Simultaneous production of IGF‐I and EGF competing growth factors by HT‐29 human colon cancer line

The conditioned medium from the HT‐29 human colonic adenocarcinoma cell line contains a potent mitogenic activity that can markedly stimulate the proliferation of both rat and human fibroblasts in the absence of serum. Fractionation of conditioned medium on Bio‐Gel P‐100 shows that HT‐29 cells simultaneously produce 2 different types of endogenous growth factors. The first one (molecular mass of 35,8 and 5.5 kDa) exhibits an IGF‐I competing activity which is positively correlated to mitogenic activity. This mitogen is recognized by anti‐IGF‐1 antibodies but Is resistant to reducing agents. It is distinct from IGF‐II, insulin and PDGF. The second one (molecular mass of 40‐and 20‐kDa) is able to displace EGF binding to its receptor. This factor is immunologically recognized by anti‐EGF antibodies but with a lower affinity as compared to EGF. This suggests that this endogenous HT‐29‐growth factor is related to but distinct from native EGF. Although more active in radioreceptor assay than in radioimmunoassay, the EGF‐competing factor is distinct from TGF α or β since it is unable to induce anchorage‐independent growth of NRK or FR3T3 target cells in the presence or absence of exogenous EGF. Moreover, free functional EGF receptors are available at the HT‐29 cell surface.