JC virus small tumor antigen promotes S phase entry and cell cycle progression

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• JC virus (JCV) early coding region produces regulatory proteins via alternative splicing.
• Large T antigen (LT-Ag) links JCV to cell transformation by targeting p53 and pRb.
• The role of small t antigen (Sm t-Ag) in JCV-mediated cell transformation is unclear.

Purpose of the Study:

• To investigate the effect of Sm t-Ag on cell cycle progression.
• To elucidate the molecular mechanisms underlying Sm t-Ag's role in cell cycle regulation.

Main Methods:

• Assessed Sm t-Ag's impact on cell cycle progression, specifically entry and exit from G0/G1 arrest.
• Analyzed cell cycle stage-specific expression of cyclins and cyclin-dependent kinases (e.g., cyclin B, cyclin E, Cdk2).
• Examined the activation of growth-promoting pathways, including the PI3K/Akt/mTOR axis, in Sm t-Ag-positive cells.

Main Results:

• Sm t-Ag facilitates both entry into and exit from S phase following G0/G1 arrest.
• Elevated expression of G1/S and G2/M transition regulators (cyclin B, cyclin E, Cdk2) observed.
• Sm t-Ag upregulates phosphorylation of Akt, Gsk3-β, and S6K1 within the PI3K/Akt/mTOR pathway.

Conclusions:

• Sm t-Ag actively promotes cell cycle progression.
• Activation of growth-promoting pathways by Sm t-Ag contributes to its role in cell transformation.
• Sm t-Ag may cooperate with LT-Ag in mediating JCV-induced cell transformation.