hMENA(11a) contributes to HER3-mediated resistance to PI3K inhibitors in HER2-overexpressing breast cancer cells.

Human Mena (hMENA), an actin regulatory protein of the ENA/VASP family, cooperates with ErbB receptor family signaling in breast cancer. It is overexpressed in high-risk preneoplastic lesions and in primary breast tumors where it correlates with HER2 overexpression and an activated status of AKT and MAPK. The concomitant overexpression of hMENA and HER2 in breast cancer patients is indicative of a worse prognosis. hMENA is expressed along with alternatively expressed isoforms, hMENA(11a) and hMENAΔv6 with opposite functions. A novel role for the epithelial-associated hMENA(11a) isoform in sustaining HER3 activation and pro-survival pathways in HER2-overexpressing breast cancer cells has been identified by reverse phase protein array and validated in vivo in a series of breast cancer tissues. As HER3 activation is crucial in mechanisms of cell resistance to PI3K inhibitors, we explored whether hMENA(11a) is involved in these resistance mechanisms. The specific hMENA(11a) depletion switched off the HER3-related pathway activated by PI3K inhibitors and impaired the nuclear accumulation of HER3 transcription factor FOXO3a induced by PI3K inhibitors, whereas PI3K inhibitors activated hMENA(11a) phosphorylation and affected its localization. At the functional level, we found that hMENA(11a) sustains cell proliferation and survival in response to PI3K inhibitor treatment, whereas hMENA(11a) silencing increases molecules involved in cancer cell apoptosis. As shown in three-dimensional cultures, hMENA(11a) contributes to resistance to PI3K inhibition because its depletion drastically reduced cell viability upon treatment with PI3K inhibitor BEZ235. Altogether, these results indicate that hMENA(11a) in HER2-overexpressing breast cancer cells sustains HER3/AKT axis activation and contributes to HER3-mediated resistance mechanisms to PI3K inhibitors. Thus, hMENA(11a) expression can be proposed as a marker of HER3 activation and resistance to PI3K inhibition therapies, to select patients who may benefit from these combined targeted treatments. hMENA(11a) activity could represent a new target for antiproliferative therapies in breast cancer.

Polyclonal antibodies against gp185HER2 peptides: their putative role in the identification of a particular HER2 status in patients with breast cancer.

The HER2 oncogene and its relative oncoprotein, gp185HER2, a transmembrane glycoprotein belonging to the epidermal growth factor receptor family, are overexpressed in a wide range of solid tumors including breast and ovarian cancer. In patients with breast cancer, both humoral and cell-mediated HER2 immune responses have been found as well as in some patients with gp185HER2 nonoverexpressing tumors. To establish whether peptide sequences identified as HLA-A2-restricted T-cell epitopes are expressed in breast tumor cell lines and tissues, we produced and characterized by different methodologic approaches polyclonal antibodies raised against four gp185HER2 peptides. Two of the antibodies recognized peptides eluted from the HLA-A2 groove of the mDAmB231 breast cancer cell line expressing a basal level of gp185HER2. Paraffin-embedded primary and metastatic breast tumors were specifically immunostained by all four reagents, thereby showing an overlapping reactivity. When this immunoreactivity was compared with that obtained using two different monoclonal antibodies, in 105 breast primary tumors and 36 corresponding lymph node metastases, we identified a subset of tumors that were negative with anti-gp185HER2 monoclonal antibodies and positive with the four antipeptide antibodies. Our novel observations provide in vivo evidence of the complexity involved in evaluating HER2 expression, and open a new path for understanding the biologic significance of HER2 status in breast tumors.

Flexibility of amino acid residues at position four of nonapeptides enhances their binding to human leucocyte antigen (HLA) molecules.

The binding affinity of synthetic nonapeptides to human leucocyte antigens (HLA) molecules of the A0201 allotype, the most common in Caucasian, is enhanced or reduced by suitable amino acid substitutions at position 4, as a result of increased or decreased chain flexibility. A higher flexibility of the bond at this position correlates with an easier accommodation of the fragment into the HLA groove, while rigidity of the peptide chain appears to interfere. These data are based on two lines of evidence: a) most natural high affinity ligands for HLA-A0201 possess, at position 4, flexible residues b) substitutions of such residues by rigid amino acids results in a decrease of binding affinity.

