pp60 c-Src Kinase Mediates Growth Effects of the Full-Length Precursor Progastrin 1–80 Peptide on Rat Intestinal Epithelial Cells, in Vitro

Growth factor effects of precursor forms of gastrins have be- come evident in recent years. However, intracellular path-ways that mediate growth effects of the precursor molecules are not known. In previous studies, we reported an increase in Tyr phosphorylation of pp60 c-Src in intestinal epithelial cells (IEC) in response to the fully processed form of gastrin [gastrin 1–17 (G17)]. We have now examined whether c-Src ki- nase is similarly phosphorylated and activated in response to the full-length precursor molecule, progastrin (PG) 1–80, (re- combinant human PG) in IEC cells. We found a significant increase in pp60 c-Src kinase activity in response to both G17 and PG (0.1–1.0 n M ), suggesting that growth effects of both the precursor and fully processed gastrin molecules may be me- diated via similar pathways. On the other hand, pp62 c-Yes was not phosphorylated or activated in response to either G17 or PG. To examine whether c-Src kinase mediates proliferative effects of PG, IEC cells were microinjected with anti-Src-IgG and 3 H-thymidine ( 3 H-Tdr) uptake of the cells measured. Con- trol cells received nonimmune IgG. The 3 H-Tdr uptake of cells stimulated with 1.0 n M PG was significantly reduced in cells microinjected with anti-c-Src-IgG; control IgG had no effect. In cells stimulated with 1.0% fetal calf serum, microinjection with c-Src-IgG had no effect on 3 H-Tdr uptake. The specificity of the effect was further confirmed by blocking the inhibitory effect of anti-c-Src-IgG with antigenic Src peptide. These results suggest that activation of c-Src kinase likely represents a critical step in mediating proliferative effects of both the precursor and fully processed forms of gastrins on IEC. ( En- docrinology 144: 201–211, 2003) c-Src