Clinical significance of apoptotic index in non-small cell lung cancer: correlation with p53, mdm2, pRb and p21WAF1/CIP1 protein expression

Purpose: The aim of this study was to assess the prognostic relevance of apoptotic index (AI), considered alone or together with expression of several proteins controlling G1 check point (p53, mdm2, pRb and p21^WAF1/CIP1) in non-small cell lung cancer (NSCLC) patients. Methods: Study group included 50 NSCLC patients who underwent curative pulmonary resection. Apoptosis was detected with the use of TUNEL technique and AI was defined as the number of apoptotic cells per 1,000 tumor cells. The expression of p53, mdm2, pRb and p21^WAF1/CIP1 was assessed immunohistochemically. Results: The mean and median AI calculated for all 50 patients was 14 and 9, respectively. Patients with lower (<14) and higher (≥14) AI constituted 35 (70%) and 15 (30%) of cases, respectively. AI was not correlated with patient clinical characteristics, and expression of p53, pRb and p21^WAF1/CIP1 . However, lower AI was correlated with over-expression of mdm2 protein (P=0.04). Median survival for patients with lower and higher AI was 43 months and 22 months, respectively, and 5-year survival probability—60 and 25%, respectively (P=0.03). In multivariate analysis, the only variable associated with shortened survival was AI (P=0.03, HR=2.9, 95% CI 1.95–3.86). Conclusions: These results suggest that AI correlates with mdm2 protein expression and influences survival in NSCLC.     

Selective inhibition of cell growth by activin in SNU-16 cells

AIM: To investigate whether activin regulates the cell proliferation of human gastric cancer cell line SNU-16 through the mRNA changes in activin receptors, Smads and p21CIP1/WAF1. METHODS: The human gastric cancer cell lines were cultured, RNAs were purified, and RT-PCRs were carried out with specifically designed primer for each gene. Among them, the two cell lines SNU-5 and SNU-16 were cultured with activin A for 24, 48 and 72 h. The cell proliferation was measured by MTT assay. For SNU-16, changes in ActRⅠA, ActRⅠB, ActRⅡA, ActRⅡB, Smad2, Smad4, Smad7, and p21CIP1/WAF1 mRNAs were detected with RT-PCR after the cells were cultured with activin A for 24, 48 and 72 h. RESULTS: The proliferation of SNU-16 cells was down regulated by activin A whereas other cells showed no change. Basal level of inhibin/activin subunits, activin receptors, Smads, and p21CIP1/WAF1 except for activinβB mRNAs was observed to have differential expression patterns in the human gastric cancer cell lines, AGS, KATOⅢ, SNU-1, SNU-5, SNU-16, SNU-484, SNU-601, SNU-638, SNU-668, and SNU-719. Interestingly, significantly higher expressions of ActRⅡA andⅡB mRNAs were observed in SNU-16 cells when compared to other cells. After activin treatment, ActRⅠA,ⅠB, andⅡA mRNA levels were decreased whereas ActRⅡB mRNA level increased in SNU-16 cells. Smad4 mRNA increased for up to 48 h whereas Smad7 mRNA increased sharply at 24 h and returned to the initial level at 48 h in SNU-16 cells. In addition, expression of the p21CIP1/WAF1, the mitotic inhibitor, peaked at 72 h after activin treatment in SNU-16 cells. CONCLUSION: Our results suggest that inhibition of cell growth by activin is regulated by the negative feedback effect of Smad7 on the activin signaling pathway, and is mediated through p21CIP1/WAF1 activation in SNU-16 cells.     

Cyclin-dependant kinase inhibitors CIP1 (p21) and KIP1 (p27) in ovarian cancer

Purpose: Deregulation of the cell cycle is one of the important prerequisites for cancer development. p21 and p27 are both universal inhibitors of cyclin-dependant kinases and can therefore influence cell cycle or tumor progression. The aim of this study was to determine the influence of p21 and p27 expression on survival and chemotherapy response. Methods: 165 patients with ovarian cancer have been examined for p21 and p27 expression by immunohistochemistry on formalin-fixed, paraffin-embedded tissue using the monoclonal primary antibody WAF1 (Oncogene Science) and KIP1 (Transduction Laboratories). Results: High p21 expression (>50%) correlates only with early tumor stage (P=0.04). There was no correlation found between p21 and p27 expression. Patients with high p27 expression (>25%) had a longer DFS (disease free survival) in both univariate and multivariate analysis (P=0.05 and P=0.043) than patients with low p27 expression. A longer overall survival (OS) could only be proven for the group of high p27 expression in univariate analysis (P=0.03). Conclusion: p27 is an independent prognostic factor for ovarian cancer for DFS though this was not true for OS.     

