Cigarette smoke disrupts the integrity of airway adherens junctions through the aberrant interaction of p120-catenin with the cytoplasmic tail of MUC1.

Adherens junctions (AJs) containing epithelial cadherin (E-cad) bound to p120-catenin (p120ctn) and ß-catenin (ß-ctn) play a crucial role in regulating cell-cell adhesion. Cigarette smoke abrogates cell-cell adhesion between epithelial cells by disrupting E-cad, a hallmark of epithelial-mesenchymal transition (EMT), yet the underlying mechanism remains unknown. We used an organotypic culture of primary human bronchial epithelial (HBE) cells treated with smoke-concentrated medium (Smk) to establish an essential role for the interaction between p120ctn and the cytoplasmic tail of MUC1 (MUC1-CT) in regulating E-cad disruption. Within the first 4 h of smoke exposure, apical MUC1-CT repositioned to the basolateral membrane of pseudo-stratified HBE cells, where it interacted with p120ctn. A time-dependent increase in MUC1-CT/p120ctn complexes occurred in conjunction with a time-dependent dissociation of p120ctn/E-cad/ß-ctn complexes, as well as the coordinated degradation of p120ctn and E-cad. Interestingly, Smk induced a similar interaction between MUC1-CT and ß-ctn, but this occurred 44 h after MUC1-CT's initial interaction with p120ctn, and well after the AJs were destroyed. Blocking MUC1-CT's interaction with p120ctn using a MUC1-CT dominant-negative peptide, PMIP, successfully abolished Smk's disruptive effects on AJs and recovered apical-basolateral polarity of HBE cells. The MUC1-CT/p120ctn interaction was highly dependent on EGFR/Src/Jnk-mediated tyrosine phosphorylation (TyrP) of MUC1-CT. Accordingly, EGFR, Src or Jnk inhibitors (AG1478, PP2, SP600125, respectively) abrogated Smk-induced MUC1-CT-TyrP, MUC1-CT/p120ctn interaction, AJ disruption, and loss of cellular polarity. Our work identified MUC1-CT and p120ctn as important regulators of epithelial polarity and cell-cell adhesion during a smoke-induced EMT-like process. Novel therapeutics designed to inhibit MUC1-CT/p120ctn complex formation may prevent EMT in the smoker's airway.

TACE/ADAM-17 phosphorylation by PKC-epsilon mediates premalignant changes in tobacco smoke-exposed lung cells.

BACKGROUND: Tobacco smoke predisposes humans and animals to develop lung tumors, but the molecular events responsible for this are poorly understood. We recently showed that signaling mechanisms triggered by smoke in lung cells could lead to the activation of a growth factor signaling pathway, thereby promoting hyperproliferation of lung epithelial cells. Hyperproliferation is considered a premalignant change in the lung, in that increased rates of DNA synthesis are associated with an increased number of DNA copying errors, events that are exacerbated in the presence of tobacco smoke carcinogens. Despite the existence of DNA repair mechanisms, a small percentage of these errors go unrepaired and can lead to tumorigenic mutations. The results of our previous study showed that an early event following smoke exposure was the generation of oxygen radicals through the activation of NADPH oxidase. Although it was clear that these radicals transduced signals through the epidermal growth factor receptor (EGFR), and that this was mediated by TACE-dependent cleavage of amphiregulin, it remained uncertain how oxygen radicals were able to activate TACE. PRINCIPAL FINDINGS: In the present study, we demonstrate for the first time that phosphorylation of TACE at serine/threonine residues by tobacco smoke induces amphiregulin release and EGFR activation. TACE phosphorylation is triggered in smoke-exposed lung cells by the ROS-induced activation of PKC through the action of SRC kinase. Furthermore, we identified PKCε as the PKC isoform involved in smoke-induced TACE activation and hyperproliferation of lung cells. CONCLUSIONS: Our data elucidate new signaling paradigms by which tobacco smoke promotes TACE activation and hyperproliferation of lung cells.

Leukotriene D4 upregulates MUC2 gene transcription in human epithelial cells.

