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Biomedical subjects

Brian I Carr

Publications and source records attributed to Brian I Carr.

At least 37 records · Page 2Linked to original sources
PubMed2005

Novel hydroxyl naphthoquinones with potent Cdc25 antagonizing and growth inhibitory properties.

Cdc25 phosphatases are important in cell cycle control and activate cyclin-dependent kinases (Cdk). Efforts are currently under way to synthesize specific small-molecule Cdc25 inhibitors that might have anticancer properties. NSC 95397, a protein tyrosine phosphatase antagonist from the National Cancer Institute library, was reported to be a potent Cdc25 inhibitor. We have synthesized two hydroxyl derivatives of NSC 95397, monohydroxyl-NSC 95397 and dihydroxyl-NSC 95397, which both have enhanced activity for inhibiting Cdc25s. The new analogues, especially dihydroxyl-NSC 95397, potently inhibited the growth of human hepatoma and breast cancer cells in vitro. They influenced two signaling pathways. The dual phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) was induced, likely due to inhibition of the ERK phosphatase activity in Hep 3B cell lysate but not the dual specificity ERK phosphatase MKP-1. They also inhibited Cdc25 enzymatic activities and induced tyrosine phosphorylation of the Cdc25 target Cdks. Addition of hydroxyl groups to the naphthoquinone ring thus enhanced the potency of NSC 95397. These two new compounds may be useful probes for the biological functions of Cdc25s and have the potential for disrupting the cell cycle of growing tumor cells.

Antineoplastic Agents↗
PubMed2004

Inhibition of rat liver regeneration after partial hepatectomy and induction of ERK phosphorylation by Cpd 5, a K vitamin-based anticancer compound.

Thioalkyl K vitamin derivatives, like 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone (Cpd 5), have been shown to inhibit both hepatoma cell growth and DNA synthesis in rat hepatocytes in vitro. We have here examined the tissue distribution, in vivo tolerance and growth inhibitory effects of a single injected dose of Cpd 5 in rats. Cpd 5 administered i.p. was sufficient to cause a 90% inhibition of the peak in DNA synthesis in rat liver 24 h after two-thirds partial hepatectomy (PH). However, DNA synthesis in post-PH, Cpd 5-treated rat livers did occur, but with a delay of 36 h. Dual phosphorylation of ERK2 was induced in rat liver dose-dependently as early as 0.5 h, but gradually returned to almost basal levels by 6 h after Cpd 5 treatment. The MEK1/2 inhibitor PD098059, administered in vivo 1 h prior to Cpd 5 treatment, antagonized both induction of ERK2 phosphorylation and inhibition of DNA synthesis in rat liver. Liver protein lysates post-PH exhibited protein phosphatase activity for phospho-ERK2, which was inhibited by Cpd 5. These results show that induction of ERK2 phosphorylation is likely involved in the mechanism by which Cpd 5 inhibits PH-induced DNA synthesis, probably as a result of its ability to inhibit the activity of ERK phosphatase(s).

Animals↗
PubMed2004

NAD(P)H:quinone oxidoreductase-1-dependent and -independent cytotoxicity of potent quinone Cdc25 phosphatase inhibitors.

Cdc25 dual-specificity phosphatases coordinate cell cycle progression and cellular signaling. Consequently, Cdc25 inhibitors represent potential anticancer agents. We evaluated >10,000 compounds for inhibition of human Cdc25 phosphatases and identified many potent and selective inhibitors, which all contained a quinone. Bioreductive enzymes frequently detoxify or activate quinones. Therefore, we evaluated the effect of NAD(P)H:quinone oxidoreductase-1 (NQO1) and reductase-rich microsomes on the activity of three quinone-containing Cdc25 inhibitors: 2-(2-hydroxyethylsulfanyl)-3-methyl-1,4-naphthoquinone (Cpd 5, compound 5; NSC 672121), 2,3-bis-(2-hydroxyethylsulfanyl)-1,4-naphthoquinone (NSC 95397), and 6-chloro-7-(2-morpholin-4-yl-ethylamino)quinoline-5,8-dione (NSC 663284). Each inhibitor was reduced by human NQO1 (K(m) of 0.3-0.5 microM) but none by microsomes. Compounds were evaluated with six cancer cell lines containing different amounts of NQO1: HT-29 (1056 nmol/mg/min), HCT116 (660 nmol/mg/min), sublines HCT116-R30A (28 nmol/mg/min) and HCT-116R30A/NQ5 (934 nmol/mg/min), MDA-MB-231/Q2 (null NQO1), and subline MDA-MB-231/Q6 (124 nmol/mg/min) but containing similar amounts of microsomal cytochrome P450 reductase and cytochrome b(5) reductase. Growth inhibition and G2/M arrest by Cpd 5 was proportional to NQO1 levels, requiring 4- to 5-fold more Cpd 5 to inhibit HCT-116 or HCT-116R30A/NQ5 compared with HCT-116R30A. In contrast, in all tested cell lines irrespective of NQO1 level, growth inhibition and G2/M arrest by NSC 95375 and NSC 663284 were similar (average IC(50) of 1.3 +/- 0.3 and 2.6 +/- 0.4 microM, respectively). NSC 95375 and NSC 663284 also caused similar Cdk1 hyperphosphorylation, indicating similar Cdc25 inhibition. However, lower Cpd 5 concentrations were needed to produce Cdk1 hyperphosphorylation in sublines with minimal NQO1. Thus, NQO1 detoxified Cpd 5, probably by reducing it to a less active hydroquinone, whereas NSC 95397- and NSC 663284-generated cytotoxicity was unaffected by NQO1.

