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Induction of the human ARF protein by serum starvation
1Microbiology and Tumor Biology Center, Karolinska Institute, Stockholm, Sweden.
Abstract:
The ARF protein encoded by the alternative transcript of the INK4a gene inhibits cell growth by stabilization of p53. ARF is induced by activated oncogenes sucll as c-myc, E1A and E2F-1. We show here that ARF protein expression is also induced by serum deprivation in the human tumor cell line MDA-MB-157 and in the SV40 large T-immortalized keratinocyte line Rhek. This increase of expression was reversed by the addition of serum. ARF mRNA levels also increased after serum starvation, suggesting that ARF upregulation is mediated, at least in part, by increased transcription and/or mRNA stability. These results indicate that ARF responds not only to oncogenic hyper-proliferative signals but also to suboptimal growth conditions.
Insights
The ARF protein (Alternative Reading Frame) is induced by serum deprivation in cancer and immortalized cells. This suggests ARF responds to suboptimal growth conditions, not just oncogenic signals.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- The ARF protein, encoded by the INK4a gene, is known to inhibit cell growth via p53 stabilization.
- ARF expression is typically induced by oncogenic signals like c-myc, E1A, and E2F-1.
Purpose of the Study:
- To investigate whether ARF protein expression is induced by conditions other than oncogenic stress.
- To explore the response of ARF to suboptimal growth conditions, specifically serum deprivation.
Main Methods:
- Utilized human tumor cell line MDA-MB-157 and SV40 large T-immortalized keratinocyte line Rhek.
- Monitored ARF protein and mRNA levels following serum deprivation and re-addition.
- Analyzed changes in gene expression in response to altered growth conditions.
Main Results:
- ARF protein expression was significantly induced by serum deprivation in both cell lines studied.
- The observed increase in ARF expression was reversible upon the addition of serum.
- ARF mRNA levels also increased during serum starvation, indicating transcriptional regulation or enhanced mRNA stability.
Conclusions:
- ARF protein is responsive to suboptimal growth conditions, such as serum deprivation, in addition to oncogenic signals.
- These findings expand the known regulatory network of ARF, highlighting its role in cellular stress responses.
- ARF may play a broader role in cell cycle control beyond response to oncogene activation.