'Bleeding Dilemma': The Story of a Periampullary Mass

Periampullary malignancies arise in the vicinity of the ampulla of Vater, a common passage for biliary and pancreatic secretions. Determining the anatomical origin of these tumors represents a diagnostic challenge. This is especially true for large tumors due to the transitional nature of this region, proximity to different structures, anatomical variations, and overlapping features among constituting structures. This determination has significant prognostic and therapeutic implications. Among them, primary ampullary adenocarcinoma is a rare malignancy that has the best overall prognosis with high rates of potentially curative resection and possible survival even in advanced disease. Due to its rarity, it is also a vague territory with no definitive guidelines regarding management and surveillance currently available. Acute gastrointestinal hemorrhage is a rare presentation of ampullary carcinoma that occurs secondary to tumor ulceration. We report an elderly male with a previously known large, initially asymptomatic periampullary mass who came for evaluation of melena and was noted to be hypotensive secondary to acute blood loss from the large tumor, later determined to be adenocarcinoma of the ampulla of Vater.

Abstract P5-06-09: Cyclin d1 binding to chromatin and the induction of chromosomal instability requires the fuzzy domain

The cyclin D1 gene encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the retinoblastoma (Rb) and the nuclear respiratory factor 1 (NRF1) proteins to regulate nuclear DNA synthesis and mitochondrial biogenesis. Cyclin D1 is required for oncogene-dependent growth and genetic ablation of the murine cyclin D1 gene resulted in resistance to Ras or ErbB2-induced mammary tumorigenesis and APC-induced gastrointestinal tumorigenesis. Cyclin D1 overexpression occurs in human breast, prostate, lung, and gastrointestinal malignancies and its abundance is induced at the level of transcription, translation and through post-translational modifications. Cyclin D1 plays a key role in transcriptional regulation inducing gene expression governing chromosomal instability (CIN) and cell-cycle progression. Cyclin D1 is also known to bind TF regulatory regions in chromatin immuno-precipitation (ChIP) assays. Genome wide analysis of cyclin D1 occupancy using ChIP-Seq identified binding sites including both the coding and non-coding genome with enrichment for genes regulating CIN and the G2/M phase (Top2A, AurkB, Cenpp, Mlf1ip, Zw10, Ckap2) consistent with enrichment of cyclin D1 at G2/M and the finding that cyclin D1 induces CIN. We sought to identify the molecular mechanisms governing the recruitment of cyclin D1 in the context of local chromatin to promote CIN. In order to define the domain of cyclin D1 involved in aneuploidy and tumorigenesis, we transduced and assessed the induction of aneuploidy in MEF cells using cyclin D1 wt (wt), cyclin D1 C-terminus domain (C4), cyclin D1 mutant lacking of the E-box motif (ΔE) or ctrl. We also searched for potential histone protein interaction motifs in cyclin D1 and determined the epigenetic motif recognized by cyclin D1 using a histone peptide array. The recognition of an epigenetic code by cyclin D1 may facilitate genome wide expression changes during cell-cycle progression and tumorigenesis. We finally identified a “fuzzy” domain of cyclin D1 which is required to local chromatin access for regulatory promoter regions governing and promoting CIN.

Citation Format: Pestell RG, Di Sante G, Di Rocco A, Pupo C, Crosariol M, Tompa P, Tantos A, Wang C, Yu Z, Vadlamudi R, Mann M, Casimiro MC. Cyclin d1 binding to chromatin and the induction of chromosomal instability requires the fuzzy domain [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-06-09.