CDC2 Protein Kinase↗
PubMed2004

Hepatic arterial 90Yttrium glass microspheres (Therasphere) for unresectable hepatocellular carcinoma: interim safety and survival data on 65 patients.

Hepatocellular carcinoma (HCC) generally arises in a cirrhotic liver and, in most cases, is multifocal and bilobar. Although trans-hepatic artery chemoembolization (TACE) can be highly affective in shrinking tumors, it is limited by virtue of the damage that it can cause to the liver that is already damaged by chronic disease. A high priority in HCC research, after primary prevention and early detection, is to find new treatment modalities that are both effective and non-toxic to the underlying cirrhotic liver. A cohort of 65 patients with biopsy-proven unresectable HCC have been treated with hepatic arterial 90Yttrium microspheres (Therasphere), and the interim results are reported here. Only 1 cycle of Therasphere treatment ever was performed on 46 patients, 17 patients had 2 cycles, and 2 patients had 3 cycles of therapy. The median dose delivered was 134 Gy, typically as either 5 or 10 GBq (2-4 million microspheres). Clinical toxicities include 9 episodes of abdominal pain and 2 episodes of acute cholecystitis, requiring cholecystectomy. A main lab toxicity was elevated bilirubin which increased by more than 200% in 25 patients (30.5%) during 6 months of therapy, although 18 of these patients had only transient elevation. A prominent finding was prolonged and profound (>70%) lymphopenia in more than 75% of the patients, but without clinical significance. Forty-two patients (64.6%) had a substantial decrease in tumor vascularity in response to therapy, and 25 patients (38.4%) had a partial response, by computed tomography scan. Median survival for Okuda stage I patients (n=42) was 649 days (historical comparison 244) and for Okuda stage II patients (n=23) was 302 days (historical comparison 64 days). All patients were followed after therapy for a minimum of 6 months. There were 42 deaths, 21 due to liver failure, 6 from HCC progression, and 3 from metastases. Therasphere appears to be a relatively safe and effective therapy for advanced-stage unresectable HCC.

Carcinoma, Hepatocellular↗
PubMed2004

Involvement of c-Myc in growth inhibition of Hep 3B human hepatoma cells by a vitamin K analog.

BACKGROUND/AIMS: A synthetic vitamin K analog, compound 5 (Cpd 5), is a potent inhibitor of cell growth. The aim was to investigate whether c-Myc was involved in Cpd 5-induced cell growth inhibition. METHODS: Human hepotoma cells (Hep 3B) were cultured and treated with Cpd 5, and c-Myc protein expression and phosphorylation were investigated using Western blot analysis. RESULTS: Cpd 5 was found to inhibit c-Myc protein expression and induce c-Myc phosphorylation in Hep 3B cells. The phosphorylation of c-Myc was induced by both Cpd 5-mediated persistent extracellular signal-regulated kinase (ERK) phosphorylation and Cpd 5 increased glycogen synthase kinase-3 (GSK-3) activity. When using GSK-3 inhibitor, SB216763, c-Myc phosphorylation was significantly decreased and c-Myc levels were restored in Cpd 5 treated cells, suggesting that Cpd 5-mediated increase of GSK-3 activity enhanced c-Myc degradation and resulted in reduction of c-Myc levels. The lower c-Myc levels were found to cause altered expression of two c-Myc target genes, growth arrest gene gadd45 and ornithine decarboxylase (ODC). CONCLUSIONS: The results suggest that Cpd 5-mediated c-Myc phosphorylation resulted in enhanced c-Myc protein degradation and reduced c-Myc protein levels, which may contribute to cell growth inhibition by Cpd 5.

