Role of c-Src in Carcinogenesis and Drug Resistance

The aberrant transformation of normal cells into cancer cells, known as carcinogenesis, is a complex process involving numerous genetic and molecular alterations in response to innate and environmental stimuli. The Src family kinases (SFK) are key components of signaling pathways implicated in carcinogenesis, with c-Src and its oncogenic counterpart v-Src often playing a significant role. The discovery of c-Src represents a compelling narrative highlighting groundbreaking discoveries and valuable insights into the molecular mechanisms underlying carcinogenesis. Upon oncogenic activation, c-Src activates multiple downstream signaling pathways, including the PI3K-AKT pathway, the Ras-MAPK pathway, the JAK-STAT3 pathway, and the FAK/Paxillin pathway, which are important for cell proliferation, survival, migration, invasion, metastasis, and drug resistance. In this review, we delve into the discovery of c-Src and v-Src, the structure of c-Src, and the molecular mechanisms that activate c-Src. We also focus on the various signaling pathways that c-Src employs to promote oncogenesis and resistance to chemotherapy drugs as well as molecularly targeted agents.

GPR68 limits the severity of chemical-induced oral epithelial dysplasia

Head and neck cancer is the sixth most common malignancy, and there is an urgent need to identify physiological processes contributing to tumorigenesis. Extracellular acidification caused by aerobic glycolysis within tumor microenvironments can stimulate proton-sensing receptors. GPR68, or ovarian cancer G protein-coupled receptor 1, responds to extracellular acidity and is highly expressed in head and neck squamous cell carcinoma (HNSCC) as well as normal esophageal tissue. To study the role of GPR68 in oral dysplasia, wild-type and GPR68^-/- mice were treated with 4-Nitroquinoline N-oxide (4NQO) in drinking water for 11-13 weeks, followed by normal water for 11-12 weeks. 4NQO treatment resulted in 45 percent of GPR68^-/- mice developing severe dysplasia or squamous cell carcinoma compared to only 10.5 percent of GPR68^+/+ mice. This correlated with increased frequencies of regulatory T cells in the spleens of male GPR68^-/- mice. Dysplastic regions of the tongue had increased CD31 staining compared to normal regions in both GPR68^-/- and GPR68^+/+ mice, suggesting that angiogenesis was GPR68-independent. RNA knockdown studies using HNSCC cell lines demonstrated no direct effect of GPR68 on survival or growth. Overall, we demonstrate that GPR68-deficiency worsens the severity of chemical-induced oral dysplasia, suggesting a protective role for this gene in tumorigenesis.

Abstract A004: Chemoprevention of head and neck cancers by the combination of epigallocatechin gallate (EGCG) and resveratrol

Head and neck cancer (HNC) is a devastating disease and the 6th most common cancer worldwide. Most HNC patients are diagnosed with advanced stage disease for which the 5-year survival is below 50%, stressing the need for chemoprevention. Recently, we have reported that the combination of resveratrol and EGCG induces synergistic apoptosis and inhibits xenografted HNC growth by inhibiting AKT-mTOR pathway. In this study, we have investigated the chemopreventive efficacy of resveratrol, EGCG and their combination using 4NQO-induced oral carcinogenesis model. C57BL/6 mice were exposed to 4-NQO (50 μg/ml) via drinking water for 10 weeks, followed by treatment with vehicle (50% sweetened condense milk), resveratrol (30 mg/kg), EGCG (30 mg/kg) and their combination for 8 weeks, 5 days/week. The mice were sacrificed on week 24 and the number of visible and microscopic lesions were counted. Resveratrol alone and in combination with EGCG significantly inhibited the number of visible lesions whereas the number of microscopic lesions and lesion area were significantly inhibited only in the combination group. Furthermore, RNASeq and qPCR analysis using a HNC cell line identified GDF15, ATF3, p21, p27 and Bim as significantly upregulated genes with GDF15 being the most upregulated one. Expression of GDF15 and ATF3 proteins were confirmed by western blotting. Taken together, our data strongly demonstrate the chemopreventive potential of the combination of EGCG and resveratrol and paves the way for further clinical developments. (Supported by NIH Grant P20GM103434 to the West Virginia IDeA Network for Biomedical Research Excellence)

Citation Format: Adeoluwa Adeluola, Lukmon Raji, Saroj Sigdel, A.S.M. Anisuzzaman, A. R. M. Ruhul Amin. Chemoprevention of head and neck cancers by the combination of epigallocatechin gallate (EGCG) and resveratrol [abstract]. In: Proceedings of the Second Biennial NCI Meeting: Translational Advances in Cancer Prevention Agent Development (TACPAD); 2022 Sep 7-9. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_2): Abstract nr A004.

Perspectives for synthetic curcumins in chemoprevention and treatment of cancer: An update with promising analogues

Curcumin, a pure compound extracted from the flowering plant, turmeric (Curcuma longa. Zingiberaceae), is a common dietary ingredient found in curry powder. It has been studied extensively for its anti-inflammatory, antioxidant, antimicrobial and anti-tumour activities. Evidence is accumulating demonstrating its potential in chemoprevention and as an anti-tumour agent for the treatment of cancer. Despite demonstrated safety and tolerability, the clinical application of curcumin is frustrated by its poor solubility, metabolic instability and low oral bioavailability. Consequently researchers have tried novel techniques of formulation and delivery as well as synthesis of analogues with enhanced properties to overcome these barriers. This review presents the synthetic analogues of curcumin that have proven their anticancer potential from different studies. It also highlights studies that combined these analogues with approved chemotherapies and delivered them via novel techniques. Currently, there are no reports of clinical studies on any of the synthetic congeners of curcumin and this presents an opportunity for future research. This review presents the synthetic analogues of curcumin and makes a compelling argument for their potential application in the management of cancerous disease.

Structural and in Vitro Functional Characterization of a Menthyl TRPM8 Antagonist Indicates Species-Dependent Regulation

TRPM8 antagonists derived from its cognate ligand, (-)-menthol, are underrepresented. We determine the absolute stereochemistry of a well-known TRPM8 antagonist, (-)-menthyl 1, using VCD and 2D NMR. We explore 1 for its antagonist effects of the human TRPM8 (hTRPM8) orthologue to uncover species-dependent inhibition versus rat channels. (-)-Menthyl 1 inhibits menthol- and icilin-evoked Ca²⁺ responses at hTRPM8 with IC₅₀ values of 805 ± 200 nM and 1.8 ± 0.6 μM, respectively, while more potently inhibiting agonist responses at the rat orthologue (rTRPM8 IC₅₀ (menthol) = 117 ± 18 nM, IC₅₀ (icilin) = 521 ± 20 nM). Whole-cell patch-clamp recordings of hTRPM8 confirm the 1 inhibition of menthol-stimulated currents, with an IC₅₀ of 700 ± 200 nM. We demonstrate that 1 possesses ≥400-fold selectivity for hTRPM8 versus hTRPA1/hTRPV1. (-)-menthyl 1 can be used as a novel chemical tool to study hTRPM8 pharmacology and differences in species commonly used in drug discovery.

