RSK promotes G2/M transition through activating phosphorylation of Cdc25A and Cdc25B

Activation of the mitogen-activated protein kinase (MAPK) cascade in mammalian cell lines positively regulates the G2/M transition. The molecular mechanism underlying this biological phenomenon remains poorly understood. Ribosomal S6 kinase (RSK) is a key downstream element of the MAPK cascade. Our previous studies established roles of RSK2 in Cdc25C activation during progesterone-induced meiotic maturation of Xenopus oocytes. In this study we demonstrate that both recombinant RSK and endogenous RSK in Xenopus egg extracts phosphorylate all three isoforms of human Cdc25 at a conserved motif near the catalytic domain. In human HEK293 and PC-3mm2 cell lines, RSK preferentially phosphorylates Cdc25A and Cdc25B in mitotic cells. Phosphorylation of the RSK sites in these Cdc25 isoforms increases their M-phase-inducing activities. Inhibition of RSK-mediated phosphorylation of Cdc25 inhibits G2/M transition. Moreover, RSK is likely to be more active in mitotic cells than in interphase cells, as evidenced by the phosphorylation status of T359/S363 in RSK. Together, these findings indicate that RSK promotes G2/M transition in mammalian cells through activating phosphorylation of Cdc25A and Cdc25B.

Effect of dual inhibition of the Src and insulin-like growth factor-1 receptor (IGF-1R) pathways on antitumor effects in prostate cancer (PCa)

21

Background: The Src and IGF-1R axes are aberrantly activated in both PCa and the microenvironment of bone metastases. Dasatinib and BMS-754807 are clinically promising small molecule inhibitors with high potency against Src family kinases and IGF-1R, respectively. The aim of this study was to establish antitumor co-operativity by combining IGF-1R and Src blockade in a preclinical PCa model.

Methods: LNCaP and PC3 cells were used as models for androgen-dependent and independent PCa, respectively. Inhibition of Src and IGF-1R pathways was accomplished by pharmacologic agents (dasatinib against Src and BMS-754807 against IGF-1R) as well as by shRNA. Serum IGF-1 levels were measured in patients (pts) with castration-resistant PCa (CRPC) treated with dasatinib and docetaxel in a phase II trial.

Results: Src inhibition decreased proliferation of PCa cells, and migration in modified Boyden Chamber and wound assays. In contrast, IGF-1R blockade induced apoptosis (increased Sub-G1 fraction cells, Annexin-V(+) cells and PARP cleavage). Phosphorylation of Akt was partially inhibited by either drug alone and almost completely abrogated by the combination. Intraprostatic injection of shIGF-1R or shSrc PC3 cells in nude mice led to an 83% and 60% decrease in tumor size compared to control shRNA, respectively. In both cell lines, all observed antitumor effects were enhanced when dual blockade was used, relative to blocking the Src or IGF-1R pathway alone. In 9/19 (47%) pts with CRPC, treatment with dasatinib resulted in a compensatory increase of serum IGF-1 levels.

Conclusions: Dual inhibition of Src and IGF-1R is effective and complementary in PCa, mediated, in part, through inhibition of the downstream target Akt. In about half of pts treated with dasatinib, an increase in soluble IGF-1 levels was observed, indicating there is a compensatory upregulation of survival pathways that might be abrogated by dual inhibition of Src and IGF-1R. The combination of dasatinib and BMS-754807 may be a rational therapeutic approach in PCa by blocking complementary processes of tumor growth and progression.

[Table: see text]

Caveolin-1 as a biomarker of Src family kinase/Abl inhibition in castrate-resistant prostate cancer

45

Background: Bone metastases cause significant morbidity in men with castrate-resistant prostate cancer (CRPC). Caveolin-1 (Cav-1), a Src kinase substrate, is overexpressed in primary prostate cancer (PCa) and in PCa bone metastases. In addition, PCa-derived and secreted Cav-1 contributes to malignant progression. We reasoned that Cav-1 may serve as a biomarker of dasatinib (a Src family kinase [SFK]/Abl inhibitor) activity in CRPC patients enrolled in a phase II clinical trial of docetaxel plus dasatinib.

Methods: Levels of prostate-specific antigen (PSA), Cav-1, and markers of bone turnover were measured from baseline and cycle-2, day-1 samples from patients (n = 32) enrolled in this trial. Changes in these markers were stratified by response (responders [R] vs. nonresponders [NR]) and by predominant disease site (lymph node vs. bone). We evaluated Cav-1 expression in human PCa bone metastases samples from trial patients by immunohistochemistry. In parallel, Cav-1 secretion in response to dasatinib treatment was analyzed in PCa cells and osteoblasts.

Results: Serum Cav-1 levels correlated directly with PSA levels in responding patients with node-positive disease (R vs. NR, p = 0.08) but correlated inversely in responding patients with bone-predominant disease (R vs. NR, p = 0.001). Serum from a separate cohort of patients treated with docetaxel only showed no effect on serum Cav-1 levels (R vs. NR, p = 0.85). Levels of Cav-1 were high in the active OBLs in bone specimens with PCa metastases, but not in bone specimens without metastases. Dasatinib treatment led to reduced secretion of Cav-1 in PC-3 and DU145 PCa cells but to increased secretion of Cav-1 in primary mouse osteoblasts or pre-osteoblast MC3T3-E1 cells.

Conclusions: Our results suggest that serum Cav-1 serves as a novel discriminating biomarker for SFK/Abl inhibition in both node-positive and bone-metastatic CRPC. The expression of Cav-1 in OBLs of patients with PCa bone metastases suggests that tumor-associated OBLs are an important source of Cav-1 production in bone marrow. Our data provide evidence that the increase in serum Cav-1 in these patients with bone disease likely occurs through a direct effect of dasatinib on osteoblasts.

No significant financial relationships to disclose.

Dasatinib and docetaxel combination treatment for patients with castration-resistant progressive prostate cancer: A phase I/II study (CA180086)

5061

Background: Dasatinib, a potent inhibitor of SRC family kinases, inhibits in vitro prostate cancer cell proliferation and migration. Consistent with those findings are the clinical observations that osteoclast activity and bone turnover are downregulated in patients treated with dasatinib. We report promising preliminary results of dasatinib in combination with docetaxel (D) for treatment of metastatic castration-resistant prostate cancer (CRPC). Methods: Male pts with progressive CRPC and castrate levels of testosterone (≤50 ng/dL) requiring chemotherapy were enrolled. Escalating doses of dasatinib (50–120 mg QD) and D (60–75 mg/m2 Q 21 days) were evaluated (n = 16) followed by enrollment of 30 pts at the phase 2-selected dose (100 mg dasatinib QD + D at 75 mg/m2 Q 21 days). Continuation of bisphosphonates was permitted; anti-androgens were discontinued. Primary endpoint (Ph. 2) was to determine drug-drug interactions. Secondary endpoints were: changes in PSA, bone scans and tumor size, bone metabolism [urinary N-telopeptide (uNTX) and bone alkaline phosphatase (BAP)] and PK. Results: 46 pts were treated with 28 pts still on therapy. Median treatment duration (n = 18, pts off study) was 4.2 months (0.13–9.63). Preliminary analysis showed no interaction between dasatinib and D. PSA response was seen in 13/32 (41%) pts, clinical benefit (PR + SD) for RECIST-evaluable pts was 21/21, [7 PR, 5 uPR and 4 SD (at ≥21 wks) and 5 SD at ≥6 wk)]. Of 31 pts with bone scans, 30 patients had a best response of either improved (32%) or stable (65%) at ≥6 weeks. For pts with measurable bone markers levels, 12/26 (46%) had a ≥35% decrease in uNTX and 17/24 (71%) had a decrease in BAP from baseline. 6 of 42 pts experienced ≥ grade 3 adverse events (AEs), including fatigue, myelosuppression and pleural effusion (n = 1). Most common grade 1/2 AEs were fatigue, dysgeusia, GI, and skin disorders. Conclusions: Dasatinib and D at doses up to 120 mg QD and 75 mg/m2 are safe with manageable toxicities and no drug-drug interactions. These data confirm the antitumor and antiosteoclast activity of dasatinib in combination with D and serve as the basis for the ongoing phase III study of this combination.