Abstract P4-07-06: Imipramine Blue - A safe and potent therapeutic regimen that suppresses breast cancer growth and progression by targeting DNA damage surveillance pathway

Despite improvement in overall survival of breast cancer patients, many women don't survive this disease. Moreover, the quality of life for patients who do survive is often substantially reduced due to the toxicity associated with the chemotherapy. Here, we report that imipramine blue (IB), a novel analogue of anti-depressant imipramine that we recently synthesized, may serve as a safe and potent therapeutic agent for treating breast cancers. We show that IB reduced cell growth, migration and invasion of breast cancer cells. Systemic delivery of IB using nanoparticle-based drug delivery approach suppressed breast cancer growth and metastasis without inducing any toxicity in pre-clinical orthotropic mouse models. Notably, using ex-vivo model of tumor explants from breast cancer patients, we demonstrated that IB inhibited breast cancer growth without affecting normal mammary epithelial cell proliferation. Furthermore, IB improved the sensitivity of breast cancer cells to chemotherapy drugs paclitaxel and doxorubicin. Our results revealed that IB mediated its anti-tumor effect by targeting genes involved in cell cycle progression, microtubule dynamics and DNA damage surveillance pathway including Forkhead Box M1 (FOXM1), stathmin1, S-phase kinase-associated protein 2 (Skp2) and XRCC3, which we show to be highly expressed in breast cancer patients. Importantly, we demonstrated that IB inhibited breast cancer cell's ability to repair DNA strand breaks by impairing homologous recombination events. These findings highlight the potential of IB to be used as a potent therapeutic regimen for treating breast cancer patients. Since IB-1 is derived from a FDA approved drug it has potential to be rapidly translated to the clinic.

Citation Format: Rajamanickam S, Subbarayalu P, Timilsina S, Gorthi A, Drake MT, Chen Y, Vadlamudi R, Bishop AJR, Arbiser JL, Rao MK. Imipramine Blue - A safe and potent therapeutic regimen that suppresses breast cancer growth and progression by targeting DNA damage surveillance pathway. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-07-06.

Abstract P4-06-01: Significance and Therapeutic Potential of PELP1 in ER-Negative Breast Cancers

Background: During the past 20 years, studies have extensively focused on the role of estrogen receptor (ER) and progesterone receptor (PR) in breast cancer. Even through ER and PR explain the biology of ER-positive tumors, it remain unknown as to what drives ER-negative metastatic tumors. Recent advances implicated potential importance of several additional nuclear receptor (NRs) including ERRα, AR, GR, and PPAR in breast cancer. NR action is complex, requires functional interactions with coregulators, and deregulation of coregulators occur during cancer progression. As a modulator of multiple NR functions, coregulators are likely to play a role in breast cancer progression to metastasis. Recent studies indicated that metastatic tumors have increased expression of corgulators. Proline glutamic acid rich protein (PELP1) is a NR coregulator, and its expression is upregulated during breast cancer progression. The objective of this study is to examine whether proto-oncogene PELP1 contributes to metastatic potential of ER-negative breast cancer cells and to test whether blocking of PELP1 signaling axis will have therapeutic effect.

Methods: We have used two ER-negative model cells; (1) MDA-MB231 cells that facilitate study of bone and lungs metastasis of breast cancer cells using Nude mice models, (2) 4T1 cells, a clinically relevant model of spontaneous breast cancer metastasis that facilitate tumor growth studies using syngenic mice. To establish the significance of PELP1 axis, we have established clones stably expressing PELP1-shRNA (MDA-MB231- PELP1 shRNA, 4T1-PELP1 shRNA). Proliferation was measured using CellTiter-Glo assays. Role of PELP1 on metastasis was studied using Boyden chamber, wound healing, invasion and MMP assays. Epithelial to Mesenchymal Transition (EMT) real time qPCR Array (Super array) was used to identify PELP1 target genes and targets were validated using ChIP assays. Nude mice based assays were performed to study the role of PELP1 on in vivo metastasis.

Results: MDA-MB231 and 4T1 cells expressing PELP1-shRNA showed decreased PELP1 expression (∼75% of endogenous levels) and exhibited decreased propensity to proliferate in in vitro growth assays. Boyden chamber and wound healing assays showed PELP1 down regulation substantially affect migratory potential of MDA-MB231 and 4T1 cells. PELP1 shRNA model cells showed alterations in the expression of the EMT markers. EMT array studies identified eight genes involved in the EMT (including MMPs, E-cadherin, MTA1) as PELP1 potential target genes and ChIP studies showed PELP1 recruitment to these gene promoters. Overexpression of PELP1 in nonmetastatic cells increases their propensity for metastasis in vivo, while, PELP1 knockdown in metastatic model cells decreased their metastatic potential. Nanopartiles delivering PELP1-siRNA significantly affected the growth and metastatic potential of ER-ve cells.

