CD44 ISOFORM EXPRESSION IN PERIODONTAL TISSUES - CELL-TYPE-SPECIFIC REGULATION OF ALTERNATIVE SPLICING

CD44 functions as a receptor for various extracellular matrices and pl ays crucial roles in homotypic and heterotypic cell-cell interactions. Recently, the molecular structure of CD44 has been extensively analyz ed and multiple isoforms produced by alternative splicing of messenger RNA have been identified. In this study, we examined the expression o f CD44 isoforms on different cell types isolated from periodontal tiss ue. In order to examine tissue differences in CD44 isoform expression, we established in vitro cell culture of human gingival fibroblasts (H GF), human periodontal ligament cells (HPDL) and human gingival epithe lial cells (HGEC). These cells all expressed CD44 protein and messenge r RNA. However, immunoprecipitation and Northern blot analysis reveale d that HGEC expressed larger CD44 isoforms than HGF and HPDL. Reverse transcription-polymerase chain reaction with primers flanking the inse rtion site of alternatively spliced exons was used to study details of the heterogeneity. All cells examined expressed a major band in the a bsence of alternatively spliced exons and additional larger bands. In particular, HGEC contained more abundant high molecular mass species. In vitro stimulation by IL-1 beta, TNF alpha or phorbol 12-myristate 1 3-acetate induced an increase in total CD44 messenger RNA in HGF but n ot change in overall patterns of CD44 isoform expression. However, the isoform expression of HGEC was sensitive to cell density. The amount of larger isoform was decreased by culturing cells beyond confluence. These findings suggest that CD44 isoform expression is cell type-speci fically regulated in periodontium and altered according to growth phas e of HGEC.