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

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Abstract
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.