Host immunosurveillance contributes to the control of erbB-2 overexpression in HLA-A2-breast-cancer patients.

Overexpression of gp185(erbB-2) has been associated with reduced survival in breast-cancer patients. Our earlier results, now confirmed in a larger cohort of patients (798), evidenced that the HLA-A2 allele may participate in the modulation of the erbB-2 tumor phenotype in vivo. In the present study, we evaluated other clinico-biopathologic parameters possibly involved in the host immune response against erbB-2. Localization of the CD3(+) T-cell infiltrate was taken into consideration in 705 primary breast tumors, and expression of HLA-class-I and HLA-A2 antigens was evaluated in a subgroup of 170 frozen primary tumors of HLA-A2-positive patients. The presence or the absence of HLA-class-I and HLA-A2 antigens in primary tumors did not correlate with erbB-2 expression. However, HLA-A2-positive tumors preferentially showed intratumoral lymphocyte localization, whereas the lesions displaying undetectable HLA-class-I expression showed peritumoral CD3(+) T-cell localization. Taking into account erbB-2 immunoreactivity, we found that the relationship between HLA-A2 expression and intratumoral CD3(+) T-lymphocyte localization is significant only in the erbB-2 negative subset, whereas the relationship between lack of HLA-class-I expression and peritumoral CD3(+) T-lymphocyte localization is significant only in the erbB-2-positive subset. These data provide novel in vivo evidence of the possible contribution of the host immune system to control of erbB-2 oncogene overexpression in breast cancer. Int. J. Cancer (Pred. Oncol.) 84:598-603, 1999.

Characterization of a dodecapeptide containing a dominant epitope of Par j 1 and Par o 1, the major allergens of P. judaica and P. officinalis pollen.

The pollen of Parietaria, a weed of the Urticaceae family, is a major cause of respiratory allergy in Europe, where the most common species are P. judaica and P. officinalis. Previously, we reported that a beta-galactosidase fusion protein (6a-BG) expressing a 26-bp cDNA fragment (6a cDNA) contained a dominant IgE-binding epitope (6a epitope) of the major allergens Par o 1 and Par j 1. The present study aimed to define the amino-acid sequence containing the 6a epitope. We analyzed the reactivity of anti-Par o 1 antibodies affinity purified from allergic patient sera with: 1) a panel of synthetic peptides deduced from the 6a nucleotide sequence using different reading frames 2) glutathione S-transferase (GST) fusion proteins containing selected peptides. The peptide NSARARADSCRI (p102) specifically bound anti-Par o 1 antibodies affinity purified from allergic patient sera or from rabbit anti-Par o 1 antiserum (ELISA). The related peptide NSARAGTSSCRI (p101) reacted to human but not to rabbit, anti-Par o 1 antibodies. GST fusion proteins containing p101 (GST 3.5) or p102 (GST 3.2) extensively inhibited the binding between Par o 1 and IgE or IgG antibodies from an allergic patient serum pool according to a dose-response curve. Percent inhibition of IgE antibodies binding obtained by absorbing a solution (50 microl) of affinity-purified antibodies with 5 microg of GST 3.2 or with 1.2 mg of GST 3.5 was 69% and 66%, respectively. In conclusion, the results of the present study indicate that the amino-acid sequences NSARARADSCRI (p102) and NSARAGTSSCRI (p101) contain the dominant epitope of Par o 1 and Par j 1 for human IgE and IgG antibodies indicated as 6a epitope. Moreover, the study shows that the epitope is conserved in recombinant molecules containing these peptides, irrespective of the fused polypeptide (beta-galactosidase or GST). The knowledge of the amino-acid sequence of this dominant epitope is important in therapeutic approaches to the development of allergen-derived haptens.

Epitope mapping of the monoclonal antibody MM12.10 to external MDR1 P-glycoprotein domain by synthetic peptide scanning and phage display technologies.

Epitope mapping of MDR1-P-glycoprotein using specific monoclonal antibodies (mAbs) may help in delineating P-glycoprotein topology and hence in elucidating the relationship between its structural organization and drug-efflux pump function. In this work, by using synthetic peptide scanning and phage display technologies, the binding sites of the mAb MM12.10, a novel antibody to intact human multidrug resistant (MDR) cells, were studied. The results we obtained confirm that two regions localized on the predicted fourth and sixth loops are indeed external and that MDR1 peptides covering the inner domain of the current 12 transmembrane segment (TMs) model of P-glycoprotein could form part of the MM12.10 epitope.

