MODULATION OF INTERLEUKIN-6-INDUCED PLASMA-PROTEIN SECRETION IN HEPATOMA-CELLS BY P53 SPECIES

The ability of p53 species (wild-type and mutant) to modulate the ''di fferentiated'' response of human hepatoma cell lines Hep3B and HepG2 t o interleukin-6 (IL-6) was investigated. Transient transfection experi ments were carried out in Hep3B and HepG2 cell cultures in which IL-6 was used to activate a beta-fibrinogen (beta Fib) enhancer/reporter co nstruct containing two copies of the 36-base pair IL-6-response elemen t (IL-6RE) (p beta FibCAT). Cotransfection with constitutive expressio n vectors for wild-type (wt) human or murine p53 inhibited the activat ion of the p beta FibCAT reporter by IL-6 in both Hep3B and HepG2 cell s. Several mutant p53 species either did not inhibit the activation of p beta FibCAT or up-regulated the response. Hepatoma cell lines stabl y expressing the Val-135 temperature-sensitive mutant of murine p53 (w t-like at 32.5 degrees C and mutant-like at 37 degrees C) were derived from Hep3B cells and tested for the temperature-sensitive phenotype o f their ability to synthesize and secrete fibrinogen and alpha(1)-anti chymotrypsin in response to IL-6. In an experimental protocol in which the parental Hep3B cells did not show a significant difference in pla sma protein secretion at the two temperatures, hepatoma line 3 (p53Val -135(+)) had a greater response to IL-6 at 37 degrees C than parental Hep3B cells, while line 3 cells had a reduced response to IL-6 at 32.5 degrees C. Similarly, hepatoma lines 1 and 2 (both p53Val-135(+)) had reduced IL-6 responsiveness at 32.5 degrees C, whereas line 22 (trans fected with pSVneo alone) and the parental Hep3B cells did not. These data indicate that mutations in p53 contained in tumor cells can modul ate the ''differentiated'' response of these cells to cytokines.