Fig. 9. Model of heterozygous expression of mutant SP-C. Schematic presentation of possible fates of synthesized proSP-C. (A) Expression of wild-type SP-C (hSP-C^1-197) results in homomeric association, sorting and direction to CD63-positive vesicles (lamellar bodies). (B) In contrast, COOH folding mutants such as Exon 4 are retrotranslocated from the ER and directed preferentially to degradative pathways. Aggresomes form if protein expression exceeds degradation. (C) In heterozygous expression in vivo or co-transfection in vitro, via heteromeric association and retrotranslocation prior to sorting in the Golgi, folding mutants interact with wild-type SP-C to alter trafficking producing dominant negatives.