Isolation, characterization and comparison of antipeptide and antiprotein rabbit antibodies to the pi-isoform of glutathione S-transferase.

The main linear epitopes of pi-glutathione transferase (pi-GST, EC 2.5.1.18), an enzyme related to cancer progression in a restricted number of tumours, were identified by testing in ELISA the reactivities of polyclonal anti-pi-GST rabbit sera against a panel of 51 overlapping decapeptides, covering the whole 216-residue sequence of the protein. Several major reactivity peaks were detected, each covering two or three adjacent peptides. The most active fragments were then reconstructed by conventional solid-phase synthesis, linked to Sepharose, and used as affinity ligands for isolating specific anti-pi-GST antibody subsets. A second group of antisera was then prepared in rabbits by using as immunogens some of the above described synthetic fragments, linked to a carrier protein, and antipeptide antibodies purified by affinity chromatography. An ELISA test was then performed, using as antigens a panel of peptides and different isoforms of GST, in order to establish whether antibodies isolated from total anti-pi-GST sera would display higher reactivity and specificity, as compared to traditional antipeptide antibodies. Binding data clearly confirm that the formers might be indeed better reagents for the detection and possibly quantitation of pi-GST.

Increased PGE2 production mediates the in vitro inhibitory effect of the human immunodeficiency virus P24 immunosuppressive heptapeptide Ch7.

Previous work from our laboratory demonstrated that a synthetic heptapeptide (Ch7), corresponding to a conserved sequence of human immunodeficiency virus (HIV) core protein p24 (amino acids 232-238), was able to specifically abrogate antigen-induced responses in cultures of normal human peripheral blood lymphocytes (PBL). Addition of recombinant human interferon-gamma (IFN-gamma) to Ch7-suppressed cultures restored the capacity to mount an antigen-specific antibody response, suggesting that a cytokine imbalance may be at the basis of the Ch7 immunosuppressive activity. In the present paper we show that the Ch7-dependent in vitro immunosuppression was accompanied by a significant up-regulation of prostaglandin E2 (PGE2) production and induction of interleukin-10 (IL-10)-secreting cells. In the presence of the PGE2 inhibitor indomethacin, IL-10 up-regulation was prevented and the induction of a specific antibody response was partially restored. PGE2 is indeed an important regulator of immune responses with the ability to differentially affect cytokine production. Thus, our results demonstrate that the Ch7 immunosuppressive epitope may primarily act by up-regulating PGE2 production and, through this mediator, by causing a cytokine dysregulation, finally responsible for immune response suppression.

Influence of both TCR repertoire and severity of the atopic status on the cytokine secretion profile of Parietaria officinalis-specific T cells.

Peripheral blood mononuclear cells (PBMC) from both nonatopic and Parietaria officinalis-sensitive donors proliferated in response to the allergen Par o 1 and developed into Par o 1-specific T cell lines and clones, which also showed reactivity for Par o 1-derived peptides. Virtually all Par o 1-specific T cell lines and large numbers of Par o 1-specific T cell clones proliferated in response to two Par o 1 nonapeptides (p92 and p96), which probably contain immunodominant epitopes of the Par o 1 allergen. Both p92- and p96-specific T cell clones showed the ability to produce IFN-gamma, but p92-specific T cell clones produced significantly lower amounts of IL-4 and IL-5 than p96-specific T cell clones, indicating that distinct epitopes, able to elicit functionally different T helper cell responses, may coexist in Par o 1. However, p92-specific T cell clones derived from atopic subjects with high IgE serum levels (high IgE producers) secreted significantly higher amounts of IL-4 and IL-5 than corresponding T cell clones generated from nonatopic subjects or patients with low IgE serum levels (low IgE producers), whereas p96-specific T cell clones secreted high IL-4 and IL-5 concentrations irrespective of whether they derived from high or low IgE producers. The addition of IL-4 and anti-IL-12 mAb to bulk culture significantly up-regulated the development of p92-specific T cells into IL-4-producing cells, whereas the addition of IL-12 and anti-IL-4 mAb shifted the differentiation of p96-specific T cells towards IFN-gamma-producing cells. Taken together, these results suggest that the cytokine profile of allergen-specific T cells is influenced by both the T cell receptor repertoire and the severity of atopic status and can be modulated, at least in vitro, by stimulation with the specific peptide in the presence, or after removal, of appropriate cytokines.