Conclusions: These results suggest that PELP1 play a role in ER-ve breast cancer metastasis by promoting cell motility and EMTand blockage of PELP1 axis reduces metastasis potential of ER-negative breast cancer cells. Understanding how NR coregulator PELP1play a role in metastasis will be useful in maximizing treatment opportunities for metastatic breast cancer. This study is funded by Komen grant KG091267.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-06-01.

Potential Role of Pargyline in Overcoming Adaptive Resistance in Breast Cancer Cells

Background: Estrogen-induced breast carcinogenesis is shown to be characterized by global changes in histone modifications. LSD1 (KDM1), a histone demethylase enzyme, play a key role in establishing specific histone methyl marks at target gene promoters. Recent evidence suggest that LSD1 is recruited to a significant fraction of estrogen receptor (ER) target genes and is required to demethylate proximal histones to enable productive ER transcription. These emerging findings also suggest that deregulation of LSD1 epigenetic pathway could contribute to hormonal independence and adaptive resistance in breast cancer cells. In this study, we examined the therapeutic efficacy of treating breast tumor cells with Pargyline, an FDA approved drug for blocking LSD1 functions, and evaluated the therapeutic benefit.Methods: To test this hypothesis, we used model cells that acquired resistance to hormonal therapy including (a) MCF7-HER2 that overexpress oncogene neu/HER2, (b) MCF7-Tam that have acquired resistance to Tamoxifen, (c) MCF7-Ca-LTLT cells that have acquired resistance to Letrozole, (d) MCF7 cells that overexpress proto-oncogene PELP1 (MCF7-PELP1). Parental MCF7 cells were used as a control. Cells were treated with LSD1 inhibitor Pargyline either alone or in combination with Letrozole and Dasatinib. Activation of ER genomic functions was studied using luciferase reporter gene assays. Epigenetic modifications at target promoters were analyzed by Chromatin immune precipitation (CHIP) assays using H3 methyl (di and Tri -H3K4, -K9) specific antibodies. Biological significance and hormonal therapy sensitivity was measured by in vitro cell proliferation assays. Xenograft studies were used to validate the drug effect in vivo. Pilot studies were performed for delivery of drug combinations using nanoparticle formulation.Results: Reporter gene assays showed that LSD1 has potential to enhance ER mediated transcription. LSD1 functionally interacts with ER coregulator PELP1 and is recruited to ER target genes. Pargyline substantially inhibited ER transactivation functions. ChIP analysis revealed that aggressively growing breast cancer cells and therapy resistant cells have distinct activating histone methyl modifications at growth regulatory ER target genes. Treatment of breast cancer models with LSD1 inhibitor Pargyline facilitated reversal of these specific modifications and thereby inhibited the growth of breast cancer cells in vitro and in vivo models. Combinatorial therapy using three agents; (a) that block Estrogen receptor genomic actions (Tamoxifen or Letrozole), (b) ER nongenomic actions (Dasatinib) and (c) ER epigenetic modifications (Pargyline) showed the most promising therapeutic effect compared to single agent therapy on the growth of therapy resistant cells.Conclusions: Our results suggest that histone methyl modification plays a role in therapy resistance and validates the therapeutic potential of Pargyline in combinational therapies. Collectively, these results suggest that targeting LSD1 axis with Pargyline in combination with current endocrine therapies will have better therapeutic effect and may inhibit or delay development of hormonal resistance, thus providing major benefits to patients care. This study is funded by Komen grant KG090447.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 409.

