Murine c-erbB2: an oncogene that could be a target for vaccination therapy? : and the effect of HER2/c-erbB2/NeuT expression on cell signaling and milk protein formation in mouse mammary epithelial cells

摘要

ErbB2 is an orphan receptor tyrosine kinase which can dimerize with other ligand-activatedudmembers of the EGF receptor family to signal in pathways inducing cell proliferation.udFrequently overexpressed in breast cancer and other human cancers, homologs of ErbB2 areudoncogenes in different animal species which have been studied for their contribution to theuddevelopment of carcinomas.udThe first part of this project was aimed at developing a method for vaccination ofudmouse, so that a transplanted tumor expressing the endogenous mouse c-erbB2 would beudrejected. Initially, it was necessary to prepare a functional expression clone of mouse cerbB2.udThen the question of how to break the natural tolerance against an immune responseudagainst the self-antigen, mouse c-erbB2, had to be approached. Several protocols wereudattempted as described below, but I was unsuccessful in obtaining the intended protectiveudeffect against transplanted tumor.udIn the second part of this work, we have examined phenotypes induced by severaludErbB2 homologs in Line 31E mouse mammary epithelial cells which are capable ofuddifferentiation in vitro to undergo dome formation and to produce milk protein in response toudlactogenic hormones. Included in this comparative study are the functional clone of the mouseudproto-oncogene c-erbB2, a human homolog overexpressed in breast cancer, HER2, and theudmutated rat homolog, NeuT, which is known to be oncogenic.udLine 31E mammary epithelial cells were infected with retroviral pBabepuro constructsudof the different ErbB2 homologs. Typical features of epithelial intercellular organization,udsuch as density of tight junctions and dome formation, were disturbed by ErbB2 expression.udWhile a dominant negative mutant of HER2 had no effect on the epithelial cells, bothudtransepithelial monolayer resistance and dome formation were reduced by all three of theudfunctional ErbB2 homologs, most dramatically by NeuT. While expression of both the mouseudproto-oncogene c-erbB2 and HER2 resulted in significant inhibition of β-casein mRNA andudprotein levels after lactogenic hormone treatment, NeuT completely abrogated β-caseinudproduction and caused oncogenic transformation as evidenced by large colonies in soft agarudand Matrigel suspension culture. While the cells expressing the homologs remain acutelyudresponsive to EGF ligand in terms of Akt/PKB, ERK 1/2 and PKCα phosphorylation, anudelevated basal phosphorylation in the absence of ligand was not apparent for PKCα.