Combination of resveratrol and green tea epigallocatechin gallate induces synergistic apoptosis and inhibits tumor growth in vivo in head and neck cancer models

Despite widespread interest in chemoprevention and therapy due to the high margin of safety of dietary natural compounds, clinical intervention with single agents has failed to yield the expected outcomes, mostly due to poor bioavailability and low potency. Combinations of natural agents with synergistic effects are gaining increasing attention. In the present study, in vitro and in vivo antitumor effects of a combination of two natural dietary agents, green tea epigallocatechin gallate (EGCG) and resveratrol were investigated. It was revealed that their combination at low doses (at which single agents induce minimal apoptosis) synergistically increased apoptosis (combination index <1) in head and neck cancer cell lines. Synergistic apoptosis was also supported by caspase-3 and PARP cleavage. The combination also significantly inhibited growth of xenografted head and neck tumors in nude mice as supported by significant inhibition of tumor volume, tumor weight and Ki67 expression, and increase in TUNEL-positive cells. Mechanistic studies revealed that the combination inhibited AKT-mTOR signaling both in vitro and in vivo. In addition, overexpression of constitutively active AKT protected cells from apoptosis induced by the combination of EGCG and resveratrol. Collectively, the present results for the first time suggest that the combination of EGCG and resveratrol has synergistic growth inhibitory effects and provide an important rationale for future clinical development for chemoprevention and treatment of head and neck cancer.

Structure-Based Design of Novel Biphenyl Amide Antagonists of Human Transient Receptor Potential Cation Channel Subfamily M Member 8 Channels with Potential Implications in the Treatment of Sensory Neuropathies

Structure-activity relationship studies of a reported menthol-based transient receptor potential cation channel subfamily M member 8 channel (TRPM8) antagonist, guided by computational simulations and structure-based design, uncovers a novel series of TRPM8 antagonists with >10-fold selectivity versus related TRP subtypes. Spiro[4.5]decan-8-yl analogue 14 inhibits icilin-evoked Ca²⁺ entry in HEK-293 cells stably expressing human TRPM8 (hTRPM8) with an IC₅₀ of 2.4 ± 1.0 nM, while in whole-cell patch-clamp recordings this analogue inhibits menthol-evoked currents with a hTRPM8 IC₅₀ of 64 ± 2 nM. Molecular dynamics (MD) simulations of compound 14 in our homology model of hTRPM8 suggest that this antagonist forms extensive hydrophobic contacts within the orthosteric site. In the wet dog shakes (WDS) assay, compound 14 dose-dependently blocks icilin-triggered shaking behaviors in mice. Upon local administration, compound 14 dose dependently inhibits cold allodynia evoked by the chemotherapy oxaliplatin in a murine model of peripheral neuropathy at microgram doses. Our findings suggest that 14 and other biphenyl amide analogues within our series can find utility as potent antagonist chemical probes derived from (-)-menthol as well as small molecule therapeutic scaffolds for chemotherapy-induced peripheral neuropathy (CIPN) and other sensory neuropathies.

In Vitro and In Vivo Synergistic Antitumor Activity of the Combination of BKM120 and Erlotinib in Head and Neck Cancer: Mechanism of Apoptosis and Resistance

We previously reported that the EGFR-targeted inhibitor erlotinib induces G₁ arrest of squamous cell carcinoma of the head and neck (SCCHN) cell lines without inducing significant apoptosis. Large-scale genomic studies suggest that >50% of SCCHN cases have activation of PI3K pathways. This study investigated whether cotargeting of EGFR and PI3K has synergistic antitumor effects and apoptosis induction. We examined growth suppression, apoptosis, and signaling pathway modulation resulting from single and combined targeting of EGFR and PI3K with erlotinib and BKM120, respectively, in a panel of SCCHN cell lines and a xenograft model of SCCHN. In a panel of 12 cell lines, single targeting of EGFR with erlotinib or PI3K with BKM120 suppressed cellular growth without inducing significant apoptosis. Cotargeting of EGFR and PI3K synergistically inhibited SCCHN cell line and xenograft tumor growth, but induced variable apoptosis; some lines were highly sensitive, others were resistant. Mechanistic studies revealed that the combination inhibited both axes of the mTORC1 (S6 and 4EBP1) pathway in apoptosis-sensitive cell lines along with translational inhibition of Bcl-2, Bcl-xL, and Mcl-1, but failed to inhibit p-4EBP1, Bcl-2, Bcl-xL, and Mcl-1 in an apoptosis-resistant cell line. siRNA-mediated knockdown of eIF4E inhibited Bcl-2 and Mcl-1 and sensitized this cell line to apoptosis. Our results strongly suggest that cotargeting of EGFR and PI3K is synergistic and induces apoptosis of SCCHN cell lines by inhibiting both axes of the AKT-mTOR pathway and translational regulation of antiapoptotic Bcl-2 proteins. These findings may guide the development of clinical trials using this combination of agents. Mol Cancer Ther; 16(4); 729-38. ©2017 AACR.

Antitumor Activity of 2,9-Di-Sec-Butyl-1,10-Phenanthroline

The anti-tumor effect of a chelating phen-based ligand 2,9-di-sec-butyl-1,10-phenanthroline (dsBPT) and its combination with cisplatin were examined in both lung and head and neck cancer cell lines and xenograft animal models in this study. The effects of this agent on cell cycle and apoptosis were investigated. Protein markers relevant to these mechanisms were also assessed. We found that the inhibitory effect of dsBPT on lung and head and neck cancer cell growth (IC₅₀ ranged between 0.1–0.2 μM) was 10 times greater than that on normal epithelial cells. dsBPT alone induced autophagy, G1 cell cycle arrest, and apoptosis. Our in vivo studies indicated that dsBPT inhibited tumor growth in a dose-dependent manner in a head and neck cancer xenograft mouse model. The combination of dsBPT with cisplatin synergistically inhibited cancer cell growth with a combination index of 0.3. Moreover, the combination significantly reduced tumor volume as compared with the untreated control (p = 0.0017) in a head and neck cancer xenograft model. No organ related toxicities were observed in treated animals. Our data suggest that dsBPT is a novel and potent antitumor drug that warrants further preclinical and clinical development either as a single agent or in combination with known chemotherapy drugs such as cisplatin.

