The inhibition of human mesangial cell proliferation by S-trans, trans-farnesylthiosalicylic acid

BACKGROUND: Many of the proliferative cytokines implicated in human mesangial cell (HMC) proliferation signal through the superfamily of Ras GTPases. The Ras antagonist, S-trans, trans- farnesylthiosalicylic acid (FTS), was used to investigate the effects of the inhibition of Ras signaling on HMC proliferation. METHODS: Ras expression and membrane localization, MAPK, and Akt activation were analyzed by Western blotting. Ras activation was determined with a pull-down assay using the Ras-binding domain of Raf. HMC growth curves were assessed using the MTS assay of viable cell number, while DNA synthesis was measured with BrdU incorporation. Hoechst 33342 staining was used to determine apoptosis. RESULTS: FTS reduced the membrane localization of Ras in both serum and platelet-derived growth factor (PDGF). FTS (7.5-20 micromol/L) potently inhibited PDGF-induced HMC proliferation but had no effect on serum-induced proliferation. FTS (10-20 micromol/L) inhibited both Ras and phospho-MAPK activation by serum and PDGF. Furthermore, FTS (10-20 micromol/L) increased HMC apoptosis in the presence of PDGF but not in serum. Moreover, PDGF-stimulated activation of the survival protein Akt was inhibited by FTS. In contrast, serum-stimulated activation of Akt was unaffected by FTS. CONCLUSION: FTS (5-20 micromol/L) inhibits PDGF-induced but not serum-induced HMC proliferation. FTS (10-20 micromol/L) also promotes HMC apoptosis in the presence of PDGF but not serum. These effects appear to be mediated by inhibitory effects on Ras-dependent signaling that occur as a result of the dislodgment of Ras from its membrane-anchorage sites by FTS. The selectivity of FTS toward PDGF-driven HMC proliferation suggests that FTS may be a valuable therapeutic in mesangioproliferative renal disease.     

Expression of Ras GTPases in normal kidney and in glomerulonephritis.

BACKGROUND: Small monomeric Ras GTPases play critical and specific roles in the control of cellular proliferation and apoptosis but the expression of the three Ras isoforms (Ha-Ras, Ki-Ras and N-Ras) in human renal tissue is unknown. This work is an immunohistochemical study of Ras expression in normal renal tissue and in membranous glomerulonephritis (MGN), IgA nephropathy (IgAN) and IgA-negative mesangioproliferative glomerulonephritis (MPGN). METHODS: Formalin-fixed, paraffin-embedded tissue was stained using pan-Ras monoclonal antibody (mAb) and Ras isoform-specific mAb. Detection employed a (DAKO Envision) modified polymer system. RESULTS: The expression of Ras isoforms in normal human kidney was cell-specific. For example, N-Ras was detected in tubule epithelial cells but not in glomerular or interstitial cells. Ki-Ras was expressed in mesangial cells, interstitial cells and in proximal convoluted tubule cells (PCT) (particularly localized at brush borders) and in collecting duct cells (CD) (localized to cell membranes) but not in podocytes. Cytoplasmic Ha-Ras was detected in all the above cell types except podocytes. MGN was associated with podocyte expression of all three Ras isoforms and with reduced mesangial cell expression of Ha-Ras and Ki-Ras. IgAN was characterized by podocyte expression of Ha-Ras (but not Ki-Ras) and reduced mesangial cell expression of Ki-Ras without alterations in mesangial Ha-Ras expression. MPGN was associated with reduced mesangial cell Ha-Ras and Ki-Ras expression without significant podocyte Ras expression. CONCLUSION: These disease-specific and isoform-specific alterations in Ras expression may be of significance in pathogenesis and warrant further functional investigation.     

Infrequent ras oncogene point mutations in renal cell carcinoma

The role of ras oncogenes in the pathogenesis of renal cell carcinoma is unclear. We have previously shown that insertion of a mutated ras oncogene into cultured human proximal tubular cells, the normal counterpart of renal cell carcinomas, initiates a series of transformation events which results in cells possessing a renal cancer phenotype. These data suggested a role for mutated ras genes in the initiation and maintenance of this disease. Therefore, to assess the involvement of ras genes in renal carcinogenesis, 51 primary and metastatic renal carcinomas, including three oncocytomas, were analyzed for point mutations in codons 12, 13 and 61 of the Ha-ras, Ki-ras and N-ras proto-oncogenes using polymerase-catalyzed chain reaction methodology. A mutated Ha-ras gene was found in one renal cancer metastatic to lung for an overall incidence of 2%. These data indicate that ras oncogenes, activated by point mutations, do not play a major role in the initiation, maintenance or metastases of renal carcinomas.     

