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'Srcasm: a novel Src activating and signaling molecule
John T Seykora1, Lijuan Mei, G Paolo Dotto
1Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Abstract:
The Src family tyrosine kinase, Fyn, can facilitate regulation of cell proliferation and differentiation. Mice with mutations in the fyn gene have defects in the brain, immune system, and epidermal differentiation. To identify molecules that may interact with Fyn in the epidermis, we performed a yeast two-hybrid interaction screen of a murine keratinocyte library. A novel adaptor-like molecule was isolated and termed Srcasm for Src activating and signaling molecule. Murine Srcasm is a 52.7-kDa protein that contains a VHS membrane association domain and a number of tyrosine motifs suggesting that it may be a substrate for Src family kinases and serve as an adaptor protein. Northern blot analysis of murine tissues demonstrates that Srcasm expression is highest in brain and kidney. In situ hybridization analysis reveals that srcasm mRNA is expressed in regions of the epidermis and hair follicle where keratinocyte differentiation occurs. In the brain, srcasm mRNA distribution correlates with that of fyn, with both being highly expressed in the hippocampal and cerebellar Purkinje neurons. Fyn can phosphorylate Srcasm, and association of these molecules relies on cooperative binding between the SH2 and SH3 domains of Fyn and corresponding canonical binding sites in Srcasm. Srcasm is capable of interacting with Grb2 and the regulatory subunit of phosphoinositide 3-kinase, p85, in a phosphorylation-dependent manner. The evidence suggests that Srcasm may help promote Src family kinase signaling in cells.
Insights
Researchers identified a novel protein, Srcasm (Src activating and signaling molecule), which interacts with Fyn kinase. This discovery sheds light on cell signaling pathways involved in differentiation and proliferation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The Src family tyrosine kinase, Fyn, plays a crucial role in regulating cell proliferation and differentiation.
- Fyn kinase is essential for normal development of the brain, immune system, and epidermis.
- Understanding Fyn's interactions is key to deciphering its role in cellular processes.
Purpose of the Study:
- To identify novel molecules that interact with Fyn kinase in the epidermis.
- To characterize the function and interactions of a newly discovered adaptor protein.
Main Methods:
- Yeast two-hybrid interaction screen using a murine keratinocyte library.
- Northern blot analysis to determine Srcasm expression levels in murine tissues.
- In situ hybridization to localize srcasm mRNA expression.
- Biochemical assays to investigate Fyn-Srcasm phosphorylation and binding interactions.
Main Results:
- A novel adaptor-like molecule, Srcasm (Src activating and signaling molecule), was identified.
- Srcasm protein contains domains suggesting it acts as a substrate and adaptor for Src family kinases.
- Srcasm expression is highest in brain and kidney, with specific localization in differentiating epidermal and hair follicle cells.
- Srcasm mRNA distribution in the brain correlates with Fyn expression, particularly in neurons.
- Fyn phosphorylates Srcasm, and their association involves Fyn's SH2 and SH3 domains binding to Srcasm.
- Srcasm interacts with Grb2 and p85 (regulatory subunit of phosphoinositide 3-kinase) in a phosphorylation-dependent manner.
Conclusions:
- Srcasm is a novel Fyn-interacting protein that may function as a key signaling adaptor.
- Srcasm's interactions suggest a role in promoting Src family kinase signaling pathways.
- This finding provides new insights into the molecular mechanisms regulating cell differentiation and proliferation.