Carcinoma, Hepatocellular↗
PubMed2004

Yttrium-90 microspheres for the treatment of hepatocellular carcinoma.

Unresectable hepatocellular carcinoma is extremely difficult to treat. TheraSphere consists of yttrium-90 (a pure beta emitter) microspheres, which are injected into the hepatic arteries. This article reviews the safety and survival of patients with hepatocellular carcinoma who were treated with yttrium-90 microspheres. Eighty patients were selected from a database of 108 yttrium-90 microsphere-treated patients and were staged by using Child-Pugh, Okuda, and Cancer of the Liver Italian Program scoring systems. Patients were treated with local, regional, and whole-liver approaches. Survival from first treatment was analyzed with Kaplan-Meier and Cox regression methods. Adverse events and complications of treatment were coded by using the Southwest Oncology Group toxicity scoring system. Patients received liver doses ranging from 47 to 270 Gy. Thirty-two patients (40%) received more than 1 treatment. Survival correlated with pretreatment Cancer of the Liver Italian Program scores ( P = .002), as well as with the individual Cancer of the Liver Italian Program components, Child-Pugh class, alpha-fetoprotein levels, and percentage of tumor replacement. Patients classified as Okuda stage I (n = 54) and II (n = 26) had median survival durations and 1-year survival rates of 628 days and 63%, and 384 days and 51%, respectively ( P = .02). One patient died of liver failure judged as possibly related to treatment. Thus, in selected patients with hepatocellular carcinoma, yttrium-90 microsphere treatment is safe and well tolerated. On the basis of these results, a randomized controlled trial is warranted comparing yttrium-90 microsphere treatment with transarterial chemoembolization by using the Cancer of the Liver Italian Program system for prospective stratified randomization.

Aged↗
PubMed2004

Hepatocellular carcinoma: current management and future trends.

The hallmarks of hepatocellular carcinoma (HCC) are that it is identified clinically at an advanced stage and usually together with cirrhosis. Surgical resection has been considered the optimal treatment approach, but only a small proportion of patients qualify for surgery, and there is a high rate of recurrence. Approaches to prevent recurrence have included chemoembolization before and neoadjuvant therapy after surgery, neither of which has proven to be beneficial. Liver transplantation has been successful in treating limited-stage HCC, affecting cure of both the tumor and underlying cirrhosis. However, only a minority of patients with HCC qualify for transplantation. Recently, chemoembolization has been shown to prolong survival in selected patients who do not qualify for transplantation or resection. Other innovative, relatively noninvasive local ablative therapies have been introduced and have been shown to be effective in reducing tumor size but not in prolonging survival. Standard chemotherapy is poorly tolerated in patients who do not qualify for resection. Both doxorubicin and cisplatin are frequently used, but overall response rates are low, and neither seems to prolong survival. Prospective, randomized controlled trials using current therapies are needed to better define optimal management of this important tumor. Most needed, however, are new therapeutic agents that are effective against HCC, are noncytotoxic, and are tolerated by the typical patient with underlying cirrhosis. Newly emerging agents with promise include 90 Y microspheres, antiangiogenesis agents, inhibitors of growth factors and their receptors, and K vitamins.

Angiogenesis Inhibitors↗
PubMed2004

Characteristics of hepatocellular carcinoma in a high arsenicism area in Taiwan: a case-control study.

Arsenic contamination of drinking water is noticeably linked to the occurrence of skin, bladder, lung cancers, and hepatocellular carcinoma (HCC). Blackfoot disease (BFD) caused by arsenicosis is endemic in southwestern Taiwan, where artesian well water contains high concentrations of arsenic, and mortality from HCC shows a dose-response increase by concentration of arsenic in the well water. This case-control study was conducted to examine the clinical characteristics of HCC patients of BFD-endemic area. A total of 65 HCC cases (54 men and 11 women) were recruited from the BFD-endemic areas. The clinicopathological features were compared with 130 age- and sex-matched HCC control patients from non-BFD-endemic areas. Characteristics analyzed included hepatitis viral infection status, hepatitis activity, liver function, histological findings, computed tomography scan characteristics, and patient survival. No differences were observed between HCC patients or their tumors, from study and control areas.

