Visualizing spatiotemporal dynamics of apoptosis after G1 arrest by human T cell leukemia virus type 1 Tax and
Mariluz Arainga1, Hironobu Murakami, Yoko Aida
1Viral Infectious Diseases Unit, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Background:
Human T cell leukemia virus type 1 (HTLV-1) Tax is a potent activator of viral and cellular gene expression that interacts with a number of cellular proteins. Many reports show that Tax is capable of regulating cell cycle progression and apoptosis both positively and negatively. However, it still remains to understand why the Tax oncoprotein induces cell cycle arrest and apoptosis, or whether Tax-induced apoptosis is dependent upon its ability to induce G1 arrest. The present study used time-lapse imaging to explore the spatiotemporal patterns of cell cycle dynamics in Tax-expressing HeLa cells containing the fluorescent ubiquitination-based cell cycle indicator, Fucci2. A large-scale host cell gene profiling approach was also used to identify the genes involved in Tax-mediated cell signaling events related to cellular proliferation and apoptosis.
Results:
Tax-expressing apoptotic cells showed a rounded morphology and detached from the culture dish after cell cycle arrest at the G1 phase. Thus, it appears that Tax induces apoptosis through pathways identical to those involved in G1 arrest. To elucidate the mechanism(s) by which Tax induces cell cycle arrest and apoptosis, regulation of host cellular genes by Tax was analyzed using a microarray containing approximately 18,400 human mRNA transcripts. Seventeen genes related to cell cycle regulation were identified as being up or downregulated > 2.0-fold in Tax-expressing cells. Several genes, including SMAD3, JUN, GADD45B, DUSP1 and IL8, were involved in cellular proliferation, responses to cellular stress and DNA damage, or inflammation and immune responses. Additionally, 23 pro- and anti-apoptotic genes were deregulated by Tax, including TNFAIP3, TNFRS9, BIRC3 and IL6. Furthermore, the kinetics of IL8, SMAD3, CDKN1A, GADD45A, GADD45B and IL6 expression were altered following the induction of Tax, and correlated closely with the morphological changes observed by time-lapse imaging.
Conclusions:
Taken together, the results of this study permit a greater understanding of the biological events affected by HTLV-1 Tax, particularly the regulation of cellular proliferation and apoptosis. Importantly, this study is the first to demonstrate the dynamics of morphological changes during Tax-induced apoptosis after cell cycle arrest at the G1 phase.
Insights
Human T cell leukemia virus type 1 (HTLV-1) Tax protein induces G1 cell cycle arrest and apoptosis. This study reveals Tax alters gene expression, impacting cell proliferation and apoptosis pathways, and clarifies the dynamics of Tax-induced apoptosis.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Human T cell leukemia virus type 1 (HTLV-1) Tax protein is a known activator of viral and cellular gene expression.
- Tax influences cell cycle progression and apoptosis, but the precise mechanisms and dependency on G1 arrest remain unclear.
Purpose of the Study:
- To investigate the spatiotemporal dynamics of cell cycle progression in Tax-expressing cells.
- To identify host genes involved in Tax-mediated signaling, proliferation, and apoptosis.
Main Methods:
- Utilized time-lapse imaging with the Fucci2 system to monitor cell cycle dynamics in Tax-expressing HeLa cells.
- Employed a large-scale host cell gene profiling approach (microarray) to analyze gene expression changes.
Main Results:
- Tax-expressing cells exhibited G1 phase cell cycle arrest and subsequent apoptosis with characteristic morphological changes.
- Seventeen cell cycle-related genes and 23 pro- and anti-apoptotic genes were significantly deregulated by Tax.
- Expression kinetics of genes like IL8, SMAD3, and IL6 correlated with observed morphological changes during apoptosis.
Conclusions:
- HTLV-1 Tax plays a significant role in regulating cellular proliferation and apoptosis.
- This study provides novel insights into the dynamic morphological changes during Tax-induced apoptosis following G1 cell cycle arrest.
