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Identification of casein kinase I substrates by in vitro expression cloning screening
Z H Gao1, J Metherall, D M Virshup
1Department of Oncological Sciences, University of Utah, Salt Lake City, Utah 84132, USA.
Abstract:
Casein kinase I (CKI) is a widely expressed protein kinase family implicated in diverse processes including membrane trafficking, DNA repair, and circadian rhythm. Despite the large number of CKI genes, few biologically relevant substrates have been identified. As an approach to better defining the spectrum of CKI substrates, we extended a recently described in vitro expression cloning (IVEC) strategy. Polypeptides pools were screened for kinase-dependent electrophoretic mobility shifts. Ten putative CKI substrates were isolated from an initial sample of 3000 random cDNA clones. Candidate substrates include proteins involved in RNA metabolism (a putative RNA helicase, the nucleolar protein hNOP56, and hnRNP A1, and ribosomal proteins L4, L8, and L13), as well as keratin 17, a necdin-related protein, and the calcium-binding proteins desmoglein 2 and annexin II. The same pools were also screened with active ERK2, and four substrates identified: aldolase, NSD-like protein, uracil-DNA glycosylase, and HHR23A. IVEC is an effective method to identify novel protein kinase substrates.
Insights
This study identifies novel protein substrates for Casein Kinase I (CKI) using an in vitro expression cloning method. This approach effectively reveals new CKI substrates involved in various cellular functions.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Casein kinase I (CKI) is a crucial protein kinase family involved in fundamental cellular processes.
- Identifying specific CKI substrates is essential for understanding its diverse biological roles.
- Current knowledge of CKI substrates is limited despite the large number of CKI genes.
Purpose of the Study:
- To expand the repertoire of identified CKI substrates.
- To validate and refine the in vitro expression cloning (IVEC) strategy for substrate discovery.
- To uncover novel proteins regulated by CKI.
Main Methods:
- Utilized an in vitro expression cloning (IVEC) strategy to screen polypeptide pools.
- Employed kinase-dependent electrophoretic mobility shifts to detect potential substrates.
- Screened against both Casein Kinase I (CKI) and Extracellular signal-regulated kinase 2 (ERK2).
Main Results:
- Identified ten putative CKI substrates, including RNA metabolism proteins (RNA helicase, hNOP56, hnRNP A1, ribosomal proteins L4, L8, L13), keratin 17, necdin-related protein, desmoglein 2, and annexin II.
- Discovered four ERK2 substrates: aldolase, NSD-like protein, uracil-DNA glycosylase, and HHR23A.
- Demonstrated the efficacy of the IVEC method in identifying novel protein kinase substrates.
Conclusions:
- The in vitro expression cloning (IVEC) method is a powerful tool for discovering novel protein kinase substrates.
- This study significantly expands the known substrates for Casein Kinase I (CKI).
- The identified substrates highlight CKI's involvement in a broad range of cellular processes, including RNA metabolism and cell structure.