Proteomic dissection of dome formation in a mammary cell line: Role of tropomyosin-5b and maspin

In this work we extended the study of genes controlling the formation of sp ecific differentiation structures called "domes" formed by the rat mammary adenocarcinoma cell line LA7 under the influence of DMSO. We have reported previously that an interferon-inducible gene, rat-8, and the beta -subunit of the epithelial sodium channel (ENaC) play a fundamental role in this pro cess. Now, we used a proteomic approach to identify proteins differentially expressed either in DMSO-induced LA7 or in 106A10 cells. Two differentiall y expressed proteins were investigated. The first, tropomyosin-56, strongly expressed in DMSO-induced LA7 cells, is needed for dome formation because its synthesis inhibition by the antisense RNA technology abolished domes. T he second protein, maspin, strongly expressed in the uninduced 106A10 cell line, inhibits dome formation because 106A10 cells, transfected with rat8 c DNA (the function of which is required for the organization of these struct ures), acquired the ability to develop domes when cultured in presence of a n antimaspin antibody. Dome formation in these cultures are accompanied by ENaC beta -subunit expression in the absence of DMSO. Therefore, dome forma tion requires the expression of tropomyosin-5b, in addition to the ENaC bet a -subunit and the rat8 proteins, and is under the negative control of masp in.