HnRNP A2/B1及p21WAF1蛋白在非小细胞肺癌中表达及意义

目的探讨核内不均一核糖核蛋白A2/B1（hnRNP A2/B1）和p21WAF1蛋白在人非小细胞肺癌（NSCLC）组织中的表达,并进行相关性分析。方法采用免疫组化S-P法检测53例NSCLC组织、40例癌旁组织、7例肺良性病变组织中hnRNPA2/B1和p21WAF1表达。结果 NSCLC组织中hnRNP A2/B1和p21WAF12种蛋白的阳性表达率分别为66.0%和45.2%,显著高于癌旁肺组织和肺良性病变肺组织,差异有统计学意义（P〈0.05）。它们均与分化程度、淋巴结转移有关（P〈0.05）,与组织类型、临床分期无关（P〉0.05）。两种蛋白在NSCLC表达呈显著负相关（P=0.001）。结论 hnRNP A2/B1可能通过下调p21WAF1的表达而缩短细胞周期,促进NSCLC的癌细胞增殖。     

In human hepatocellular carcinoma in cirrhosis proliferating cell nuclear antigen (PCNA) is involved in cell proliferation and cooperates with P21 in DNA repair

BACKGROUND: Proliferating cell nuclear antigen (PCNA) is a nuclear protein involved in DNA-synthesis and repair. During DNA-synthesis and repair the only active PCNA fraction is tightly bound to DNA. Similarly, during DNA-repair, a fraction of p21 colocalizes with PCNA in a detergent-insoluble form. AIM: The aim of the study was to analyze to what extent the presence of DNA-bound PCNA and p21 correlates with cell proliferation and DNA-repair in hepatocellular carcinoma (HCC). METHODS: Twenty-six HCCs and surrounding cirrhosis were studied. The DNA-bound and detergent-soluble fractions of PCNA and p21 were analyzed by immunoblotting. P53 and Ki67-Labeling Index (Ki67-LI) were evaluated by immunocytochemistry. RESULTS: Soluble fractions of PCNA and p21 were found in all samples. One out of 26 cirrhotic samples displayed a DNA-bound fraction of PCNA while no case expressed DNA-bound p21. Fourteen HCCs showed a DNA-bound PCNA fraction. A highly significant correlation was found between Ki67-LI and DNA-bound PCNA but not with detergent-soluble PCNA. DNA-bound p21 and PCNA, indicating ongoing DNA repair activity, were present in 6 of these 14 HCCs and correlated with a high histological grade and high Ki67-LI. CONCLUSIONS: Our results suggest that in HCC PCNA participates both in DNA synthesis and repair and that highly proliferating HCCs may display a sustained DNA-repair.     

Nucleostemin knocking-down causes cell cycle arrest and apoptosis in human T-cell acute lymphoblastic leukemia MOLT-4 cells via p53 and p21Waf1/Cip1 up-regulation

Objectives

Nucleostemin (NS), a recently discovered nucleolar protein, is essential for maintaining self-renewal and proliferation of embryonic and adult stem cells as well as cancerous cells. The aim of this study was to determine biological function of NS in MOLT-4 cells as a human T-cell acute lymphocytic leukemia (T-ALL) model.

Methods

Efficacy of a specific small interference RNA on NS depletion was studied by quantitative polymerase chain reaction and western blotting. The growth rate and viability were analyzed by trypan blue exclusion test. Fluorescent microscopy was used for detecting apoptosis. Cell cycle and apoptosis were mechanistically studied by flow cytometry and western blotting.

Results

Knockdown of NS inhibited proliferation, arrested the cell cycle, and induced apoptosis through p53 and p21^Waf1/Cip1 pathways in MOLT-4 cells.

Discussion

These findings demonstrate critical roles of NS in MOLT-4 cells and may implicate on its therapeutic potential in this human T-ALL model.     