BACKGROUND/AIMS: Leukotriene (LT) D(4) has been shown to induce mucus secretion in the airways. Excessive mucus secretion characterizes airway inflammatory disease such as asthma, allergic rhinitis. However, little is known about the effect of LTD(4) on mucin gene expression. The aim of this study was to investigate the effect of LTD(4) on MUC2 gene expression in cultured epithelial cells (HM3-MUC2 cells). METHODS: HM3-MUC2 cells were treated with LTD(4) for 2 or 6 h. Reporter gene assay was mainly used for analysis.MUC2 protein levels were measured using an enzyme-linked immunosorbent assay. RESULTS: LTD(4) significantly increased MUC2 gene transcriptional activity in a dose-dependent manner. Pranlukast, which is a selective antagonist of CysLT(1) receptor, inhibited LTD(4)-induced MUC2 gene transcriptional activity in a dose-dependent manner. LTD(4)-induced MUC2 gene transcriptional activity was also suppressed by a G-protein inhibitor (pertussis toxin),a protein kinase C (PKC) inhibitor (bisindolylmaleimide), a mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitor (PD98059), an extracellular signal regulated kinase-2 (ERK-2) inhibitor (AG126) and a nuclear factor kappaB (NF-kappaB) inhibitor. In addition, pranlukast inhibited LTD(4)-induced NF-kappaB activity. CONCLUSION: These results suggest that LTD(4 )upregulates MUC2 gene transcription via a signaling pathway involving CysLT(1) receptor, G-protein, PKC, MEK, ERK and NF-kappaB.

Wnt and Hedgehog are critical mediators of cigarette smoke-induced lung cancer.

BACKGROUND: Lung cancer is the leading cause of cancer death in the world, and greater than 90% of lung cancers are cigarette smoke-related. Current treatment options are inadequate, because the molecular basis of cigarette-induced lung cancer is poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that human primary or immortalized bronchial epithelial cells exposed to cigarette smoke for eight days in culture rapidly proliferate, show anchorage-independent growth, and form tumors in nude mice. Using this model of the early stages of smoke-induced tumorigenesis, we examined the molecular changes leading to lung cancer. We observed that the embryonic signaling pathways mediated by Hedgehog and Wnt are activated by smoke. Pharmacological inhibition of these pathways blocked the transformed phenotype. CONCLUSIONS/SIGNIFICANCE: These experiments provide a model in which the early stages of smoke-induced tumorigenesis can be elicited, and should permit us to identify molecular changes driving this process. Results obtained so far indicate that smoke-induced lung tumors are driven by activation of two embryonic regulatory pathways, Hedgehog (Hh) and Wnt. Based on the current and emerging availability of drugs to inhibit Hh and Wnt signaling, it is possible that an understanding of the role of Hh and Wnt in lung cancer pathogenesis will lead to the development of new therapies.

MUC5AC mucin gene regulation in pancreatic cancer cells.

MUC5AC is a secretory mucin normally expressed by the surface mucous cells of the human stomach and in the bronchial tract. It is absent from normal pancreas, but de novo expression of this mucin occurs in early-stage pancreatic intraepithelial neoplasias and in the invasive ductal adenocarcinoma of the pancreas, prompting this study of MUC5AC gene regulation in pancreatic cancer cells. Promoter deletion constructs and EMSA studies revealed that transcription factors Sp1 and AP-1 are both involved in basal transcription of the MUC5AC gene. Phorbol 12-myrisate 13-acetate (PMA) increased MUC5AC mRNA expression and transcriptional activities of MUC5AC promoter-reporter deletion constructs containing AP-1 consensus sites. EMSA studies showed that Fos/Jun binding to putative AP-1 sites is increased by PMA treatment. Western blot analysis showed that ERK, JNK and p38 are all activated by PMA treatment in SW1990 cells. Inhibitors of mitogen-activated protein/extracellular signal regulated kinase (MEK), such as ERK inhibitor PD98059 and JNK inhibitors dicumarol and SP60015, but not p38 inhibitor SB203580, inhibited PMA-induced MUC5AC reporter activity. Our studies indicate that Sp1 is involved in basal MUC5AC promoter activity while AP-1 is involved in basal and PMA-induced MUC5AC promoter activation in pancreatic cancer cells. Furthermore, PMA-induced MUC5AC gene transcription appears to be mediated by activating Sp1, PKC/ERK/AP-1 and PKC/JNK/AP-1 pathways.

AsialoGM1 and TLR5 cooperate in flagellin-induced nucleotide signaling to activate Erk1/2.