Aged↗
PubMed2003

Binding and inhibition of Cdc25 phosphatases by vitamin K analogues.

A synthetic K vitamin analogue, 2-(2-mercaptothenol)-3-methyl-1,4-naphthoquinone or Cpd 5, was previously found to be a potent inhibitor of cell growth [Nishikawa et al., (1995) J. Biol. Chem. 270, 28304-28310]. The mechanisms of cell growth were hypothesized to include the inactivation of cellular protein tyrosine phosphatases, especially the Cdc25 family [Tamura et al. (2000) Cancer Res. 60, 1317-1325]. In this study, we synthesized PD 49, a new biotin containing Cpd 5 derivative, to search for evidence of direct interaction of these arylating analogues with Cdc25A, Cdc25B, and Cdc25C phosphatases. PD 49 was shown to directly bind to GST-Cdc25A, GST-Cdc25B, their catalytic fragments, and GST-Cdc25C. The binding could be competed with excess glutathione or Cpd 5, and a cysteine-to-serine mutation of the catalytic cysteine abolished binding. This was consistent with an involvement in binding of cysteine in the catalytic domain. This interaction between PD 49 and Cdc25 also occurred in lysates of treated cells. PD 49 also bound to protein phosphatases other than Cdc25. We found that the new analogue also inhibited Hep3B human hepatoma cell growth. This growth inhibition involved ERK1/2 phosphorylation and was inhibited by a MEK antagonist. The results demonstrate a direct interaction and binding between this growth-inhibiting K vitamin derivative with both purified as well as with cellular Cdc25A, Cdc25B, and Cdc25C.

Antifibrinolytic Agents↗
PubMed2003

Differential effects of two growth inhibitory K vitamin analogs on cell cycle regulating proteins in human hepatoma cells.

A comparison was made between two K vitamin analogs. Growth in vitro of Hep G2 hepatoma cells was inhibited both by Compound 5 (Cpd 5), a recently synthesized thioalkyl analog of vitamin K or 2-(2-mercaptoethanol)-3-methyl-1, 4-naphthoquinone, as well as by synthetic vitamin K3 (menadione). Using synchronized Hep G2 hepatoma cells, the actions of both Cpd 5 and vitamin K3 on cell cycle regulating proteins were examined. Cpd 5 decreased the levels of cyclin D1, Cdk4, p16, p21 and cyclin B1. By contrast, VK3 only decreased the level of cyclin D1, but had no effect on the levels of Cdk4, p16 or p21. Interestingly, both VK3 and VK2 increased the levels of p21. The naturally occurring K vitamins had little effect on cell growth and none on the cyclins or Cdks. Amounts and activity of the G1/S phase controlling Cdc25A were measured. We found that Cpd 5 directly inhibited both Cdc25A activity and its protein expression, whereas VK3 did not. Thus, the main effects of Cpd 5 were on G1 and S phase proteins, especially Cdk4 and Cdc25A amounts in contrast to VK3. Computer docking studies of Cpd 5 and VK3 to Cdc25A phosphatase showed three binding sites. In the best conformation, Cpd 5 was found to be closer to the enzyme active site than VK3. These findings show that Cpd 5 represents a new class of anticancer agent, being a protein tyrosine phosphatase (PTP) antagonist, that binds to Cdc25A with suppression of its activity. Tumors expressing high levels of oncogenic Cdc25A phosphatase may thus be susceptible to the growth inhibitory activities of this class of compound.

Blotting, Western↗
PubMed2003

A Cdc25A antagonizing K vitamin inhibits hepatocyte DNA synthesis in vitro and in vivo.

