Abstract
The receptor tyrosine kinase c-Kit, also known as the stem cell factor receptor, plays a key role in several developmental processes. Activating mutations in c-Kit lead to alteration of these cellular processes and have been implicated in many human cancers such as gastrointestinal stromal tumors, acute myeloid leukemia, testicular seminomas and mastocytosis. Regulation of the catalytic activity of several kinases is known to be governed by phosphorylation of tyrosine residues in the activation loop of the kinase domain. However, in the case of c-Kit phosphorylation of Tyr-823 has been demonstrated to be a late event that is not required for kinase activation. However, because phosphorylation of Tyr-823 is a ligand-activated event, we sought to investigate the functional consequences of Tyr-823 phosphorylation. By using a tyrosine-to-phenylalanine mutant of tyrosine 823, we investigated the impact of Tyr-823 on c-Kit signaling. We demonstrate here that Tyr-823 is crucial for cell survival and proliferation and that mutation of Tyr-823 to phenylalanine leads to decreased sustained phosphorylation and ubiquitination of c-Kit as compared with the wild-type receptor. Furthermore, the mutated receptor was, upon ligand-stimulation, quickly internalized and degraded. Phosphorylation of the E3 ubiquitin ligase Cbl was transient, followed by a substantial reduction in phosphorylation of downstream signaling molecules such as Akt, Erk, p38, Shc, and Gab2. Thus, we propose that activation loop tyrosine 823 is crucial for activation of both the MAPK and PI3K pathways and that its disruption leads to a destabilization of the c-Kit receptor and decreased survival of cells.
Highlights
Phosphorylation of Tyr-823 in the A-loop of c-Kit is not required for kinase activity but might have other functions
The Activation Loop Y823F Mutation Accelerates Receptor Phosphorylation—The kinase domain of c-Kit is known to interact with juxtamembrane (JM) domain to maintain the kinase in an inhibitory state
What is Tyr823 doing in the activation loop? Does it have any role in downstream signaling through the c-Kit receptor?
Summary
Phosphorylation of Tyr-823 in the A-loop of c-Kit is not required for kinase activity but might have other functions. We demonstrate here that Tyr-823 is crucial for cell survival and proliferation and that mutation of Tyr-823 to phenylalanine leads to decreased sustained phosphorylation and ubiquitination of c-Kit as compared with the wild-type receptor. C-Kit belongs to the family of type III receptor tyrosine kinases and is known for its critical role in hematopoiesis, pigmentation, and reproduction It is important for survival, proliferation, and differentiation of hematopoietic progenitor cells [1, 2]. Activation of the receptor is initiated by binding of its ligand, stem cell factor (SCF), which leads to receptor dimerization and transphosphorylation on specific tyrosine residues These phosphorylated residues serve as docking sites for signal transduction molecules containing SH2 (Src homology 2) domains such as Cbl, Gab, Shc, and SHP2. This study adds a novel perspective toward understanding the role of the activation loop tyrosine in c-Kit that is related to downstream signaling rather than kinase activity
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