Gastrinomas demonstrate amplification of the HER-2/neu proto-oncogene.

OBJECTIVE: This study determined whether genomic amplification of HER-2/neu or mutations of the p53 and ras genes were present in gastrinomas. SUMMARY BACKGROUND DATA: Amplification of HER-2/neu, a proto-oncogene related to the epidermal growth factor receptor, and mutation of the ras proto-oncogene and p53 tumor suppressor gene appear to play a role in the pathogenesis of some human cancers. Little is known about possible molecular alterations in gastrinomas, tumors that may be particularly virulent because of gastrin overproduction, resulting in the severe ulcer diathesis, the Zollinger-Ellison syndrome. METHODS: The differential polymerase chain reaction (PCR) procedure was used to detect amplification of the HER-2/neu gene in DNA samples from the novel human gastrinoma cell line (PT) and from paraffin-embedded samples of gastrinomas. Sequencing techniques were used to determine whether mutations of the p53 or ras (Ha-ras, N-ras, Ki-ras) genes were present. RESULTS: Amplification (> twofold) occurred in all gastrinoma tumor samples. Compared with normal pancreas or ileum, a 4- to 12-fold amplification of HER-2/neu was found in 3 gastrinomas, 3 to 3.3-fold in four samples and 2.1- to 2.4-fold in the remaining five tumors. A heterozygous point mutation in the p53 gene (codon 273) was found in a single sample; none of the gastrinomas contained a mutation of the ras genes. CONCLUSIONS: Amplification of the HER-2/neu gene, but not alterations of either p53 or ras, may be involved in the pathogenesis of gastrinomas. The unique PT cell line will be a useful model to further elucidate the molecular mechanisms that contribute to gastrinoma formation and growth.     

YAP 基因干扰对乳腺癌细胞增殖和凋亡的影响

目的：探讨干扰YAP基因的表达对乳腺癌细胞增殖和凋亡的影响。 方法：通过逆转录病毒介导的方法,分别用YAP shRNA（实验组）或阴性对照shRNA（对照组）转染MCF-7乳腺癌细胞,用qRT-PCR和Western blot方法检测干扰效率;溴脱氧核苷尿嘧啶（BrdU）结合实验和MTT法检测细胞增殖活性;流式细胞术和DAPI染色检测细胞凋亡情况。 结果：干扰效率检测显示,转染72 h后,实验组MCF-7细胞YAP mRNA表达量明显降低（P<0.05）,同时YAP蛋白表达也明显下调;细胞增殖检测显示,与对照组比较,实验组MCF-7细胞BrdU结合与OD值明显降低（P<0.05）,转染后24、48、72 h增殖抑制率分别为19.1%、38.5%、53.5%;凋亡检测显示,实验组细胞凋亡率与凋亡细胞数较对照组明显增加（均P<0.05）。 结论：干扰YAP基因的表达能有效抑制乳腺癌细胞的增殖并促进凋亡,YAP可能是乳腺癌潜在治疗靶点。     

