Procyanidins Alleviated Cerebral Ischemia/Reperfusion Injury by Inhibiting Ferroptosis via the Nrf2/HO-1 Signaling Pathway.

Procyanidins (PCs), which are organic antioxidants, suppress oxidative stress, exhibit anti-apoptotic properties, and chelate metal ions. The potential defense mechanism of PCs against cerebral ischemia/reperfusion injury (CIRI) was investigated in this study. Pre-administration for 7 days of a PC enhanced nerve function and decreased cerebellar infarct volume in a mouse middle cerebral artery embolization paradigm. In addition, mitochondrial ferroptosis was enhanced, exhibited by mitochondrial shrinkage and roundness, increased membrane density, and reduced or absent ridges. The level of Fe2+ and lipid peroxidation that cause ferroptosis was significantly reduced by PC administration. According to the Western blot findings, PCs altered the expression of proteins associated with ferroptosis, promoting the expression of GPX4 and SLC7A11 while reducing the expression of TFR1, hence inhibiting ferroptosis. Moreover, the treatment of PCs markedly elevated the expression of HO-1 and Nuclear-Nrf2. The PCs' ability to prevent ferroptosis due to CIRI was decreased by the Nrf2 inhibitor ML385. Our findings showed that the protective effect of PCs may be achieved via activation of the Nrf2/HO-1 pathway and inhibiting ferroptosis. This study provides a new perspective on the treatment of CIRI with PCs.

[Expressions of pannexin proteins in I-10 Leydig tumor cells and TM3 Leydig cells and their regulatory effect on the channel function in mice].

OBJECTIVE: To investigate the expressions of the pannexin (Panx) proteins in I-10 Leydig tumor cells and TM3 Leydig cells and their regulatory effect on the Panx channel function in mice. METHODS: The expressions of the Panx-1 and Panx-2 proteins in the mouse Leydig tumor cells were determined by Western blot. The I-10 Leydig tumor cells were treated with carbenoxolone (CBX) at 100 µmol/L or probenecid (PBN) at 200 µmol/L, the fluorescence resonance energy transfer (FRET) detected by time-lapse fluorescence imaging, and the extracellular adenosine 5'-triphosphate (eATP) level measured with the commercial detection kit. Molecular biological methods were used to interfere with shRNA and overexpress mPanx-1 the Panx-1 gene and regulate the expression and function of the Panx-1 protein. RESULTS: The expressions of Panx-1 (ï¼»289.5 ± 55.8ï¼½%) and Panx-2 (ï¼»264.5 ± 24.6ï¼½%) were significantly increased in the I-10 Leydig tumor cells as compared with those in the normal TM3 Leydig cells (both P < 0.05). FRET was remarkably reduced after treated with CBX (ï¼»87.5 ± 17.7ï¼½%) and PBN (ï¼»89.3 ± 14.3ï¼½%) in comparison with that in the control group (both P < 0.01). At 8, 16 and 24 hours, the eATP level was decreased by (57.3 ± 7.2)%, (56.4 ± 9.6)% and (63.4 ± 6.4)% in the CBX group (P < 0.01) and (61.7 ± 2.5)%, (35.8 ± 1.6)% and (13.5 ± 8.3)% in the PBN group (P < 0.01). Molecular biological treatment down-regulated the expression of Panx-1 by (38.3 ± 5.2)% and (31.8 ± 5.1)% in the shRNA1 and shRNA2 groups, respectively (both P < 0.01), but up-regulated that of Panx-1 by (128.4 ± 7.5)% in the mPanx-1 group (P < 0.01) as compared with the negative control. FRET was reduced by (72.4 ± 39.4)% in the shRNA group (P < 0.01) and the eATP level by (14.7 ± 0.1)%, (13.7 ± 0.3)% and (13.1 ± 0.3)% at 8, 16 and 24 hours, respectively (P < 0.01) while FRET elevated by (122.5 ± 17.1)% in the mPanx-1 group (P < 0.01) and the eATP level by (886.1 ± 82.1)%, (885.8 ± 83.3)% and (841.5 ± 21.8)% at 8, 16 and 24 hours, respectively (P < 0.01). CONCLUSIONS: The expressions of Panx-1 and Panx-2 are increased in I-10 mouse Leydig tumor cells, and inhibiting the Panx channel with CBX, PBN and shRNA reduces FRET and the eATP level in the I-10 cells.