Growth factors regulate heterogeneous nuclear ribonucleoprotein K expression and function

Epidermal growth factor (EGF) family of growth factors and their receptors regulate normal and cancerous epithelial cell proliferation, a process that can be suppressed by antireceptor blocking antibodies. To identify genes whose expression may be modulated by antireceptor blocking antibodies, we performed a differential display screen with cells grown in the presence or absence of antireceptor blocking antibodies; isolates from one cDNA clone were 100% identical to human heterogeneous nuclear ribonucleoprotein K (hnRNP K), a protein with a conserved KH motif and RGG boxes, has been implicated in such functions as sequence-specific DNA binding, transcription, RNA binding, and nucleocytoplasmic shuttling. Both EGF and heregulin-beta1 induced expression of hnRNP K mRNA and protein in human breast cancer cells. This growth factor-mediated hnRNP K expression was effectively blocked by pretreatment of cultures with humanized anti-EGF receptor (EGFR) antibody C225, or anti-human epidermal growth factor receptor-2 (HER2) antibody. Anti-EGFR monoclonal antibody also caused regression of human tumor xenografts and reduction in hnRNP K levels in athymic mice. Samples from grade III human breast cancer contained more hnRNP K protein than samples from grade II cancer. Finally, overexpression of hnRNP K in breast cancer cells significantly increased target c-myc promoter activity and c-Myc protein, hnRNP K protein levels, and enhanced breast cancer cell proliferation and growth in an anchorage-independent manner. These results suggested that the activity of human EGF receptor family members regulates hnRNP K expression by extracellular growth promoting signals and that therapeutic humanized antibodies against EGFR and HER2 can effectively block this function.

New insights into anti-HER-2 receptor monoclonal antibody research

Abnormalities in the expression, structure, or activity of proto-oncogene products contribute to the development and maintenance of the malignant phenotype. For example, c-erbB-2 encodes the HER-2 receptor (also known as c-erbB-2 or c-neu) that is overexpressed, amplified, or both in a number of human malignancies including breast, ovarian, colon, lung, prostate, and cervical cancers. In addition to deregulation of cell-surface HER receptors, cancer cells often show excessive activation and/or nonattenuation of growth factor--inducible signaling components, as well as their downstream transcription factors. Current approaches to target HER-2 pathways include downregulation of HER-2 by the adenovirus 5E1A, antisense phosphothionate oligonucleotides, ribozyme, and targeting tyrosine kinase using specific inhibitors. Because growth factors regulate the proliferation of cancer cells by activating receptors on the surface of cells, one obvious approach to control cell proliferation is to interfere with the growth factor receptor-mediated autocrine/ paracrine growth stimulation by antireceptor-blocking monoclonal antibodies. Therefore, a large number of scientists are attempting to control the growth of cancer cells using agents that inhibit one or more of the above steps of growth factor action. Recently completed clinical trials established the usefulness of a humanized form of 4DS monoclonal antibody, trastuzumab (Herceptin; Genentech, Inc, South San Francisco, CA), against some forms of breast tumors overexpressing HER-2 receptors. Using in vitro models, recent studies have shown that HER-2 overexpression may not be a prerequisite for invasion of breast cancer cells, as HER-2 activation by heregulin, which binds to HER-3 or HER-4 and transphosphorylates HER in noninvasive breast cancer cells, could lead to increased motility, enhanced gelatinolytic activity, and invasion. Furthermore, these ligand-driven phenotypic changes were completely suppressed by trastuzumab, which also blocked interactions between HER-2 and HER-3 receptors in heregulin-treated breast cancer cells, and inhibited the phosphatidylinositol-3' kinase-dependent pathway, but not the mitogen-activated protein kinase pathway. These phenotypic effects of anti-HER-2 monoclonal antibody are of special interest, because they point to potential therapeutic effects of trastuzumab in inhibiting the invasion and metastasis of breast cancer with low receptor expression.

