A role for the perlecan protein core in the activation of the keratinocytegrowth factor receptor

Perlecan, a widespread heparan sulphate (HS) proteoglycan, is directly invo lved in the storing of angiogenic growth factors, mostly members of the fib roblast growth factor (FGF) gene family. We have previously shown that anti sense targeting of the perlecan gene causes a reduced growth and responsive ness to FGF7 [also known as keratinocyte growth factor (KGF)] in human canc er cells, and that the perlecan protein core interacts specifically with FG F7. In the present paper, we have investigated human colon carcinoma cells in which the perlecan gene was disrupted by targeted homologous recombinati on. After screening over 1000 clones, we obtained two clones heterozygous f or the null mutation with no detectable perlecan. indicating that the other allele was non-functioning. The perlecan-deficient cells grew more slowly, did not respond to FGF7 with or without the addition of heparin, and were less tumorigenic than control cells. Paradoxically, the perlecan-deficient cells displayed increased FGF7 surface binding. However, the perlecan prote in core was required for functional activation of the KGF receptor and down stream signalling. Because heparin could not substitute for perlecan. the H S chains are not critical for FGF7-mediated signalling in this cell system. These results provide the first genetic evidence that the perlecan protein core is a molecular entity implicated in FGF7 binding and activation of it s receptor.