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The murine PKR tumor suppressor gene is rearranged in a lymphocytic leukemia
N Abraham1, M L Jaramillo, P I Duncan
1Ottawa Regional Cancer Center Research Laborotories, 501 Smyth Road, Ottawa, Ontario, K1H 8L6, Canada.
Abstract:
The double-stranded RNA-dependent kinase, PKR, is encoded by an interferon inducible gene and is largely responsible for the anti-viral effects of this cytokine. Recent studies have shown that PKR may also play a role in the regulation of normal cellular growth. Although numerous examples of viral strategies for inactivation of PKR exist, there is no evidence of PKR inactivation in tumors. We demonstrate here that the Tik gene, which encodes a dual-specificity kinase, is the murine homolog of PKR, the dsRNA-dependent kinase, and has undergone a rearrangement of one allele in a murine lymphocytic leukemia cell. We have cloned a cDNA that corresponds to a mutated transcript from the rearranged mPKR gene and show that while the mutated polypeptide retains its ability to dimerize and bind dsRNA, it is catalytically inactive. Although this mutated mPKR lacks apparent dominant-negative function, the net effect of reduced PKR activity in these cells may be significant.
Insights
The double-stranded RNA-dependent kinase (PKR) plays a role in cellular growth. A mutated, inactive form of PKR was identified in a murine leukemia cell line, suggesting reduced PKR activity in tumors.
Area of Science:
- Molecular biology
- Virology
- Cancer research
Background:
- The double-stranded RNA-dependent kinase (PKR) is an interferon-inducible enzyme crucial for antiviral defense.
- PKR is also implicated in regulating normal cellular growth.
- While viral inactivation of PKR is known, its inactivation in tumors remains uncharacterized.
Purpose of the Study:
- To investigate the role of PKR in cellular growth regulation and tumor development.
- To identify potential mechanisms of PKR inactivation in cancer.
- To characterize the murine homolog of PKR and its potential mutations in leukemia.
Main Methods:
- Gene cloning and sequencing
- Analysis of mutated PKR transcripts
- Biochemical assays to assess kinase activity and dsRNA binding
Main Results:
- The Tik gene, the murine homolog of PKR (mPKR), was identified.
- A rearranged mPKR allele was found in a murine lymphocytic leukemia cell line.
- A mutated mPKR transcript encoded a catalytically inactive but dsRNA-binding and dimerizing polypeptide.
Conclusions:
- Reduced PKR activity may occur in tumors due to mutations.
- The identified mutated mPKR, while not dominant-negative, contributes to decreased PKR function in leukemia cells.
- This finding highlights a potential role for PKR dysregulation in cancer development.