The role of geranylgeranylated proteins in human mesangial cell proliferation

The Rho family of guanine 5'-triphosphatases (GTPases) play a key role in regulating cell proliferation, tubulointerstitial fibrosis, and glomerular hemodynamics. The post-translational prenylation of RhoGTPases by the addition of a geranylgeranyl moiety is critical for cellular localization and signaling activity. This study investigates the effects of (i) inhibiting geranylgeranylation (GG) in human mesangial cell (HMC) proliferation and apoptosis, using GGTI 298, a specific inhibitor of GG and (ii) lovastatin, an HMG-coacetyl A-reductase inhibitor, which depletes the availability of prenylation substrates. HMC proliferation was assessed using an assay of viable cell number and measuring bromodeoxyuridine (BrdU) incorporation. Hoechst 33342 staining was used to determine apoptosis. Extracellular signal-regulated protein kinase (Erk)1/2 and Akt activation were analysed by Western blotting. Rho activation was determined using the Rhotekin pull-down assay. Immunocytochemistry was performed to study the effects on the actin cytoskeleton and RhoA localization. GGTI 298 (10-20 muM) and lovastatin (5-10 muM) potently inhibited platelet-derived growth factor and serum-stimulated HMC proliferation and induced apoptosis. These effects of lovastatin were attenuated by co-incubation with geranylgeranylpyrophosphate. C3 exoenzyme, a clostridial toxin that specifically targets Rho also inhibited BrdU incorporation and promoted apoptosis. GGTI 298 increased cytosolic expression of RhoA, prevented RhoA activation, and inhibited the activation of Erk1/2 and the survival protein Akt. GGTI 298, lovastatin, and C3 exoenzyme inhibit HMC proliferation and promote apoptosis. Inhibiting GG increases cytosolic RhoA expression, disrupts the actin cytoskeleton, and inhibits RhoA activation. These results suggest that targeting geranylgeranylated proteins with statins or GGTI 298 is a promising therapeutic strategy in human mesangioproliferative renal disease.     

Subcellular distribution of Ras GTPase isoforms in normal human kidney.

BACKGROUND: Ras GTPase isoforms have been implicated in proliferative renal disease and are known to have differential cellular expression in kidney. However, their exact subcellular location in various cells is unknown. METHODS: Immunogold labelling for Ras isoforms (Harvey, Kirsten and Neural) was performed for subcellular localization under electron microscopy in fresh normal kidney specimens, obtained from the opposite pole of kidneys removed for renal cell cancer. RESULTS: There was prominent staining shown by Ha-Ras only on the glomerular foot processes as compared with basement membrane or the endothelial cells. Mesangial cells showed intense staining in the cytosol with Ha-Ras (absent in the nucleus), minimal staining with Ki-Ras and none with N-Ras. In both the proximal and distal convoluted tubules, there was a clear staining of the mitochondria with Ha-Ras, with mild cytosolic staining with all of the isoforms. CONCLUSIONS: Ras isoforms have distinct and separate subcellular distributions in normal kidney cells. Understanding the functional aspects of this distribution pattern is essential if Ras is to be targeted by genetic or molecular therapeutic tools.     

Effect of norcantharidin on the proliferation,apoptosis, and cell cycle of human mesangial cells

Aims: Norcantharidin (NCTD) regulates immune system function and reduces proteinuria. We sought to investigate the effect of NCTD on proliferation, apoptosis and cell cycle of cultured human mesangial cells (HMC) in vitro.

Methods: HMC cells were divided into a normal control group, and various concentrations of NCTD group (2.5, 5, 10, 20, or 40?μg/mL). Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, apoptosis was detected by Annexin V/propidium iodide (PI) assays, and morphological analysis was performed by Hoechest 33258 staining. Finally, cell cycle was analyzed by flow cytometry.

Results: NCTD dose and time dependently inhibits HMC proliferation significantly (p?Conclusion: NCTD inhibits HMC cell proliferation, induces apoptosis, and affects the cell cycle.     

Ras antagonist farnesylthiosalicylic acid (FTS) reduces glomerular cellular proliferation and macrophage number in rat thy-1 nephritis

Targeting the Ras family of monomeric GTPases has been suggested as a therapeutic strategy in proliferative renal diseases. This article reports the effects of Ras antagonist farnesylthiosalicylic acid (FTS) in rat thy-1 nephritis, a model in which cytokine-driven glomerular cell proliferation and invasion is likely to involve Ras signaling pathways. FTS in vitro specifically inhibits the binding of Ras to discrete membrane sites, thereby downregulating several Ras-dependent signaling functions and accelerating Ras degradation. Forty-four Lewis rats were given nephritis by day zero injection of a monoclonal thy-1 antibody ER4 (2.5mg/kg body wt). Twenty-two rats were then treated with daily intraperitoneal injection of FTS (5 mg/kg body wt) until sacrifice, and the remaining control rats were given vehicle alone (C). Six rats from each group were sacrificed at day 1 to establish equal injury; other sacrifice points were day 7 and day 10. Bromo-deoxyuridine (BrdU) was injected 1 h before sacrifice, after which sections were used for immunohistochemistry, which included detection of Ras expression, BrdU+ cells and macrophages/monocytes (ED1+). Thy-1 nephritis was associated with an increase in glomerular expression of Ki-Ras and N-Ras isoforms, which was almost fully prevented by FTS. FTS treatment was associated with: (a) a 54% reduction in the mean number of BrdU+ cells per glomerulus (P < 0.01), (b) a 50% reduction in macrophages/monocytes (ED1+) per glomerulus (P < 0.01), and (c) a reduction in 24-h proteinuria at day 10 (P < 0.05). These results show that Ras inhibition can reduce both glomerular cell proliferation and glomerular macrophage cell number in the thy-1 model and justify further study of FTS as a potential therapeutic in proliferative nephritis.     

