Cell division cycle 25 homolog c effects on low-dose hyper-radiosensitivity and induced radioresistance at elevated dosage in A549 cells

Abstract

The underlying mechanisms behind both low-dose hyper-radiosensitivity (HRS) and induced radioresistance (IRR), generally occurring at elevated radiation levels, remain unclear; however, elucidation of the relationship between cell cycle division 25 homolog c (Cdc25c) phosphatase and HRS/IRR may provide important insights into this process. Two cell lines with disparate HRS status, A549 and SiHa cells, were selected as cell models for comparison of dose-dependent Cdc25c phosphatase expression subsequent to low-dose irradiation. Knockdown of Cdc25c in A549 cells was mediated by transfection with a pGCsi-RAN-U6neo vector containing hairpin siRNA sequences. S216-phosphorylated Cdc25c protein [p-Cdc25c (Ser216)], cell survival and mitotic ratio were measured by western blot, colony-forming assay and histone H3 phosphorylation analysis. Variant p-Cdc25c (Ser216) expression was observed in the two cell lines after irradiation. The p-Cdc25c (Ser216) expression noted in SiHa cells after administration of 0–1 Gy radiation was similar to the radioresistance model; however, in A549 cells, the dose response for the phosphorylation of the Cdc25c Ser216 residue overlapped the level required to overcome the HRS response. Furthermore, Cdc25c repression prior to low-dose radiation induced more distinct HRS and prevented the development of IRR. The dose required to overcome the HRS response coincided with the effect of early G2-phase checkpoint arrest in A549 cells (approximately 0.3 Gy), and Cdc25c knockdown in A549 cells (approximately 0.5 Gy) corresponded to the phosphorylation of the Cdc25c Ser216 residue. Resultant data confirmed that dose-dependent Cdc25c phosphatase does effectively act as an early G2-phase checkpoint, thus indicating mechanistic importance in the HRS to IRR transition in A549 cells.

Radiation-induced G2/M arrest rarely occurred in glioblastoma stem-like cells

“…Activation of the ATM/Chk1 pathway could phosphorylate Cdc25c at Serine-216 (Ser-216) (Peng et al 1997;Zhao et al 2012;Xue et al 2016). The protein phosphatase Cdc25c regulates entry into mitosis by activating the Cdc2/CyclinB1 kinase complex.…”

“…The expression of Cdc25c was apparently higher in GSLCs than in GDCs and was almost unchanged after irradiation. Considering that Cdc25c is considered to be related to radioresistance (Zhao et al 2012;Li et al 2013), high expression of Cdc25c in GSLCs also indicates that GSLCs are more resistant to irradiation. Because the quantity of total Cdc25c protein in GSLCs is large, phosphorylated Cdc25c only accounts for a very small proportion of total protein: the remaining phosphatase Cdc25c remains sufficient to drive the cell cycle.…”

Involvement of Cdc25c in Cell Cycle Alteration of a Radioresistant Lung Cancer Cell Line Established with Fractionated Ionizing Radiation

“…Zhao et al (2012) found that knockdown of Cdc25c induced a significantly more distinct hyperradiosensitivity and prevented the development of induced radioresistance. However, few studies have been carried out to explore the different roles of Cdc25a and Cdc25c in mediating the radioresistance through the activation of cell cycle checkpoint.…”

Determining if low dose hyper-radiosensitivity (HRS) can be exploited to provide a therapeutic advantage: A cell line study in four glioblastoma multiforme (GBM) cell lines

“…The transition from HRS to IRR is determined by cell-cycle related events involving the ataxia telangiectasiamutated (ATM)-dependent G2-phase cell-cycle checkpoint (Krueger et al 2007a(Krueger et al , 2010. Recently, a dose-dependent Cdc25c (cell division cycle 25C) phosphatase that effectively acts as an early G2-phase checkpoint regulator was implicated as being mechanistically important in the HRS to IRR transition in human A549 cells (Zhao et al 2012).…”