Immunohistochemical expression of Cyclin D1, Cyclin E,p21/waf1 and p27/kip1 in inflammatory bowel disease: correlation with other cell-cycle-related proteins (Rb,p53, ki-67 and PCNA) and clinicopathological features

Background and aims The expression patterns of cyclins D1 and E as well as cyclin-dependent kinase inhibitors p21/waf1 and p27/kip1 and their correlation with clinical parameters and other cell cycle regulators was investigated in inflammatory bowel disease (IBD).Patients and methods These molecular markers were localized immunohistochemically using the monoclonal antibodies anti-cyclin D1 (DCS-6), anti-cyclin E (13A3), anti-p21 (4D10) and anti-p27 (1B4) in 70 patients with IBD, 30 patients with colorectal cancer and eight healthy subjects. Data were analyzed statistically using the software program.Results Cyclin D1 expression was higher in both UC and CD compared with the healthy control group. In addition, CD cyclin D1 expression was higher compared with UC cases and colorectal carcinomas. Cyclin D1 expression was correlated with disease activity and cell proliferation in UC cases. A positive relationship of cyclin D1 with p27/kip1 in both UC and CD was detected. Cyclin E expression was higher in UC, CD and carcinomas compared with healthy control group and its expression correlated with proliferative activity in both UC and CD cases. p21/waf1 expression was higher in IBD cases compared with that of the control group, while a decreased p21/waf1 expression in the group of carcinomas was noted. This expression was correlated with disease activity in UC and the proliferative activity in both UC and CD. The expression of cyclins D1 and E as well as p21/waf1 was also correlated with the existence of dysplastic lesions. A lower p27/kip1 expression in the group of carcinomas compared with IBD cases and healthy controls was found.Conclusions The expression patterns of cyclin D1, cyclin E, p21/waf1 and p27/kip1 in IBD may indicate their contribution in epithelial cell turnover and their possible implication in IBD-related dysplasia-carcinoma.     

Differential expression of cell cycle regulators in HCV-infection and related hepatocellular carcinoma

AIM: To investigate cell cycle proteins in chronic hepatitis C virus infection in order to analyze their role in the process of hepatocyte transformation and to characterize their prognostic properties.METHODS: Subjects of the current study included 50 cases of chronic hepatitis C (CHC) without cirrhosis, 30 cases of CHC with liver cirrhosis (LC), and 30 cases of hepatitis C-related hepatocellular carcinoma (HCC) admitted to the Department of Hepato-Gastroenterology, Theodor Bilharz Research Institute (TBRI), Giza, Egypt. Fifteen wedge liver biopsies, taken during laparoscopic cholecystectomy, were also included as normal controls. Laboratory investigations including urine and stool analysis, liver function tests and prothrombin concentration; serologic markers for viral hepatitis and ultrasonography were done for all cases of the study together with immunohistochemical analysis using primary antibodies against Cyclin D1, Cyclin E, p21, p27 and Rb/p105 proteins.RESULTS: Normal wedge liver biopsies didn’t express Cyclin E or Rb/p105 immunostaining but show positive staining for Cyclin D1, p21 and p27. Cyclin D1 expressed nuclear staining that was sequentially increased from CHC to LC (P < 0.01) to HCC (P < 0.001) cases; meanwhile, Cyclin E revealed nuclear positivity only in the case of HCCs patients that was directly correlated to Rb/p105 immuno-reactivity. The expression of p21 and p27 was significantly increased in CHC and LC cases compared to normal controls and HCCs with no significant difference between well- and poorly-differentiated tumors. p21 showed only a nuclear pattern of staining, while, p27 presented with either cytoplasmic and/or nuclear reactivity in all studied cases. Correlation analysis revealed a direct relation between Cyclin D1 and p21 in CHC cases (P < 0.001), between Cyclin D1 and Cyclin E in HCCs (P < 0.01); however, an inverse relationship was detected between Cyclin D1 and p21 or p27 (P < 0.001) and between p21 and Rb/p105 (P < 0.05) in HCCs.CONCLUSION: Upregulation of Cyclin D1 in CHC plays a vital role in the development and differentiation of HCC; while, Cyclin E may be a useful marker formonitoring tumor behavior. p21 and p27 can be used as predictive markers for HCC. Furthermore, higher expression of Rb/p105 as well as inverse relation with p21 and histologic grades suggests its important role in hepatic carcinogenesis.     