Induction of cyclooxygenase-2 and invasiveness by transforming growth factor-β1 in immortalized mouse colonocytes expressing oncogenic ras

Cyclooxygenase-2 (COX-2) expression appears to be important in colorectal carcinogenesis. Elevated COX-2 expression and activity have been observed in several different transformed cell types. Prior studies implicating involvement of the Ras oncogene and growth factors on COX-2 expression were largely derived from rat small intestinal cell lines. We have investigated whether mouse colonocyte COX-2 levels are regulated by oncogenic Ras or transforming growth factor-β₁ (TGF-β₁), and whether these factors also serve to regulate cellular invasiveness. Young adult mouse colonocyte cells are colonocytes derived from the "Immortomouse" and immortalized by the SV40 large T antigen. Young adult mouse colonocyte Ras cells were derived by transfection of young adult mouse colonocyte cells with oncogenic Ha-Ras and are known to be tumorigenic. We found that the induction of COX-2 and eicosanoid release were augmented in the presence of activated Ras and that TGF-β₁ caused a further increase in COX-2 in the Ras-transformed mouse colonocytes. Increased COX-2 expression was correlated with increased release of prostaglandins E₂ and I₂. Activated Ras and TGF-β increased the invasiveness of the young adult mouse colonocyte cells, but treatment with a COX-2 inhibitor did not inhibit invasiveness. Thus we found that transforming growth factor-β collaborates to increase COX-2 expression, protaglandin release, and invasiveness in mouse colonocytes, but the increased COX-2 activity does not appear to contribute to the invasive response. Presented at the Forty-Second Annual Meeting of The Society for Surgery of the Alimentary Tract, Atlanta, Georgia, May 20–23, 2001 (poster presentation). Supported by National Institutes of Health grants CA69457, CA77839, and DK52334 (R.D.B.), and by an American College of Surgeons Resident Research Scholarship (C.D.R.).     

Transmembrane signalling in human monocyte/mesangial cell co-cultures: role of cytosolic Ca(2+).

BACKGROUND: Adhesion of monocytes triggers apoptosis, cytotoxicity, cytokine release, and later proliferation of cultured human mesangial cells (HMC). In the search for transmembrane signals transducing the interaction of HMC adhesion molecules with leukocyte counterreceptors, we measured variations of cytosolic Ca(2+) ([Ca(2+)](i)) in HMC and monocytes of the U937 cell line during 6-h co-cultures. METHODS: Monolayer cultures of HMC and suspensions of U937 cells were loaded with the fluoroprobe fura 2-AM and subsequently co-cultured for 6 h while separately monitoring by microfluorometry the Ca(2+)-dependent 500 nm fluorescent emission of each cell line at fixed intervals upon excitation at 340/380 nm. RESULTS: U937 and peripheral blood monocyte adhesion was followed in HMC by a slow, progressive rise of [Ca(2+)](i) from basal levels of 96+/-9 nM to 339+/-54 at 60 min and 439+/-44 nM at 3 h. The [Ca(2+)](i) elevation reached a steady state thereafter, while parallel monolayers incubated with control media maintained resting levels throughout the co-culture with stable fluoroprobe retention. Receptor sensitivity to vasoconstrictor agents, including compounds not released by monocytes, such as angiotensin II, was rapidly downregulated in HMC co-cultured with U937 cells. No [Ca(2+)](i) changes could be elicited by the octapeptide or by the TxA(2) analogue, U-46619, as early as 30 min after exposure to U937 cells. No [Ca(2+)](i) changes were observed in U937 cells throughout the co-culture. Conditioned media from monocytes and from co-cultured HMC+U937 cells had no effect on [Ca(2+)](i) of HMC. Ca(2+) entry leading to fura 2 saturation was still inducible by Ca(2+) ionophores, such as ionomycin and 4-Br-A23187, which also inhibited the responses to vasoconstrictors. Ca(2+)-free solutions prevented the [Ca(2+)](i) rise as well as subsequent receptor inactivation, implicating Ca(2+) influx through store-operated Ca(2+) channels (SOC), a major pathway for Ca(2+) entry in these cultured cells. Ca(2+) influx was confirmed by Mn(2+)-quenching of fura 2. CONCLUSIONS: In HMC, early changes in [Ca(2+)](i) signal for monocyte adhesion in a co-culture model of glomerular inflammation. This signalling mechanism may mediate the functional responses elicited in glomerular cells by leukocytes, including downregulation of receptors for vasoactive agents.     