[Effect of SRC Kinase on Adriamycin Resistance and Invasion and Metastasis in Human Breast Cancer Cells].

OBJECTIVE: To investigate the role of SRC kinase inhibitor PP2 in drug resistance to adriamycin (ADM) in breast cancer cells and invasion, metastasis of cells. METHODS: MTT assay was used to detect the inhibitory effect of ADM on MCF-7 and MCF-7/ADM cells. The 50% inhibitory concentration (IC50) and resistance index (RI) of cells were calculated. The expression of MDR1, connexin 43 (Cx43) and SRC proteins in breast cancer cells were detected by Western blot assay. Transwell experiment and cell scratch test were used to determine the invasion and migration of cells respectively [MCF-7, MCF-7/ADM, PP2 (1, 2, 4 µmol/L)]. Standard colony formation assay was used to detect the cytotoxicity effect of 4 µmol/L PP2 pretreatment on ADM. RESULTS: ADM inhibited the proliferation of MCF-7 more than MCF-7/ADM cells (P<0.01). The IC50 of MCF-7/ADM cells was 24.55 µmol/L, the IC50 of MCF-7/ADM cells was 770.57 µmol/L, the RI was 31. Compared with MCF-7 cells, expressions of the multidrug resistance proteins MDR1 and SRC were significantly increased (P<0.01). The invasion and migration ability of the MCF-7/ADM cells was stronger than that of the sensitive cells (P<0.01). When MCF-7/ADM was exposed to SRC inhibitor PP2, the invasion and metastasis ability of cells were inhibited (P<0.01) and the rate of colony formation was decreased, that is, more sensitivity to ADM (P<0.01). CONCLUSION: The resistance of MCF-7 to ADM is accompanied by increased expression of SRC. SRC inhibitor PP2 can reduce the cell resistance, ability of invasion and metastasis.

[Inhibition of gap junctional intercellular communication protects astrocytes from hypoxia/reoxygenation injury].

OBJECTIVE: To investigate the effects of inhibiting gap junctional intercellular communication on hypoxia/reoxygenation injury in astrocytes. METHODS: Primary cultured cerebral cortical astrocytes of neonate rats were divided into normal control group, hypoxia reoxygenation injury group and 18-α-glycyrrhetinic acid and oleamide (gap junctional intercellular channel inhibitors) group. The gap junction intercellular communication was determined by Parachute assay. The viability of astrocyes was detected by MTT assay. The apoptosis of astrocytes were detected with annexin V/PI and Hoechst 33258 staining. RESULTS: Compared with the normal control group, the gap junctional function of astrocytes was increased significantly in ischemia/reperfusion group (P<0.01), the surviving fraction of astrocytes decreased significantly (P<0.01) and its cell apoptosis ratio increased significantly (P<0.01). Compared with the ischemia/reperfusion group, the gap junctional function of astrocytes in18-α-glycyrrhetinic acid and oleamide group decreased significantly (P<0.01), the viability of astrocytes increased significantly (P<0.01), while cell apoptosis decreased significantly (P<0.01). CONCLUSION: Inhibition of intercellular gap junction has protective effect against hypoxia/reoxygenation injury in astrocytes.

[Baicalein enhances the gap junction in the TM4 Sertoli cells of mice].

