Endogenous basic fibroblast growth factor isoforms involved in different intracellular protein complexes

Abstract

Four forms of basic fibroblast growth factor (bFGF or FGF-2) result from an alternative initiation of translation involving one AUG (155-amino acid form) and three CUGs (210-, 201- and 196-amino acid forms). These different forms of bFGF show different intracellular biological activities. To identify their intracellular targets, the 210- and 155-amino acid forms of bFGF were independently transfected into CHO cells and their correct subcellular localizations were verified, the 155-amino acid bFGF form being essentially cytoplasmic whereas the 210-amino acid protein was nuclear. The radiation fragmentation method was used to determine the target size of the different bFGF isoforms in the transfected CHO cells and to show that the 210- and 155-amino acids bFGF isoforms were included in protein complexes of 320 and 130 kDa respectively. Similar results were obtained using the SK-Hep1 cell line, which naturally expressed all forms of bFGF. Co-immunoprecipitation assays using different chimaeric bFGF–chloramphenicol acetyltransferase proteins showed that different cellular proteins are associated with different parts of the bFGF molecule. We conclude that bFGF isoforms are involved in different molecular complexes in the cytosol and nucleus, which would reflect different functions for these proteins.

Functional diversity of FGF‐2 isoforms by intracellular sorting

“…Using a radiation-fragmentation method to determine the target size of two different FGF-2 isoforms, it was found that the 24 kDa and 18 kDa isoforms were in protein complexes of 320 and 130 kDa, respectively. (75) Using the yeast two-hybrid screen and an in vitro proteinprotein interaction assay, it was found that the ribosomal protein L6/TAXREB107 is an intracellular binding partner for FGF-2. It was shown that L6/TAXREB107 has two binding sites for hmw FGF-2 and one site for the 18 kDa FGF-2 isoform, indicating that the N-terminal extension of the hmw isoforms is involved in the binding.…”

Comparison of neuregulin-1 expression in olfactory ensheathing cells, Schwann cells and astrocytes

“…This raises the possibility that NRG-1 may have a role in transcription. Other growth factors have been found to act inside the cell, for example, FGF (Patry et al, 1994(Patry et al, , 1997Kolpakova et al, 1998), IGF (Hartshorn et al, 1989;Li et al, 1997), TGF␤ (Jingush et al, 1995) and NGF (Marchisio et al, 1980). FGF has been found to directly regulate transcription Bouche et al, 1987) and it has also been suggested that different internal localization of FGF may result in different biological activities (Bugler et al, 1991;Prats et al, 1992;Vagner et al, 1995).…”

TGF-beta1 regulates TGF-beta1 and FGF-2 mRNA expression during fibroblast wound healing

“…5 22 FGF-2 is an 18 kDa protein, and three high molecular mass forms have been described (22, 22.5, and 24 kDa). [23][24][25] FGF-2 belongs to a family containing more than 20 heparin binding proteins and its activity is mediated by binding to heparan sulfate proteoglycans and to high affinity cell surface receptor tyrosine kinases. 22 The transient localisation of FGF-2 six weeks after injury in vivo and the coincident expression of heparan sulfate suggest that changes in growth factors in an avascular tissue may be used to mediate the crucial regulation of proteoglycans.…”