Genetic dissection of dome formation in a mammary cell line: Identification of two genes with opposing action

In this work, we extend the study of the genes controlling the formation of domes in the rat mammary cell line LA7 under the influence of DMSO. The ro le of the rat8 gene has already been demonstrated. We have now studied two additional genes. The first, called 133, is the rat ortholog of the human e pithelial membrane protein 3 (EMP3), a member of the peripheral myelin prot ein 22 (PMP22)/EMP/lens-specific membrane protein 20 (MP20) gene family tha t encodes for tetratransmembrane proteins; it is expressed in the LA7 line in the absence of DMSO hut not in its presence. The second gene is the beta subunit of the amiloride-sensitive Na+ channel. Studies with antisense oli gonucleotides show that the formation of domes is under the control of all three genes: the expression of rat8 is required for both their formation an d their persistence; the expression of the Na+ channel beta subunit is requ ired for their formation; and the expression of gene 133 blocks the express ion of the Naf channel genes, thus preventing formation of the domes. The f ormation of these structures is also accompanied by the expression of alpha (6)beta(1) integrin, followed by that of E-cadherin and cytokeratin 8. It a ppears, therefore, that dome formation requires the activity of the Na+ cha nnel and the rat8-encoded protein and is under the negative control of gene 133. DMSO induces dome formation by blocking this control.