OBJECTIVE: To investigate the effect of baicalein on the gap junction intercellular communication (GJIC) in the TM4 Sertoli cells of the mouse testis and its related mechanism. METHODS: We measured the cytotoxicity of different concentrations of baicalein on the TM4 Sertoli cells in the mouse testis by MTT, detected the fluorescence transfer of the TM4 Sertoli cells by parachute assay, and determined the expression of the protein connexin 43 ( Cx43) in the baicalein-treated cells by Western blot and immunofluorescence assay. RESULTS: Baicalein produced no obvious cytotoxicity on the TM4 Sertoli cells at the concentration below 60 µmol/L but significantly increased their GJIC at 0-20 µmol/L (P < 0.01). Western blot and immunofluorescence assay showed that 0-20 µmol/L baicalein remarkably elevated the expression of Cx43 in the TM4 cells (P < 0.01) and on the membrane of the TM4 cells. CONCLUSION: Baicalein at the concentration of 0-20 µmol/L can significantly enhance GJIC in mouse TM4 Sertoli cells by increasing the expression of the Cx43 protein.

[Gefitineb inhibits the growth and induces the apoptosis of mouse I-10 Leydig testicular cancer cells in vitro].

OBJECTIVE: To observe the inhibitory effect of gefitineb on the proliferation and its inducing effect on the apoptosis of mouse I-10 Leydig testicular cancer cells in vitro. METHODS: We treated I-10 Leydig testicular cancer cells of mice with gefitineb at 0, 1.25, 2.5, 5, 10, 20, and 40 µmol/L. Then we determined the inhibitory effect of gefitineb on the growth of the cells by MTT, detected their early and late apoptosis by Annexin V-FITC/propidium iodide double staining and Hoechst 33258 nuclear staining, respectively, and observed the expressions of apoptosis-related proteins Bcl-2, Bax and caspase 3/9 by Western blot. RESULTS: Compared with the blank control group, gefitineb significantly inhibited the proliferation of the I-10 cells at 10 and 20 µmol/L (P < 0.05). The survival rate of the cells was (32.4 ± 2.8)% (P < 0.01) and their early and late apoptosis rates were (26.7 ± 4.2)% and (59.33 ± 10.2)% in the 40 µmol/L group, significantly different from those in the control (P < 0.05 and P <0.01). In comparison with the blank control group, gefitineb at 10, 20, and 40 µmol/L increased the expression of pro-apoptotic protein Bax by (41.9 ± 7.1), (60.1 ± 9.8), and (69.0 ± 11.3)% (all P < 0.05), decreased that of apoptosis-inhibitory protein Bcl-2 by (50.3 ± 8.9), (63.9 ± 6.9), and (88.7 ± 13.9)% (all P < 0.05), and elevated that of the cleft proteins caspase-3 by (69.0 ± 6.9)% (P < 0.05), (71.5 ± 8.1)% (P < 0.05), and (110.9 ± 14.2)% (P < 0.01) and caspase-9 by (51.8 ± 4.9), (54.7 ± 6.7), and (43.8 ± 11.8)% (all P < 0.05). CONCLUSION: Gefitineb can increase the cytotoxicity of I-10 Leydig testicular cancer cells of mice and induce their apoptosis via the mitochondria-mediated apoptosis signaling pathway.

Total flavonoids of litsea coreana enhance the cytotoxicity of oxaliplatin by increasing gap junction intercellular communication.

Oxaliplatin is widely used in the treatment of variety of cancers, including cancer of the testis and colorectum. Gap junctions (GJs) can amplify the cytotoxicity of antinoeoplastic drugs through the bystander effect in different cancer cells. In this study, we demonstrate that total flavonoids of litsea coreana (TFLC), one extract from the dried leaves of litsea coreana leve, increase the cytotoxicity of oxaliplatin in mouse testicular cancer I-10 cells. We found that cell survival was substantially decreased only when functional GJs formed in I-10 cells. TFLC increased oxaliplatin cytotoxity (inducing cell death and apoptosis) by enhancing gap junction intercellular communication (GJIC) through elevated Cx43 protein expression. Furthermore, apoptosis-related protein (Bax, Bcl-2, caspase-3/9) results showed that the Bax/Bcl-2 ratio and activated caspase-3/9 increased when TFLC was used compared with treatment with oxaliplatin alone, which suggests that the mechanism of increased oxaliplatin-induced apoptosis was through the mitochondrial pathway. These results demonstrate that TFLC can enhance the cytotoxicity of oxaliplatin, and that these processes may be regulated in testicular tumor cells through GJ-mediated regulation of tumor cell apoptosis.