MHC-peptide binding: dimers of cysteine-containing nonapeptides bind with high affinity to HLA-A2.1 class I molecules.

Small peptides, 8-10 amino acids long, derived from degradation of cytoplasmic proteins by a proteasome-proteinase complex, are usually presented and recognized by CD8+ cytolytic T lymphocytes (CTLs) associated with major histocompatibility complex (MHC) class I molecules. Recently synthetic peptides were used for the in vitro induction of tumor-specific CTLs, offering another strategy in the study of the immune-response repertoire and providing a new tool in cancer vaccination and immunotherapy. Peptides derived from otherwise normal proteins, overexpressed in many tumors as products of the protooncogene, may represent a target for an immune response. This is the case of HER-2/neu gene (also known as ErbB-2), encoding a cysteine-rich glycoprotein transmembrane receptor with tyrosine kinase activity (gp185neu). Recent data, demonstrating that HLA-A2.1-related peptides are able to stimulate in vitro CD8+ lymphocytes, Prompted us to study the binding to HLA-A2.1 molecules of several gp185 synthetic peptides containing a cystein residue and to define the relevance of this amino acid residue in the reduced or oxidated form of the sulfhydryl group. We found that monomers and their homodimers, linked by a disulfide bridge, bind to HLA-A2.1 molecules with overlapping affinity. These results suggest that additional amino acids of the nonapeptide do not prevent the binding and the HLA refolding through chemical or sterical interactions. This might be of particular relevance for the in vivo processing of cysteine-rich proteins. Because ErbB-2 molecules, as tumor-differentiation antigens in melanoma, are cysteine-rich molecules, it may be relevant to evaluate the possible role of the cystine residues interacting with the T-cell receptor. The recognition of these heterodimers by CD8+ lymphocytes will require functional in vivo studies.

Aims and limitations in the use of antipeptide antibodies in molecular biology.

Antibodies to peptides obtained by synthesis and, to a much lesser extent, prepared by enzymatic digestion of proteins, have been widely used in the last ten years in a variety of immunochemical and biological investigations. There are however several limitations in the correct utilization of such reagents. In fact, in spite of their 'predetermined specificity', antipeptide antibodies often fail to discriminate related molecules, and their reactivity with native proteins may be scarce or even absent, even if the peptide has been selected from surface regions of the protein. Our critical point of view, concerning two main aspects of antipeptide antibody features, i.e. specificity and reactivity, will be presented here, as confronted with information from the available literature. We have selected a restricted number of references among hundreds of publications dealing with antipeptide antibodies: for sure we neglected outstanding papers on the subject, and we apologize in advance.

Selective 'in synthesis' labelling of peptides by fluorochromes.

A new method is described for producing fluorescently-tagged peptides containing specific internal derivatives of lysyl residues. The technique employs the base-labile Boc-Lys(Fmoc)-COOH derivative with base-catalyzed removal of the Fmoc protecting group during peptide synthesis and subsequent fluorescent derivatization of the deprotected epsilon-amino group of lysine. By this technique, other lysine residues and the alpha-amino group of the fragment remain unmodified, which could have some value in studies where it might be required to tag a single individual lysine residue within the peptide, but not the amino terminus. In spite of the fact that poly-substituted peptides are badly soluble and might seldom find a practical application, this technique also allows the introduction of different fluorochromes at different lysyl residues within the peptide, thus obtaining double fluorescence. The method, fast and easy, requires a limited number of manual operations during the automatic synthesis of peptides. Although peptide synthesizers provided with an oscillating glass reactor are more suitable for the manual interventions described, this technique might be also adapted to the newer instruments utilizing continuous-flow columns.

Definition of essential amino acid residues in the recognition of a peptide by a mouse monoclonal antibody.