[Table: see text]

Therapeutic targeting of Id2 reduces growth of human colorectal carcinoma in the murine liver

During development inhibitor of DNA-bind-2 (Id2) regulates proliferation and differentiation. Id2 expression has been detected in cancer cells, yet its cellular function and validity as a therapeutic target remains largely unknown. Immunohistochemical analysis of colorectal cancer (CRC) specimens revealed that Id2 was undetectable in normal colonic mucosa, but occurs in 40% of primary tumors and in most CRC liver metastases (P<0.0001). Additionally, Id2 was expressed in all CRC cell lines assayed. CRC cells with reduced Id2 expression demonstrated reduced proliferation. Analysis of CRC cell cycle regulatory proteins showed that reducing Id2 levels reduces cyclin D1 levels and increased p21 levels. Reduction of Id2 expression also enhanced tumor cell apoptosis, increasing levels of the pro-apoptotic protein Bim/Bod, and cleavage of caspase-7 and poly (ADP-ribose) polymerase. In vivo studies show tumors derived from cells with decreased Id2 levels formed smaller tumors with fewer metastases compared with tumors with normal levels (P<0.05). Furthermore, intraperitoneal administration of Id2 small interfering RNA (siRNA) conjugated with the neutral liposome 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine decreased tumor burden in mice compared with control treatment (P=0.006). We conclude that Id2 is upregulated in CRC, and is important in promoting cell survival. In vivo targeting of Id2 by siRNA establishes that it is a valid therapeutic target where its expression occurs.

Inhibition of colon tumor metastasis in an orthotopic nude mouse model with the dual selective Src/Abl kinase inhibitor, AZD0530

14032

Background: Colorectal cancer is the leading cause of cancer deaths in the USA, largely due to metastatic disease in the liver. The specific activity of the non-receptor protein tyrosine kinase, Src, is increased during colon tumor progression and contributes to metastasis; thus, Src inhibitors may have efficacy in the treatment of advanced-stage colon cancer. AZD0530 is a potent, orally available Src/Abl kinase inhibitor currently in clinical trials. Methods: We examined the effects of AZD0530 alone and in combination with oxaliplatin on two colon tumor cell lines, KM12L4 and LS174T in vitro and in orthotopic nude mouse models. AZD0530 inhibits in vitro proliferation and cellular migration of KM12L4 and LS174T, and decreases phosphorylation of the Src substrates FAK and paxillin in a dose- dependent manner. To examine the ability of AZD0530 to affect colon cancer growth and metastasis in a nude mouse model, we inoculated 1x106 cells into the cecum of nude mice. After 2 weeks, mice were treated with vehicle (n=12), AZD0530 alone (n=13; 25mg/kg/day by oral gavage), oxaliplatin alone (n=13; 5mg/kg/day twice weekly), or AZD0530 and oxaliplatin (n=13). Mice were sacrificed after 4 weeks of treatment. Results: Tumor incidence in all groups of mice was greater than 80%. Mice treated with AZD0530 had an average cecal tumor weight of 0.26 g compared with 0.32 g for control (P=0.24). In contrast, the incidence of liver metastases was reduced by 50% in mice treated with AZD0530 alone or oxaliplatin alone, and no mice developed pathologically evident liver metastases when the combination of inhibitors was used. Furthermore, in mice that developed liver metastases, AZD0530 decreased the size of these metastases 9-fold compared with control. Immunohistochemical analysis of primary cecal tumors demonstrated a decrease in phosphorylated Src (Y418) and FAK (Y861) in AZD0530-treated mice compared with control. Conclusions: These results support further investigation of AZD0530, both alone and in combination, as a new therapeutic strategy for the treatment of advanced colon cancer.

No significant financial relationships to disclose.

Vascular endothelial growth factor receptor-1 mediates migration of human colorectal carcinoma cells by activation of Src family kinases

Vascular endothelial growth factor (VEGF) is the predominant pro-angiogenic cytokine in human malignancy, and its expression correlates with disease recurrence and poor outcomes in patients with colorectal cancer. Recently, expression of vascular endothelial growth factor receptors (VEGFRs) has been observed on tumours of epithelial origin, including those arising in the colon, but the molecular mechanisms governing potential VEGF-driven biologic functioning in these tumours are not well characterised. In this report, we investigated the role of Src family kinases (SFKs) in VEGF-mediated signalling in human colorectal carcinoma (CRC) cell lines. Vascular endothelial growth factor specifically activated SFKs in HT29 and KM12L4 CRC cell lines. Further, VEGF stimulation resulted in enhanced cellular migration, which was effectively blocked by pharmacologic inhibition of VEGFR-1 or Src kinase. Correspondingly, migration studies using siRNA clones with reduced Src expression confirmed the requirement for Src in VEGF-induced migration in these cells. Furthermore, VEGF treatment enhanced VEGFR-1/SFK complex formation and increased tyrosine phosphorylation of focal adhesion kinase, p130 cas and paxillin. Finally, we demonstrate that VEGF-induced migration is not due, at least in part, to VEGF acting as a mitogen. These results suggest that VEGFR-1 promotes migration of tumour cells through a Src-dependent pathway linked to activation of focal adhesion components that regulate this process.

Overexpression of neuropilin-1 promotes constitutive MAPK signalling and chemoresistance in pancreatic cancer cells

Neuropilin-1 (NRP-1) is a novel co-receptor for vascular endothelial growth factor (VEGF). Neuropilin-1 is expressed in pancreatic cancer, but not in nonmalignant pancreatic tissue. We hypothesised that NRP-1 expression by pancreatic cancer cells contributes to the malignant phenotype. To determine the role of NRP-1 in pancreatic cancer, NRP-1 was stably transfected into the human pancreatic cancer cell line FG. Signal transduction was assessed by Western blot analysis. Susceptibility to anoikis (detachment induced apoptosis) was evaluated by colony formation after growth in suspension. Chemosensitivity to gemcitabine or 5-fluorouracil (5-FU) was assessed by MTT assay in pancreatic cancer cells following NRP-1 overexpression or siRNA-induced downregulation of NRP-1. Differential expression of apoptosis-related genes was determined by gene array and further evaluated by Western blot analysis. Neuropilin-1 overexpression increased constitutive mitogen activated protein kinase (MAPK) signalling, possibly via an autocrine loop. Neuropilin-1 overexpression in FG cells enhanced anoikis resistance and increased survival of cells by >30% after exposure to clinically relevant levels of gemcitabine and 5-FU. In contrast, downregulation of NRP-1 expression in Panc-1 cells markedly increased chemosensitivity, inducing >50% more cell death at clinically relevant concentrations of gemcitabine. Neuropilin-1 overexpression also increased expression of the antiapoptotic regulator, MCL-1. Neuropilin-1 overexpression in pancreatic cancer cell lines is associated with (a) increased constitutive MAPK signalling, (b) inhibition of anoikis, and (c) chemoresistance. Targeting NRP-1 in pancreatic cancer cells may downregulate survival signalling pathways and increase sensitivity to chemotherapy.

Vascular endothelial growth factor is upregulated by interleukin-1 beta in human vascular smooth muscle cells via the P38 mitogen-activated protein kinase pathway

Small tumor vessels are composed of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). These cells have been shown to communicate with each other via cytokine signaling during neovascularization. We previously demonstrated that interleukin-1 beta (IL-1 beta) leads to induction of vascular endothelial growth factor (VEGF) in human colon carcinoma cells. As pericytes play a role in regulating EC function, we hypothesized that IL-1 beta may mediate EC survival by induction of VEGF in a paracrine manner. We investigated the effects of IL-1 beta on VEGF expression in human VSMCs (hVSMCs) and the signal transduction pathways that may be involved. Treatment of hVSMCs with IL-1 beta induced VEGF expression in a time- and concentration-dependent manner and increased both the VEGF promoter activity and the mRNA half-life. Treatment with IL-1 beta induced the expression of P38 mitogen-activated protein kinase (MAPK) within 5 min but did not activate extracellular signal-regulated kinases (Erk)-1/2, c-jun amino terminal kinase (JNK), or Akt. SB203580, a specific P38 MAPK inhibitor, blocked the ability of IL-1 beta to induce VEGF mRNA and promoter activity. Conditioned media from hVSMCs pretreated with IL-1 beta prevented apoptosis of ECs, an effect that was partially abrogated by VEGF-neutralizing antibodies. These data demonstrate that IL-1 beta may induce VEGF in hVSMCs, and suggest that this paracrine signaling pathway, may prevent, in part, apoptosis of ECs.