Bacterial flagellin can interact with both Toll-like receptor 5 (TLR5) and the cell surface glycolipid, asialoGM1, to activate an innate immune response. The induction of mucin by flagellin in human lung epithelial cells (NCIH292) is dependent on asialoGM1 ligation, ATP receptor signaling, Ca2+ mobilization, and Erk1/2 activation. Conversely, the activation of NF-kappaB by flagellin is dependent on signaling through TLR5. These results prompted us to ask whether the flagellin-induced TLR5 signaling pathway was intersecting with or mutually independent of the nucleotide receptor pathway activated downstream of asialoGM1. Herein, we demonstrate that the release of ATP induced by flagellin is dependent on a Toll signaling cascade. Although Toll was able to activate NF-kappaB in the absence of extracellular ATP, Toll required ATP to activate Erk1/2. These results suggest interdependence between the asialoGM1 and TLR5 pathways and reveal a previously unsuspected role for autocrine extracellular ATP signaling in TLR signaling.

Immune complex-dependent remodeling of the airway vasculature in response to a chronic bacterial infection.

Chronic inflammation in the airways is associated with dramatic architectural changes in the walls of the airways and in the vasculature they contain. In this study, we show that the adaptive immune system is essential for airway remodeling that occurs in mice that are chronically infected with the respiratory pathogen Mycoplasma pulmonis. Angiogenesis, lymphangiogenesis, and epithelial remodeling were greatly reduced in mice that lacked B cells. Substantiating a role for Ab and airway immune complexes, we found that the transfer of immune serum to B cell-deficient mice could reconstitute pathogen-induced angiogenesis. Inflammatory cells recruited to the infected airways were activated by the humoral response, and this activation correlated with the induction of genes for remodeling factors such as vascular endothelial growth factor-D. The results reveal a novel pathway whereby T cell-dependent humoral immunity to a persistent airway infection can induce inflammation-dependent angiogenesis, lymphangiogenesis, and chronic airway pathology.

CXCR4 expression reflects tumor progression and regulates motility of bladder cancer cells.

Transitional cell carcinoma of the urinary bladder remains life threatening due to the high occurrence of metastases. Emerging evidence suggests that chemokines and their receptors play a critical role in tumor metastases. In our study, we performed a systematic analysis of the mRNA and protein expression levels of all 18 chemokine receptors in normal urothelium and bladder cancer. CXCR4 was the only chemokine receptor whose mRNA expression level was upregulated in bladder cancer cell lines as well as in invasive and locally advanced bladder cancer tissue samples (pT2-pT4). In contrast, superficial bladder tumors (pTa and pT1) displayed low CXCR4 expression levels and normal urothelial cells were negative for CXCR4. Immunohistochemistry of a bladder cancer tissue microarray (TMA) confirmed that a subgroup of invasive bladder cancers revealed a high CXCR4 protein expression, while superficial bladder tumors showed low immunoreactivity. To investigate the functional significance of CXCR4 expression, we performed migration and invasion assays. Exposure of CXCR4-positive bladder cancer cells to CXCL12 in a Boyden chamber type assay provoked a significant increase in migration as well as invasion across a Matrigel barrier. Enhanced migration and invasion were inhibited by a CXCR4-specific blocking antibody. In contrast, normal urothelial cells did not respond to CXCL12 and lacked chemotactic migration. In conclusion, bladder cancer cells express CXCR4 progressively with advanced tumorigenesis and this receptor interacts with CXCL12 to mediate tumor chemotaxis and invasion through connective tissue. These properties identify CXCR4 as a potential target for the attenuation of bladder cancer metastases.

Pranlukast inhibits NF-kappaB activation and MUC2 gene expression in cultured human epithelial cells.

Pranlukast is a selective cysteinyl leukotriene(1 )(cysLT(1)) receptor antagonist, and is now widely used in the treatment of asthma. The anti-asthmatic effect of pranlukast may be rendered not only by antileukotriene activity, but also by other pharmacological activity. This study was designed to investigate whether pranlukast had inhibitory effects on nuclear factor-kappaB (NF-kappaB) activation and mucin gene expression in cultured human epithelial cells. Luciferase assay was mainly used for analysis. Cultured epithelial cells were transfected with NF-kappaB luciferase vector, MUC2 or MUC5AC luciferase vectors. Lipopolysaccharide (LPS) significantly increased NF-kappaB activation in NCI-H292 cells, which was inhibited by the pretreatment by pranlukast in a dose-dependent manner. Either LTD(4) or pranlukast alone did not increase NF-kappaB activation in NCI-H292 cells. Pranlukast also inhibited NF-kappaB activation induced by phorbol 12-myristate 13-acetate (PMA). Pranlukast also significantly inhibited LPS-induced MUC2 mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR) analysis in NCI-H292 cells. Pranlukast also inhibited LPS-induced MUC2 gene expression in HM3-MUC2 cells. However, pranlukast did not inhibit MUC5AC gene transcription activity induced by lipoteichoic acid (LTA) in NCI-H292 cells. These results suggest that pranlukast may inhibit NF-kappaB activation and MUC2 gene transcription through pathways distinct from cysLT(1) receptor antagonism in cultured human epithelial cells.

