Two common human CLDN5 alleles encode different open reading frames but produce one protein isoform

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Claudins are crucial for tight junction barrier selectivity.
• The human CLDN5 gene has a frequent single-nucleotide polymorphism (rs885985) leading to two protein variants.
• These variants result from distinct open reading frames (ORFs) encoding 303-amino acid (long) and 218-amino acid (short) claudin-5 proteins.

Purpose of the Study:

• To investigate the expression and localization of the two claudin-5 protein variants in human tissues and cells.
• To determine the functional consequences of the long claudin-5 protein variant.

Main Methods:

• Screening of genotyped human lung tissue using immunoblotting.
• Forced expression of long and short claudin-5 variants in transfected cells.
• Analysis of protein localization via immunofluorescence.

Main Results:

• Immunoblotting of human lung tissue revealed only the 218-amino acid claudin-5 protein; the long form was undetectable.
• In transfected cells, the short claudin-5 variant localized to the plasma membrane at intercellular junctions.
• The long claudin-5 variant was retained in intracellular compartments and did not reach the plasma membrane.

Conclusions:

• The 303-amino acid claudin-5 protein is rarely expressed in human lung tissue.
• If expressed, the long claudin-5 variant is mislocalized and predicted to impair cell function.
• Upstream ORFs may play a role in regulating claudin-5 expression.