In vivo intracellular signaling as a marker of antiangiogenic activity

Alterations in endothelial cell (EC) signaling could serve as a marker of effective antiangiogenic therapy. We determined the effect of an antiangiogenic tyrosine kinase inhibitor, SU6668, on tumor EC signaling in liver metastases in mice. In vitro immunofluorescence verified that pretreatment of ECs with SU6668 before exposure to VEGF decreased in vitro phosphorylation of Erk and Akt. Using double-fluorescence immunohistochemistry, phosphorylated Erk and Akt were constitutively expressed in ECs in liver metastases in untreated mice, but SU6668 blocked activation of these signaling intermediates. Determining the activation status of the Erk and Akt signaling pathways in tumor ECs may serve as a surrogate marker for the effectiveness of antiangiogenic regimens.

Differential effects of phosphatidylinositol-3/Akt-kinase inhibition on apoptotic sensitization to cytokines in LNCaP and PCc-3 prostate cancer cells

Alterations in phosphatidylinositol 3'-kinase (PI3'-kinase) and Akt activation frequently occur in prostate cancer and may disrupt apoptotic induction by such cytokines as tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand (TRAIL). To examine the role of PI3' phosphorylation in the cellular response to cytokines, two prostate cancer cell lines with constitutively activated PI3'-kinase cascades (LNCaP and PC-3) were examined for direct sensitivity to cytokines. TNF or TRAIL alone failed to activate apoptosis in either LNCaP or PC-3 cells, and drug-mediated inhibition of the PI3k/Akt cascade caused only minimal activation of apoptosis in either cell line. Suppression of PI3'-kinase/Akt signaling markedly enhanced the apoptotic activity of both TNF and TRAIL in LNCaP cells but not in PC-3 cells. Adenovirus-mediated PTEN/MMAC1 expression in LNCaP cells reduced Akt activation, activated apoptosis, and sensitized cells to TNF but not to TRAIL. Together, these results suggest that PI3'-kinase signaling inhibits both TNF-mediated and TRAIL-mediated apoptosis but may represent one of several apoptotic resistance mechanisms that inhibit cytokine-mediated killing of prostate cancer cells.

EGCG, a major component of green tea, inhibits tumour growth by inhibiting VEGF induction in human colon carcinoma cells

Catechins are key components of teas that have antiproliferative properties. We investigated the effects of green tea catechins on intracellular signalling and VEGF induction in vitro in serum-deprived HT29 human colon cancer cells and in vivo on the growth of HT29 cells in nude mice. In the in vitro studies, (-)-epigallocatechin gallate (EGCG), the most abundant catechin in green tea extract, inhibited Erk-1 and Erk-2 activation in a dose-dependent manner. However, other tea catechins such as (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epicatechin (EC) did not affect Erk-1 or 2 activation at a concentration of 30 microM. EGCG also inhibited the increase of VEGF expression and promoter activity induced by serum starvation. In the in vivo studies, athymic BALB/c nude mice were inoculated subcutaneously with HT29 cells and treated with daily intraperitoneal injections of EC (negative control) or EGCG at 1.5 mg day(-1)mouse(-1)starting 2 days after tumour cell inoculation. Treatment with EGCG inhibited tumour growth (58%), microvessel density (30%), and tumour cell proliferation (27%) and increased tumour cell apoptosis (1.9-fold) and endothelial cell apoptosis (3-fold) relative to the control condition (P< 0.05 for all comparisons). EGCG may exert at least part of its anticancer effect by inhibiting angiogenesis through blocking the induction of VEGF.

Extracellular signal-regulated kinase activation is required for up-regulation of vascular endothelial growth factor by serum starvation in human colon carcinoma cells

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor important for colon cancer neovascularization. In previous studies, serum starvation led to induction of VEGF in human colon carcinoma cells. We investigated the possible participation of mitogen-activated protein kinases in serum starvation induction of VEGF in the HT29 human colon carcinoma cell line. The extracellular signal-regulated kinases (Erks) 1 and 2 were activated after 3-6 h of serum starvation. Using transient transfection of VEGF promoter-reporter constructs, serum starvation led to an increase in VEGF promoter activity. An inhibitor of phosphorylation of Erk-1/2 blocked the increase of VEGF expression and promoter activity induced by serum starvation. Serum starvation activates several mitogen-activated protein kinases, but activation of Erk-1/2 is critical for the up-regulation of VEGF mRNA in colon carcinoma cells.

Decreased Src tyrosine kinase activity inhibits malignant human ovarian cancer tumor growth in a nude mouse model

The Src protein tyrosine kinase is overexpressed and activated in a number of human cancers, including some human ovarian cancers. To determine whether Src activity plays a role in ovarian tumor growth, stable derivatives of the SKOv-3 human ovarian cancer cell line that exhibited reduced Src tyrosine kinase activity were generated by transfection with an antisense c-src construct. Comparison of these cell lines with parental SKOv-3 cells and stable sense c-src vector-transfected control lines revealed no phenotypic alterations in anchorage-dependent proliferation, adherence, density saturation, or wound migration. However, reduction in Src activity was associated with altered cellular morphology, dramatically reduced anchorage-independent growth, and, when assessed for tumor development in a xenograft nude mouse model, diminished tumor growth. Furthermore, reduction of Src activity in the antisense c-src cell lines was associated with reduced vascular endothelial growth factor mRNA expression in vitro, and tumors derived from these cell lines displayed a phenotype indicative of abortive microvessel vascularization. These results strongly suggest that Src is involved in critical oncogenic pathways that modulate tumor growth from this ovarian cell line. Furthermore, this evidence suggests that as in other tumor systems, Src activity is required for vascular endothelial growth factor induction and angiogenic development.

Transcriptional induction of the urokinase receptor gene by a constitutively active Src. Requirement of an upstream motif (-152/-135) bound with Sp1

Since c-src overexpression increases colonic cell invasiveness and because both Src activity and urokinase receptor protein are elevated in invasive colon cancers, the present study was undertaken: 1) to determine if a constitutively active Src regulates urokinase receptor expression and 2) to identify required cis-elements and trans-acting factors. SW480 colon cancer cells transfected with an expression plasmid (c-srcY527F) encoding a constitutively active Src protein manifested increased urokinase receptor gene expression and Src activity. Treatment of the src transfectants with a Src-inhibitor (PD173955) reduced urokinase receptor protein levels and laminin degradation. Inasmuch as we recently implicated an upstream region of the urokinase receptor promoter (-152/-135) in constitutive urokinase receptor expression, we determined its role for the induction by src. Whereas the activity of a CAT reporter driven by this region was stimulated by c-srcY527F, the u-PAR promoter mutated at the Sp1-binding motif in the -152/-135 region was not. Nuclear extracts from the src transfectants demonstrated increased Sp1 binding to region -152/-135 compared with those from SW480 cells. Finally, endogenous urokinase receptor protein amounts in 10 colon cancers and corresponding normal colon correlated with Src specific activity. These data suggest that urokinase receptor gene expression is regulated by Src partly via increased Sp1 binding.

