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AtT20 cells express modified forms of pp60c-src
K L Gould1, L M Bilezikjian, T Hunter
1Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92138.
Abstract:
We have compared the properties of pp60c-src from the mouse pituitary tumor cell line, AtT20, and from mouse fibroblasts. In vitro, pp60c-src phosphotransferase activity from AtT20 cells is 2- to 3-fold that of mouse NIH 3T3 fibroblast pp60c-src. In analyzing the reason for this elevation in specific activity, we found that pp60c-src from AtT20 cells differs structurally in at least three ways from pp60c-src in fibroblasts. First, AtT20 cells and primary rat anterior pituitary cells express low levels of the neuronal form of pp60c-src. Second, pp60c-src from AtT20 cells is phosphorylated at two additional N-terminal serine residues. Last, AtT20 pp60c-src is phosphorylated to a lower overall stoichiometry.
Insights
Mouse pituitary tumor cells (AtT20) exhibit higher pp60c-src phosphotransferase activity than fibroblasts. This difference is linked to structural variations in pp60c-src, including altered phosphorylation patterns and expression of specific forms.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- pp60c-src is a proto-oncogene tyrosine kinase involved in cell growth and differentiation.
- Variations in pp60c-src activity and structure can impact cellular functions.
- The AtT20 cell line, derived from a mouse pituitary tumor, serves as a model for studying specific cellular processes.
Purpose of the Study:
- To compare the properties of pp60c-src in AtT20 cells versus mouse fibroblasts.
- To investigate the molecular basis for differences in pp60c-src activity between these cell types.
Main Methods:
- In vitro phosphotransferase assays were used to measure enzyme activity.
- Structural analysis of pp60c-src was performed by examining phosphorylation sites and stoichiometry.
- Expression levels of different pp60c-src forms were assessed.
Main Results:
- pp60c-src from AtT20 cells displayed 2- to 3-fold higher phosphotransferase activity compared to fibroblast pp60c-src.
- AtT20 cells express lower levels of the neuronal form of pp60c-src.
- AtT20 pp60c-src is phosphorylated at two additional N-terminal serine residues and has lower overall phosphorylation stoichiometry.
Conclusions:
- Structural differences in pp60c-src, particularly in phosphorylation, contribute to its elevated activity in AtT20 cells.
- These findings highlight cell-type-specific regulation of pp60c-src activity and structure.
- Understanding these variations is crucial for comprehending the role of pp60c-src in cellular signaling and tumorigenesis.