Regulation of thyroidal inducibility of Na,K-ATPase and binding of epidermal growth factor in wild-type and cold-sensitive E1a mutant type 5 adenovirus-transformed CREF cells

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Abstract
We have analyzed the relationship between expression of the transformed phenotype and thyroid hormone (triiodothyronine, T3) inducibility of Na,K‐ATPase and binding of 125I‐epidermal growth factor (EGF) to cell membrane receptors in wild‐type (wt) and mutant type 5 adenovirus (Ad5)‐transformed CREF cells displaying a cold‐sensitive (cs) expression of the transformed phenotype. CREF cells respond to thyroid hormone treatment with increased Na,K‐ATPase activity and bind similar levels of 125I‐EGF at 32°C, 37°C and 39.5°C. In contrast, CREF cells transformed by wt Ad5 or the E1A plus E1b‐transforming genes of wt Ad5 are refractile to T3 treatment and bind lower levels of 125I‐EGF than CREF cells at all three temperatures. By employing a series of cloned CREF cell lines transformed by a host‐range cold‐sensitive mutant virus, H5hr1 or H5dl101, or the E1a or E1a plus E1b genes from these viruses, we have investigated expression of the transformed state and its relationship with hormone inducibility and EGF binding. When cs virus‐, cs E1a‐ or cs E1a plus E1b‐transformed CREF clones were grown at 32°C, a nonpermissive transforming temperature in which cs‐transformed cells exhibit properties similar to untransformed CREF cells, T3 induced Na,K‐ATPase activity and these cells bound similar levels of 125I‐EGF as CREF cells. However, when cs virus‐and cs Ela plus Elb‐transformed CREF clones were incubated at 37°C or 39.5°C, temperatures at which cs‐transformed cells exhibit properties similar to wt Ad5‐transformed CREF cells, they did not respond to T3 and bound lower levels of 125I‐EGF than CREF cells. In the case of cs E1a‐transformed CREF clones, thyroid hormone responsiveness was observed at both 32°C and 37°C, but not at 39.5°C. By performing temperature shift experiments‐i.e. 32°C to 37°C, 32°C to 39.5°C, 37°C to 32°C, and 39.5°C to 32°C, it was demonstrated that after a shift from lower to higher temperature a 24‐hr lag period was required for cs‐transformed CREF cells to lose T3 inducibility and exhibit reduced EGF binding, whereas 96 hr after a shift from higher to lower temperature a 96‐hr lag period was required for cs‐transformed cells to regain T3 inducibility and increased 125I‐EGF binding. Flow cytometric analysis indicated that the ability of T3 to induce Na,K‐ATPase in CREF cells was not a consequence of alterations in cell‐cycle distribution. These results indicate that the loss of thyroid hormone inducibility of Na,K‐ATPase and a decreased binding of 125I‐EGF are properties which correlate with expression of the transformed phenotype in Ad5‐transformed CREF cells.