Stimulation of the protein tyrosine kinase c-Yes but not c-Src by neurotrophins in human brain-metastatic melanoma cells

The c-Yes proto-oncogene (pp62c-Yes) encodes a non-receptor-type protein tyrosine kinase (NRPTK) of the Src family. c-Yes activities and protein levels are elevated in human melanoma and melanocyte cell lines. Because the neurotrophins (NT) are important in the progression of melanoma to the brain-metastatic phenotype, we determined whether NT stimulate c-Yes activity in human MeWo melanoma cells and two variant sublines with opposite metastatic capabilities, 3 S 5 and 70W. The highly brain-metastatic 70W subline had an intrinsically higher c-Yes activity than parental MeWo or poorly metastatic 3 S 5 cells. c-Yes kinase was further induced by the prototypic human NT, nerve growth factor (NGF) in a dose and time-dependent manner. In contrast, c-Src activity (pp60-Src) was similar in all these cells and unaffected by NGF exposure. Additionally, human NGF and neurotrophin-3 stimulated c-Yes in brain-metastatic 70W cells. The magnitude of c-Yes activation correlated with the degree of invasion of 70 W cells following incubation of these neurotrophins. To further examine NT stimulation of c-Yes in melanoma cells, three additional cell lines were examined. Metastatic TXM-13 and TXM-18 increased c-Yes activity in response to NGF. In contrast, no increase was observed in low-metastatic TXM-40 cells. Together, these data suggest that altered c-Yes expression may play a role in the malignant progression of the human melanocyte towards the brain-metastatic phenotype and that NT enhance the activity of c-Yes in signaling penetration into the matrix of NT-rich stromal microenvironments such as the brain.

Down-regulation of vascular endothelial growth factor in a human colon carcinoma cell line transfected with an antisense expression vector specific for c-src

Vascular endothelial growth factor (VEGF) is implicated in the angiogenesis of human colon cancer. Recent evidence suggests that factors that regulate VEGF expression may partially depend on c-src-mediated signal transduction pathways. The tyrosine kinase activity of Src is activated in most colon tumors and cell lines. We established stable subclones of the human colon adenocarcinoma cell line HT29 in which Src expression and activity are decreased specifically as a result of a transfected antisense expression vector. This study determined whether VEGF expression is decreased in these cell lines and whether the smaller size and reduced growth rate of antisense vector-transfected cell lines in vivo might result, in part, from reduced vascularization of tumors. Northern blot analysis of these cell lines revealed that VEGF mRNA expression was decreased in proportion to the decrease in Src kinase activity. Under hypoxic conditions, cells with decreased Src activity had a <2-fold increase in VEGF expression, whereas parental cells had a >50-fold increase. VEGF protein in the supernatants of cells was also reduced in antisense transfectants compared with that from parental cells. In nude mice, subcutaneous tumors from antisense transfectants showed a significant reduction in vascularity. These results suggest that Src activity regulates the expression of VEGF in colon tumor cells.

Regulation of vascular endothelial growth factor expression in human colon carcinoma cells by activity of src kinase

BACKGROUND

The c-src protooncogene encodes a protein tyrosine kinase, pp60c-src, that is a mediator in many signal transduction pathways. One pathway in which pp60c-src protein tyrosine kinase activity is implicated involves regulation of vascular endothelial growth factor (VEGF), an angiogenic factor important to neovascularization of growing tumors. Recently we demonstrated that decreased activity of pp60c-src in colon tumor cells contributes to decreased expression of VEGF. This study examined the relationship between pp60c-src activation, cell density, and VEGF production in a colon tumor cell line.

METHODS

Parental HT-29 colon adenocarcinoma cells and stable subclones created by transfection with c-src antisense and sense (control) expression vectors were plated under sparse (2 x 10(4) cells/cm2) and confluent (20 x 10(4) cells/cm2) conditions and grown for 36 hours. Protein and RNA were extracted from cells to determine pp60c-src levels, c-Src tyrosine kinase activity, and VEGF mRNA expression.

RESULTS

The pp60c-src kinase activity of HT-29 cells and control sense-transfected clones grown under confluent conditions was increased threefold to fivefold compared with cells grown under sparse conditions. In contrast, the ability of confluent culture conditions to increase pp60c-src activity was blunted in antisense transfectants. By regression analysis, VEGF expression was found to vary directly with pp60c-src levels (r2 = 0.886).

CONCLUSIONS

Cell density contributes to the regulation of c-src kinase activity and VEGF expression in HT-29 cells. When the steady-state level of pp60c-src is reduced in antisense transfectants, not only is the steady-state level of VEGF reduced, but the ability of confluence to stimulate pp60c-src activity and VEGF production is too. These data suggest that c-src may be an intermediary of both constitutive and inducible pathways for VEGF production in colon tumor cells.

Overexpression of focal adhesion kinase (p125FAK) in human colorectal carcinoma liver metastases: independence from c-src or c-yes activation

BACKGROUND

p125FAK, pp60C-src, and pp62c-yes are protein tyrosine kinases that function in signaling pathways regulating cell adhesion, migration, and growth. The expression and tyrosine kinase activities of pp60c-src and pp62c-yes, and the expression of p125FAK are increased in colorectal tumor metastases relative to normal mucosa. This study investigates whether differences in the activation of pp60c-src and pp62c-yes in colorectal liver metastases correlated with differences in p125FAK expression and whether prognostic significance could be demonstrated from the extent of expression of p125FAK in metastases.

METHODS

Activities of pp60c-src and pp62c-yes were measured in the immune complex kinase assay. Relative levels of p125FAK, pp60c-src, and pp62c-yes were determined by immunoblotting.

RESULTS

p125FAK was overexpressed in 29 of 30 colorectal cancer liver metastases (range of two-to 195-fold increase compared with normal mucosa). The degree of overexpression of p125FAK was not a significant prognostic factor in survival. A differential activation of pp60c-src and pp62c-yes in colorectal carcinoma liver metastases was observed. However, overexpression of p125FAK was observed in metastases with either pp60c-src or pp62c-yes activated in colorectal carcinoma liver metastases.

CONCLUSIONS

p125FAK overexpression appears to be a marker present in colorectal cancer cells with a metastatic phenotype. Furthermore, p125FAK overexpression is independent of pp60c-src or pp62c-yes activation in human colorectal carcinoma liver metastases.

Decreased tumorigenicity of a human colon adenocarcinoma cell line by an antisense expression vector specific for c-Src

In greater than 80% of colon tumors and established cell lines, the specific activities of the protein tyrosine kinases pp60(c-src) and pp62(c-yes) are increased with respect to normal colonic epithelial cells. However, no mutations in either gene have been identified in colon tumors. Therefore, the possible biological consequences of activations of these protein tyrosine kinases in colon tumors have been unclear. To determine if pp60(c-src) activation affects growth and tumorigenicity of established colon tumor cell lines, an antisense expression vector that specifically reduces pp60(c-src) expression was constructed. The vector was transfected into HT 29 cells, an established colon tumor cell line in which both pp60(c-src) and pp62(c-yes) are activated. Two stable subclones were isolated in which pp60(c-src) but not pp62(c-yes) expression and activity were reduced. These established cell lines proliferated more slowly than parental cells proportionately to reduction in pp60(c-src) expression. When injected into nude mice, antisense transfected cells formed slow-growing tumors; however, the rate of tumor growth was reduced far greater than would be predicted from decreased proliferation rates in tissue culture. In contrast, stable subclones transfected with a comparable "sense" expression vector were unaltered in growth rates in tissue culture and in nude mice with respect to parental HT 29 cells. These data demonstrate that the activation of pp60(c-src) alone contributes to the tumorigenicity of HT 29 cells, a cell line widely used as a model for biological properties of colon carcinoma. Furthermore, because pp60(c-src) and pp62(c-yes) appear redundant to the growth regulation of normal colonic epithelial cells, the data suggest that src-specific inhibitors might be of therapeutic value for colon cancer.