[Total flavonoids of litsea coreana decreases the cytotoxicity of oxaliplatin in TM3 Leydig cells via enhancing the function of gap junction].

OBJECTIVE: To investigate the effects of total flavonoids of Litsea Coreana (TFLC) on the gap junction (GJ) intercellular communication in TM3 testicular Leydig cells and whether TFLC can reduce the cytotoxicity of oxaliplatin (OHP) in vitro. METHODS: We detected the effect of TFLC on the dye spread of the in vitro cultured TM3 cells by parachute assay, observed changes in the expression of connexin 43 (Cx43) total protein in the TFLC-treated TM3 cells by Western blot, and determined the effects of TFLC on the expression of Cx43 on the membrane of the TM3 cells by immunofluorescence assay and on the cytotoxicity of OHP by MTT assay. RESULTS: TFLC obviously enhanced the GJ function with the increasing of the TFLC concentration in the TM3 cells. Western blot and immunofluorescence assay confirmed that TFLC significantly enhanced the expression of Cx43 total protein and Cx43 expression on the membrane of the TM3 cells. MTT assay showed that at a high cell density (confluent with GJ formation), 20 microg/ml TFLC enhanced the GJ function of the TM3 cells and reduced the cytotoxicity of OHP (P < 0.05), while at a low density (preconfluent with no GJ formation), TFLC exhibited no effect on the cytotoxicity of OHP (P > 0.05). CONCLUSION: TFLC increases the Cx43 expression and GJ function in normal TM3 Leydig cells, and the enhancement of GJ function reduces the cytotoxicity of OHP.

[PP2 enhances intercellular communication of gap junction in breast cancer Hs578T cells].

OBJECTIVE: To investigate the effect of Src kinase inhibitor PP2 on intercellular communication of gap junction in breast cancer cells. METHODS: Cultured breast cancer Hs578T cells were treated with various concentrations of pp2 (0,1,2,4,8,16,32 µmol/L) for 24h. Cell growth was determined by MTT assay; dye spread in Hs578T cells was measured by Parachute assay; and the expression of Src kinase in Hs578T cells was detected by Western blot. RESULTS: MTT assay showed that the survive rate of Hs578T cells treated with PP2 (1 ≊ 8 µmol/L) was 98% ± 3% ≊ 94 % ± 4%. Parachute assay showed that compared to control group the standard normalized dye spread rates of Hs578T cells treated with 1,2,4 and 8 µmol/L PP2 were 1.60 ± 0.08,2.00 ± 0.05,2.20 ± 0.05 and 2.70 ± 0.09,respectively (all P<0.01). Moreover,compared to control group at the same time points,the standard normalized dye spread of Hs578T cells treated with 8 µmol/L PP2 for 6,12 and 24 h were 1.4 ± 0.05,1.7 ± 0.06,and 2.2 ± 0.07,respectively (all P<0.01). Western blot showed that the expression ratios of Src kinase/ß-actin of Hs578T cells treated with 1,2,4 and 8 µmol/L PP2 for 24 h were 0.93 ± 0.02,0.70 ± 0.09,0.66 ± 0.09 and 0.36 ± 0.10,which were significantly inhibited compared with control group (P<0.05 or 0.01). And the expression ratio of Src kinase/ß-actin of Hs578T cells treated with 8 µmol/L PP2 for 6,12 and 24h was 0.82 ± 0.03,0.66 ± 0.08 and 0.59 ±0.09, which were all inhibited significantly compared to control group (P<0.01). CONCLUSION: PP2 enhances the gap junction function in breast cancer Hs578T cells, which is probably related to the inhibition of Src kinase.

[Effects of retinoic acid on the expression of Cx43 and its gap juncion intercellular communication function in testicular cancer cell].