Inhibitory effect of tumor suppressor p33(ING1b) and its synergy with p53 gene in hepatocellular carcinoma

AIM: To investigate the inhibitory effect of tumor suppressor p33ING1b and its synergy with p53 gene in hepatocellular carcinoma (HCC). METHODS: Recombinant sense and antisense p33ING1b plasmids were transfected into hepatoma cell line HepG2 with lipofectamine. Apoptosis, G0/G1 arrest, cell growth rate and cloning efficiency in soft agar of HepG2 were analyzed after transfection. In three hepatoma cell lines with different endogenous p53 gene expressions, the synergistic effect of p33ING1b with p53 was analyzed by flow cytometry and luciferase assay was performed to detect the activation of p53 downstream gene p21WAF1/CIP1. In addition, the expression and mutation rates of p33ING1b in HCC tissues were measured by immunohistochemistry and polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). RESULTS: Overexpression of p33ING1b inhibited cell growth of HepG2, induced more apoptosis and protected cells from growth in soft agar. Combined transfer of p33ING1b and p53 gene promoted hepatoma cell apoptosis, G0/G1 arrest and elevated expression of p21WAF1/CIP1. Immunostaining results showed co-localized P33ING1b with P53 protein in HCC tissues and there was a significant relation between protein expression rates of these two genes (P<0.01). Among 28 HCC samples, p33ING1b presented a low gene mutation rate (7.1%). CONCLUSION: p33ING1b collaborates with p53 in cell growth inhibition, cell cycle arrest and apoptosis in HCC. Loss or inactivation of p33ING1b normal function may be an important mechanism for the development of HCC retaining wildtype p53.     

Effect of p27(KIP1) on cell cycle and apoptosis in gastric cancer cells

AIM: To elucidate the effect of p27KIP1 on cell cycle and apoptosis regulation in gastric carcinoma cells. METHODS: The whole length of p27KIP1 cDNA was transfected into human gastric cancer cell line SCG7901 by lipofectamine. Expression of p27KIP1 protein or mRNA was analyzed by Western blot and RNA dot blotting, respectively. Effect of p27KIP1 on cell growth was observed by MTT assay and anchorage-independent growth in soft agar. Tumorigenicity in nude mice was used to assess the in vivo biological effect of p27KIP1. Flow cytometry, TUNEL, and electron microscopy were used to assess the effect of p27KIP1 on cell cycle and apoptosis. RESULTS: Expression of p27KIP1 protein or mRNA increased evidently in SCG7901 cells transfected with p27KIP1. The cell growth was reduced by 31% at 48 h after induction with zinc determined by cell viability assay. The alteration of cell malignant phenotype was evidently indicated by the loss of anchorage-independent growth ability in soft agar. The tumorigenicity in nude mice was reduced evidently (0.55±0.14 cm vs 1.36±0.13 cm, P<0.01). p27KIP1 overexpression caused cell arrest with 36% increase (from 33.7% to 69.3%, P<0.01) in G1 population. Prolonged p27KIP1 expression induced apoptotic cell death reflected by pre-G1 peak in the histogram of FACS, which was also confirmed by TUNEL assay and electron microscopy. CONCLUSION: p27KIP1 can prolong cell cycle in G1 phase and lead to apoptosis. p27KIP1 may be a good candidate for cancer gene therapy.     

Early apoptosis and cell death induced by ATX-S10Na ( Ⅱ)-mediated photodynamic therapy are Bax- and p53-dependent in human colon cancer cells

AIM: To investigate the roles of Bax and p53 proteins in photosensitivity of human colon cancer cells by using lysosome-localizing photosensitizer, ATX-S10Na (Ⅱ).METHODS: HCT116 human colon cancer cells and Bax-null or p53-null isogenic derivatives were irradiated with a diode laser. Early apoptosis and cell death in response to photodynamic therapy were determined by MTT assays, annexin V assays, transmission electron microscopy assays, caspase assays and western blotting.RESULTS: Induction of early apoptosis and cell death was Bax- and p53-dependent. Bax and p53 were required for caspase-dependent apoptosis. The levels of anti-apoptotic Bcl-2 family proteins, Bcl-2 and Bcl-XL,were decreased in Bax- and p53-independent manner.CONCLUSION: Our results indicate that early apoptosis and cell death of human colon cancer cells induced by photodynamic therapy with lysosome-localizingphotosensitizer ATX-S10Na (Ⅱ) are mediated by p53-Bax network and Iow levels of Bcl-2 and Bcl-XL proteins.Our results might help in formulating new therapeutic approaches in photedynamic therapy.     

