GAST and colonic neoplasm: For instance, constitutive activation of the Ras-Erk pathway, such as that observed in K-ras-mutated colon cancers, induces phosphorylation of Sp1 and enhances its binding affinity to the human gastrin promoter.107 Interaction of Sp1 with AP-1 transcription factor family members at the proximal gastrin promoter has also been reported.