transmembrane protein in hemidesmosomes , is involved in the anchorage of stratified epithelia to the underlying mesenchyme . Its functions are regulated by ectodomain shedding , and its genetic defects lead to epidermal detachment in junctional epidermolysis bullosa (JEB ), a heritable skin fragility syndrome , but the molecular disease mechanisms remain elusive . Here we used a spontaneously occurring homozygous COL 17 A 1 deletion mutant in JEB to discern glycosylation of collagen XVII . The mutation truncated the distal ectodomain and positioned the only N-glycosylation site 34 amino acids from the newly formed C terminus , which impaired efficient N-glycosylation . Immunofluorescence staining of authentic JEB keratinocytes and of COS -7 cells transfected with the mutant indicated intracellular accumulation of collagen XVII precursor molecules . Cell surface biotinylation and quantification of ectodomain shedding demonstrated that only about 15 % of the truncated collagen XVII reached the cell surface . The cell surface-associated molecules were N-glycosylated in a normal manner , in contrast to the molecules retained within the cells , indicating that N-glycosylation of the ectodomain is required for targeting of collagen XVII to the plasma membrane and that reduced accessibility of the N-glycosylation site negatively regulates this process . Functional consequences of the strong reduction of collagen XVII on the cell surface included scattered deposition of cell adhesion molecule laminin 5 into the extracellular environment and , as a consequence of faulty collagen XVII-laminin ligand interactions , aberrant motility of the mutant cells .

Diseases
Validation

Diseases presenting "functional consequences of the strong reduction" symptom

junctional epidermolysis bullosa

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