Lamin A

Nuclear lamina is a protein scaffold on the inner edge of the nucleus that helps organize nuclear processes such as RNA and DNA synthesis.

preLamin A contains a CAAX box at the C-terminus of the protein (where C is a cysteine and A is any aliphatic amino acids). This ensures that the cysteine is farnesylated, and this allows preLamin A to bind membranes, specifically the nuclear membrane. After Prelamin A has been localized to the cell nuclear membrane the C-terminal amino acids, including the farnesylated cysteine, are cleaved off by a specific protease. The resulting protein is now Lamin A, is no longer membrane-bound and carries out functions inside the nucleus.

In HGPS the recognition site that the enzyme requires for cleavage of Prelamin A to Lamin A is mutated. Lamin A cannot be produced and preLamin A builds up on the nuclear membrane, causing a characteristic nuclear blebbing. This results in the premature aging symptoms of progeria, although the mechanism connecting the misshapen nucleus to the symptoms is not known.

A study which compared HGPS patient cells with the skin cells from LMNA young and elderly human subjects found similar defects in the HGPS and elderly cells, including down-regulation of certain nuclear proteins, increased DNA damage and demethylation of histone leading to reduced heterochromatin. Nematodes over their lifespan show progressive lamin changes comparable to HGPS in all cells but neurons and gametes. These studies suggest that lamin A defects contribute to normal aging.

related story :Premature Oldness ; A Story on Progeria.