A novel glycosaminoglycan attachment domain identified in two alternative splice variants of human versican.

We have cloned an alternatively spliced glycosaminoglycan attachment domain (GAG-alpha) of human versican from cDNA libraries derived from U251MG glioma cells. Inserted carboxyl-terminal of the hyaluronan-binding region, this domain adds another 987 amino acids to the original versican (V1) core protein giving rise to the large V0 isoform with 3396 amino acids and 17-23 putative glycosaminoglycan attachment sites. The GAG-alpha domain is encoded by exon 7 of the human versican gene (Naso et al., J. Biol. Chem., 32999-33008). Sequence comparisons revealed a slight similarity to the alternative splice domain of PG-M, further supporting the notion that PG-M is the chicken homologue of versican. On immunoblots of a proteoglycan preparation from U251MG culture medium, anti-GAG-alpha antibodies reacted exclusively with the larger of two versican core proteins recognized by antibodies against the original GAG-beta domain. Using reverse transcription-polymerase chain reaction, we detected both the V0 and V1 isoforms in the cerebral cortex, aorta, intervertebral disc, liver, myometrium, and prostate, whereas keratinocytes exclusively expressed versican V1. In brain tissue, we identified a short versican variant (V2) including only the GAG-alpha domain. By expressing particular splice forms of versican, cells may control the hydration properties of their pericellular hyaluronan coat and thus could modulate interactions with the extracellular matrix or neighboring cells.