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The activation loop in Lck regulates oncogenic potential by inhibiting basal kinase activity and restricting
L E Laham1, N Mukhopadhyay, T M Roberts
1Department of Cancer Biology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, Massachusetts, MA 02115, USA.
Abstract:
The activities of Src-family non-receptor tyrosine kinases are regulated by structural changes that alter the orientation of key residues within the catalytic domain. In this study, we investigate the effects of activation loop mutations on regulation of the lymphocyte-specific kinase Lck (p56lck). Substitution of 5 - 7 residues amino terminal to the conserved activation loop tyrosine (Y394) increases kinase activity and oncogenic potential regardless of regulatory C-terminal tail phosphorylation levels (Y505), while most mutations in the 13 residues carboxyl to Y394 decrease kinase activity. Phosphorylation of the C-terminal regulatory tail is carried out by the cytosolic tyrosine kinase Csk and we find that mutations upstream or downstream of Y394 or mutation of Y394 do not affect the level of Y505 phosphorylation. In addition, we report that mutations on either side of Y394 affect substrate specificity in vivo. We conclude that the high degree of conservation across the entire activation loop of Src-family kinases is critical for normal regulation of kinase activity and oncogenicity as well as substrate selection. Oncogene (2000) 19, 3961 - 3961.
Insights
Activation loop mutations in lymphocyte-specific kinase (Lck) impact its activity and oncogenic potential. Residues N-terminal to Y394 enhance kinase activity, while mutations elsewhere decrease it, affecting substrate specificity.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- Src-family kinases, including lymphocyte-specific kinase (Lck), are crucial non-receptor tyrosine kinases.
- Their activity is tightly regulated by structural rearrangements within the catalytic domain, particularly involving the activation loop.
Purpose of the Study:
- To investigate the impact of activation loop mutations on the regulation of Lck kinase activity.
- To determine how these mutations affect Lck's oncogenic potential and substrate specificity.
Main Methods:
- Site-directed mutagenesis of the Lck activation loop.
- Assays to measure kinase activity and C-terminal tail phosphorylation (Y505).
- In vivo analysis of substrate specificity.
Main Results:
- Mutations N-terminal to the activation loop tyrosine (Y394) increased Lck activity and oncogenic potential.
- Mutations within the activation loop generally decreased kinase activity.
- Mutations did not affect C-terminal phosphorylation (Y505) by Csk.
- Mutations flanking Y394 altered Lck substrate specificity in vivo.
Conclusions:
- The conserved activation loop of Src-family kinases is critical for regulating kinase activity and oncogenicity.
- Activation loop integrity is essential for proper substrate selection by Lck.