Identification of Site-Specific Degradation in Bacterially Expressed Human Fibroblast Growth Factor 4 and Generation of an Aminoterminally Truncated,Stable Form

Fibroblast growth factor 4 (FGF4) is considered as a crucial gene for tumorigenesis in humans and the development of mammalian embryos. The secreted, mature form of human FGF4 is thought to be comprised of 175 amino acid residues (proline³² to leucine²⁰⁶, Pro³²-Leu²⁰⁶). Here, we found that bacterially expressed, 6× histidine (His)-tagged human FGF4 (Pro³²-Leu²⁰⁶) protein, referred to as HishFGF4, was unstable such as in phosphate-buffered saline. In these conditions, site-specific cleavage, including between Ser⁵⁴ and Leu⁵⁵, in HishFGF4 was identified. In order to generate stable human FGF4 derivatives, a 6× His-tagged human FGF4 (Leu⁵⁵-Leu²⁰⁶), termed HishFGF4L, was expressed in Escherichia coli. HishFGF4L could be purified from the supernatant of cell lysates by heparin column chromatography. In phosphate-buffered saline, HishFGF4L was considered as sufficiently stable. HishFGF4L exerted significant mitogenic activities in mouse embryonic fibroblast Balb/c 3T3 cells. In the presence of PD173074, an FGF receptor inhibitor, the growth-stimulating activity of HishFGF4L disappeared. Taken together, we suggest that HishFGF4L is capable of promoting cell growth via an authentic FGF signaling pathway. Our study provides a simple method for the production of a bioactive human FGF4 derivative in E. coli.