The mechanisms of somatostatin induced enhanced chemosensitivity of gallbladder cancer cell line to doxorubicin: cell cycle modulation plus target enzyme up-regulation.
BACKGROUND
Gallbladder carcinoma is known to be an aggressive malignancy and nonsensitive to routine chemotherapy. Its prognosis is quite poor. We have illustrated that somatostatin (SST) can enhance chemosensitivity of gallbladder cancer to Doxorubicin (DOX) in our precious studies. Here, we explored the possible mechanisms by which SST used to enhance the cytotoxicity of DOX on gallbladder carcinoma cell line.


METHODS
Human gallbladder cancer cells line (GBC-SD cell line) were divided into four groups: control group, SST group, DOX group, SST+DOX co-treated-group. Cell cycle was detected by flow cytometry (FCM). Cell apoptosis index was detected by using Annexin V/Propidium Iodide Binding on FCM. The expressions of certain key cell cycle-related factors, including retinoblastoma protein (Rb) and E2F-1 protein were investigated by western blotting. ICBP90 protein, which could be a new downstream effector of E2F-1, was also detected by western blotting. The expression of Topo IIα protein, target enzyme of DOX, was assessed in synchronized GBC-SD cells by western blotting.


RESULTS
After 24h treatment with SST alone, cell cycle was arrested at S phase in GBC-SD cells line, followed by indistinctive increment of apoptosis index. After 24h treatment with SST and DOX, apoptosis index significantly increased than that of DOX alone (P<0.05). Compared with control group, the expressions of Rb and E2F-1 protein were significantly up-regulated at 24h after treatment with SST. Similarly, the expressions of ICBP90 and Topo IIα protein were also enhanced at 24h after treatment with SST.


CONCLUSIONS
These results suggested that SST could induce cell cycle block in S phase in GBC-SD cells line, the most sensitive phase of the cell cycle for DOX, through up-regulating Rb, E2F-1 and ICBP90 protein expression. Furthermore, ICBP90 induced the enhanced expression of Topo IIα protein which is the target enzyme of DOX and enhanced its cytotoxic effect on GBC-SD cells. We concluded that the mechanisms of SST enhanced chemosensitivity of GBC-SD cell line to DOX might be cell cycle arrest plus up-regulated target enzyme.
Quan
Zhi Wei
ZW
Department of General Surgery, Xinhua Hospital, School of medicine, Shanghai Jiaotong University, Shanghai 200092, PR China.
Yang
Yong
Y
Li
Ji Yu
JY
Gong
Wei
W
Qin
Yi Yu
YY
Li
Song Gang
SG
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D023081:CCAAT-Binding Factor / Q000378:metabolism; D022762:CCAAT-Enhancer-Binding Proteins / Q000032:analysis / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D004359:Drug Therapy, Combination; D050687:E2F1 Transcription Factor / Q000378:metabolism; D005706:Gallbladder Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D016160:Retinoblastoma Protein / Q000378:metabolism; D013004:Somatostatin / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases; D015854:Up-Regulation / Q000187:drug effects
D000903:Antibiotics, Antineoplastic; D000951:Antigens, Neoplasm; D023081:CCAAT-Binding Factor; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D016160:Retinoblastoma Protein; D013004:Somatostatin; D004317:Doxorubicin; C406364:UHRF1 protein, human; D044767:Ubiquitin-Protein Ligases; D004250:DNA Topoisomerases, Type II