Thioalkyl containing K vitamin analogs have been shown to be potent inhibitors of hepatoma cell growth and antagonizers of protein tyrosine phosphatase activity. We now show that they inhibit the activity of specific protein tyrosine phosphatases (PTP) in cell-free conditions in vitro, particularly the dual specificity phosphatase Cdc25A. Using primary cultures of adult rat hepatocytes that are in G0/G1 phase until stimulated into DNA synthesis by epidermal growth factor, we found that 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone or Compound 5 (Cpd 5) inhibited hepatocyte DNA synthesis and PTP activity in cell culture and in vivo after a two-thirds partial hepatectomy. We found a selective inhibition of Cdc25A activity in vitro, using both synthetic substrates and authentic cellular substrate, immunoprecipitated phospho-Cdk4. Intact Cpd 5-treated cells had decreased cellular Cdc25A activity and increased tyrosine phosphorylation of Cdk4, resulting in decreased phosphorylation of retinoblastoma (Rb). Loss of Cdk4 activity was confirmed using Cdk4 immunoprecipitates from either Cpd 5-treated or untreated cells and measuring its kinase activity using GST-Rb as target. We found a similar order of activity for inhibition of growth and Cdc25A activity using several thiol-containing analogs. Cdc25A inhibitors may thus be useful for defining biochemical pathways involving protein tyrosine phosphorylation that mediate cell growth inhibition.

Animals↗
PubMed2003

Evaluation of responses to chemoembolization in patients with unresectable hepatocellular carcinoma.

BACKGROUND: The authors used computed tomography (CT) scans to correlate the changes in tumor vascularity, necrosis, and size with response and survival after transcatheter arterial chemoembolization (TACE) in patients with advanced, unresectable, hepatocellular carcinoma (HCC). METHODS: The authors studied 72 patients with biopsy-proven, unresectable HCC and focused on 186 individual tumor masses. A baseline, multiphase, helical CT was performed and at least three follow-up CT scans were performed after treatment by TACE. Tumors were classified as hypervascular or hypovascular and patients were classified as responders or nonresponders based on CT evidence of altered tumor size, tumor necrosis, and the appearance of new tumors. A new scoring system was used to monitor patient response to TACE. RESULTS: Thirty-eight patients were responders and 34 were nonresponders. Patient survival was significantly increased (P = 0.009) in patients who were hypervascular responders. Survival also was increased in hypervascular nonresponders compared with hypovascular nonresponders (P = 0.008) and in hypovascular responders compared with hypovascular nonresponders (P = 0.002). Response to chemoembolization was found to be significantly (P = 0.02) and inversely proportional to tumor size, but the number of tumor foci in an individual patient was not predictive. CONCLUSIONS: TACE appears to result in improved survival among HCC patients with hypervascular tumors who responded to therapy. However, even patients classified by CT as hypervascular nonresponders and hypovascular responders have improved survival.

Adult↗
PubMed2003

Persistent ERK phosphorylation negatively regulates cAMP response element-binding protein (CREB) activity via recruitment of CREB-binding protein to pp90RSK.

Compound 5 (Cpd 5) or 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone, is an inhibitor of protein phosphatase Cdc25A and causes persistent activation of extracellular signal-regulated kinase (ERK) and cell growth inhibition. To study the mechanism(s) by which persistent ERK phosphorylation might induce cell growth inhibition, we used Cpd 5 as a tool to examine its effects on the activity of CREB (cAMP response element-binding protein) transcription factor in Hep3B human hepatoma cells. We found that CREB activity, including its DNA binding ability and phosphorylation on residue Ser-133, was strongly inhibited by Cpd 5, followed by suppression of CRE-mediated transcription of cyclin D1 and Bcl-2 genes. Cpd 5-mediated suppression of CREB phosphorylation and transcriptional activity was antagonized by mitogen-activated protein kinase kinase inhibitors PD 98059 and U-0126, implying that this inhibition of CREB activity was regulated at least in part by the ERK pathway. The phosphorylation of ribosomal S6 kinase (pp90(RSK)), a CREB kinase in response to mitogen stimulation, was also found to be inhibited by Cpd 5 action. This inhibition of pp90(RSK) phosphorylation is likely the result of its increased association with CREB-binding protein (CBP), which subsequently caused inhibition of CREB phosphorylation and activity. To support the hypothesis that Cpd 5 effects on Cdc25A inhibition with subsequent ERK activation could cause CREB inhibition, we examined the effects of Cdc25A inhibition without the use of Cpd 5. Hep3B cells were transfected with C430S Cdc25A mutant, and ERK was found to be phosphorylated in a constitutively activated manner, which was accompanied by decreased CREB phosphorylation and increased recruitment of CBP to pp90(RSK). These data provide evidence that CBP.RSK complex formation in response to persistent ERK phosphorylation by Cpd 5 down-regulates CREB activity, leading to inhibition of both cAMP response element-mediated gene expression and cell growth.

