MAMMALIAN-CELLS TRANSFECTED WITH THE LISTERIOLYSIN GENE EXHIBIT ENHANCED PROLIFERATION AND FOCUS FORMATION

Mouse 3T6 and 3T3 fibroblasts and rat epithelial L2 cells were transfe cted with recombinant plasmids containing the listeriolysin gene (hly) of Listeria monocytogenes. This bacterial gene (,vith and without the 5' signal sequence) was cloned under the control of a murine metallot hionein promoter, resulting in elevated transcription of both forms of the hly gene after induction with ZnSO4. However, the gene product co uld be observed only when the listeriolysin gene lacking the 5' signal sequence was used. Intact listeriolysin could not be detected in the cytoplasm or in the supernatant of the hly-transfected cells. 3T6 and L2 cells transfected with the intact hly gene exhibited significantly increased cell proliferation and increased formation of actin microfil aments upon induction of hly expression with ZnSO4. Both cell types ar e not contact inhibited and formed large piles of spherical cells afte r transfection with hly. In contrast, contact-inhibited 3T3 cells tran sfected with the hly gene showed increased proliferation but no format ion of such cell aggregates. When 3T6 fibroblasts were transfected wit h the hly gene without the 5' signal sequence, inhibition of growth, l ack of cell layer confluency, and altered (spherical) cell morphology were observed.