Sp1 is involved in the transcriptional activation of lysozyme in epithelial cells.

Lysozyme protects us from the ever-present danger of bacterial infection. The expression of lysozyme is, in part, regulated by the Ets factor, myeloid elf-1-like factor (MEF). MEF binds to the ETS site of the lysozyme promoter at -46 to -40bp. Closer analysis of the promoter using a series of deletion mutants and point mutants indicated that the region around -75bp is also essential in regulating the activity of lysozyme. The sequences in this region correspond to the Sp1 consensus binding site. Sp1 is known to regulate a variety of house-keeping and tissue-specific genes by itself or with other transcription factors like AP-1 or ETS. We indicate here that Sp1 regulates the lysozyme gene by binding to the GT-core sequences of lysozyme promoter. Treatment with mithramycin A down-regulated the promoter activity and the transfection of anti-sense Sp1 induced a decrease in the endogenous expression of lysozyme.

Nontypeable Haemophilus influenzae lipoprotein P6 induces MUC5AC mucin transcription via TLR2-TAK1-dependent p38 MAPK-AP1 and IKKbeta-IkappaBalpha-NF-kappaB signaling pathways.

Mucin overproduction is a hallmark of nontypeable Haemophilus influenzae (NTHi) infections. The molecular mechanisms underlying up-regulation of mucin in NTHi infections especially during the initial phase remain unknown. Here we show that P6, a 16-kDa outer membrane lipoprotein well conserved in NTHi, up-regulates MUC5AC mucin gene transcription in vitro and in vivo. Moreover, P6 induces MUC5AC transcription via TLR2-MyD88-IRAK1-TRAF6-TAK1-dependent p38 MAPK-AP1 and IKKbeta-IkappaBalpha-NF-kappaB signaling pathways. This study may bring new insights into the molecular pathogenesis of NTHi-induced infections and lead to novel therapeutic intervention for inhibiting mucin overproduction in patients with NTHi infections.

Adenosine up-regulation of the mucin gene, MUC2, in asthma.

Mucus hypersecretion is a hallmark of asthma that contributes to airway obstruction. While the etiology is not well understood, hypersecretion has been linked to the presence of cytokines such as IL-4, IL-5, IL-9, and IL-13 in the inflamed airway. The presence of adenosine has also been noted in asthmatic airways, and adenosine-mediated signaling in mast cells has been implicated in the severe bronchoconstriction and inflammation prevalent in these patients (1, 2). Here we examine the possibility that adenosine also contributes to mucus hypersecretion by airway epithelial cells. Results in cultured airway epithelial cells showed that MUC2 mucin expression increased in response to adenosine. This appeared to be mediated by a pathway initiated at the adenosine A1 receptor that transduced signals through a Ca2+-activated Cl- channel and EGFR. That this signaling cascade is relevant to asthmatic hypersecretion was indicated by results showing that mucin induction by asthmatic tracheal aspirates was reduced by A1, CLCA1, and EGFR inhibitors. These results suggest that adenosine cooperates with inflammatory cytokines to stimulate mucin production in the asthmatic airway and supports the use of A1, CLCA1, and EGFR inhibitors in the treatment of asthma.

Roxithromycin suppresses mucin gene expression in epithelial cells.

Macrolide antibiotics are believed to inhibit mucus secretion but the mechanism of action is unclear. This study was designed to investigate an effect of roxithromycin on MUC2 gene expression in cultured intestinal epithelial cells (HM3-MUC2 cells). A reporter gene assay was used for analysis. Roxithromycin suppressed MUC2 gene transcriptional activity in a dose-dependent manner in HM3-MUC2 cells. Phorbol 12-myristate 13-acetate (PMA), lipoteichoic acid (LTA), lipopolysaccharide (LPS) and leukotriene D4 (LTD4) significantly increased MUC2 luciferase activities in the following order: PMA > LTA > LTD4 > LPS. Roxithromycin also decreased MUC2 gene transcriptional activity induced by PMA in a dose-dependent manner. NF-kappaB activation, but not AP-1 activation, was significantly suppressed by roxithromycin in HM3-MUC2 cells. A suppression of NF-kappaB activation was also observed in NCI-H292 cells. These results suggest that roxithromycin suppresses MUC2 gene expression in epithelial cells and that this suppression is probably via inhibition of NF-kappaB activation.

