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Prk, a cytokine-inducible human protein serine/threonine kinase whose expression appears to be down-regulated in lung
1Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
Abstract:
We have cloned and characterized a putative protein serine/threonine kinase termed prk through a combination of polymerase chain reaction and conventional cDNA library screening approaches. There are apparently two distinct domains within prk protein deduced from its nucleotide sequences. The amino-terminal portion has the feature of the catalytic domain of a serine/threonine kinase and shows strong homology to mouse fnk and other polo family kinases including mouse snk, human and murine plk, Drosophila polo, and yeast Cdc5. The carboxyl-terminal portion, presumably the regulatory domain, shares extensive homology to mouse fnk. Northern blotting analyses reveal that prk expression is restricted to a very limited number of tissues with placenta, ovaries, and lung containing detectable amounts of prk mRNA. prk mRNA expression is also detected at a low level in the megakaryocytic cell line Dami, MO7e, and three brain glioma cell lines. In addition, refeeding of serum-deprived MO7e, Dami, and K562 cells of hematopoietic origin and GMOO637D of lung fibroblasts rapidly activates prk mRNA expression with its peak induction around 2 h after serum addition. prk gene activation by the serum requires no new protein synthesis. The recombinant cytokines such as interleukin-3 and thrombopoietin also activate prk mRNA expression in MO7e cells. Furthermore, a survey of RNAs isolated from the tumor and the uninvolved tissues from 18 lung cancer patients reveals that prk mRNA expression is significantly down-regulated in tumor tissues. Southern blotting analysis indicates that the prk gene is present in a single copy in the genome of tumors and normal cells. Taken together, these results suggest that prk expression may be restricted to proliferating cells and involved in the regulation of cell cycle progression. The molecular cloning of prk cDNA will facilitate the study of its biological role as well as its potential role in tumorigenesis.
Insights
We identified a novel protein kinase, prk, involved in cell proliferation. Its expression is regulated by serum and cytokines, and it is downregulated in lung tumors, suggesting a role in cell cycle regulation and tumorigenesis.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The protein serine/threonine kinase (prk) is a newly identified kinase with potential roles in cell regulation.
- prk possesses distinct catalytic and regulatory domains, showing homology to the polo family of kinases.
Purpose of the Study:
- To clone and characterize the prk gene and its encoded protein.
- To investigate the expression patterns and regulation of prk mRNA.
- To explore the potential role of prk in cell cycle progression and tumorigenesis.
Main Methods:
- Polymerase chain reaction (PCR) and cDNA library screening for gene cloning.
- Northern blotting for mRNA expression analysis.
- Southern blotting for gene copy number determination.
Main Results:
- prk gene cloned, revealing kinase and regulatory domains homologous to polo-like kinases.
- prk mRNA expression is tissue-specific (placenta, ovaries, lung) and detected in certain cell lines.
- Serum and cytokines rapidly induce prk mRNA expression in a serum-starved cell line, independent of new protein synthesis.
- prk mRNA is significantly downregulated in lung tumor tissues compared to normal tissues.
- prk gene exists as a single copy in the genome.
Conclusions:
- prk expression is linked to proliferating cells and may regulate cell cycle progression.
- The downregulation of prk in lung tumors suggests a potential role in tumorigenesis.
- Further studies on prk are warranted to elucidate its biological functions and involvement in cancer.