Polyomavirus middle T selective action on cytokeratin 14 gene expression in liver nonparenchymal epithelial cells

We reported recently that liver nonparenchymal epithelial cells (LECs) constitute a small population of cells scattered throughout biliary structures and the Glisson's capsule, containing the unusual cytokeratin (CK) pair CK8/CK14 (Blouin et al., Differentiation, 1992, 52, 45). The transfection of polyomavirus middle T oncogene (MT) into the LEC line T51B leads to the loss of their CKs, due to a down-regulation of CK14 gene expression (Royal et al., Cell Growth Differ., 1992, 3, 589). In the present work, we examined CK gene expression at both mRNA and protein levels following polyomavirus small T oncogene (ST), MT, or large T oncogene (LT) transfection of T51B cells, MT transfection of rat hepatic cell lines containing different subsets of CKs, and MT transfection of rat keratinocytes. Immunofluorescence staining revealed that MT indeed induced an inhibition of CK14 gene expression and a loss of CK8/CK14 intermediate filaments (IFs) in liver cells, whereas ST and LT had no effect. Moreover, CK14 was the only CK gene whose expression was inhibited in MT-containing hepatic cells, in the sense that the expression of the CK7, CK8, CK18, and CK19 genes was not affected. Two-dimensional SDS-PAGE of the Triton-resistant cytoskeletal proteins and Northern blotting of the CK mRNA content confirmed these findings. The transfer of the MT oncogene into the keratinocytes did not result in the loss of CK5/CK14 IFs nor the inhibition of CK14 gene expression. These results show that the polyomavirus oncogene action on CK gene expression is restricted to an MT effect on CK14 in rat LECs.