Tobacco smoke control of mucin production in lung cells requires oxygen radicals AP-1 and JNK.

In smokers' lungs, excessive mucus clogs small airways, impairing respiration and promoting recurrent infection. A breakthrough in understanding this pathology was the realization that smoke could directly stimulate mucin synthesis in lung epithelial cells and that this phenomenon was dependent on the cell surface receptor for epidermal growth factor, EGFR. Distal steps in the smoke-triggered pathway have not yet been determined. We report here that the predominant airway mucin (MUC5AC) undergoes transcriptional up-regulation in response to tobacco smoke; this is mediated by an AP-1-containing response element, which binds JunD and Fra-2. These transcription factors require phosphorylation by upstream kinases JNK and ERK, respectively. Whereas ERK activation results from the upstream activation of EGFR, JNK activation is chiefly EGFR-independent. Our experiments demonstrated that smoke activates JNK via a Src-dependent, EGFR-independent signaling cascade initiated by smoke-induced reactive oxygen species. Taken together with our earlier results, these data indicate that the induction of mucin by smoke is the combined effect of mutually independent, reactive oxygen species activation of both EGFR and JNK.

Detection of occult tumor cells in lymph nodes from bladder cancer patients by MUC7 nested RT-PCR.

OBJECTIVE: Systemic progression is the prevalent form of bladder tumor recurrence after radical cystectomy. The detection of occult bladder tumor cells in histopathologically normal lymph nodes could be of prognostic value. We examined the possibility that mucin 7 (MUC7) RNA might reflect the presence of occult tumor cells in lymph nodes from bladder cancer patients. We used the polymerase chain reaction (RT-PCR), a highly sensitive assay, to monitor MUC7 RNA. METHODS: We collected 240 pelvic lymph nodes from 25 bladder cancer patients undergoing radical cystectomy. We also obtained 20 lymph nodes from patients with prostate cancer and interstitial cystitis to use as negative controls. Each lymph node was divided in two parts to provide tissue for both histopathological and PCR analysis. RESULTS: 166/240 lymph nodes from bladder cancer patients were usable for MUC7 RT-PCR. By conventional histopathology, six of these nodes contained metastases. MUC7 RT-PCR analysis was positive for five of the six histologically proven lymph node metastases. Histopathological reevaluation of the sixth node revealed tumor in an adjacent vein, not in the lymph node, itself. In contrast, 46/160 (29%) histologically classified normal lymph nodes (pN0) from 17 bladder cancer patients were positive for MUC7. All 20 lymph nodes from control patients were MUC7-negative. CONCLUSION: MUC7 RT-PCR is a specific and sensitive method for the detection of occult tumor cells in lymph nodes from bladder cancer patients. Long-term observation will be necessary to evaluate the clinical value of MUC7 as a prognostic indicator of lymph node metastasis and disease progression.

The microvesicle as a vehicle for EMMPRIN in tumor-stromal interactions.

EMMPRIN is a transmembrane glycoprotein expressed at high levels by tumor cells. It has been identified as a tumor-derived factor that can stimulate matrix metalloproteinase expression in fibroblasts and hence facilitate tumor invasion and metastasis. Recent studies have shown that full-length EMMPRIN is released by tumor cells, but the mechanism of release remains unclear. Here, we show that EMMPRIN is released from the surface of NCI-H460 cells via microvesicle shedding. However, these vesicles are unstable and rapidly break down to release bioactive EMMPRIN. Although microvesicle shedding has been considered a constitutive process in tumor cells, our data show that it can be amplified upon cell exposure to PMA, elucidating at least one signalling cascade responsible for EMMPRIN release. This pathway is dependent on protein kinase C, calcium mobilization and mitogen-activated protein kinase kinase (MEK 1/2). Thus, the results outline a novel form of tumor-stromal interaction in which extracellular matrix degradation by fibroblasts is controlled through the microvesicular release of EMMPRIN from tumor cells.

Viral dsRNA activates mucin transcription in airway epithelial cells.