Differential activation of pp60(c-src) and pp62(c-yes) in human colorectal carcinoma liver metastases

pp60(c-src) and pp62(c-yes) are protein tyrosine kinases whose specific activities are increased in primary colorectal carcinomas. Activity of pp60(c-src) is further increased in colorectal liver metastases. This study was undertaken to compare pp60(c-src) and pp62(c-yes) expression and activity in human colorectal carcinoma liver metastases and to determine the potential prognostic significance of differences in activation of these two kinases. The pp60(c-src) and pp62(c-yes) tyrosine kinase activities and protein levels relative to those in normal colonic mucosa were determined using an immune complex kinase assay and immunoblot analysis in tissue specimens from 22 patients with primary colorectal carcinoma and synchronous metastatic liver disease and from 9 patients with metachronous colorectal carcinoma liver metastases. Of the primary colon tumors, 64% of the tumors contained elevated activities of both pp60(c-src) and pp62(c-yes). For liver metastases, however, only 10% had activation of both tyrosine kinases, 61% had elevated pp60(c-src) activity only, and 23% had elevated pp62(c-yes) activity only. Analysis of synchronous metastases from primary tumors with elevated activities in both kinases demonstrated that in 71% of these patients, the activity of either pp60(c-src) or pp62(c-yes) decreases relative to the primary tumor. Protein levels of pp60(c-src) and pp62(c-yes) in primary carcinomas and metastases remained unchanged from levels in normal colonic mucosa. These results demonstrate that differential regulation of the activities of pp60(c-src) and pp62(c-yes) occurs during tumor progression. Patients with either synchronous or metachronous liver metastases and elevated pp62(c-yes) kinase activity have biologically more aggressive disease and a worse prognosis than patients without elevated pp62(c-yes) activity in their liver metastases (median survival, 13 months versus 30 months, P < 0.005, Wilcoxon signed rank test). Analysis of patients with synchronous liver metastases also demonstrated a worse prognosis for those with elevated pp62(c-yes) kinase activity (P < 0.05, Wilcoxon signed rank test).

A tyrphostin-derived inhibitor of protein tyrosine kinases: isolation and characterization

We recently reported that tyrphostin 23 (3,4-dihydroxybenzylidene malononitrile) is unstable in solution and that some of the degradation products are better inhibitors of the tyrosine kinase activity of Src and the EGF-receptor kinase than the parent compound itself (Ramdas et al., Cancer Res. 54, 867-868, 1994). In this study, the tyrphostin 23-derived compound designated P3, which is a more stable and potent protein tyrosine kinase inhibitor, was isolated. P3 was purified from oxidized tyrphostin 23 by solvent extraction, silica-gel flash chromatography, and reverse-phase high-pressure liquid chromatography. The physical characteristics of the isolated compound were determined and its chemical structure elucidated by 1H and 13C NMR spectroscopy. The proposed structure of this new inhibitor is that of a tyrphostin 23 dimer joined at the benzylidene carbon. P3 was evaluated in vitro as an inhibitor of four different protein tyrosine kinases (Src, Csk, EGF-receptor, and FGF-receptor) and two protein serine kinases (PK-A and PK-C). This compound exhibited the most inhibitory activity against Src with a Ki value of 6 microM and was less inhibitory toward the other protein kinases with Ki values ranging from 35 to 300 microM. P3 did not inhibit other nucleotide-utilizing enzymes such as lactate dehydrogenase and hexokinase. The growth and colony formation of HT-29 colon adenocarcinoma cells that contain activated Src was inhibited by P3 with an IC50 value of approximately 10 microM.

Down-modulation of epidermal growth factor receptor accompanies TNF-induced differentiation of the DiFi human adenocarcinoma cell line toward a goblet-like phenotype

Although the biologic response modifier tumor necrosis factor-alpha (TNF) is a known differentiation inducer in hematopoietic cells, its role in differentiation of other tissue types has yet to be elucidated. In the studies presented here, TNF treatment of the human rectal adenocarcinoma cell line, DiFi, elicits characteristics of early stage differentiating, mucin-producing colonocytes. Not only are TNF-treated DiFi cells growth-inhibited by TNF, but they also display a unique morphology. Additionally, TNF treatment of DiFi cells enhances > fivefold the expression of high molecular weight mucin glycoproteins, as measured by [125I]-wheat germ agglutinin (WGA) binding and the human milk fat globule-1 (HMFG-1) anti-MUC1 antibody reactivity. The induction of these differentiation characteristics correlates with novel alterations in epidermal growth factor receptor (EGF-R). Following 5-day TNF treatment of DiFi cultures, EGF receptor levels, kinase autophosphorylation activity, and receptor tyrosine phosphorylation are reduced by > fourfold. The establishment of a model system in which goblet-like cell characteristics and alterations in a growth factor receptor can be induced in vitro may be potentially useful in studying the underlying mechanisms of colonic epithelial cell proliferation and differentiation.

Bacterial expression of an active tyrosine kinase from a protein A/truncated c-src fusion protein

The carboxy-terminal half of the c-src protein fused to the protein A moiety was expressed in bacteria. The protein A/truncated c-src fusion protein, which does not have SH2 and SH3 domains, is found in the periplasmic space allowing for a simple one-step purification and demonstrated high efficiency in autophosphorylation and exogeneous substrate phosphorylation. The missense mutation at codon 294 (Ile-->Thr), which is located in the ATP-binding domain of the c-src, resulted in dramatic reduction of tyrosine kinase activity of the fusion protein. Using the fusion protein, we also revealed that staurosporin, a well-known kinase inhibitor, directly affects autophosphorylation of the C-terminal half of the c-src protein. This truncated c-src expression system provides a good source of enzyme for diverse experiments and is an ideal model for understanding the implication of structural alterations in the catalytic activity of the c-src kinase by site-directed mutagenesis experiments.

Transforming growth factor-alpha production and autoinduction in a colorectal carcinoma cell line (DiFi) with an amplified epidermal growth factor receptor gene

The DiFi colorectal carcinoma cell line, derived from a patient with familial adenomatous polyposis, was examined for gene expression and production of the autocrine growth factor transforming growth factor alpha (TGF-alpha) and for epidermal growth factor receptor (EGFR) gene expression and gene copy number. DiFi cells expressed TGF-alpha transcripts as identified on Northern (RNA) blots. Addition of TGF-alpha (10 ng/ml) or EGF (10 ng/ml) to DiFi cell cultures (lacking EGF or serum) up-regulated DiFi cell basal TGF-alpha mRNA levels, suggesting that autoinduction of TGF-alpha occurs in these cells. DiFi cell cultures in log phase growth secreted measurable amounts of TGF-alpha (347 pg/10(6) cells/24 h) into their culture medium, as determined by radioimmunoassay. DiFi cells showed strong overexpression of the EGFR gene on Northern blots relative to three other colon cancer cell lines examined. Immunoperoxidase staining showed enhanced EGFR expression in a cell subpopulation among the original (uncultured) ascitic fluid cells from which the DiFi cell line was established. This cell subpopulation was observed to expand dramatically between passages 1 and 25. Immune complex kinase assay of DiFi cells showed that EGFR were functional as determined by their ability to autophosphorylate. The EGFR gene in these cells was not found to be rearranged or genetically altered using Southern blot analysis. Dot blot analysis of DiFi cell DNA revealed EGFR gene amplification in the range of 60-80 copies/cell, which is approximately twice the copy number seen in A-431 epidermoid carcinoma cells. To our knowledge DiFi cells represent the first example of EGFR gene amplification in a colorectal adenocarcinoma. Because DiFi colorectal cancer cells uniquely show production and auto-induction of TGF-alpha in addition to amplification and overexpression of the EGFR gene, these cells represent a valuable tool for studying the role(s) of the EGFR in the regulation of tumor cell growth.