Designing a broad-spectrum integrative approach for cancer prevention and treatment

Targeted therapies and the consequent adoption of "personalized" oncology have achieved notable successes in some cancers; however, significant problems remain with this approach. Many targeted therapies are highly toxic, costs are extremely high, and most patients experience relapse after a few disease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistant immortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are not reliant upon the same mechanisms as those which have been targeted). To address these limitations, an international task force of 180 scientists was assembled to explore the concept of a low-toxicity "broad-spectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspects of relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a wide range of high-priority targets (74 in total) that could be modified to improve patient outcomes. For these targets, corresponding low-toxicity therapeutic approaches were then suggested, many of which were phytochemicals. Proposed actions on each target and all of the approaches were further reviewed for known effects on other hallmark areas and the tumor microenvironment. Potential contrary or procarcinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixed evidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of the relationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. This novel approach has potential to be relatively inexpensive, it should help us address stages and types of cancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for future research is offered.

HER3 Targeting Sensitizes HNSCC to Cetuximab by Reducing HER3 Activity and HER2/HER3 Dimerization: Evidence from Cell Line and Patient-Derived Xenograft Models

PURPOSE

Our previous work suggested that HER3 inhibition sensitizes head and neck squamous cell carcinoma (HNSCC) to EGFR inhibition with cetuximab. This study aimed to define the role of HER3 in cetuximab resistance and the antitumor mechanisms of EGFR/HER3 dual targeting in HNSCC.

EXPERIMENTAL DESIGN

We treated cetuximab-resistant HNSCC UMSCC1-C and parental UMSCC1-P cell lines with anti-EGFR antibody cetuximab, anti-HER3 antibody MM-121, and their combination. We assessed activities of HER2, HER3, and downstream signaling pathways by Western blotting and cell growth by sulforhodamine B (SRB) and colony formation assays. HER3-specific shRNA was used to confirm the role of HER3 in cetuximab response. The combined efficacy and alterations in biomarkers were evaluated in UMSCC1-C xenograft and patient-derived xenograft (PDX) models.

RESULTS

Cetuximab treatment induced HER3 activation and HER2/HER3 dimerization in HNSCC cell lines. Combined treatment with cetuximab and MM-121 blocked EGFR and HER3 activities and inhibited the PI3K/AKT and ERK signaling pathways and HNSCC cell growth more effectively than each antibody alone. HER3 knockdown reduced HER2 activation and resensitized cells to cetuximab. Cetuximab-resistant xenografts and PDX models revealed greater efficacy of dual EGFR and HER3 inhibition compared with single antibodies. In PDX tissue samples, cetuximab induced HER3 expression and MM-121 reduced AKT activity.

CONCLUSIONS

Clinically relevant PDX models demonstrate that dual targeting of EGFR and HER3 is superior to EGFR targeting alone in HNSCC. Our study illustrates the upregulation of HER3 by cetuximab as one mechanism underlying resistance to EGFR inhibition in HNSCC, supporting further clinical investigations using multiple targeting strategies in patients who have failed cetuximab-based therapy. Clin Cancer Res; 23(3); 677-86. ©2016 AACR.

Combination of erlotinib and EGCG induces apoptosis of head and neck cancers through posttranscriptional regulation of Bim and Bcl-2

Combinatorial approaches using two or more compounds are gaining increasing attention for cancer therapy. We have previously reported that the combination of the EGFR-TKI erlotinib and epigallocatechin-3-gallate (EGCG) exhibited synergistic chemopreventive effects in head and neck cancers by inducing the expression of Bim, p21, p27, and by inhibiting the phosphorylation of ERK and AKT and expression of Bcl-2. In the current study, we further investigated the mechanism of regulation of Bim, Bcl-2, p21 and p27, and their role in apoptosis. shRNA-mediated silencing of Bim significantly inhibited apoptosis induced by the combination of erlotinib and EGCG (p = 0.005). On the other hand, overexpression of Bcl-2 markedly protected cells from apoptosis (p = 0.003), whereas overexpression of constitutively active AKT only minimally protected cells from apoptosis induced by the combination of the two compounds. Analysis of mRNA expression by RT-PCR revealed that erlotinib, EGCG and their combination had no significant effects on the mRNA expression of Bim, p21, p27 or Bcl-2 suggesting the post-transcriptional regulation of these molecules. Furthermore, we found that erlotinib or the combination of EGCG and erlotinib inhibited the phosphorylation of Bim and stabilized Bim after inhibition of protein translation by cycloheximide. Taken together, our results strongly suggest that the combination of erlotinib and EGCG induces apoptosis of SCCHN cells by regulating Bim and Bcl-2 at the posttranscriptional level.

Preclinical In Vitro, In Vivo, and Pharmacokinetic Evaluations of FLLL12 for the Prevention and Treatment of Head and Neck Cancers

Despite its high promise for cancer prevention and therapy, the potential utility of curcumin in cancer is compromised by its low bioavailability and weak potency. The purpose of the current study was to assess the in vitro and in vivo efficacy and pharmacokinetic parameters of the potent curcumin analogue FLLL12 in SCCHN and identify the mechanisms of its antitumor effect. IC50 values against a panel of one premalignant and eight malignant head and neck cancer cell lines as well as apoptosis assay results suggested that FLLL12 is 10- to 24-fold more potent than natural curcumin depending on the cell line and induces mitochondria-mediated apoptosis. In vivo efficacy (xenograft) and pharmacokinetic studies also suggested that FLLL12 is significantly more potent and has more favorable pharmacokinetic properties than curcumin. FLLL12 strongly inhibited the expression of p-EGFR, EGFR, p-AKT, AKT, Bcl-2, and Bid and increased the expression of Bim. Overexpression of constitutively active AKT or Bcl-2 or ablation of Bim or Bid significantly inhibited FLLL12-induced apoptosis. Further mechanistic studies revealed that FLLL12 regulated EGFR and AKT at transcriptional levels, whereas Bcl-2 was regulated at the translational level. Finally, FLLL12 strongly inhibited the AKT downstream targets mTOR and FOXO1a and 3a. Taken together, our results strongly suggest that FLLL12 is a potent curcumin analogue with more favorable pharmacokinetic properties that induces apoptosis of head and neck cancer cell lines by inhibition of survival proteins including EGFR, AKT, and Bcl-2 and increasing of the proapoptotic protein Bim.

FLLL12 induces apoptosis in lung cancer cells through a p53/p73-independent but death receptor 5-dependent pathway

Unlike chemotherapy drugs, the safety of natural compounds such as curcumin has been well established. However, the potential use of curcumin in cancer has been compromised by its low bioavailability, limited tissue distribution and rapid biotransformation leading to low in vivo efficacy. To circumvent these problems, more potent and bioavailable analogs have been synthesized. In the current study, we investigated the mechanism of anti-tumor effect of one such analog, FLLL12, in lung cancers. IC50 values measured by sulforhodamine B (SRB) assay at 72 h and apoptosis assays (annexin V staining, cleavage of PARP and caspase-3) suggest that FLLL12 is 5-10-fold more potent than curcumin against a panel of premalignant and malignant lung cancer cell lines, depending on the cell line. Moreover, FLLL12 induced the expression of death receptor-5 (DR5). Ablation of the expression of the components of the extrinsic apoptotic pathway (DR5, caspase-8 and Bid) by siRNA significantly protected cells from FLLL12-induced apoptosis (p < 0.05). Analysis of mRNA expression revealed that FLLL-12 had no significant effect on the expression of DR5 mRNA expression. Interestingly, inhibition of global phosphatase activity as well as protein tyrosine phosphatases (PTPs), but not of alkaline phosphatases, strongly inhibited DR5 expression and significantly inhibited apoptosis (p < 0.05), suggesting the involvement of PTPs in the regulation of DR5 expression and apoptosis. We further showed that the apoptosis is independent of p53 and p73. Taken together, our results strongly suggest that FLLL12 induces apoptosis of lung cancer cell lines by posttranscriptional regulation of DR5 through activation of protein tyrosine phosphatase(s).

