PROCESSING OF TRANSFORMING GROWTH-FACTOR-BETA-1 PRECURSOR BY HUMAN FURIN CONVERTASE

Proteolytic processing of the transforming growth factor beta precurso r (pro-TGF beta) is an essential step in the formation of the biologic ally active TGF beta homodimeric protein (TGF beta). The 361-amino-aci d precursor pro-TGF beta 1 has within its primary structure the R-H-R- R processing signal found in many constitutively secreted precursor pr oteins and potentially recognized by members of the mammalian converta se family of endoproteases. To determine whether cleavage of pro-TGF b eta 1 can be achieved by the furin convertase in vitro, purified precu rsor was incubated in the presence of a truncated/secreted form of the enzyme. Immunoblots showed that the 55-kDa pro-TGF beta 1 was convert ed into the 44 and 12.5 kDa bands corresponding to the proregion and t he mature monomer, respectively. Treatment of pro-TGF beta 1 with furi n resulted in a 5-fold increase in the production of biologically acti ve TGF beta 1. Furthermore, when expressed in the furin-deficient LoVo cells, no processing of pro-TGF beta 1 was observed. In contrast, eff icient processing was oberved when pro-TGF beta 1 was coexpressed with the furin convertase. Collectively, these results provide evidence th at in our experimental systems the TGF beta 1 precursor is efficiently and correctly processed by human furin thus permitting release of the biologically active peptide.