Differential signaling by an anti-p185(HER2) antibody and heregulin

To understand the molecular mechanisms by which anti-p185HER2 antibody and the ligand heregulin inhibit tumor growth, we have investigated several signaling proteins and pathways. We report here that anti-p185HER2 monoclonal antibody ID5 induced tyrosine phosphorylation of HER2 in SKBr3 breast cancer cells that overexpress p185HER2. Heregulin beta1 induced phosphorylation of both HER3 and HER2. ID5 produced a greater association of phospholipase C (PLC)-gamma1 with HER2 than did heregulin. Concordantly, ID5, but not heregulin, increased PLC-gamma1 activity. However, the G1 cell cycle arrest and induction of p27Kip1 produced by ID5 were not affected by the inhibition of PLC-gamma. ID5 preferentially induced binding of the Mr 46,000 isoform of SHC to HER2, whereas heregulin preferentially induced binding of the Mr 52,00 isoform of SHC to HER3. Heregulin, but not ID5, induced the p85 subunit of phosphatidylinositol 3'-kinase (PI3-K) to interact with HER3. Heregulin induced sustained activation of P13-K signaling, whereas ID5 had only a transient effect. Heregulin, but not ID5, activated the c-Jun-NH2-terminal kinase cascade. Pretreatment of SKBr3 cells with ID5 decreased heregulin-induced association of HER2 with HER3 as well as the activation of c-Jun-NH2-terminal kinase and PI3-K activities. Inhibition of the mitogen-activated protein kinase pathway in SKBr3 cells did not affect heregulin-induced G2-M-phase arrest, apoptosis, and differentiation. Heregulin-induced apoptosis could be blocked by inhibition of p70s6k, but not by inhibition of PI3-K. Heregulin-induced differentiation could be eliminated by inhibition of PI3-K. We conclude that ID5 and heregulin signal via different pathways, although both agents can inhibit the clonogenic growth of cells that overexpress HER2.

Regulation of microfilament reorganization and invasiveness of breast cancer cells by kinase dead p21-activated kinase-1

Stimulation of growth factor signaling has been implicated in the development of invasive phenotype and p21-activated kinase (PAK1) activation in human breast epithelial cancer cells. To further explore the roles of PAK1 in the invasive behavior of breast cancer cells, in the present study we investigated the influence of inhibition of PAK1 activity on the reorganization of cytoskeleton components that control motility and invasiveness of cells, using a highly invasive breast cancer MDA-MB435 as a model system. Our results demonstrate that overexpression of a kinase dead K299R PAK1 mutant leads to suppression of motile phenotypes as well as invasiveness of cells both in the absence or presence of exogenous heregulin-beta1. In addition, these phenotypic changes were accompanied by a blockade of disassembly of focal adhesion points, stabilization of stress fibers, and enhanced cell spreading and were dependent on the presence of the kinase dead domain but independent of the presence of the Rac/cdc42 intact (Cdc42/Rac interactive binding) domain of PAK1. We also demonstrated that in K299R PAK1-expressing cells, F-actin filaments were stabilized by persistent co-localization with the actin-binding proteins tropomyosin and caldesmon. Extension of these studies to invasive breast cancer MDA-MB231 cells illustrated that conditional expression of kinase-defective K299R PAK1 was also accompanied by persistent cell spreading, multiple focal adhesion points, and reduced invasiveness. Furthermore, inhibition of PAK1 activity in breast cancer cells was associated with a reduction in c-Jun N-terminal kinase activity, inhibition of DNA binding activity of transcription factor AP-1, and suppression of in vivo transcription driven by AP-1 promoter (known to be involved in breast cancer invasion). These findings suggest that PAK1 downstream pathways have a role in the development and maintenance of invasive phenotypes in breast cancer cells.