Luteolin nanoparticle in chemoprevention: in vitro and in vivo anticancer activity

Cancer prevention (chemoprevention) by using naturally occurring dietary agents has gained immense interest because of the broad safety window of these compounds. However, many of these compounds are hydrophobic and poorly soluble in water. They frequently display low bioavailability, poor systemic delivery, and low efficacy. To circumvent this problem, we explored a novel approach toward chemoprevention using nanotechnology to deliver luteolin, a natural compound present in green vegetables. We formulated water-soluble polymer-encapsulated Nano-Luteolin from hydrophobic luteolin, and studied its anticancer activity against lung cancer and head and neck cancer. In vitro studies demonstrated that, like luteolin, Nano-Luteolin inhibited the growth of lung cancer cells (H292 cell line) and squamous cell carcinoma of head and neck (SCCHN) cells (Tu212 cell line). In Tu212 cells, the IC50 value of Nano-Luteolin was 4.13 μmol/L, and that of luteolin was 6.96 μmol/L. In H292 cells, the IC50 of luteolin was 15.56 μmol/L, and Nano-Luteolin was 14.96 μmol/L. In vivo studies using a tumor xenograft mouse model demonstrated that Nano-Luteolin has a significant inhibitory effect on the tumor growth of SCCHN in comparison to luteolin. Our results suggest that nanoparticle delivery of naturally occurring dietary agents like luteolin has many advantages and may have potential application in chemoprevention in clinical settings.

Combination of anti-HER3 antibody MM-121/SAR256212 and cetuximab inhibits tumor growth in preclinical models of head and neck squamous cell carcinoma

The EGFR monoclonal antibody cetuximab is the only approved targeted agent for treating head and neck squamous cell carcinoma (HNSCC). Yet resistance to cetuximab has hindered its activity in this disease. Intrinsic or compensatory HER3 signaling may contribute to cetuximab resistance. To investigate the therapeutic benefit of combining MM-121/SAR256212, an anti-HER3 monoclonal antibody, with cetuximab in HNSCC, we initially screened 12 HNSCC cell lines for total and phosphorylated levels of the four HER receptors. We also investigated the combination of MM-121 with cetuximab in preclinical models of HNSCC. Our results revealed that HER3 is widely expressed and activated in HNSCC cell lines. MM-121 strongly inhibited phosphorylation of HER3 and AKT. When combined with cetuximab, MM-121 exerted a more potent antitumor activity through simultaneously inhibiting the activation of HER3 and EGFR and consequently the downstream PI3K/AKT and ERK pathways in vitro. Both high and low doses of MM-121 in combination with cetuximab significantly suppressed tumor growth in xenograft models and inhibited activations of HER3, EGFR, AKT, and ERK in vivo. Our work is the first report on this new combination in HNSCC and supports the concept that HER3 inhibition may play an important role in future therapy of HNSCC. Our results open the door for further mechanistic studies to better understand the role of HER3 in resistance to EGFR inhibitors in HNSCC.

Honokiol enhances paclitaxel efficacy in multi-drug resistant human cancer model through the induction of apoptosis

Resistance to chemotherapy remains a major obstacle in cancer therapy. This study aimed to evaluate the molecular mechanism and efficacy of honokiol in inducing apoptosis and enhancing paclitaxel chemotherapy in pre-clinical multi-drug resistant (MDR) cancer models, including lineage-derived human MDR (KB-8-5, KB-C1, KB-V1) and their parental drug sensitive KB-3-1 cancer cell lines. In vitro analyses demonstrated that honokiol effectively inhibited proliferation in KB-3-1 cells and the MDR derivatives (IC₅₀ ranging 3.35±0.13 µg/ml to 2.77±0.22 µg/ml), despite their significant differences in response to paclitaxel (IC₅₀ ranging 1.66±0.09 ng/ml to 6560.9±439.52 ng/ml). Honokiol induced mitochondria-dependent and death receptor-mediated apoptosis in MDR KB cells, which was associated with inhibition of EGFR-STAT3 signaling and downregulation of STAT3 target genes. Combined treatment with honokiol and paclitaxel synergistically augmented cytotoxicity in MDR KB cells, compared with treatment with either agent alone in vitro. Importantly, the combined treatment significantly inhibited in vivo growth of KB-8-5 tumors in a subcutaneous model. Tumor tissues from the combination group displayed a significant inhibition of Ki-67 expression and an increase in TUNEL-positive cells compared with the control group. These results suggest that targeting multidrug resistance using honokiol in combination with chemotherapy drugs may provide novel therapeutic opportunities.

OCT4 as a target of miR-34a stimulates p63 but inhibits p53 to promote human cell transformation

Human cell transformation is a key step for oncogenic development, which involves multiple pathways; however, the mechanism remains unclear. To test our hypothesis whether cell oncogenic transformation shares some mechanisms with the process of reprogramming non-stem cells to induced pluripotent stem cells (iPSC), we studied the relationship among the key factors for promoting or inhibiting iPSC in radiation-transformed human epithelial cell lines derived from different tissues (lung, breast and colon). We unexpectedly found that p63 and OCT4 were highly expressed (accompanied by low expressed p53 and miR-34a) in all transformed cell lines examined when compared with their non-transformed counterparts. We further elucidated the relationship of these factors: the 3p strand of miR-34a directly targeted OCT4 by binding to the 3′ untranslated region (3′-UTR) of OCT4 and, OCT4, in turn, stimulated p63 but inhibited p53 expression by binding to a specific region of the p63 or p53 promoter. Moreover, we revealed that the effects of OCT4 on promoting cell oncogenic transformation were by affecting p63 and p53. These results support that a positive loop exists in human cells: OCT4 upregulation as a consequence of inhibition of miR-34a, promotes p63 but suppresses p53 expression, which further stimulates OCT4 upregulation by downregulating miR-34a. This functional loop contributes significantly to cell transformation and, most likely, also to the iPSC process.

