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Properties of tripartite chimeras between Src and Lck.
A Kashishian1, A MacAuley, J A Cooper
1Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Oncogene
|October 1, 1990
Summary
Chimeric Src-Lck kinases show in-cell regulation, with C-terminal tyrosines repressing activity. Unlike in vitro, these hybrid proteins demonstrate cellular control mechanisms crucial for protein-tyrosine kinase function.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Src-family kinases (SFKs) are critical regulators of cell signaling pathways.
- Interactions between different SFK domains can influence their kinase activity and cellular function.
- Understanding SFK regulation is key to deciphering oncogenic transformation and cellular processes.
Purpose of the Study:
- To investigate the regulatory effects of domain interactions within Src-family kinases.
- To construct and analyze chimeric molecules combining p60c-src (Src) and p56lck (Lck) domains.
- To determine how domain composition affects kinase activity, cellular transformation, and localization.
Main Methods:
- Construction of five chimeric Src-Lck hybrid proteins with varying domain combinations (N-terminal, kinase, C-terminal).
- Assay of morphological transformation and tyrosine phosphorylation in NIH3T3 cells.
- Two-dimensional peptide mapping to identify phosphorylation sites.
- Analysis of in vitro kinase activity and response to dephosphorylation.
Main Results:
- Full-length chimeras did not induce transformation, indicating appropriate repression in fibroblasts.
- Specific hybrids (SLS, SLL) induced anchorage-independent growth and showed increased phosphorylation at Tyr416.
- A truncated chimera (SLO) fully transformed cells, suggesting C-terminal tyrosines repress full-length hybrids in vivo.
- Cytoskeletal localization was linked to the N-terminal region, with Lck N-termini conferring cytoskeletal association.
- Hybrid molecules showed cellular regulation but not in vitro, with dephosphorylation affecting parental Src but not chimeras.
Conclusions:
- C-terminal phosphorylated tyrosines play a significant role in repressing the in vivo activity of full-length chimeric Src-Lck kinases.
- The N-terminal region dictates cytoskeletal localization, independent of transforming potential.
- Src-Lck chimeric molecules exhibit complex regulation within the cell, which is not recapitulated in vitro.