Heregulin induces expression, DNA binding activity, and transactivating functions of basic leucine zipper activating transcription factor 4

Heregulin beta1 (HRG), a combinatorial ligand for human epidermal growth factor receptor 3 and human epidermal growth factor receptor 4 receptors, is a regulatory secretory polypeptide with distinct biological effects such as growth stimulation, differentiation, invasiveness, and migration in breast cancer cells. The mechanism underlying the diverse functions of HRG is not well established, but it is believed to be dependent on the induced changes in expression of specific cellular gene products, their modification, or both. The binding of basic leucine zipper transcription factors to the cAMP response element is known to activate a variety of gene products with a role or roles in growth regulation. In the studies presented here, we identified basic leucine zipper activating transcription factor (ATF) 4 as one of the HRG-inducible gene product. We demonstrated that HRG stimulation of human cancer cells induces expression of ATF4 mRNA and protein, ATF4 DNA binding activity, and ATF4 transactivating function. Consistent with its role as a transcriptional activator, HRG-stimulated ATF4 protein stimulated the transcription from an artificial promoter with three tandem ATF sites or from a naturally occurring promoter with ATF4 sites such as E-selectin. We also demonstrated a preferential role of the HRG-stimulated mitogen-activated protein kinase pathway, but not the phosphatidylinositol 3'-kinase pathway, in supporting the observed increase in ATF4 DNA binding activity and transcription from E-selectin promoter in HRG-stimulated cells. Because ATF4 binding sites are present in a variety of growth-regulating cellular genes, these findings suggest that the stimulation of ATF4 expression and its transactivating functions may constitute an important mechanism of HRG-mediated regulation of putative genes with diversified functions. The present study is the first demonstration of regulation of expression and transactivation ability of ATF4 by any polypeptide growth factor.

Serine phosphorylation of paxillin by heregulin-beta1: role of p38 mitogen activated protein kinase

The mechanisms through which heregulin (HRG) regulates the progression of breast cancer cells to a more invasive phenotype are currently unknown. Recently we have shown that HRG treatment of breast cancer cells leads to the formation of lamellipodia/filopodia, and increased cell migration and invasiveness through the phosphatidylinositol 3-kinase (PI-3 kinase). Since the process of cell migration must involve changes in adhesion, we explored the potential HRG regulation of paxillin, a major cytoskeletal phosphoprotein of focal adhesion. We report that HRG stimulation of non-invasive breast cancer cells resulted in stimulation of p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-regulated kinases (ERK) and PI-3K, and a concurrent unexpected increase in the level of paxillin phosphorylation on serine residue which was sensitive to protein-phosphatase 2b but not to protein tyrosine phosphatase 1. In addition, HRG triggered a rapid redistribution of paxillin to the perinuclear regions from the tyrosine-phosphorylated focal adhesions, and increased cell scattering. There was no effect of HRG on the state of phosphorylation and localization of focal adhesion kinase. The HRG-induced increase in serine phosphorylation of paxillin and cell scattering were selectively inhibited by a specific inhibitor of p38MAPK or a dominant-negative p38MAPK mutant, but not by inhibitors of p42/44MAPK or PI-3 kinase pathways. For the first time our results have shown that HRG, a potent migratory growth factor stimulates serine phosphorylation of paxillin. These findings suggest a role of p38MAPK-dependent signal transduction pathway(s) in serine phosphorylation and disassembly of the paxillin from the focal complexes during HRG-induced cell shape alterations and motility.

Transcriptional up-regulation of paxillin expression by heregulin in human breast cancer cells

Activation of heregulin (HRG) signaling has been implicated in the development of aggressive phenotype in breast cancer cells. The mechanisms through which HRG regulates the progression of breast cancer cells to a more invasive or motile phenotype are currently unknown. Because the process of cell migration must involve dynamic changes in the formation of new focal adhesions at the leading edge and dissolution of preexisting focal points, we explored the potential HRG regulation of paxillin, a major component of focal adhesion. Here, we report that HRG stimulation of noninvasive breast cancer MCF-7 cells resulted in the up-regulation of paxillin mRNA and protein. The observed HRG stimulation of paxillin mRNA expression was completely blocked by actinomycin D (a transcriptional inhibitor) as well as by cycloheximide (a protein synthesis inhibitor), suggesting the involvement of an inducible protein factor(s) and transcriptional regulation of paxillin mRNA by HRG. Extension of these observations to other HRG-responsive human cell lines also demonstrated that HRG has a significant capacity to up-regulate the paxillin expression. Furthermore, the levels of paxillin expression were closely linked with the coexpression of human epidermal growth factor receptor 2 (HER2)/HER3 receptors in breast cancer cell lines and in grade III human breast tumors. This study is the first demonstration of regulation of paxillin expression by a polypeptide growth factor, and it suggests a potential role for paxillin in the HER2 pathway in breast cancer.

