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Published on: August 25, 2023
Tnk1/Kos1: a novel tumor suppressor
William Stratford May1, Kishalay Hoare, Sarasija Hoare
1University of Florida, Shands Cancer Center, P.O. Box No: 100232, Gainesville, FL 326100, USA. Stratford.May@medicine.ufl.edu
Summary
Tnk1/Kos1 acts as a tumor suppressor by inhibiting Ras activation. Loss of Tnk1/Kos1 leads to Ras overactivation and spontaneous tumor development in mice and potentially humans.
Area of Science:
- Molecular Biology
- Oncology
- Biochemistry
Background:
- Tnk1/Kos1 is a non-receptor protein tyrosine kinase.
- It negatively regulates cell growth by inhibiting Ras activation.
- Its catalytic activity is essential for this function.
Purpose of the Study:
- To investigate the role of Tnk1/Kos1 in tumor suppression.
- To elucidate the mechanism by which Tnk1/Kos1 regulates Ras activation.
- To explore the relevance of Tnk1/Kos1 downregulation in human cancers.
Main Methods:
- Homologous recombination was used to create Tnk1/Kos1 null mice (Tnk1-/-).
- Tumor development rates in aging Tnk1+/- and Tnk1-/- mice were assessed.
- Ras activation levels and Grb2 phosphorylation were analyzed in Tnk1-null tissues.
Main Results:
- Tnk1/Kos1 null mice developed spontaneous tumors (lymphomas, carcinomas) at high rates.
- Tissues from Tnk1/Kos1-null mice showed elevated basal and growth factor-stimulated Ras activation.
- Tnk1/Kos1's catalytic activity and specific tyrosine sites (Y277, Y287) are crucial for phosphorylating Grb2, disrupting the Grb2-Sos1 complex and reversing Ras activation.
- Loss of Tnk1/Kos1 leads to constitutive Ras activation via Grb2-Sos1 complex stabilization.
Conclusions:
- Tnk1/Kos1 is the first identified tyrosine kinase with tumor suppressor activity.
- Spontaneous tumorigenesis in Tnk1/Kos1-deficient models is driven by indirect, constitutive Ras activation.
- Downregulation of Tnk1/Kos1 in human diffuse large B-cell lymphoma (DLBCL) suggests its role in human tumorigenesis.
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