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Published on: November 29, 2016
Human VRK1 is an early response gene and its loss causes a block in cell cycle progression
Alberto Valbuena1, Inmaculada López-Sánchez, Pedro A Lazo
1Programa de Oncología Translacional, Instituto de Biología Molecular y Celular del Cáncer, Centro de Investigación del Cáncer (CIC), Consejo Superior de Investigaciones Científicas (CSIC), Universidad de Salamanca, Salamanca, Spain.
Background:
In mammalian cells regulatory proteins controlling the cell cycle are necessary due to the requirements of living in a heterogeneous environment of cell-interactions and growth factors. VRK1 is a novel serine-threonine kinase that phosphorylates several transcription factors and is associated with proliferation phenotypes.
Methodology/Principal Findings:
In this report VRK1 has been identified as regulated in the cell cycle. VRK1 gene expression is activated by the addition of serum to starved cells, indicating it is required for the exit of G0 phase and entry in G1; a response that parallels the re-expression of MYC, FOS and CCND1 (cyclin D1) genes, suggesting that VRK1 is an early-response gene. VRK1 gene expression is also shutdown by serum withdrawal. The human VRK1 gene promoter cloned in a luciferase reporter responds similarly to serum. In response to serum, the level of VRK1 protein expression has a positive correlation with cell proliferation markers such as phosphorylated-Rb or PCNA, and is inversely correlated with cell cycle inhibitors such as p27. The elimination of VRK1 by siRNA results in a G1 block in cell division, and in loss of phosphorylated-Rb, cyclin D1, and other proliferation markers. Elimination of VRK1 by siRNA induces a reduction of cell proliferation. VRK1 colocalizes with p63 in proliferating areas of squamous epithelium, and identifies a subpopulation in the basal layer.
Conclusions/Significance:
VRK1 is an immediate early response gene required for entry in G1, and due to its implication in normal cell proliferation and division, might be a new target for development of inhibitors of cellular proliferation.
Insights
Vaccinia related kinase 1 (VRK1) is an early response gene crucial for cell cycle entry into G1 phase. Its regulation is vital for normal cell proliferation and division, suggesting VRK1 as a potential target for anti-cancer therapies.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Mammalian cells require regulatory proteins for cell cycle control in response to environmental cues.
- Vaccinia related kinase 1 (VRK1) is a serine-threonine kinase implicated in cell proliferation phenotypes.
- VRK1 phosphorylates various transcription factors, influencing cellular processes.
Purpose of the Study:
- To investigate the role of VRK1 in cell cycle regulation.
- To determine if VRK1 is an early-response gene.
- To explore VRK1 as a potential therapeutic target for inhibiting cell proliferation.
Main Methods:
- Analyzing VRK1 gene expression in response to serum stimulation and withdrawal in starved cells.
- Cloning and assaying the human VRK1 gene promoter using a luciferase reporter.
- Utilizing siRNA to eliminate VRK1 and assessing its impact on cell cycle markers and proliferation.
- Examining VRK1 protein expression correlation with proliferation markers (phosphorylated-Rb, PCNA) and inhibitors (p27).
- Investigating VRK1 localization in squamous epithelium.
Main Results:
- VRK1 gene expression is upregulated by serum addition (indicating G0 to G1 transition) and downregulated by serum withdrawal.
- VRK1 acts as an immediate early-response gene, paralleling MYC, FOS, and cyclin D1 re-expression.
- VRK1 protein levels correlate positively with proliferation markers and inversely with cell cycle inhibitors.
- siRNA-mediated VRK1 depletion causes a G1 cell cycle block, reduces proliferation markers, and inhibits cell division.
- VRK1 is found in proliferating areas of squamous epithelium, specifically in the basal layer.
Conclusions:
- VRK1 is an immediate early-response gene essential for G1 phase entry.
- VRK1 plays a critical role in normal cell proliferation and division.
- VRK1 represents a potential novel target for developing inhibitors of cellular proliferation.
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