CDKN1A and osteosarcoma: Liu et al. (2008) have also showed cell cycle arrest at G1 phase triggered by Tax viral protein transfection and subsequent apoptosis. In the same work, the authors demonstrated the effects of HTLV-1 on HeLa cells, human osteosarcoma (HOS) cell line and T lymphoblast (SupT1). Both HTLV-1 infected HeLa cells and Tax-transduced cells exhibited high expression of anti-oncogenes p21Cip1/WAF1 and p27KIP1, mitotic abnormalities, and cell cycle arrest at G1. Similarly, SupT1 cells infected with HTLV-1 also revealed arrest at G1 phase (Liu et al., 2008).