New perspectives of curcumin in cancer prevention

Numerous natural compounds have been extensively investigated for their potential for cancer prevention over the decades. Curcumin, from Curcuma longa, is a highly promising natural compound that can be potentially used for chemoprevention of multiple cancers. Curcumin modulates multiple molecular pathways involved in the lengthy carcinogenesis process to exert its chemopreventive effects through several mechanisms: promoting apoptosis, inhibiting survival signals, scavenging reactive oxidative species (ROS), and reducing the inflammatory cancer microenvironment. Curcumin fulfills the characteristics for an ideal chemopreventive agent with its low toxicity, affordability, and easy accessibility. Nonetheless, the clinical application of curcumin is currently compromised by its poor bioavailability. Here, we review the potential of curcumin in cancer prevention, its molecular targets, and mechanisms of action. Finally, we suggest specific recommendations to improve its efficacy and bioavailability for clinical applications.

Chemoprevention of head and neck cancer by simultaneous blocking of epidermal growth factor receptor and cyclooxygenase-2 signaling pathways: preclinical and clinical studies

PURPOSE

We investigated the efficacy and underlying molecular mechanism of a novel chemopreventive strategy combining EGF receptor (EGFR) tyrosine kinase inhibitor (TKI) with cyclooxygenase-2 inhibitor (COX-2I).

EXPERIMENTAL DESIGN

We examined the inhibition of tumor cell growth by combined EGFR-TKI (erlotinib) and COX-2I (celecoxib) treatment using head and neck cancer cell lines and a preventive xenograft model. We studied the antiangiogenic activity of these agents and examined the affected signaling pathways by immunoblotting analysis in tumor cell lysates and immunohistochemistry (IHC) and enzyme immunoassay (EIA) analyses on the mouse xenograft tissues and blood, respectively. Biomarkers in these signaling pathways were studied by IHC, EIA, and an antibody array analysis in samples collected from participants in a phase I chemoprevention trial of erlotinib and celecoxib.

RESULTS

The combined treatment inhibited head and neck cancer cell growth significantly more potently than either single agent alone in cell line and xenograft models, and resulted in greater inhibition of cell-cycle progression at G1 phase than either single drug. The combined treatment modulated the EGFR and mTOR signaling pathways. A phase I chemoprevention trial of combined erlotinib and celecoxib revealed an overall pathologic response rate of 71% at time of data analysis. Analysis of tissue samples from participants consistently showed downregulation of EGFR, pERK, and pS6 levels after treatment, which correlated with clinical response.

CONCLUSION

Treatment with erlotinib combined with celecoxib offers an effective chemopreventive approach through inhibition of EGFR and mTOR pathways, which may serve as potential biomarkers to monitor the intervention of this combination in the clinic. Clin Cancer Res; 19(5); 1244-56. ©2013 AACR.

Systemic delivery of siRNA nanoparticles targeting RRM2 suppresses head and neck tumor growth

Systemic delivery of siRNA to solid tumors remains challenging. In this study, we investigated the systemic delivery of a siRNA nanoparticle targeting ribonucleotide reductase subunit M2 (RRM2), and evaluated its intratumoral kinetics, efficacy and mechanism of action. Knockdown of RRM2 by an RNAi mechanism strongly inhibited cell growth in head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) cell lines. In a mouse xenograft model of HNSCC, a single intravenous injection led to the accumulation of intact nanoparticles in the tumor that disassembled over a period of at least 3days, leading to target gene knockdown lasting at least 10days. A four-dose schedule of siRNA nanoparticle delivering RRM2 siRNA targeted to HNSCC tumors significantly reduced tumor progression by suppressing cell proliferation and inducing apoptosis. These results show promise for the use of RRM2 siRNA-based therapy for HNSCC and possibly NSCLC.

Chemopreventive potential of natural compounds in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is one of the most fatal cancers worldwide. Despite advances in the management of HNSCC, the overall survival for patients has not improved significantly due to advanced stages at diagnosis, high recurrence rate after surgical removal, and second primary tumor development, which underscore the importance of novel strategies for cancer prevention. Cancer chemoprevention, the use of natural or synthetic compounds to prevent, arrest, or reverse the process of carcinogenesis at its earliest stages, aims to reverse premalignancies and prevent second primary tumors. Genomics and proteomics information including initial mutation, cancer promotion, progression, and susceptibility has brought molecularly targeted therapies for drug development. The development of preventive approaches using specific natural or synthetic compounds, or both, requires a depth of understanding of the cross-talk between cancer signaling pathways and networks to retain or enhance chemopreventive activity while reducing known toxic effects. Many natural dietary compounds have been identified with multiple molecular targets, effective in the prevention and treatment of cancer. This review describes recent advances in the understanding of the complex signaling networks driving cancer progression and of molecularly targeted natural compounds under preclinical and clinical investigation.

Enhanced anti-tumor activity by the combination of the natural compounds (-)-epigallocatechin-3-gallate and luteolin: potential role of p53

Natural dietary agents have drawn a great deal of attention toward cancer prevention because of their wide safety margin. However, single agent intervention has failed to bring the expected outcome in clinical trials; therefore, combinations of chemopreventive agents are gaining increasingly popularity. In the present study, we investigated a combinatorial approach using two natural dietary polyphenols, luteolin and EGCG, and found that their combination at low doses (at which single agents induce minimal apoptosis) synergistically increased apoptosis (3-5-fold more than the additive level of apoptosis) in both head and neck and lung cancer cell lines. This combination also significantly inhibited growth of xenografted tumors in nude mice. The in vivo findings also were supported by significant inhibition of Ki-67 expression and increase in TUNEL-positive cells in xenografted tissues. Mechanistic studies revealed that the combination induced mitochondria-dependent apoptosis in some cell lines and mitochondria-independent apoptosis in others. Moreover, we found more efficient stabilization and ATM-dependent Ser(15) phosphorylation of p53 due to DNA damage by the combination, and ablation of p53 using shRNA strongly inhibited apoptosis as evidenced by decreased poly(ADP-ribose) polymerase and caspase-3 cleavage. In addition, we observed mitochondrial translocation of p53 after treatment with luteolin or the combination of EGCG and luteolin. Taken together, our results for the first time suggest that the combination of luteolin and EGCG has synergistic/additive growth inhibitory effects and provides an important rationale for future chemoprevention trials of head and neck and lung cancers.

Cancer prevention with natural compounds

Botanical and nutritional compounds have been used for the treatment of cancer throughout history. These compounds also may be useful in the prevention of cancer. Population studies suggest that a reduced risk of cancer is associated with high consumption of vegetables and fruits. Thus, the cancer chemopreventive potential of naturally occurring phytochemicals is of great interest. There are numerous reports of cancer chemopreventive activity of dietary botanicals, including cruciferous vegetables such as cabbage and broccoli, Allium vegetables such as garlic and onion, green tea, Citrus fruits, soybeans, tomatoes, berries, and ginger, as well as medicinal plants. Several lead compounds, such as genistein (from soybeans), lycopene (from tomatoes), brassinin (from cruciferous vegetables), sulforaphane (from asparagus), indole-3-carbinol (from broccoli), and resveratrol (from grapes and peanuts) are in preclinical or clinical trials for cancer chemoprevention. Phytochemicals have great potential in cancer prevention because of their safety, low cost, and oral bioavailability. In this review, we discuss potential natural cancer preventive compounds and their mechanisms of action.

