Abstract
Expression of epidermal growth factor receptor (EGF-R) antisense RNA results in a drastic reduction of EGF-R levels in the human carcinoma KB cell line and induces a reversion of their transformed phenotype (Moroni, M. C., Willingham, M. C., and Beguinot, L. (1992) J. Biol. Chem. 267, 2714-2722). We used parental and EGF-R antisense KB clones as a genetic system to study, in the same cell line, the role of transforming growth factor alpha (TGF-alpha) in the establishment and maintenance of the transformed phenotype. KB cells produce TGF-alpha mRNA, and their conditioned medium is able to sustain growth of antisense cells, mimicking the effect of exogenous EGF or TGF-alpha. In antisense cells there is a marked reduction of TGF-alpha mRNA steady-state levels. In addition, the decrease in TGF-alpha parallels the levels of residual EGF-R in the various antisense clones, indicating a direct correlation between receptors and growth factor levels. The addition of exogenous TGF-alpha (10 ng/ml) to antisense clones induces TGF-alpha levels. The half-life of TGF-alpha mRNA is 40-60 min in antisense cells and more than 8 h in parental KB cells, as determined by actinomycin D decay curves. This result indicates a predominant regulation of TGF-alpha mRNA at the post-transcriptional level. Nuclear run-on experiments show that there is only a marginal effect at the transcriptional level. We conclude that the autocrine loop responsible for the transformed phenotype of the human carcinoma KB cell line is dependent on both elevated levels of EGF-R and the presence of TGF-alpha. In addition, TGF-alpha is able to induce its own mRNA via a signal due to activation of the EGF-R acting predominantly at the post-transcriptional level.
Highlights
Receptor (EGF-R)1 together with expression of one of its physiological ligands, transforming growth factor ␣ (TGF-␣; 7)
We have demonstrated previously the primary role played by overexpression of epidermal growth factor receptor (EGF-R) in the EGF-independent growth of KB cells [1]
KB cells express TGF-␣, as shown by the presence of TGF-␣ mRNA in these cells and by the ability of KB-conditioned medium to sustain the growth of the EGF-R antisense cells and to mimic EGF-dependent growth
Summary
Receptor (EGF-R)1 together with expression of one of its physiological ligands, transforming growth factor ␣ (TGF-␣; 7). The 3-kb and a longer transcript of betacellulin mRNA are only present in antisense-expressing cells but are not detected in parental KB cells (Fig. 5B, lanes 1 and 2).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