CREB-Binding Protein↗
PubMed2003

JS-K, a novel non-ionic diazeniumdiolate derivative, inhibits Hep 3B hepatoma cell growth and induces c-Jun phosphorylation via multiple MAP kinase pathways.

JS-K, a non-ionic diazeniumdiolate derivative, is capable of arylating nucleophiles and spontaneously generating nitric oxide (NO) at physiological pH. This recently synthesized low molecular weight compound is shown here to be an inhibitor of cell growth with concomitant activation of mitogen-activated protein kinase (MAPK) members ERK, JNK, and p38 and their downstream effectors c-Jun and AP-1. Inhibitors of these MAPK pathways abrogated the growth inhibitory actions of JS-K. In addition to the well-described actions of JNK as a kinase for c-Jun, we show that c-Jun is also an ERK target. Furthermore, JS-K generated NO in culture and NO inhibitors antagonized both MAPK induction and the growth inhibitory effects of JS-K. These results suggest two possible mechanisms for the mediation of JS-K growth inhibitory actions, namely NO-induction of MAPK pathway constituents as well as possible arylation reactions. The data support the idea that prolonged MAPK activation by JS-K action is important in mediating its growth-inhibitory actions. JS-K thus represents a promising platform for novel growth inhibitory analog synthesis.

Apoptosis↗
PubMed2003

Antitumor and anticarcinogenic actions of Cpd 5: a new class of protein phosphatase inhibitor.

Dual specificity phosphatases (DSP) play an important role in control of the cell cycle and signal transduction. We have synthesized a new class of DSP inhibitors. Cpd 5 or [2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone] is one of the most potent of these. It inhibits DSPs of cells in culture and induces tyrosine phosphorylation of various DSP substrates, including the Cdc25 target Cdks and it potently inhibits cell growth. In this study, we have evaluated Cpd 5 in vivo for its antitumor and growth inhibitory activity on carcinogen-altered foci. Cpd 5 inhibited growth of the transplantable rat hepatoma cell line JM-1 in vitro, with concomitant phosphorylation of the mitogen-activated protein kinase ERK1/2 but not JNK1/2 or p38. This ERK phosphorylation was associated with growth inhibition, as the ERK phosphorylation inhibitor PD098059 antagonized both ERK phosphorylation and growth inhibition. JM-1 cell lysates were found to contain ERK1/2-specific phosphatase(s) that could be inhibited by Cpd 5 and which are thought to be its major targets. Cpd 5 caused significant inhibition of both intrahepatic and subcutaneous (s.c.) growth of transplanted JM-1 cells in male Fischer F344 rats. The treatment was equally effective whether Cpd 5 was administered either as a single, acute dose or chronically as several lower doses. However, toxicity was much lower with chronic treatment. As in JM-1 cells in vitro, ERK1/2 was phosphorylated when rats in vivo were treated with Cpd 5 and tumor growth inhibition in vivo also was antagonized by treating rats with the ERK1/2 phosphorylation inhibitor PD098059. A single dose of Cpd 5 also inhibited the formation of glutathione S-transferase-pi enzyme-altered cells induced by the hepatocarcinogen N-nitrosodiethylamine. This is the first report of the in vivo activity and growth inhibitory mechanism of a novel class of K vitamin growth inhibitors that have potent tyrosine phosphatase activity.

Animals↗
PubMed2002

Identification of epidermal growth factor receptor as a target of Cdc25A protein phosphatase.

Cdc25A, a dual-specificity protein phosphatase, plays a critical role in cell cycle progression. Although cyclin-dependent kinases are established substrates, Cdc25A may also affect other proteins. We have shown here that Cdc25A interacts with epidermal growth factor receptor (EGFR) both physically and functionally in Hep3B human hepatoma cells. Cdc25A inhibitor Cpd 5, a vitamin K analog, inhibited Cdc25A activity in the Cdc25A-EGFR immunocomplex and consequently caused prolonged EGFR tyrosine phosphorylation. Both purified GST-Cdc25A protein and endogenous Hep3B cellular Cdc25A dephosphorylated tyrosine-phosphorylated EGFR, and Cpd 5 antagonized the phosphatase activity of Cdc25A. A functional Cdc25A-EGFR interaction was seen in NR-6 fibroblasts expressing ectopic EGFR but not with a receptor lacking the C terminus or a mutated kinase domain. These data link the cell cycle control Cdc25A phosphatase to an EGFR-linked mitogenic signaling pathway specifically involving EGFR dephosphorylation.

3T3 Cells↗