Double-stranded (ds) RNA is a biologically active component of many viruses including rhinoviruses infecting the upper respiratory tract. Mucus production is a common symptom of such infections. Here, we show that mucin, the glycoprotein subunit of mucus gels, is transcriptionally upregulated in an NF-kappaB- and p38-dependent manner when homogeneous cultures of epithelial cells are exposed to dsRNA. Furthermore, upstream of p38 in this system, dsRNA stimulates the extracellular release of ATP and activation of cell surface ATP receptors, which are G protein-coupled. This results in the stimulation of phospholipase C and protein kinase C. These findings suggest that ATP receptor antagonists could be used to modulate mucus production induced by virus.

Toxicity of chemical components of fine particles inhaled by aged rats: effects of concentration.

This study tested the hypothesis that exposure to mixtures containing fine particles and ozone (O3) would cause pulmonary injury and decrements in functions of immunological cells in exposed rats (22-24 months old) in a dose-dependent manner. Rats were exposed to high and low concentrations of ammonium bisulfate and elemental carbon and to 0.2 ppm O3. Control groups were exposed to purified air or O3 alone. The biological end points measured included histopathological markers of lung injury, bronchoalveolar lung fluid proteins, and measures of the function of the lung's innate immunological defenses (macrophage antigen-directed phagocytosis and respiratory burst activity). Exposure to O3 alone at 0.2 ppm did not result in significant changes in any of the measured end points. Exposures to the particle mixtures plus O3 produced statistically significant changes consistent with adverse effects. The low-concentration mixture produced effects that were statistically significant compared to purified air but, with the exception of macrophage Fc receptor binding, exposure to the high-concentration mixture did not. The effects of the low- and high-concentration mixtures were not significantly different. The study supports previous work that indicated that particle + O3 mixtures were more toxic than O3 alone.

Tobacco smoke-induced lung cell proliferation mediated by tumor necrosis factor alpha-converting enzyme and amphiregulin.

Cells dividing at the time of carcinogen exposure are at particular risk for neoplasia. Tobacco smoke contains numerous carcinogens, and we find that smoke, in the absence of exogenous growth factors, is capable of stimulating cell proliferation. The smoke-triggered mechanism includes the generation of oxygen radicals, which in turn stimulate tumor necrosis factor alpha-converting enzyme (a disintegrin and metalloproteinase (ADAM) 17) to cleave transmembrane amphiregulin, a ligand for the epidermal growth factor receptor (EGFR). The binding of amphiregulin to EGFR then stimulates proliferation of lung epithelial cells. These results shed light on the pathogenesis of lung cancer, suggest novel drug targets for the reduction of cancer risk in smokers, and provide insight into how EGFR integrates responses to diverse noxious stimuli.

Phorbol 12-myristate 13-acetate up-regulates the transcription of MUC2 intestinal mucin via Ras, ERK, and NF-kappa B.

MUC2 is a secretory mucin normally expressed by goblet cells of the intestinal epithelium. It is overexpressed in mucinous type colorectal cancers but down-regulated in colorectal adenocarcinoma. Phorbol 12-myristate 13-acetate (PMA) treatment of colon cancer cell lines increases MUC2 expression, so we have undertaken a detailed analysis of the effects of PMA on the promoter activity of the 5'-flanking region of the MUC2 gene using stably and transiently transfected promoter reporter vectors. Protein kinase C inhibitors (bisindolylmaleimide, calphostin C) and inhibitors of mitogen-activated protein/extracellular signal regulated kinase kinase (MEK) (PD98059 and U0126) suppressed up-regulation of MUC2. Src tyrosine kinase inhibitor PP2, a protein kinase A inhibitor (KT5720), and a p38 inhibitor (SB 203580) did not affect transcription. Western blotting and reverse transcription-PCR analysis confirmed these results. In addition, co-transfections with mutants of Ras, Raf, and MEK showed that the induction of MUC2 promoter activity by PMA required these three signaling proteins. Our results demonstrate that PMA activates protein kinase C, stimulating MAP kinase through a Ras- and Raf-dependent mechanism. An important role for nuclear factor kappaB (NF-kappaB) was also demonstrated using the inhibitor caffeic acid phenethyl ester and electrophoretic mobility shift assays. Such identification of pathways involved in MUC2 up-regulation by PMA in the HM3 colon cancer cell line may serve as a model for the effects of cytokines and growth factors, which regulate MUC2 expression during the progression of colorectal cancer.