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Positive and negative tissue-specific signaling by a nematode epidermal growth factor receptor
1Howard Hughes Medical Institute, California Institute of Technology, Pasadena, USA.
Abstract:
The major determinants of receptor tissue tyrosine kinase (RTK) signaling specificity have been proposed to be Src homology 2 (SH2) binding sites, phosphotyrosine-containing oligopeptides in the cytoplasmic domain of the receptor. The Caenorhabditis elegans epidermal growth factor receptor homologue LET-23 has multiple functions during development and has eight potential SH2-binding sites in a region carboxyl terminal to its kinase domain. By analyzing transgenic nematodes for three distinct LET-23 functions, we show that six of eight potential sites function in vivo and that they are required for most, but not all, of LET-23 activity. A single site is necessary and sufficient to promote wild-type fertility. Three other sites activate the RAS pathway and are involved only in viability and vulval differentiation. A fifth site is promiscuous and can mediate all three LET-23 functions. An additional site mediates tissue-specific negative regulation. Putative SH2 binding sites are thus key effectors of both cell-specific and negative regulation in an intact organism. We suggest two distinct mechanisms for tissue-specific RTK-mediated signaling. A positive mechanism would promote RTK function through effectors present only in certain cell types. A negative mechanism would inhibit RTK function through tissue-specific negative regulators.
Insights
Receptor tyrosine kinase (RTK) signaling specificity is determined by Src homology 2 (SH2) binding sites. These sites regulate diverse functions, including fertility and tissue development, through distinct positive and negative regulatory mechanisms.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- Receptor tyrosine kinases (RTKs) are crucial for cell signaling.
- Signaling specificity is often determined by interactions with Src homology 2 (SH2) binding sites.
- The Caenorhabditis elegans epidermal growth factor receptor homologue LET-23 has multiple developmental roles.
Purpose of the Study:
- To investigate the in vivo function of potential SH2 binding sites in LET-23.
- To determine how these sites contribute to RTK signaling specificity.
- To elucidate mechanisms of tissue-specific RTK regulation.
Main Methods:
- Analysis of transgenic nematodes expressing altered LET-23.
- Assessing three distinct LET-23 functions in vivo.
- Site-directed mutagenesis to probe SH2 binding site function.
Main Results:
- Six of eight potential SH2 binding sites in LET-23 are functional in vivo.
- A single site is essential and sufficient for wild-type fertility.
- Three sites regulate viability and vulval differentiation via the RAS pathway.
- One site mediates negative regulation in a tissue-specific manner.
Conclusions:
- SH2 binding sites are critical effectors of both positive and negative regulation in RTK signaling within an intact organism.
- Two mechanisms for tissue-specific RTK signaling are proposed: positive regulation via cell-type specific effectors and negative regulation via tissue-specific inhibitors.
- These findings provide insights into the complex regulation of RTK signaling pathways.