Chemoprevention of head and neck cancer with green tea polyphenols

Recently, squamous cell carcinoma of the head and neck chemoprevention research has made major advances with novel clinical trial designs suited for the purpose, use of biomarkers to identify high-risk patients, and the emergence of numerous molecularly targeted agents and natural dietary compounds. Among many natural compounds, green tea polyphenols, particularly (-)-epigallocatechin-3-gallate (EGCG), possess remarkable potential as chemopreventive agents. EGCG modulates several key molecular signaling pathways at multiple levels and has synergistic or additive effects when combined with many other natural or synthetic compounds. This review will provide an update of the potential of green tea polyphenols, particularly EGCG, for the chemoprevention of squamous cell carcinoma of the head and neck.

p53-Dependent p21-mediated growth arrest pre-empts and protects HCT116 cells from PUMA-mediated apoptosis induced by EGCG

The tumor suppressor protein p53 plays a key role in regulation of negative cellular growth in response to EGCG. To further explore the role of p53 signaling and elucidate the molecular mechanism, we employed colon cancer HCT116 cell line and its derivatives in which a specific transcriptional target of p53 is knocked down by homologous recombination. Cells expressing p53 and p21 accumulate in G1 upon treatment with EGCG. In contrast, same cells lacking p21 traverse through the cell cycle and eventually undergo apoptosis as revealed by TUNEL staining. Treatment with EGCG leads to induction of p53, p21 and PUMA in p21 wild-type, and p53 and PUMA in p21(-/-) cells. Ablation of p53 by RNAi protects p21(-/-) cells, thus indicating a p53-dependent apoptosis by EGCG. Furthermore, analysis of cells lacking PUMA or Bax with or without p21 but with p53 reveals that all the cells expressing p53 and p21 survived after EGCG treatment. More interestingly, cells lacking both PUMA and p21 survived ECGC treatment whereas those lacking p21 and Bax did not. Taken together, our results present a novel concept wherein p21-dependent growth arrest pre-empts and protects cells from otherwise, in its absence, apoptosis which is mediated by activation of pro-apoptotic protein PUMA. Furthermore, we find that p53-dependent activation of PUMA in response to EGCG directly leads to apoptosis with out requiring Bax as is the case in response to agents that induce DNA damage. p21, thus can be used as a molecular switch for therapeutic intervention of colon cancer.

Restoration of p53 functions protects cells from concanavalin A-induced apoptosis

A great majority of human cancers encounter disruption of the p53 network. Identification and characterization of molecular components important in both p53-dependent and p53-independent apoptosis might be useful in developing novel therapies. Previously, we reported that concanavalin A (Con A) induced p73-dependent apoptosis of cells lacking functional p53. In the present study, we investigated the mechanism and role of p53 in protection from apoptosis induced by Con A. Treatment with Con A resulted in apoptosis of p53-null ovarian cancer, SKOV3, or Li-Fraumeni syndrome, MDAH041 (041), cells. However, their isogenic pairs, SKP53 and TR9-7, expressing wild-type p53 were much less sensitive and were protected by G(1) arrest. Inhibition of p53 function rendered these cells sensitive to Con A. Con A-induced apoptosis was accompanied by upregulation of forkhead box O1a (FOXO1a) and Bcl-2-interacting mediator (Bim), which were strongly inhibited after p53 expression and rescued after p53 ablation. Moreover, ablation of Bim by short hairpin RNA protected cells from apoptosis. Taken together, our study suggests that Con A induces apoptosis of cells lacking p53 by activating FOXO1a-Bim signaling and that expression of p53 protects these cells by inducing G(1) arrest and by downregulating the expression of both FOXO1a and Bim, identifying a novel cross-talk between FOXO1a and p53 transcription factors.

Synergistic growth inhibition of squamous cell carcinoma of the head and neck by erlotinib and epigallocatechin-3-gallate: the role of p53-dependent inhibition of nuclear factor-kappaB

We have previously reported that the green tea polyphenol epigallocatechin-3-gallate (EGCG) and the epidermal growth factor receptor-tyrosine kinase inhibitor erlotinib had synergistic growth-inhibitory effects in cell culture and a nude mouse xenograft model of squamous cell carcinoma of the head and neck. However, the mechanism of their antitumor synergism is not fully understood. In the current study, we investigate the mechanism of their synergistic growth-inhibitory effects. The treatment of squamous cell carcinoma of the head and neck cell lines with erlotinib time-dependently increased the expression of cell cycle regulatory proteins p21 and p27 and apoptosis regulatory protein Bim. EGCG alone had very little or no effect on the expression of these proteins among the cell lines. However, simultaneous treatment with EGCG and erlotinib strongly inhibited erlotinib-induced expression of p21 and p27 without affecting the expression of Bim. Moreover, erlotinib increased the expression of p53 protein, the ablation of which by short hairpin RNA strongly inhibited EGCG- and erlotinib-mediated growth inhibition and the expression of p21, p27, and Bim. In addition, combined treatment with erlotinib and EGCG inhibited the protein level of p65 subunit of nuclear factor-kappaB and its transcriptional target Bcl-2, but failed to do so in cells with ablated p53. Taken together, our results, for the first time, suggest that erlotinib treatment activates p53, which plays a critical role in synergistic growth inhibition by erlotinib and EGCG via inhibiting nuclear factor-kappaB signaling pathway. Characterizing the underlying mechanisms of EGCG and erlotinib synergism will provide an important rationale for chemoprevention or treatment trials using this combination.

A role for SHPS-1/SIRPalpha in Concanavalin A-dependent production of MMP-9

SHPS-1/SIRPalpha1 is a transmembrane glycoprotein that belongs to the immunoglobulin (Ig) super family. In the present study, we show that SHPS-1 strongly associates with Concanavalin A (Con A), a plant lectin obtained from jack beans. Further studies with SHPS-1 mutants reveal that the extracellular domain of SHPS-1 containing the Ig sequence is responsible for its association with Con A. Con A treatment induces cross-linking and multimerization of the SHPS-1 protein in the plasma membrane, accompanied by its tyrosine phosphorylation and recruitment of SHP-2. In contrast, Ricinus communis agglutinin (RCA), another lectin obtained from castor bean, does not bind or activate tyrosine phosphorylation of SHPS-1. Moreover, Con A activates Akt in a SHP-2-dependent manner. Treatment of mouse embryonic fibroblasts (MEFs) with Con A induces secretion of matrix metalloproteinase (MMP)-9, a phenomenon that is inhibited in cells expressing YF mutant of SHPS-1, a dominant negative form of Akt or in cells pre-treated with an Akt inhibitor, LY294002 or extracellular-signal regulated kinase (Erk) inhibitor, U0126. In addition, expression of the YF mutant of SHPS-1 inhibits Con A-dependent activation of Akt and Erk kinases. Taken together, our results suggest that SHPS-1 is a receptor for Con A that mediates Con A-dependent MMP-9 secretion through SHP-2-promoted activation of both Akt and Erk pathways.