Farnesyl:protein transferase inhibitors as potential agents for the management of human prostate cancer

The effects of farnesyl:protein transferase inhibitors (FTIs) were evaluated against hormone-dependent and hormone-independent prostate cancer cell lines harboring mutant and wild type Ras. The combinations of the FTI with hormones and chemotherapy were explored. The effect of FTI on the growth of human prostate cancer lines was examined under anchorage-dependent and -independent conditions. Changes in Ras processing and cellular localization were examined by immunoblotting and immunocytochemistry. Hormone-dependent (LNCaP) and -independent (TSU-Pr1, PC3 and DU145) human prostate cancer cell lines were growth-inhibited by the FTI L-744,832 at concentrations ranging from 100 nM to 20 &mgr;M. The inhibition was accompanied by loss of protein farnesylation and with the accumulation of Ha-Ras as its unprocessed, cytosolic form. No effect on N- and Ki-Ras processing was observed. The transformed phenotype of TSU-Pr1 cells, which possess a Ha-Ras Gly-12-Val activating mutation, reverted following FTI treatment. Enhanced antitumor effects were observed when the FTI was combined with gamma-radiation, etoposide, doxorubicin, cisplatin, estramustine and the antihormone bicalutamide. In particular, the combination of taxol and FTI was synergistic for DU145 cells, a cell line that is only marginally sensitive to the FTI alone. The sensitivity of human prostate cancer cell lines to the FTI is independent of the presence of mutations of tumor suppressors, cell cycle regulators and of the activation of a variety of oncogenes, including Ras. A cell line expressing mutated Ha-Ras is particularly sensitive. Enhanced antitumor effects were observed with an anti-androgen, gamma-irradiation, and several chemotherapeutic agents. These findings support the clinical evaluation of FTIs alone or in combination as treatment for this disease. Prostate Cancer and Prostatic Diseases (2001) 4, 33-43     

Pretreatment of Transfused Donor Splenocytes and Allografts With Mitomycin C Attenuates Acute Rejection in Heart Transplantation in Mice

Objective

The aim of this study was to investigate the effect of pretreatment of donor splenocytes and grafts with mitomycin C (MMC) on heart allograft survival, as well as to demonstrate the mechanism of function.

Methods

Donor splenocytes from Balb/C mice were incubated with MMC (40 μg/mL) in vitro and then transfused into recipients (C57BL/6 mice). The heart allograft was perfused with MMC before harvest. Graft survival and histopathology were examined. Lymphocyte activation, regulatory T cells, and donor splenocyte apoptosis were examined with the use of flow cytometry.

Results

MMC incubation in vitro induced apoptosis of donor splenocytes (15.5 ± 2.3% vs 23.2 ± 4.2%; P < .01). Either intravenous injection of MMC-treated donor splenocytes or transplantation of allograft pretreated with MMC prolonged heart allograft mean survival time from 7 ± 0.8 days to 20.5 ± 1.9 days or 10 ± 0.9 days, respectively (both P < .01). A combination of MMC-pretreated donor splenocyte transfusion and allografts showed the best effect on prolongation of graft survival (28.5 ± 1.8 days). Activation of CD4⁺ T cells in spleen and peripheral lymph nodes of recipients was significantly inhibited by either MMC-splenocyte transfusion or the combination treatment. Meanwhile, the percentage of CD4⁺CD25⁺Foxp3⁺ regulatory T cells in the spleen was increased in the MMC-splenocyte transfusion group (15.5 ± 1.1% vs 18.2 ± 0.9%; P < .05).

