Enhancing radiosensitivity in osteosarcoma via CDKN2C overexpression: A mechanism involving G1 phase arrest mediated by inhibition of CDK4 expression and Thr172 phosphorylation.

Background: The limited radiosensitivity of osteosarcoma poses a challenge in applying radiotherapy, necessitating the search for effective radiosensitizing targets.

Methods: The lentiviral vectors were employed to establish CDKN2C-overexpressing (CDKN2C-OE) and CDKN2C-negative control (CDKN2C-NC) HOS and U2OS osteosarcoma cells. Cells were treated with or without irradiation (IR) to assess radiosensitization via viability, proliferation, apoptosis, and cell cycle analysis. A mouse model with subcutaneous tumors from CDKN2C-OE and CDKN2C-NC HOS cells evaluated tumor growth post-IR. Immunohistochemical staining and Western blot analysis were conducted to confirm model establishment and explore mechanisms.

Results: CDKN2C-OE combined with IR inhibited cell viability and proliferation, promoting apoptosis in vitro and inhibiting tumor growth in vivo. CDKN2C-OE inhibited G1 phase progression post-IR by suppressing Cyclin-dependent kinase 4 (CDK4) expression and Thr172 phosphorylation, reducing retinoblastoma protein (RB) phosphorylation at Ser807/811. CDKN2C-OE did not primarily impact the cell cycle by regulating the expression of CDK6 and Cyclin D1. Furthermore, when CDKN2C-OE was combined with IR, the expression of BAX, Caspase-3, and its active cleavage product, cleaved Caspase-3, was upregulated.

Conclusions: Our research results indicate that overexpression of CDKN2C enhances radiosensitivity in osteosarcoma through the induction of G1 phase arrest and subsequent apoptosis. G1 phase arrest is mediated by the suppression of CDK4 expression and Thr172 phosphorylation, which consequently affects the expression of phosphorylated RB at the Ser807/811 sites.