A Novel Role for p73 in the Regulation of Akt-Foxo1a-Bim Signaling and Apoptosis Induced by the Plant Lectin, Concanavalin A

Virtually all human cancers encounter disruption of the "p53 network." From a therapeutic point of view, it is important to devise strategies that eliminate cancer cells, which are often defective in functional p53 and protect p53-expressing normal cells. By comparing the response of a pair of isogenic cell lines, we identify a plant-derived compound, Concanavalin A (Con A), which differentially kills p53-null cells. Further, we find that p53 family member, p73, plays a critical role that is unmasked in the absence of p53. Con A treatment leads to induction of p73 and several others that are important mediators of apoptosis and act downstream, such as p21, Bax, Foxo1a, and Bim. Inactivation of p73 reverses the expression of these proteins and apoptosis. Inhibition of Akt activation sensitizes otherwise resistant cells. These observations thus reveal a novel role for p73 in the regulation of Akt-Foxo1a-Bim signaling and apoptosis especially when p53 is absent.

SHP-2 tyrosine phosphatase inhibits p73-dependent apoptosis and expression of a subset of p53 target genes induced by EGCG

Green tea polyphenol, epigallocatechin-3-gallate (EGCG) differentially regulates the cellular growth of cancer cells in a p53-dependent manner through apoptosis and/or cell cycle arrest. In an effort to further elucidate the mechanism of differential growth regulation by EGCG, we have investigated the role of the tyrosine phosphatase, SHP-2. Comparing the responses of mouse embryonic fibroblasts (MEFs), expressing either WT or functionally inactive/truncated SHP-2, we find that inactivation of SHP-2 remarkably sensitizes cells to EGCG-mediated killing. MEFs lacking functional SHP-2 undergo massive apoptosis upon treatment with EGCG. By comparing gene expression profiles, we have identified a set of transcriptional targets of p53 that are differentially modulated in cells undergoing apoptosis. Western blot and real-time PCR analyses of a select group of genes further confirm that the expression is SHP-2-dependent. Similar observations were made in MEFs lacking p53, confirming that the expression of these "p53 target genes" is p53-independent. In addition, EGCG treatment induced the expression of p73 mRNA and protein in both cell types, but not p63. Inactivation of p73 in cells expressing nonfunctional SHP-2 markedly inhibited apoptosis and p53 target gene expression. Although phosphorylation of JNK is differentially regulated by SHP2, it was found to be dispensable for EGCG-induced apoptosis and p53 target gene expression. Our results have identified SHP-2 as a negative regulator of EGCG-induced-apoptosis and have identified a subset of p53 target genes whose expression is paradoxically not mediated by p53 but by one of its family members, p73.

DNA replication licensing factor minichromosome maintenance deficient 5 rescues p53-mediated growth arrest

Inactivation of p53 signaling by mutation of p53 itself or abrogation of its normal function by other transfactors, such as MDM2, is a key event in the development of most human cancers. To identify novel regulators of p53, we have used a phenotype-based selection in which a total cDNA library in a retroviral vector has been introduced into TR9-7ER cells, which arrest when p53 is expressed from a tetracycline-regulated promoter. We have isolated several clones derived from cells that are not growth-arrested when p53 is overexpressed. In one clone, the levels of p53, p21, and MDM2 are comparable with those in TR9-7ER cells and, therefore, the abrogation of growth arrest by an exogenous cDNA is likely to be distal to p21. Using reverse transcription-PCR, we were able to isolate a cDNA of approximately 2.2 kb, which was found to have 99% identity to the nucleotides between about 80 and 2,288 of the open reading frame of a gene encoding DNA replication licensing factor. It encodes complete peptide of 734 residues of this protein also called minichromosome maintenance deficient 5 (MCM5) or cell division cycle 46 (Saccharomyces cerevisiae). Northern and Western blot analyses revealed that the expression of MCM5 and its transcriptional regulator, E2F1, is negatively regulated by p53. When MCM5 cDNA was reintroduced into fresh TR9-7ER cells, numerous colonies that grow in the absence of tetracycline were formed. This novel observation establishes a role for MCM5 in negating the growth arrest function of p53.

SHP-2-Erk signaling regulates Concanavalin A-dependent production of TIMP-2

To search for the signaling critical for the production of tissue inhibitor of metalloproteinase-2 (TIMP-2), we investigated the role of SHP-2 in TIMP-2 production with Concanavalin A (Con A)-treated cells. In wild-type fibroblasts, Con A-treatment dramatically activated TIMP-2 production. In contrast, production of TIMP-2 in response to Con A-treatment was severely impaired in cells expressing mutant SHP-2 whose 65 amino acids in the SH2-N domain were deleted. Con A-treatment activated dual signaling pathways, Erk and p38, in a SHP-2-dependent manner. Pretreatment of wild-type cells with U0126, a potent inhibitor of MEK1, significantly inhibited the production of TIMP-2, whereas SB203580, a specific inhibitor for p38, could not. Finally, expression of exogenous wild-type SHP-2 in SHP-2 mutant cells clearly rescued Erk activation and TIMP-2 production in response to Con A-treatment. Taken together, our results strongly suggest that SHP-2 plays a critical role as a positive modulator for the production of TIMP-2 via MEK1-Erk signaling in fibroblasts.

The PLC-PKC cascade is required for IL-1beta-dependent Erk and Akt activation: their role in proliferation

We investigated the signaling mechanisms that lead to IL-1beta-induced cell proliferation. Treatment of Balb 3T3 cells with IL-1beta activated two signaling pathways, Erk and Akt. IL-1beta also increased tyrosine phosphorylation of PLC-gamma in Src kinase-dependent manner. Pharmacological inhibition of the PLC-PKC cascade by using specific inhibitor for PLC-gamma (U73122) and PKC (GFX) strongly inhibited IL-1beta-induced Erk and Akt activation. Inhibition of MEK1 by its specific inhibitor, PD98059 substantially inhibited Erk activation. Similarly, inhibition of PI3K activation by its specific inhibitor LY294002 suppressed Akt phosphorylation. Moreover, IL-1beta-induced association of PLC-gamma with SHPS-1. SHPS-1 mutants lacking the tyrosine phosphorylation sites failed to associate with PLC-gamma. Finally, IL-1beta-induced proliferation of Balb 3T3 cells and inhibition of Erk and Akt signalings or their upstream signaling molecules, Src kinase and PKC by their inhibitors strongly inhibited IL-1beta-dependent cell proliferation. Taken together, our results suggest that a SHPS-1-PLC-gamma complex activate the PLC-PKC cascade, which is required for the activation of IL-1beta-dependent Erk and Akt signalings and cell proliferation.

