EXPRESSION AND FUNCTIONAL-ANALYSIS OF A NOVEL ISOFORM OF GICERIN, AN IMMUNOGLOBULIN SUPERFAMILY CELL-ADHESION MOLECULE

We have cloned a novel cDNA of gicerin, a cell adhesion molecule belon ging to the immunoglobulin super-family. Both gicerin isoforms share t he same extracellular domain, which has five immunoglobulin-like loop structures and a transmembrane domain as s-gicerin, but differ in the cytoplasmic tail domain. As the newly identified form has a larger cyt oplasmic domain than the previously reported form, we refer to them as l-gicerin and s-gicerin, respectively, l-gicerin is transcribed from a distinct mRNA containing an inserted sequence not found in s-gicerin mRNA which caused a frameshift for the coding region for a cytoplasmi c domain. Previous studies demonstrated that gicerin showed a doublet band of 82 and 90 kDa in chicken gizzard smooth muscle. We report that the 82-kDa protein corresponds to s-gicerin and the 90-kDa protein to l-gicerin. We also found that the two gicerin isoforms are expressed differentially in the developing nervous system, Functional analysis o f these gicerin isoforms in stable transfectants revealed that they ha d differ in their hemophilic adhesion properties, as well as in hetero philic cell adhesion assayed with neurite outgrowth factor. In additio n, these isoforms have neurite-promoting activity by their hemophilic adhesion, but differ in their ability to promote neurite outgrowth.