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Phosphorylation of the glycoprotein hormone alpha-subunit secreted by human tumor cell lines
Abstract:
The synthesis of ectopic proteins by tumors is thought to result from derepression of normally silent genes. One approach to a better understanding of this phenomenon is to characterize the physicochemical properties of the ectopic products, comparing them to their normal counterparts. In the following communication, evidence will be presented to indicate that the glycoprotein hormone alpha-subunits secreted by a number of human tumor cell lines are phosphorylated. This novel covalent modification occurs in cell lines derived from both trophoblastic (JAR, JEG) and nontrophoblastic (HeLa, ChaGo) tumors. A choriocarcinoma cell line (JAR), which secretes both hCG-alpha and hCG-beta, phosphorylates only the alpha-subunit.
Insights
Tumors can produce ectopic proteins from silent genes. This study found that human tumor cells phosphorylate glycoprotein hormone alpha-subunits, a novel modification in both trophoblastic and nontrophoblastic cancers.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Tumors synthesize ectopic proteins via derepression of silent genes.
- Understanding these ectopic products requires characterizing their physicochemical properties.
- Comparing ectopic proteins to normal counterparts aids in understanding tumor biology.
Purpose of the Study:
- To investigate the post-translational modifications of ectopic glycoprotein hormone alpha-subunits in human tumor cell lines.
- To determine if phosphorylation is a common modification of these ectopic alpha-subunits.
- To compare modification patterns between trophoblastic and nontrophoblastic tumor-derived cell lines.
Main Methods:
- Culturing human tumor cell lines (JAR, JEG, HeLa, ChaGo).
- Analyzing secreted glycoprotein hormone alpha-subunits for phosphorylation.
- Utilizing biochemical assays to detect covalent modifications.
Main Results:
- Glycoprotein hormone alpha-subunits secreted by multiple human tumor cell lines are phosphorylated.
- This phosphorylation occurs in cell lines from both trophoblastic (JAR, JEG) and nontrophoblastic (HeLa, ChaGo) tumors.
- A choriocarcinoma cell line (JAR) phosphorylates its secreted hCG-alpha subunit but not hCG-beta.
Conclusions:
- Phosphorylation represents a novel covalent modification of ectopic glycoprotein hormone alpha-subunits in human cancers.
- This modification is not restricted to trophoblastic tumors, indicating a broader phenomenon in oncogenesis.
- The selective phosphorylation of the alpha-subunit in choriocarcinoma cells suggests specific regulatory mechanisms.