Conclusions

Both injection of MMC-conditioned donor splenocytes and MMC-conditioned allograft have effects on prolongation of heart allograft survival in mice, and MMC-conditioned donor splenocytes might play an essential role. MMC pretreatment induced regulatory T cells likely through induction of donor splenocyte apoptosis, and thus it inhibited T-cell activation.     

低剂量丝裂霉素短时加药诱导膀胱癌细胞凋亡的研究

目的探讨低剂量丝裂霉素（MMC）短时处理,诱导膀胱癌细胞凋亡的可能性。方法应用细胞和分子生物学技术检测各MMC处理条件对靶细胞生长和凋亡的影响。结果低剂量MMC处理EJ细胞1小时或2小时,均出现典型凋亡特征．其中,100mg／L,和20mg／L,MMC对凋亡的诱导作用最佳且处理时间的长短,对抑癌结果无明显影响。结论以一半的临床MMC用药剂量和时间即可有效诱导膀胱癌EJ细胞凋亡,为拟定更合理的膀胱癌腔内化疗方案提供可靠的实验佐证。     

Cell adhesion to fibronectin induces mitomycin C resistance in bladder cancer cells

OBJECTIVE

To investigate whether cell adhesion to fibronectin induces drug resistance in human bladder cancer cells, and to study the survival signalling pathway in cell adhesion to fibronectin‐mediated chemotherapy resistance in vitro.

MATERIALS AND METHODS

T24 cells (human bladder cancer cell lines) were pre‐coated with fibronectin, and treated with mitomycin C (MMC) and the specific phosphoinositide‐3 kinase (PI3‐K) inhibitor LY294002. The apoptosis and cell cycles were analysed. The activity of the caspase‐8, ‐9 and apoptosis‐inducing factor (AIF) apoptosis pathways were assessed using colorimetric assay, immunofluorescence, Western blot and flow cytometry. The expression of glycogen synthase kinase‐3β (GSK‐3β) and cyclin D1, as the key regulator of G1/S phase transition, were determined by Western blot. The expression of PI3‐K, Akt, phospho‐Akt and β1‐integrin were also examined by Western blot.

RESULTS

Apoptosis induced by MMC was significantly resisted by fibronectin adhesion in T24 cells, and this effect was through inhibition of the caspase‐9 and AIF apoptosis pathways, but not the caspase‐8 pathway. Fibronectin antagonized MMC‐induced G0/G1‐phase arrest by inactivating GSK‐3β to stabilize cyclin D1 expression in T24 cells. Furthermore, fibronectin‐mediated protection of T24 cells was dependent on the activity of the PI3‐K/Akt signalling pathway, and the protection could be abolished by the PI3‐K inhibitor LY294002.

CONCLUSIONS

Fibronectin‐mediated PI3‐K/Akt activation protects T24 cells from MMC‐induced cell death through inhibition of both caspase‐9 and AIF‐mediated apoptosis and GSK‐3β/cyclin D1 involved G0/G1‐phase arrest.     

纤维连接蛋白及精-甘-天冬-丝氨酸多肽对肝癌细胞化疗敏感性的影响

目的 探讨纤维连接蛋白(FN)和精-甘-天冬-丝氨酸多肽(RGDS多肽)对肝癌细胞化疗敏感性的影响.方法 将肝癌细胞株7721分为胎牛血清BSA处理组(BO组)、纤维连接蛋白FN处理组(FO组)、精-甘-天冬-丝氨酸RGDS多肽处理组(RO组)、FN+RGDS多肽共同处理组(FR组),加入不同浓度的丝裂霉素C(MMC)作用2 h、12 h和24 h,用MTT比色法检测不同时间肿瘤细胞的存活率,用荧光染色法和流式细胞术检测肿瘤细胞凋亡,比较FN和RGDS对化疗作用结果的影响.结果 不同浓度MMC作用2 h后,FO组及BO组、FO组与FR组之间的存活率比较,差异无统计学意义(P＞0.05),而作用12 h、24 h后,FO组及BO组、FO组与FR组之间的存活率比较,差异有统计学意义(P＜0.05).结论 药物作用一定时间后,FN能使MMC对肝癌细胞的促凋亡作用下降,产生药物耐受;而RGDS多肽上调肿瘤细胞对化疗药物的敏感性.