Site-specific differences in pp60c-src activity in human colorectal metastases

The c-src proto-oncogene has been implicated in the progression of primary human colorectal carcinoma to hepatic metastasis. To determine if increased pp60c-src tyrosine kinase activity is a colon-specific phenomenon present in colorectal metastases to all sites, the pp60c-src-specific kinase activity of noncolon tumor metastases to the liver was compared to that of colorectal liver metastases. Activity of extrahepatic colon carcinoma metastases was compared to that of colorectal liver metastases as well as that of normal colonic mucosa. The specific activity of pp60c-src in multiple synchronous metastases from colon carcinoma was also examined. Tyrosine kinase activity was determined by immune complex kinase assay; protein levels were determined by immunoblotting. Specific activity was calculated for each group by dividing the total activity by protein level. Colon carcinoma metastases to the liver had significantly (P < 0.04) increased pp60c-src activity with an average 2.2-fold increase over normal mucosa. In contrast, noncolon tumor metastases to the liver showed minimal pp60c-src kinase activity. Extrahepatic colorectal metastases demonstrated significantly increased (P < 0.005) pp60c-src activity with an average 12.7-fold increase over normal mucosa. When compared to colon liver metastases, extrahepatic colorectal tumor metastases show a significant difference in activity (P < 0.05) with an average 5.7-fold increase. Examination of multiple synchronous colon carcinoma metastases confirmed these results. In summary, we conclude that (1) the activation of pp60c-src between primary tumors and metastases is specific to colon metastases, and (2) although pp60c-src activity is significantly increased in colorectal metastases, site-specific differences in the magnitude of activity are evident.

Increase in activity and level of pp60c-src in progressive stages of human colorectal cancer

Activation of the tyrosine kinase of the c-src gene product, pp60c-src, has been shown to occur in nearly every primary colorectal carcinoma, and is found as early as in polyps of high malignant potential. However, no studies have addressed potential pp60c-src changes which occur during progression. To examine this question, we have studied kinase activity and protein levels in 7 colonic polyps, 19 primary lesions, and 19 liver metastases relative to normal colonic mucosa. Significant increases in tyrosine kinase activity were seen as early as in colonic polyps of high malignant potential. Further increases were observed in activity and level in primary tumors. However, the greatest increases in activity and protein levels were observed in liver metastases. Additionally, six metastatic lesions were obtained in which synchronous primary tumor was resected. In each of these liver metastases, pp60c-src activity and level were significantly increased relative to the corresponding primary tumor, as well as to normal colonic mucosa. Our results demonstrate that progression of colon primary tumors to liver metastases correlates with increased pp60c-src kinase activity and protein level.

The biology of colorectal carcinoma

Rapid progress in understanding the biology of colorectal carcinoma has occurred in the last decade. During this time, the importance of tumor suppressor genes has been delineated. Mutations in proto-oncogenes, and some of the genetic and epigenetic defects that occur during neoplastic transformation, have been characterized. The very recent identification of a technology that detects some mutations in genes by analyzing fecal specimens offers the real prospect of effective, low-cost screening of large segments of the population at risk for the development of large bowel cancer. A better understanding of the mechanisms involved in metastasis is slowly leading to better methods of prognostication for patients with carcinoma of the colon or rectum. This is important because a better biologic identification of patients at high risk for subsequent metastasis will help determine which patients should receive adjuvant therapy. Further, the development of new approaches to inhibit various aspects of the cascade of events necessary to produce metastasis, notably the inhibition of neovascularization, suggests the real possibility that established metastases may be treated by relatively nontoxic medical therapies. As a result, further knowledge of the biology of colorectal cancer will translate into strategies that will continue to improve the control of this prevalent carcinoma.

Transfection of activated c-H-rasEJ/pSV2neo or pSV2neo genes into rat mammary cells: rapid stimulation of clonal diversification of spontaneous metastatic and cell-surface properties

We examined whether the conversion of benign rat mammary cells to metastatic cells by transfection of c-H-rasEJ/pSV2neo or control pSV2neo genes results in rapid stimulation of diversification of cellular phenotypes. Transfection of c-H-rasEJ into twice-cloned, stable (greater than 1 year) rat mammary MTC.4 cells, followed quickly by cell cloning, revealed differences in transfected oncogene copy numbers and expression of p21rasEJ. No correlation between c-H-rasEJ copy numbers or the cellular amounts of p21rasEJ or total p21ras and spontaneous metastatic potentials was found. By subcloning transfected cells as soon as possible after gene transfer, we found some rearrangements and amplifications of c-H-rasEJ and heterogeneous spontaneous metastatic potentials. In addition, the expression of the mammary tumor metastasis-associated cell-surface glycoprotein gp580 on untransfected and transfected MTC.4 cells indicated that the cell populations of higher metastatic potential were also more diverse in their cell-to-cell antigen expression than untransfected or non-metastatic, transfected MTC.4 cells. In contrast, the expression of a putative metastasis-suppressor gene, nm23, was unchanged after transfection and subcloning. Control pSV2neo transfections or calcium phosphate treatment alone also resulted in the generation of cellular heterogeneity, although at an apparently lower frequency than c-H-rasEJ transfections, suggesting that transfection of activated, dominantly acting oncogenes, or in some cases control genes, can result in destabilization of transfected cells, rapid diversification and generation of heterogeneity in growth rate, spontaneous metastatic potential and antigen expression.

Growth inhibition of human colorectal carcinoma cell lines by tumor necrosis factor-alpha correlates with reduced activity of pp60c-src

One molecular alteration that has been observed in the majority of colorectal carcinomas is the activation of pp60c-src kinase. To address the role of pp60c-src in growth control of colon carcinoma cell lines, the effects of the biologic response modifier, tumor necrosis factor (TNF)-alpha were studied on the established HT29 colorectal carcinoma cell line and two clonal variants derived from the parental line. In one clone, HT29-A34, approximately 55% growth inhibition was observed following a 120-h incubation period with 10(3) U/ml TNF. In this TNF-sensitive cell line, pp60c-src immune complex kinase activity was reduced 3.9-fold accompanied by only a slight reduction in pp60c-src protein levels. Growth inhibition and decreased pp60c-src kinase activity correlated in a dose-dependent manner. The HT29-A14 TNF-resistant clone was not growth-inhibited by TNF, and no changes in pp60c-src were observed following treatment. Growth inhibition also correlated with reduced pp60c-src kinase specific activity in a number of other established colon carcinoma cell lines that were TNF-sensitive. In TNF-resistant colon carcinoma cell lines, pp60c-src kinase activity and levels remained unchanged. When changes in specific activity of pp60c-src were observed in sensitive cells, they occurred after decreased [3H]-thymidine uptake was observed. Therefore, these changes in pp60c-src activity are not the earliest event in TNF-induced growth inhibition. Nevertheless, our results suggest that modulation of pp60c-src kinase activity may be important in growth control of colorectal carcinoma cell lines.

Autocrine growth stimulation by transforming growth factor-alpha in human non-small cell lung cancer

We studied the biological response to and production of transforming growth factor-alpha (TGF-alpha) by the non-small cell lung carcinoma (NSCLC) clonal cell lines H226b, H322a, H460a, H596b. Each of these cell lines expressed epidermal growth factor receptor (EGFR) as determined by [125I]EGF competitive binding and Scatchard analysis and by phosphorylation. The receptors were functionally active as determined in immune complex kinase assays. H322a, H226b, H460a, and H596b cells showed stimulated [3H]thymidine (Thd) uptake in response to TGF-alpha. Exogenously added TGF-alpha increased colony formation in soft agar for three of the cell lines in media containing serum. All cell lines expressed TGF-alpha detected by immunohistochemistry and TGF-alpha mRNA, although to differing degrees. Cell lysates and spent media competed for EGFR binding with EGF, thus demonstrating production of TGF-alpha-like activity. The anti-TGF-alpha monoclonal antibody AB-3 inhibited the uptake of [3H]Thd by proliferating H322a and H226b cells but not H460a and H596b cells. No inhibition occurred with MOPC21 antibody and inhibition was completely reversed by addition of TGF-alpha to the culture. Suramin inhibited cell proliferation and [3H]Thd uptake by all cell lines. Inhibition of H460a and H596b cells was reversed with exogenous TGF-alpha but not PDGF. Our data suggests that TGF-alpha is a mediator of autocrine growth stimulation for NSCLC cells, and that for some NSCLC cells cytoplasmic binding of receptor and ligand is the primary mechanism for autocrine growth stimulation.