OBJECTIVE: To investigate the effects of retinoic acid (RA) on the expression of Cx43 and its gap junction intercellular communication function in testicular cancer cells. METHODS: Cultured testicular cancer cells I-10 were treated with different concentration of RA (2.5, 5.0,10.0 micromol/L). The expression of Cx43 in 1-10 cells was detected by Western blot, and the distribution and location of Cx43 on cellular membrane was studied with immunofluorescence assay. Parachute assay was used to detect the function of gap junction intercellular communication composed of Cx43 in 1-10 cells. RESULTS: RA (2.5, 5.0, 10.0 micromol/L) markedly increased the expression of Cx43 in I-10 cells, the enhancement ratios were 43.14% +/- 2.1%, 58.09% +/- 1.8%, 143.13% +/- 1.6%, respectively. The result of immunofluorescence assay showed that RA (2.5, 5.0, 10.0 micromol/L) obviously increased the level of Cx43 located on the cellular membrane of I-10 cells. The result of parachute assay demonstrated that RA (2.5,5.0,10.0 gmol/L) could enhance the intercellular dye coupling through gap junction, the enhancement ratios were 26.1% +/- 2.3%, 63.3% +/- 1.6%, 140.5% +/- 3.4%, respectively. CONCLUSION: RA could enhance the gap junction intercellular communication by increasing the expression of Cx43 in I-10 cells.

The role of mitochondrial dynamics in cerebral ischemia-reperfusion injury.

Stroke is one of the leading causes of death and long-term disability worldwide. More than 80 % of strokes are ischemic, caused by an occlusion of cerebral arteries. Without question, restoration of blood supply as soon as possible is the first therapeutic strategy. Nonetheless paradoxically, reperfusion can further aggravate the injury through a series of reactions known as cerebral ischemia-reperfusion injury (CIRI). Mitochondria play a vital role in promoting nerve survival and neurological function recovery and mitochondrial dysfunction is considered one of the characteristics of CIRI. Neurons often die due to oxidative stress and an imbalance in energy metabolism following CIRI, and there is a strong association with mitochondrial dysfunction. Altered mitochondrial dynamics is the first reaction of mitochondrial stress. Mitochondrial dynamics refers to the maintenance of the integrity, distribution, and size of mitochondria as well as their ability to resist external stimuli through a continuous cycle of mitochondrial fission and fusion. Therefore, improving mitochondrial dynamics is a vital means of treating CIRI. This review discusses the relationship between mitochondria and CIRI and emphasizes improving mitochondrial dynamics as a potential therapeutic approach to improve the prognosis of CIRI.

Upregulation of CDGSH iron sulfur domain 2 attenuates cerebral ischemia/reperfusion injury.

CDGSH iron sulfur domain 2 can inhibit ferroptosis, which has been associated with cerebral ischemia/reperfusion, in individuals with head and neck cancer. Therefore, CDGSH iron sulfur domain 2 may be implicated in cerebral ischemia/reperfusion injury. To validate this hypothesis in the present study, we established mouse models of occlusion of the middle cerebral artery and HT22 cell models of oxygen-glucose deprivation and reoxygenation to mimic cerebral ischemia/reperfusion injury in vivo and in vitro, respectively. We found remarkably decreased CDGSH iron sulfur domain 2 expression in the mouse brain tissue and HT22 cells. When we used adeno-associated virus and plasmid to up-regulate CDGSH iron sulfur domain 2 expression in the brain tissue and HT22 cell models separately, mouse neurological dysfunction was greatly improved; the cerebral infarct volume was reduced; the survival rate of HT22 cells was increased; HT22 cell injury was alleviated; the expression of ferroptosis-related glutathione peroxidase 4, cystine-glutamate antiporter, and glutathione was increased; the levels of malondialdehyde, iron ions, and the expression of transferrin receptor 1 were decreased; and the expression of nuclear-factor E2-related factor 2/heme oxygenase 1 was increased. Inhibition of CDGSH iron sulfur domain 2 upregulation via the nuclear-factor E2-related factor 2 inhibitor ML385 in oxygen-glucose deprived and reoxygenated HT22 cells blocked the neuroprotective effects of CDGSH iron sulfur domain 2 up-regulation and the activation of the nuclear-factor E2-related factor 2/heme oxygenase 1 pathway. Our data indicate that the up-regulation of CDGSH iron sulfur domain 2 can attenuate cerebral ischemia/reperfusion injury, thus providing theoretical support from the perspectives of cytology and experimental zoology for the use of this protein as a therapeutic target in patients with cerebral ischemia/reperfusion injury.