SH2 domain containing protein tyrosine phosphatase 2 regulates concanavalin A-dependent secretion and activation of matrix metalloproteinase 2 via the extracellular signal-regulated kinase and p38 pathways

We investigated the role of SH2 domain containing protein tyrosine phosphatase (SHP) 2 in Concanavalin A (Con A) -dependent signaling that leads to the augmented secretion and activation of matrix metalloproteinase (MMP) 2. In cells expressing mutant SHP-2 in which 65 amino acids in the SH2-N domain were deleted, we found that production, secretion, and proteolytic activation of MMP-2 in response to Con A treatment was severely impaired. Under Con A stimulation, complex formation of SHP-2 with SOS-1 and Grb-2 together with the activation of Ras signaling was clearly observed in wild-type cells, but not in SHP-2 mutant cells. In wild-type cells, Con A-treatment activated dual signaling pathways, extracellular signal-regulated kinase (Erk) and p38, in a Ras-dependent manner, whereas Con A-dependent activation of these signaling pathways was absent in SHP-2 mutant cells. In addition, pretreatment of wild-type cells with U0126, a potent inhibitor for mitogen-activated protein/ERK kinase 1, or with SB203580, a specific inhibitor for p38, significantly inhibited the Con A-dependent secretion and activation of MMP-2. However, overexpression of active mitogen-activated protein/ERK kinase 1 in SHP-2 mutant cells could not induce clear activation of MMP-2 secretion, although these cells responded well to the Con A treatment in a p38-dependent manner. Finally, reintroduction of wild-type SHP-2 into SHP-2 mutant cells rescued Erk and p38 activation, and also MMP-2 secretion, whereas dominant-negative SHP-2 could block the Con A-dependent activation of Erk and p38. Taken together, our results strongly suggest that SHP-2 plays a critical role as a positive mediator for Con A-dependent activation of MMP-2 secretion via Ras-Erk and Ras-p38 signalings.

Secretion of matrix metalloproteinase-9 by the proinflammatory cytokine, IL-1beta: a role for the dual signalling pathways, Akt and Erk

BACKGROUND

Matrix metalloproteinases including MMP-9 mediate matrix destruction during chronic inflammatory diseases such as arthritis and atherosclerosis. MMP-9 up-regulation by inflammatory cytokines involve interactions between several transcription factors including activator protein-1 and NFkappaB. The upstream regulatory pathways are less well understood.

RESULTS

To search for the mechanism of tissue destruction in the process of inflammatory disorders, we investigated the signalling pathway critical for the activation of MMP-9 expression and secretion by IL-1beta. Treatment of Balb 3T3 cells with IL-1beta activated MMP-9 transcription and subsequent secretion in a time- and dose-dependent manner. Concomitantly, IL-1beta treatment of cells activated phosphorylation of Akt, Erk and p38. Treatment of cells with either LY294002, a PI3K inhibitor, or expression of a dominant negative form of Akt drastically suppressed the IL-1beta-dependent secretion of MMP-9. Pretreatment of cells with a MEK1 inhibitor, U0126, also strongly inhibited IL-1beta-dependent secretion of MMP-9. In contrast, pre-treatment with a specific p38 kinase inhibitor, SB203580, had no effect on IL-1beta-dependent secretion of MMP-9. In addition, cells expressing constitutively active form of Akt or MEK1 showed no clear activation of MMP-9 secretion, whereas these cells responded well to IL-1beta treatment. However, co-transfection of cells with both active Akt and MEK1 was sufficient to induce MMP-9 secretion without stimulation with IL-1beta.

CONCLUSION

Taken together, our results suggest that IL-1beta stimulation of cells activates MMP-9 secretion by the activation of the dual signalling pathways, the PI3K-Akt and MEK1-Erk and constitutive activation of these pathways were sufficient to induce MMP-9 secretion.

Cysteine residues in the C-terminal lobe of Src: their role in the suppression of the Src kinase

To evaluate the function of cysteine residues of the Src kinase, we constructed a series of Src mutants in which some of cysteines were replaced to alanines. With these mutants, we studied the effect of SH-alkylating agents, N-[p-(2-benzimidazolyl)phenyl] maleimide (BIPM) and N-(9-acridinyl) maleimide (NAM), on their kinase activity. Of 10 cysteine residues scattered over v-Src, either a single mutation at Cys520 or multiple mutations at the four clustered cyteines, Cys483, Cys487, Cys496 and Cys498, yielded clear resistance to the treatment with 10 microM BIPM or 1 microM NAM. In contrast, other cysteines including those in the SH2 domain and those in the catalytic cleft of the kinase domain were dispensable for the inactivation by BIPM and NAM. Similarly, deletion of SH2 and SH3 did not confer the resistance to v-Src, suggesting the inactivation by the SH-alkylating agents is SH2/SH3-independent. Although Cys520-mutated v-Src was resistant to 1 microM NAM, it was inactivated by 5 microM NAM. However, combined mutation including all of Cys483, Cys487, Cys496, Cys498 and Cys520 yielded clear resistance to 5 microM NAM. Among these mutants, those with double mutations in the four clustered cysteines yielded a temperature sensitive phenotype in the transfected cells, whereas Cys520 did not, suggesting that Cys520 has, at least in part, a discrete function. In contrast to v-Src, c-Src, which lacks cysteine at position 520, was resistant to 1 microM NAM but sensitive to 5 microM NAM. While replacement of Phe520 of c-Src to cysteine made it sensitive to 1 microM NAM, double mutation in clustered cysteines again yielded resistance to 5 microM NAM. Taken together, our results strongly suggest that the multiple cysteine residues clustered at the end of the C-terminal lobe are critical for the inhibition by the SH-alkylating agents and, thereby, have an allosteric repressor effect on the catalytic activity of Src in a SH2-phosphoTyr527 independent manner.

SHPS-1, a multifunctional transmembrane glycoprotein

Src homology 2 (SH2) domain-containing protein tyrosine phosphatase substrate 1 (SHPS-1) is a member of the signal regulatory protein (SIRP) family. The amino-terminal immunoglobulin-like domain of SHPS-1 is necessary for interaction with CD47, a ligand for SHPS-1, which plays an important role in cell-cell interaction. The intracellular region of SHPS-1, on the other hand, may act as a scaffold protein, binding to various adapter proteins. Interestingly, increasing evidence has shown that SHPS-1 is involved in various biological phenomena, including suppression of anchorage-independent cell growth, negative regulation of immune cells, self-recognition of red blood cells, mediation of macrophage multinucleation, skeletal muscle differentiation, entrainment of circadian clock, neuronal survival and synaptogenesis. Recent progress has been made in attributing these novel exciting functions. Here we discuss how this interesting molecule works and consider its true role in biology.