Regulation of cyclooxygenase-2 pathway by HER2 receptor

Emerging lines of evidence suggest that in addition to growth factors, the process of colorectal tumorigenesis may also be driven by the upregulation of the inducible form of cyclooxygenase-2 (COX-2), an enzyme responsible for the conversion of arachidonic acid to PGEs. The present study was undertaken to investigate the expression and activation of the HER family members, and to explore the regulation of COX-2 expression by the HER2 pathway in human colorectal cancer cells. Here, we report that human colorectal cancer cell lines express abundant levels of HER2 and HER3 receptors, and are growth-stimulated by recombinant neu-differentiation factor-beta 1 (NDF). NDF-treatment of colorectal cancer cells was accompanied by increased tyrosine phosphorylation and heterodimerization of HER3 with HER2. In addition, we demonstrated that HER2 and HER3 receptors in colorectal cancer cells are constitutively phosphorylated on tyrosine residues and form heterodimeric complexes in the absence of exogenous NDF. Inhibition of HER2/HER3 signaling by an anti-HER3 mAb against the ligand binding site resulted in a decrease in the levels of constitutively activated HER2/ HER3 heterodimers, and the unexpected reduction of COX-2 expression. Activation of the HER2/HER3 pathway by NDF induced the activation of COX-2 promoter, expression of COX-2 mRNA, COX-2 protein and accumulation of prostaglandin E2 in the culture medium. Finally, we demonstrated that NDF promotes the ability of colorectal cancer cells to survive in an extracellular matrix milieu, such as Matrigel, and also to invade through a 8 microm porous membrane. These biological activities of NDF and its stimulation of cell proliferation are blocked by a specific inhibitor of COX-2. Taken together, our findings provide the first biochemical evidence of a possible role of the COX-2 pathway in the mitogenic action of NDF in colorectal cancer cells where it may be constitutively upregulated due to the autocrine/paracrine activation of HER2/ HER3 heterodimers.

Heregulin regulates cytoskeletal reorganization and cell migration through the p21-activated kinase-1 via phosphatidylinositol-3 kinase

The mechanisms through which heregulin (HRG) regulates the activities of breast cancer cells are currently unknown. We demonstrate that HRG stimulation of noninvasive breast cancer cells enhanced the conversion of globular to filamentous actin and the formation of membrane ruffles, stress fibers, filopodia, and lamellipodia and accompanied by increased cell migration. In addition, HRG triggered a rapid stimulation of p21-activated kinase1 (PAK1) activity and its redistribution into the leading edges of motile cells. The HRG-induced stimulation of PAK1 kinase activity followed phosphatidylinositol-3 kinase (PI-3 kinase) activation. Inhibition of PI-3 kinase activity blocked the activation of PAK1 kinase and also blocked cell migration in response to HRG. Furthermore, direct inhibition of PAK1 functions by the dominant-negative mutant suppressed the capacity of HRG to reorganize actin cytoskeleon structures. We also demonstrated that HRG stimulation promoted physical interactions between PAK1, actin, and human epidermal growth factor receptor 2 (HER2) receptors, and these interactions were dependent on the activation of PI-3 kinase. The blockade of HER2 receptor by an anti-HER2 monoclonal antibody resulted in the inhibition of HRG-mediated stimulation of PI-3 kinase/PAK pathway and also the formation of motile actin cytoskeleton structures but not extracellular signal-regulated kinases. These findings suggest a role of PI-3 kinase/PAK1-dependent reorganization of the cortical actin cytoskeleton in HRG-mediated increased cell migration, and these changes may have significant consequences leading to enhanced invasion by breast cancer cells.