Effect of herbimycin A on growth and pp60c-src activity in human colon tumor cell lines

The effect of herbimycin A, an ansamycin antibiotic which inhibits cellular transformation by retroviral tyrosine kinases, on the monolayer growth of seven colon tumor cell lines and one cell line established from normal colonic mucosa, CCL239, was examined. Each colon tumor cell line tested showed dose-dependent growth inhibition in response to herbimycin A. A 125ng ml-1 dose of the antibiotic caused greater than 40% growth inhibition in all colon tumor cell lines after two cell doublings. In contrast, at similar herbimycin A concentrations only 12% inhibition was observed in 'normal' CCL239 cells. No major morphologic changes were observed at the light microscopic level in any of the tumor cell lines or CCL239 cells in response to treatment with herbimycin A. Studies using the HT29 colon adenocarcinoma cell line showed dose-dependent inactivation of pp60c-src by herbimycin A, resulting in decreased autophosphorylation, enolase phosphorylation and steady-state levels, which correlated with cellular growth inhibition. Herbimycin A-induced reductions in pp60c-src kinase activity preceded changes in pp60c-src steady-state levels. Growth and pp60c-src inhibition were reversible following removal of herbimycin A from cell culture media. Our results suggest that regulation of pp60c-src tyrosine kinase activity may be important in growth control of colon tumor cells.

Susceptibility to ras oncogene transformation is coregulated with signal transduction through growth factor receptors

The human teratocarcinoma cell line PA-1 was derived from culturing ascites fluid cells from a patient with an ovarian germ line tumor. We previously described a non-neoplastic variant cloned from the PA-1 human teratocarcinoma cell line, clone 6, which at passage 40 was resistant to transformation by activated ras oncogenes. However, these cells could be transformed by a plasmid containing both myc and ras. Another PA-1 cell variant, clone 1, isolated at passage 63 and used 50 passages later becomes tumorigenic in nude mice after transfection with an activated ras oncogene (Tainsky et al., Anticancer Res., 8, 899-914, 1988). We report here that the progression from ras resistance to ras susceptibility occurs in both clone 1 and clone 6 cells during 25 passages in culture. In the presence of epidermal growth factor, transforming growth factor-alpha, and basic fibroblast growth factor, the ras-transformable cells exhibit anchorage independent growth, whereas the ras-resistant cells can not be growth stimulated by these growth factors. Similarly, ornithine decarboxylase (ODC) activity was inducible in ras susceptible and ras transformed cells by these growth factors, but not in the ras resistant cells. These differences are not due to the level and activity of epidermal growth factor receptor or to the level of expression of 25 proto-oncogenes.

Cellular growth response to epidermal growth factor in colon carcinoma cells with an amplified epidermal growth factor receptor derived from a familial adenomatous polyposis patient

The receptor binding and cellular growth responses to exogenous epidermal growth factor (EGF) were studied using the DiFi cell line established from a familial adenomatous polyposis patient. The number of cell membrane EGF receptors on DiFi cells, as measured by competitive radioligand binding assays and Scatchard analysis of 125I-EGF binding isotherms, was calculated to be 4.8 x 10(6) receptors/cell. An acid prewash step performed prior to ligand binding assays did not reveal additional receptor numbers. A single, low-affinity receptor population was identified by Scatchard analysis, with an apparent Kd of 4.6 nM. This result was confirmed by radioligand binding studies performed in the presence and absence of the receptor-antagonist monoclonal antibody 528 IgG that binds predominantly to the low-affinity form of the EGF receptor. DiFi cells at 50-60% confluence, when exposed to 50 nM exogenous EGF, exhibited a rapid but partial (30%) reduction in their cell membrane-associated receptor, characteristic of sequestration. Exposure of DiFi cells to 50 nM EGF for longer periods of time (4 h) did not result in any further reduction in EGF-receptor number. The cellular growth response of DiFi cells to exogenous EGF was studied in monolayer cultures as well as in a soft agarose assay. Inhibition of soft agar colony formation was observed at exogenous EGF concentrations greater than 1.7 nM, and inhibition of monolayer growth occurred at EGF concentrations greater than 1 nM. In immune complex kinase assays, the DiFi receptor showed similar specific activity to that from the well-characterized A431 cell line. Additionally, phosphorylation of the receptor on tyrosine was qualitatively similar to that of A431 cells, further suggesting that the DiFi receptors identified by EGF-binding studies were biologically functional.

Lack of correlation between intercellular junctional communication, p21rasEJ expression, and spontaneous metastatic properties of rat mammary cells after transfection with c-H-rasEJ or neo genes

The loss of intercellular junctional communication between rat 13762NF mammary carcinoma cells and their spontaneous metastatic potentials from the mammary fat pad show a high degree of correlation. We examined a stable, benign, completely junctionally coupled cell clone (MTC.4) of this system after calcium phosphate-mediated transfection with c-H-rasEJ/pSV2neo and control pSV2neo-containing plasmids. There was a good correlation between the copy numbers of c-H-rasEJ incorporated into MTC.4 cells and their contents of p21rasEJ; however, there was not always a correspondence between spontaneous metastatic potential and copy number of c-H-rasEJ or amount of p21rasEJ. After c-H-rasEJ/pSV2neo transfection, some MTC.4 cells lost intercellular junctional communication and became spontaneously metastatic, although some nonmetastatic transfectants also had low percentages of junctionally coupled cells. One of the control pSV2neo transfectants also became metastatic and lost intercellular junctional coupling, and calcium phosphate treatment itself resulted in increased growth rates at mammary fat pad sites and a marginal increase in incidence of spontaneous metastases, both of which preceded loss of intercellular junctional coupling in some cells. Examination of 12 subclones derived from two cloned transfectants, however, revealed a poor correlation between spontaneous metastatic potential and intercellular junctional coupling. The results suggest that loss of junctional communication between cells is often but not always associated with the progression of cells from benign to metastatic states.

Tumor necrosis factor modulates epidermal growth factor receptor phosphorylation and kinase activity in human tumor cells. Correlation with cytotoxicity

Tumor necrosis factor (TNF) is a cytokine which induces cytotoxicity in some but not all tumor cells. Initial studies of five tumor cell lines demonstrated that TNF was able to rapidly (within 30 min) modulate tyrosine protein kinase activity of epidermal growth factor (EGF) receptors on tumor cell lines which were sensitive to the cytotoxic effects of TNF but not alter EGF receptor kinase activity in TNF-resistant tumor cells. Two tumor cell lines (ME-180 cervical carcinoma and T24 bladder carcinoma) which have been shown to express similar TNF-binding characteristics but differ in their sensitivity to the cytotoxic actions of TNF were chosen for further characterization. Treatment of TNF-sensitive ME-180 cells with 1 nM TNF resulted in a 3-fold stimulation of EGF receptor tyrosine protein kinase activity within 10 min which correlated with increased phosphorylation of EGF receptor protein itself. In addition, dose-response studies indicate that similar concentrations of TNF modulate both ME-180 cell growth and EGF receptor kinase activity. Treatment of TNF-resistant T24 cells showed that TNF had no significant effect on their growth, EGF receptor tyrosine protein kinase activity, or phosphorylation of EGF receptor protein although EGF receptor kinase activity was stimulated by EGF. Quantitation of receptors expressed on the surface of ME-180 and T24 cells demonstrated a 3-fold difference between the number of EGF-binding sites on T24 (100,000) versus ME-180 cells (300,000), suggesting the relative abundance of EGF receptor does not solely account for differential effects of TNF on EGF receptor activation in these two cell lines. Phosphoamino acid analysis of EGF receptor from 32P-equilibrated ME-180 cells demonstrated that TNF-induced phosphorylation of amino acids which was quantitatively similar to that of EGF but distinct from the effects of phorbol ester. However, unlike EGF, TNF was unable to stimulate EGF receptor kinase activity in ME-180 cell lysates. The kinetics of EGF receptor activation and the metabolic consequence of activation of EGF receptor activity by TNF appear to be distinct from those induced by EGF. These results suggest that TNF-induced modulation of EGF receptor occurs through a unique mechanism and may play a role in the cytotoxic actions of TNF.

