Alterations of cell cycle control proteins SHP-1/2, p16, CDK4 and cyclin D1 in radioresistant nasopharyngeal carcinoma cells

Abstract

The primary treatment for nasopharyngeal carcinoma (NPC) is radiotherapy, with or without concurrent chemotherapy. However, resistance to radiotherapy is not uncommon. The aim of the present study was to establish a radioresistant NPC cell line to study the molecular mechanisms of radioresistance by measuring the expression of cell cycle control proteins src homology 2 domain-containing phosphatase (SHP)-1/2, p16, CDK4 and cyclin D1. Human nasopharyngeal carcinoma CNE-2 cells were cultured, divided into two groups (CNE-2S1 and CNE-2S2) and irradiated with a dose of 6 Gy x5 or 2 Gy x15, respectively. The cells were subcultured between doses of irradiation. The surviving sublines (CNE-2S1 and CNE-2S2 clones) were then passaged for three months and their radiosensitivity was determined. The cell cycle distribution and protein expression of SHP-1/2, p16, CDK4 and cyclin D1 in parental and progenitor cell lines were measured. Small interfering (si)RNA-mediated knockdown of SHP-1 and SHP-2 in the NPC cells was used to further examine their roles in radiosensitivity and cell cycle distribution. CNE-2S1, a radio-resistant cell line, had a significantly higher percentage of cells in S phase and a lower percentage of cells in G1 phase, enhanced expression levels of SHP-1, CDK4 and cyclin D1, and reduced expression of p16, respectively, as compared with the parent cells. Stable suppression of SHP-1 mRNA in CNE-2 cells resulted in increased radiosensitivity compared with the parental cells, a decrease in the number of cells in S phase and an increase in the expression of p16. The results suggested that the SHP-1/p16/cyclin D1/CDK4 pathway may have a role in regulating radiosensitivity and cell cycle distribution in nasopharyngeal cells.

SHP-1 overexpression increases the radioresistance of NPC cells by enhancing DSB repair, increasing S phase arrest and decreasing cell apoptosis

“…We showed that overexpression of SHP-1 enhanced DNA DSB repair, increased IR-induced S phase arrest and decreased cell apoptosis, thus resulting in radioresistance in CNE-2 cells. The result was consistent with previous observations (15,16).…”

“…However, our previous research found that SHP-1 was overexpressed in NPC tissues and was associated with local recurrence and metastasis after radiotherapy (4). Suppression of SHP-1 expression resulted in a higher radiosensitivity (15,16). These results suggest that overexpression of SHP-1 may be related to radioresistance and that it may be a potential target to enhance NPC radiosensitivity.…”

“…Knockdown of SHP-1 by siRNA in the NPC cell line CNE-2 and in the non-small cell lung cancer (NSCLC) cell line A549 resulted in increased radiosensitivity (15,16). These results suggest that overexpression of SHP-1 may be related to radioresistance.…”

Functions of Shp2 in cancer

“…Shp2 and Stat5 function as proximal effectors of the Kit oncogene, and cell survival is driven by the Shp2/Erk pathway; conversely, G1/S transition during the cell cycle is accelerated by the Kit/Stat5 and Kit/PI3K/Akt pathways [87]. Shp2 is also involved in radioresistance by controlling cell cycle distribution in nasopharyngeal carcinoma cell lines [88]. In HeLa cell line, Shp2 depletion arrests checkpoint-mediated cell; these results indicated the importance of Shp2 in checkpoint control and revealed a novel link between Shp2 and cell cycle checkpoints [89].…”

MicroRNA-4649-3p inhibits cell proliferation by targeting protein tyrosine phosphatase SHP-1 in nasopharyngeal carcinoma cells

“…PTP SHP-1 expression increased in NPC tissue and was associated with radiation resistance and local recurrence (17). Knocking down SHP-1 by siRNA resulted in higher radiosensitivity in the NPC and lung cancer cell lines (18,19). According to these studies, SHP-1 may be a potential target in NPC treatment and silencing SHP-1 may help improve the NPC prognosis.…”