Mechanisms through which Rat Mammary Gland Carcinogenesis is Preferentially Initiated by H-Ras over K-Ras Signaling Pathways

Abstract

Abstract : This research distinguishes mechanisms through which activated Ras induces rat mammary gland carcinogenesis. Experiments expressing H-Ras and K-Ras chimeric proteins in mammary gland (Aim 1A) investigate hypothesis one: greater frequency of H-Ras carcinogenesis than K-Ras carcinogenesis in rat mammary gland results from differences in the last 20 amino acids of H-Ras and K-Ras. K-Ras with an H-Ras c-terminus is as tumorgenic as H-Ras, supporting hypothesis one: however, H-Ras with a K-Ras c-terminus is also as tumorgenic as H-Ras, suggesting a unique characteristic of intact K-Ras limits mammary carcinogenesis. Expression of Raf-Caax (Aim 1B), does not induce tumors, suggesting hypothesis two: individual Ras effectors won't initiate rat mammary carcinogenesis, rather multiple effectors must act synergistically. However, each Ras effector loop mutant (G37-Ras activates RalGDS, E38-Ras activates Raf, and C40-Ras activates PI3K) (Aim 2A), individually induces mammary carcinomas. Carcinoma induction from n-terminus truncated Raf (DELTA-Raf) confirms Raf activation alone will induce carcinomas, eliminating hypothesis two. To investigate the apparent inconsistency that E38-Ras and DELTA-Raf cause tumors but Raf-Caax does not, these Raf mutations were combined (DELTA-Raf-Caax). Since DELTA-Raf-Caax constructs also fail to induce mammary carcinomas, we conclude that c-terminal lipid modification of Raf is not oncogenic in rat mammary gland.