Panax notoginseng saponins enhances the cytotoxicity of cisplatin via increasing gap junction intercellular communication.

Panax Notoginseng Saponins (PNS) have been well known to have anti-tumor activity and enhance cytotoxicity of some cancer chemotherapy agents, but the mechanisms underlying these effects are still unknown. This study investigates the effect of PNS on cytotoxicity of cisplatin and the relationship between this effect and the modulation of gap junctions (GJ) function by PNS in a transfected cell line. The cytotoxicity of cisplatin (0.25-1 µg/mL) was increased in the presence of GJ. Inhibition of gap junction by either GJ blocker or interception of Connexin (Cx) expression decreased the cytotoxicity of cisplatin. Increasing GJ function enhanced cytotoxicity of cisplatin, only in the cells with functional GJ. PNS (50-200 µg/mL) significantly enhanced cisplatin cytotoxicity, but this effect required functional gap junctions between the cells. Exposure of the cells to PNS (50-200 µg/mL) for 4 h leads to a significant enhance in dye coupling of GJ in a dose-dependent manner. These results suggest that PNS increases the cytotoxicity of cisplatin through enhancement of GJ activity.

[Role of pannexin 1 channels in cisplatin-induced apoptosis in I-10 cells].

OBJECTIVE: To investigate the role of pannexin 1 channels in cisplatin-induced apoptosis in I-10 cells and the mechanisms. METHODS: MTT assay was used to assess the cytotoxicity of cisplatin (DDP) in I-10 cells. Annexin V/PI double staining and Hoechst 33258 fluorescence staining were employed to detect early- and late-stage apoptosis of the cells, respectively. Extracellular ATP level and intracellular IP3 level in the cells were detected using commercial detection kits. RESULTS: I-10 cells exposed to both CBX (a pannexin 1 channel inhibitor) and DDP showed a higher cell viability compared with the cells exposed to DDP alone (P<0.01). CBX significantly decreased cisplatin-induced early-stage apoptosis (P<0.001) and late-stage apoptosis (P<0.01), and cause obvious reductions in extracellular ATP and intracellular IP3 levels during cisplatin-induced apoptosis (P<0.05). CONCLUSION: Pannexin 1 channels participate in cisplatin-induced apoptosis in I-10 cells possibly through the ATP/IP3 pathway.

Gefitinib enhances oxaliplatin-induced apoptosis mediated by Src and PKC-modulated gap junction function.

Chemotherapeutic drug-induced apoptosis is enhanced by gap junction intercellular communication (GJIC) in a variety of tumor cells. Oxaliplatin and gefitinib are the most widely used chemotherapeutic drugs. However, the synergistic influence remains unknown in testicular cancer chemotherapy. The aim of the present study was to investigate the apoptosis induced by oxaliplatin combined with gefitinib and the potential mechanisms in I-10 testicular cancer cells. The results showed that gefitinib significantly enhanced oxaliplatin-induced apoptosis. Furthermore, the ratio of Bcl-2/Bax and the cleavage of caspase-3 and -9 were increased by gefitinib during oxaliplatin-induced apoptosis. The oxaliplatin-induced apoptosis was enhanced through the upregulation of gap junction (GJ) channels composed of connexin 43 (Cx43) by gefitinib. The mechanism of GJIC enhancement involved the suppression by gefitinib of the expression levels of Src and PKC, which phosphorylate Cx43 and reduce GJIC. PP2 (Src inhibitor) and GF109203X (PKC inhibitor) also enhanced GJIC function. Our findings demonstrated that gefitinib enhanced oxaliplatin-induced apoptosis in I-10 cells and gefitinib upregulated the GJIC by inhibiting Src and PKC-modulated Cx43 phosphorylation.

[Sodium valproate enhances doxorubicin cytotoxicity in breast cancer cells in vitro].