The role of XPB in cell apoptosis and viability and its relationship with p53, p21 and c-myc in hepatoma cells

BACKGROUND: Accumulation of DNA damage has been implicated in hepatocarcinogenesis. XPB plays a pivotal part in repairing damaged DNA. However, up to now, the biological effect of XPB on hepatoma cells remains elusive. MATERIALS AND METHODS: Here, we investigated the role of XPB in the apoptosis and the viability of hepatoma cells by using the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labelling and cell viability assay; we also investigated their relationship with p53, p21(waf1/cip1) and c-myc by using the RT-PCR and Western blot. RESULTS: Compared with the control cells HepG2/pcDNA3.1 or HepG2, XPB-transfected HepG2 cells (HepG2/pcDNA3.1-XPB) displayed lower viability, weaker activity and higher apoptosis index. At the same time, an increased expression of p21(waf1/cip1) mRNA, protein and p53 protein in addition to a decreased expression of c-myc mRNA and protein were detected in HepG2/pcDNA3.1-XPB cells. CONCLUSIONS: Our results indicated that XPB could inhibit the proliferation of hepatoma cells and had a positive effect on the expression of p53 and p21(waf1/cip1) but a negative effect on c-myc.     

Paris chinensis dioscin induces G2/M cell cycle arrest and apoptosis in human gastric cancer SGC-7901 cells

AIM:To investigate the anti-tumor effects of Paris chinensis dioscin(PCD)and mechanisms regarding cell cycle regulation and apoptosis in human gastric cancer SGC-7901 cells.METHODS:Cell viability was analyzed by the 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay.Cell apoptosis was evaluated by flow cytometry and laser scanning confocal microscope(LSCM)using Annexin-V/propidium iodide(PI)staining,and the cell cycle was evaluated using PI staining with flow cytom-etry.Intracellular calci...     

Expression of Apo-1/Fas (CD95), Bcl-2, Bax and Bcl-x in myeloma cell lines: relationship between responsiveness to anti-Fas mab and p53 functional status

The down-regulation of apoptosis may be an essential mechanism for tumour cell expansion in slowly proliferating tumours such as multiple myeloma. We studied eight myeloma cell lines for the presence of Bcl-2, which inhibits apoptosis, of Bax, which counteracts Bcl-2, of Bcl-x_L and Bcl-x_S, which act in an anti- and pro-apoptotic fashion, respectively, and of Apo-1/Fas, which induces programmed cell death, when activated by the Apo-1/Fas ligand or the relevant monoclonal antibody (mab). All cell lines constitutively expressed homogenous amounts of Bcl-2, but displayed different amounts of Bax and Bcl-x proteins. The Apo-1/Fas antigen could be detected in seven out of eight myeloma lines, but expression levels varied considerably. The relative expression levels of Apo-1/Fas correlated with that of Bax, but not with that of Bcl-2 or Bcl-x subtypes. Furthermore, the effectiveness of the Apo-1/Fas mab was associated with the relative expression levels of the Apo-1/Fas and with that of the Bax antigen, but not with that of the Bcl-2 and Bcl-x antigens. We further showed that wild-type p53 function is not required for Apo-1/Fas-induced apoptosis, nor is it necessary for the expression of Bax or Apo-1/Fas antigens in myeloma.   In conclusion, our results suggest a p53-independent co-regulation of Apo-1/Fas and Bax, as well as a role for Bax in Apo-1/Fas-induced apoptosis in myeloma.     