Early events in the antiproliferative action of tumor necrosis factor are similar to the early events in epidermal growth factor growth stimulation

The process of TNF-induced cytotoxicity is complex but appears to be mediated through a TNF-specific cell surface receptor. Recent evidence suggests that TNF action on tumor cells may be antagonized by epidermal growth factor (EGF) and other EGF-receptor modulatory peptides implicating a role for EGF-R in the process of TNF-induced cytotoxicity. In the present report, we investigated the biochemical actions of TNF on several biochemical events known to occur in the process of EGF signal transduction in intact cells. The actions of TNF were compared directly to those of EGF in both TNF-sensitive and -resistant tumor cell lines. In TNF-sensitive ME-180 cervical carcinoma cells, TNF (20 ng/ml) stimulated the tyrosine protein kinase activity of the EGF-receptor (EGF-R) fivefold when measured by receptor autophosphorylation in an immune complex kinase assay. TNF activation of EGF-R kinase activity in ME-180 was measurable 10 min after TNF incubation and enzymatic activity remained elevated 20 min after TNF addition. Activation of the receptor by TNF correlated with increased 32P incorporation into EGF-R protein when receptor was immunoprecipitated from 32P-equilibrated cells following a 20 min incubation with TNF. Acid hydrolysis of EGF-R protein isolated from TNF-treated ME-180 cells demonstrates an increase in the phosphotyrosine content of EGF-R when compared to receptor isolated from untreated cells. The results suggest that TNF increased EGF-R tyrosine protein kinase activity and the state of EGF-receptor tyrosine phosphorylation in a manner similar to that reported for EGF. However, TNF does not appear to be structurally related to EGF since TNF was unable to directly activate EGF-R when incubated with extensively washed immunoprecipitates of EGF-R. In TNF-resistant T24 bladder carcinoma cells, TNF failed to alter EGF-R tyrosine protein kinase activity although both EGF and phorbol ester were shown to modulate the enzymatic activity of the receptor in these cells. These results indicate that the ability of TNF to modulate EGF-R kinase in target cells may correlate with its cytotoxic actions on TNF-sensitive tumor cells. Other biochemical activities associated with the induction or regulation of cellular growth were examined in TNF- or EGF-treated tumor cells. EGF stimulated a rapid 8-16-fold increase in the expression of the proto-oncogene c-myc when analyzed by dot-blot analysis of total cellular RNA or Northern blot hybridization of polyadenylated RNA. TNF treatment failed to alter c-myc expression in ME-180 cells when analyzed by either technique.(ABSTRACT TRUNCATED AT 400 WORDS)

Epidermal growth factor receptor protein-tyrosine kinase activity in human cell lines established from squamous carcinomas of the head and neck

Two cell lines established from tumors of the head and neck area at different clinical stages were found to differ in the expression and in the tyrosine kinase activity of the epidermal growth factor (EGF) receptor. Cell line 183A was derived from an early-stage tumor and cell line 1483 was derived from a tumor that had metastasized to lymph nodes. The 1483 cells displayed a higher plating efficiency and clonogenicity in soft agar, suggesting a more tumorigenic phenotype over the 183A cells. Analyses of EGF receptor levels by using R1 anti-EGF receptor serum indicated that the 1483 cells expressed 5-fold more receptor than did the 183A cells. EGF receptors isolated from each cell line were active for kinase activity in an immune complex kinase assay, using monoclonal R1 anti-EGF receptor antibody. The autophosphorylation activity of both receptors was stimulated by addition of EGF to isolated membrane preparations and intact cells, although the EGF receptor of the 1483 cells was much less responsive to EGF than the receptor from 183A cells. In addition, the 1483 receptor consistently incorporated about twice as much phosphate as did the 183A receptor in an immune complex kinase assay. These data suggest that the basal tyrosine kinase activity of the EGF receptor from 1483 cells may be more active than the EGF receptor kinase from 183 cells.

Effect of epidermal growth factor (EGF) on a newly established head and neck squamous carcinoma cell line

A new cell line designated 584A2 has been recently established from a patient with squamous cell carcinoma of the larynx. Cytogenetic analysis of the cell line revealed multiple copies of chromosome 7, as well as a homogeneous staining region (HSR) on one chromosome 7. Since overexpression of epidermal growth factor (EGF) cell surface receptors (EGFr) often occurs in other squamous carcinoma cell lines, it was predicted that 584A2 might overexpress EFGr. This was confirmed by: (1) metabolic labeling, with subsequent immunoprecipitation of EGFr and comparing autoradiographs to a cell line without an HSR and fewer copies of chromosome 7, and (2) performing EGF binding assays with Scatchard analysis. Since overexpression of EGFr correlates with an inhibitory effect of EGF on cell culture, the biological effects of EGF on 584A2 were examined in this study. At 5 ng/ml (serum-free medium), EFG stimulated incorporation of [3H] thymidine into trichloroacetic acid-precipitable material compared with controls. Incorporation increased between days 0 to 1 and 1 to 2 days with a 6- to 7-fold maximum. Dose-response studies (0 to 100 ng/ml) indicated maximum incorporation (6- to 7-fold) occurred between 0.1 ng/ml and 1.0 ng/ml. Cell growth was monitored over 7 days and, during this time, 5 ng/ml EGF produced a 10- to 12-fold increase in absolute cell numbers when compared with controls. We concluded that, unlike other squamous carcinoma lines with elevated EGFr, EGF stimulates rather than inhibits 584A2 cell proliferation.

Pyrimido-pyrimidine modulation of EGF growth-promoting activity and p21ras expression in rat mammary adenocarcinoma cells

RA 233, a pyrimido-pyrimidine analogue developed originally as an antiplatelet agent, has reduced the incidence of tumor metastases in clinical trials. However, in animal tumor models antimetastatic therapy using RA 233 has been inconsistent. We therefore tested RA 233 for additional effects, such as its direct action on tumor cells. Using the rat 13726NF mammary adenocarcinoma tumor system, low, nontoxic concentrations of RA 233 had pleiotropic and differential effects on two 13762NF tumor cell clones. The growth of MTC cells (low spontaneous metastatic potential) was not affected by low concentrations of RA 233 (50 microM) or epidermal growth factor (EGF) (up to 10 ng/ml) for 3 days in 0.5-10% fetal bovine serum. In contrast, MTLn3 (high spontaneous metastatic potential) cell cultures maintained for 3 days in low (0.5-1%) serum in the presence of 1.25-10 ng/ml EGF doubled in cell numbers compared with control cultures, and addition of 50 microM RA 233 abrogated the growth-stimulatory effect of EGF. The inhibitory effect of RA 233 on MTLn3 cells was dose dependent and not due to cell toxicity as determined by cell viability, cell growth, and colony formation properties after drug removal. In addition, incubation of MTLn3 cells with 50 microM RA 233 resulted in an increase of p21ras protein expression, whereas there was no effect on the level of p21ras in identically treated MTC cells or when either clone was treated with 10 ng/ml EGF. The results suggest that among the heterogeneous effects of RA 233 on tumor cells, modulation of growth factor responses and regulatory molecules may be important.

Establishment and characterization of two new squamous cell carcinoma cell lines derived from tumors of the head and neck

Two human cell lines were established from untreated squamous cell carcinomas of the head and neck. Line 183 was derived from a head and neck squamous cell carcinoma of the tonsil and 1483 from a head and neck squamous cell carcinoma of the retromolar trigone. Both lines grow in a cobblestone pattern demonstrating their epithelial heritage. Immunofluorescence studies and one-dimensional polyacrylamide gel electrophoresis indicated that both lines contain cytokeratins. Line 1483 is more aggressive in nude mice, has a higher efficiency for anchorage-independent growth, expresses p21ras (product of the ras oncogene) at a higher level, and is more aneuploid than 183. 1483 also grows as a multicellular tumor spheroid. Line 1483, which was established from the primary tumor of a patient with nodal metastasis, thus displays more progressed characteristics than line 183, which was established from a patient with no clinically positive nodes.