OBJECTIVE: To investigate the effect of sodium valproate, a histone deacetylase inhibitor, on the cytotoxicity of doxorubicin in breast cancer cells. METHODS: Western blotting was used to assess Cx43 protein expression in breast cancer Hs578T cells exposed to doxorubicin and sodium valproate. MTT assay was used to determine the cytotoxicity of doxorubicin; annexin V/PI double staining and Hochest 33258 fluorescence staining were employed to detect doxorubicin-induced early and late apoptosis, respectively. RESULTS: Western blotting showed that sodium valproate significantly increased Cx43 protein expression in Hs578T cells (P/0.01). The cells exposed to both sodium valproate and doxorubicin showed significantly lowered cell viability compared with the cells exposed to doxorubicin alone (P/0.01). Exposure to both sodium valproate and doxorubicin resulted in significantly increased early and late cell apoptosis rate compared with doxorubicin treatment alone (P/0.01). CONCLUSION: sodium valproate can significantly enhance the cytotoxicity of doxorubicin and increase doxorubicin-induced apoptosis in breast cancer cells in vitro possibly by enhancing the gap junction function.

Connexin-dependent gap junction enhancement is involved in the synergistic effect of sorafenib and all-trans retinoic acid on HCC growth inhibition.

Increasing gap junction activity in tumor cells provides a target by which to enhance antineoplastic therapies. Previously, several naturally occurring agents, including all-trans retinoic acid (ATRA) have been demonstrated to increase gap junctional intercellular communication (GJIC) in a number of types of cancer cells. In the present study, we investigated in vitro whether ATRA modulates the response of human hepatocellular carcinoma (HCC) cells to sorafenib, the only proven oral drug for advanced HCC, and the underlying mechanisms. HepG2 and SMMC-7721 cells were treated with sorafenib and/or ATRA, and cell proliferation and apoptosis were analyzed; the role of GJIC was also explored. We found that ATRA, at non-toxic concentrations, enhanced sorafenib-induced growth inhibition in both HCC cell lines, and this effect was abolished by two GJIC inhibitors, 18-α-GA and oleamide. Whereas lower concentrations of sorafenib (5 µM) or ATRA (0.1 or 10 µM) alone modestly induced GJIC activity, the combination of sorafenib plus ATRA resulted in a strong enhancement of GJIC. However, the action paradigm differed in the HepG2 and SMMC-7721 cells, with the dominant effect of GJIC dependent on the cell-specific connexin increase in protein amounts and relocalization. RT-PCR assay further revealed a transcriptional modification of the key structural connexin in the two cell lines. Thus, a connexin-dependent gap junction enhancement may play a central role in ATRA plus sorafenib synergy in inhibiting HCC cell growth. Since both agents are available for human use, the combination treatment represents a future profitable strategy for the treatment of advanced HCC.

[Influence of Cx26/Cx32 gap junction channel on antineoplastic effect of etoposide in Hela cells].

OBJECTIVE: To observe the influence of Cx26/Cx32 gap junction channel on the antineoplastic effect of etoposide in Hela cervical cancer cells. METHODS: Fluorescence trace was used to assay the gap junction intercellular communication mediated by Cx26/Cx32 in Hela cells and its functional modulation by the pharmacological agents (oleamide, retinoid acid). A standard colony-forming assay was applied to determine the cell growth-inhibiting effect of etoposide in Hela cells with functional modulation of the gap junction. Hoechst 33258 staining was used to assess the changes in etoposide-induced apoptosis of Hela cells with altered gap junction functions. RESULTS: Oleamide markedly decreased while retinoid acid obviously increased the gap junction function in Hela cells. Standard colony-forming assay showed that etoposide produced a lowered antiproliferative effect in Hela cells with reduced gap junction and an increased antiproliferative effect in cells with enhanced gap junction function. In cells with a reduced gap junction function, etoposide induced a lowered apoptosis rate, which increased obviously in cells with an enhanced gap junction function. CONCLUSION: The antineoplastic effect of etoposide is reduced in Hela cells with a decreased gap junction intercellular communication mediated by Cx26/Cx32 and is enhanced in cells with an increased gap junction intercellular communication.