Differentiation of functional dendritic cells and macrophages from human peripheral blood monocyte precursors is dependent on expression of p21 (WAF1/CIP1) and requires iron

Summary. Iron is required for monocyte/macrophage differentiation of HL‐60 leukaemia cells. Differentiation requires induction of the cyclin‐dependent kinase inhibitor p21 (WAF1/CIP1), and cell cycle arrest at the G1/S checkpoint. With iron depletion, p21 induction and differentiation are blocked. To establish the roles of iron and p21 in normal monocyte/macrophage differentiation, we examined generation of dendritic cells (DCs) and macrophages from peripheral monocytes. Monocytes were cultured with interleukin 4 and granulocyte–macrophage colony‐stimulating factor (GM‐CSF), then treated with lipopolysaccharide to produce DCs or with M‐CSF to produce macrophages. Iron deprivation was induced by desferrioxamine (DF). Monocyte‐derived DCs had characteristic phenotype and morphology, and stimulated proliferation of naïve allogeneic T lymphocytes. In contrast, DCs generated under iron deprivation were phenotypically undifferentiated and did not stimulate T cells. Similarly, macrophages expressed a characteristic phenotype and morphology, and phagocytosed latex beads, but macrophages generated under iron deprivation failed to develop a mature phenotype and had impaired phagocytosis. Iron deprivation blocked induction of p21 (WAF1/CIP1) expression in both DC and macrophage cultures. Furthermore, p21 antisense oligonucleotides, but not sense oligonucleotides, inhibited both DC and macrophage differentiation. These data indicate that a key role of iron in haematopoiesis is to support induction of p21 which, in turn, is required for DC and macrophage differentiation.     

Reduced levels of the adenomatous polyposis coli (APC) protein are associated with ceramide-induced apoptosis of colon cancer cells

Purpose Mutations of the adenomatous polyposis coli (APC) and p53 genes are commonly found in colorectal cancers. We therefore analyzed the relative roles of APC and p53 in the induction of apoptosis of colon cancer cells by comparing the effects of the natural chemopreventive agent, C₂-ceramide, on different human colon cancer cell lines with and without wild-type p53 and APC genes.Methods We studied the effect of C₂-ceramide and C₂-dihydroceramide on proliferation and/or apoptosis of colon cancer cell lines in vitro and determined the role of p53 and APC proteins in these processes. The protein and mRNA levels in colon cancer cell lines with and without treatments were determined by Western and Northern blot analysis, respectively. The cell cycle and apoptosis profiles were determined by FACS analysis and PARP-1 cleavage.Results Our findings indicate that C₂-ceramide can induce apoptosis independently of the p53/p21(Waf-1/Cip-1) pathway. In addition, the C₂-ceramide induction of apoptosis showed a correlation with a reduction in the levels of the APC protein and mRNA. Moreover, the C₂-ceramide-induced apoptosis was blocked by pre-treatment with ZnCl₂, which stabilizes APC protein levels.Conclusions These results suggest that C₂-ceramide treatment reduces the levels of APC protein and that the reduction in the levels of this protein plays a key role in the ability of C₂-ceramide to induce apoptosis of colon cancer cells.     

p21<Superscript>WAF1/CIP1</Superscript> is more effective than p53 in growth suppression of mouse renal carcinoma cell line Renca in vitro and in vivo

Purpose Although there are many controversial reports about the effect of p53 and p21^WAF1/CIP1 overexpression in different human tumor cells, the p53 gene is shown to be a more effective candidate for cancer gene therapy because of its more pronounced ability to induce apoptosis. In the present study, we present the effect of p53 and p21^WAF1/CIP1 overexpression on mouse renal carcinoma cells in vitro and in vivo.Methods p53 and p21^WAF1/CIP1 genes were introduced into Renca cells using adenoviral vectors (Ad5CMV-p53 and Ad5CMV-p21). The induction of apoptosis was measured using Annexin V assay and DNA fragmentation analysis. The expression of proteins was examined using immunocytochemistry and Western blot methods. The ability of adenoviral vectors to inhibit tumorigenicity of Renca cells, as well as the growth of pre-established tumors was measured.Results In vitro growth assays revealed higher growth suppression after Ad5CMV-p21 infection. Although both vectors induced apoptosis, Ad5CMV-p53 was slightly more efficient. In vivo studies in Balb/c mice, demonstrated that tumorigenicity was completely suppressed by Ad5CMV-p21. Besides this, Ad5CMV-p21 significantly inhibited the growth of established tumors, while Ad5CMV-p53 did not.Conclusions These data suggest that p21^WAF1/CIP1 is a more potent growth suppressor than p53 of mouse tumor cells Renca. The divergent responses of tumor cells to p21^WAF1/CIP1 overexpression could be due to various networks that differ between species.