Groups of cell growth factors belonging to the heparin-binding growth factor (HBGF) family show homology with one another on amino acid sequences and are commonly characterized by strong heparin-binding activity. The cell growth factors belonging to this family include acidic and basic fibroblast growth factors (aFGF and bFGF), hst-1, INT2, FGF5 and keratinocyte growth factor (KGF). Of these cell growth factors, there is a report that FGF has activity on various cells and particularly has growth promoting activity and differentiation promoting activity on mesodermal cells [Gospodarowicz et al., J. Cell. Physiol., supplt., 5, 15 (1987)]. FGF has also been investigated for application to drugs for promoting wound healing, or repair of the cardiac muscle or the nervous tissue after ischemia.
An hst-1 gene is a transforming gene identified by a focus forming method, and a product thereof has cell growth promoting activity and angiogenesis inducing activity in vivo (Japanese Unexamined Patent Publication No. 3-218398: European Patent Publication No.421455) as well as FGF. An hst-2 gene was identified as a gene having high homology with the hst-1 gene by a DNA blot hybridization method [Sakamoto et al., Biochem. Biophys. Res. Commun., 151, 965 (1988)]. The same gene was also reported as an FGF6 gene [Marios I. et al., Oncogene, 4, 335(1989) and Coulier F. et al., Oncogene 6(4), 1433(1991)]. They also report that the FGF6 gene codes three in frame ATG codons which are able to initiate the translation of three peptides of 175, 198 and 208 residues. Further, hst-2 was considered by the present inventors to actually have biological activity and to be a novel growth factor belonging to the HST family, because hst-2 gene-introduced fibroblasts formed tumors on nude mice [Naito et al., Jpn. J. Cancer Res. Abstr., 500 (1989)]. Products of the hst-2 genes have therefore also been expected to be applicable to drugs as promoters for wound healing, or repair of the cardiac muscle after cardiac ischemia and the nervous tissue after brain ischemia.
In order to promote the investigation of the hst-2 protein, it is necessary to obtain the protein in large amounts and in high purity. In Oncogene, 5, 823 (1990), de Lapeyriere et al. reported that the protein having growth promoting activity on the animal cells was possibly localized in the muscles or the testes. The leukemia cell line HEL [Martin and Papayannoponlou, Science, 216, 1223 (1982)] or CMK [Sato et al., British Journal of Hematology, 72, 184 (1989)] which possibly produces the peptide has been reported. The isolation and purification of the protein from such sources are complicated and the desired protein has heretofore been obtained only in small amounts. Accordingly, a method for obtaining the hst-2 protein in large amounts and in high purity has been earnestly desired.
For the hst-2 gene, the nucleotide sequence thereof has recently been reported [S. Iida et al., Oncogene, 7, 303 (1992) and European Patent Publication No. 421455], and these reports also provide constituent amino acids deduced therefrom. However, a method for producing hst-2 by the use of recombinant technology has not been reported.
Although some of the properties and biological activity of hst-2 remain to be studied, as described above, the application of hst-2 to drugs and reagents has generally been expected. However, it has hitherto been impossible to obtain sufficient amounts of hst-2 as described above, which has hindered investigation and development.