Isoforms and splice variant of transforming growth factor beta-binding protein in rat hepatic stellate cells.

BACKGROUND & AIMS: Hepatic stellate cells (HSCs) are one important source for transforming growth factor beta (TGF-beta). They produce TGF-beta in a latent form associated with latency-associated peptide and latent TGF-beta-binding protein (LTBP). This study was designed to investigate, on RNA and protein levels, which isoforms of LTBP and TGF-beta are expressed in HSCs and myofibroblasts.

METHODS

HSCs isolated from rat liver were analyzed for LTBP and TGF-beta at various times of culture during transdifferentiation into myofibroblasts using immunocytochemical staining, metabolic labeling and immunoprecipitation, reverse-transcription polymerase chain reaction (RT-PCR), and sequencing.

RESULTS

Alkaline phosphatase-anti-alkaline phosphatase staining and fluorescence immunostainings indicated the expression of all three components of the large latent TGF-beta complex in HSCs and myofibroblasts. Transcripts of three TGF-beta and LTBP isoforms were detected by RT-PCR and confirmed by sequence analyses. A new LTBP-1 splice form was found lacking part of the hinge region with a potential proteinase cleavage site. Metabolic labeling followed by immunoprecipitation with LTBP antiserum confirmed the synthesis and secretion of various LTBP-related proteins.

CONCLUSIONS

The existence of different LTBP isoforms and splice variants in HSCs and myofibroblasts suggests multiple functions of the LTBP family in rat liver, which might not be restricted to the maintenance of TGF-beta latency.