A mouse monoclonal antibody reacting in ELISA with a synthetic peptide representing a linear amino acid stretch of the protein antigen was tested on all overlapping 5-mer to 9-mer fragments of the peptide, as prepared by multi-pin synthesis. Analysis of the binding data suggests that several residues in the peptide might be relatively unrelevant for recognition, while few others seem to play a critical role as key residues. On the basis of such observations, we attempted to reconstruct an alternative essential epitope by introducing multiple amino acid substitutions in the 9-mer peptide exhibiting the best binding activity, and then tested its ability to be recognized by the monoclonal antibody.

Interferon-gamma (IFN-gamma) can counteract the in vitro inhibitory effect of an HIV p24 immunosuppressive heptapeptide.

Previous work from our laboratory demonstrated that a synthetic heptapeptide (Ch7), corresponding to a conserved sequence of HIV core protein p24 (aa 232-238), was able to specifically abrogate antigen-induced responses in cultures of normal human peripheral blood lymphocytes (PBL). In the present study we show that Ch7 did not inhibit the induction of IFN-gamma-secreting cells nor the accumulation of IFN-gamma mRNA in antigen-stimulated cultures. However, delayed addition of recombinant human IFN-gamma to Ch7-suppressed cultures was able to restore fully the capacity to mount an antigen-specific antibody response. Thus, although the Ch7 immunosuppressive effect may not be directly related to a decreased production of IFN-gamma, an increased level of this cytokine is certainly able to counteract the negative effect of the peptide.

Specificities of rabbit antisera to multiple antigen (MAP) peptides.

Two multiple antigen peptides consisting of 6 and 7 aminoa cid residues, respectively, plus a 12-residue fragment, used as a control, all linked to a polylysine core, were used as immunogens in rabbits in order to obtain an immune response. Rabbit antisera against such polymers were then tested in ELISA against a panel of antigens in order to analyze the specificities of the resulting antibodies. The responses were different for all three immunogens, being partially or totally directed, for two of the three compounds, including the 12-residue control MAP peptide, against the polylysyl core, which is considered as non immunogenic. The third MAP polymer was practically unable to elicit an immune response.

P-glycoprotein epitope mapping. II. The murine monoclonal antibody MM6.15 to human multidrug-resistant cells binds with three distinct loops in the MDR1-P-glycoprotein extracellular domain.

A new murine monoclonal antibody (MAb), MM6.15, to human MDR1 P-glycoprotein was found to be reactive in ELISA with synthetic peptides selected from the predicted sequences of the first, fourth and sixth extracellular loop of MDR1-P-glycoprotein. In order to precisely define the MM6.15-binding site, a peptide library of overlapping 5- to 9-mer residues covering the entire sixth extracellular loop of both human and rodent class-1 P-glycoproteins was synthesized on polyethylene pins and tested for MAb binding. The results of this ELISA demonstrated that the MAb MM6.15 reacts only with human synthetic peptides and that the critical component of the MAb recognition is made up of the amino-acid sequence LVAHKL (residues 963-968 of the MDR1-P-glycoprotein) with histidine (H), lysine (K) and possibly leucine (L), key residues of this immunogenic domain.

Thermosensitization, heat shock protein synthesis and development of thermotolerance in M-14 human tumor cells subjected to step-down heating.

M-14 human tumor cells have been subjected to two regimens of step-down heating (SDH) consisting of a conditioning treatment at 42 degrees C for 1 h or at 44.5 degrees C for 20 min, immediately followed by heating at 40 degrees C. Both conditioning treatments thermosensitize the cells towards the subsequent heating at 40 degrees C; the thermosensitization ratio is 6.4 for cells conditioned at 42 degrees C for 1 h and 32.3 for cells conditioned at 44.5 degrees C for 20 min. The overall protein synthetic activity is reduced to 32.7% or 18.4% of control values following 1 h at 42 degrees C and 20 min at 44.5 degrees C, respectively; this inhibition is followed by a full recovery of the synthetic activity during the subsequent exposure at 40 degrees C. SDH-treated cells synthetize four heat shock proteins, with approximate molecular weights of 28, 64, 70 and 90 kDa. The pattern of HSPs induction observed in SDH-treated cells is similar to that found in cells subjected to single hyperthermic exposures. Cells subjected to the SDH sequence 42 degrees C/1 h-->40 degrees C/4 h develop thermotolerance, as indicated by a reduced sensitivity to further hyperthermic challenges.