Mapping the CD4 binding domain of gp17, a glycoprotein secreted from seminal vesicles and breast carcinomas

Prognostic Role of Prolactin-Induced Protein (PIP) in Breast Cancer

Prolactin-inducible protein (PIP), also referred to as gross cystic disease fluid protein 15 (GCDFP-15), has been a trending topic in recent years due to its potential role as a specific marker in breast cancer. PIP binds to aquaporin-5 (AQP5), CD4, actin, fibrinogen, β-tubulin, serum albumin, hydroxyapatite, zinc α2-glycoprotein, and the Fc fragment of IgGs, and the expression of PIP has been demonstrated to be modulated by various cytokines, including IL4/13, IL1, and IL6. PIP gene expression has been extensively studied due to its captivating nature. It is influenced by various factors, with androgens, progesterone, glucocorticosteroids, prolactin, and growth hormone enhancing its expression while estrogens suppress it. The regulatory mechanisms involve important proteins such as STAT5A, STAT5B, Runx2, and androgen receptor, which collaborate to enhance PIP gene transcription and protein production. The expression level of PIP in breast cancer is dependent on the tumor stage and subtype. Higher expression is observed in early-stage tumors of the luminal A subtype, while lower expression is associated with luminal B, basal-like, and triple-negative subtypes, which have a poorer prognosis. PIP expression is also correlated with apocrine differentiation, hormone receptor positivity, and longer metastasis-free survival. PIP plays a role in supporting the immune system's antitumor response during the early stages of breast cancer development. However, as cancer progresses, the protective role of PIP may become less effective or diminished. In this work, we summarized the clinical significance of the PIP molecule in breast cancer and its potential role as a new candidate for cell-based therapies.

Unraveling Human AQP5-PIP Molecular Interaction and Effect on AQP5 Salivary Glands Localization in SS Patients

Saliva secretion requires effective translocation of aquaporin 5 (AQP5) water channel to the salivary glands (SGs) acinar apical membrane. Patients with Sjögren’s syndrome (SS) display abnormal AQP5 localization within acinar cells from SGs that correlate with sicca manifestation and glands hypofunction. Several proteins such as Prolactin-inducible protein (PIP) may regulate AQP5 trafficking as observed in lacrimal glands from mice. However, the role of the AQP5-PIP complex remains poorly understood. In the present study, we show that PIP interacts with AQP5 in vitro and in mice as well as in human SGs and that PIP misexpression correlates with an altered AQP5 distribution at the acinar apical membrane in PIP knockout mice and SS hMSG. Furthermore, our data show that the protein-protein interaction involves the AQP5 C-terminus and the N-terminal of PIP (one molecule of PIP per AQP5 tetramer). In conclusion, our findings highlight for the first time the role of PIP as a protein controlling AQP5 localization in human salivary glands but extend beyond due to the PIP-AQP5 interaction described in lung and breast cancers.

Deficiency of prolactin-inducible protein leads to impaired Th1 immune response and susceptibility to Leishmania major in mice

Although the strategic production of prolactin-inducible protein (PIP) at several ports of pathogen entry into the body suggests it might play a role in host defense, no study has directly implicated it in immunity against any infectious agent. Here, we show for the first time that PIP deficiency is associated with reduced numbers of CD4(+) T cells in peripheral lymphoid tissues and impaired CD4(+) Th1-cell differentiation in vitro. In vivo, CD4(+) T cells from OVA-immunized, PIP-deficient mice showed significantly impaired proliferation and IFN-γ production following in vitro restimulation. Furthermore, PIP-deficient mice were highly susceptible to Leishmani major infection and failed to control lesion progression and parasite proliferation. This susceptibility was associated with impaired NO production and leishmanicidal activity of PIP KO macrophages following IFN-γ and LPS stimulation. Collectively, our findings implicate PIP as an important regulator of CD4(+) Th1-cell-mediated immunity.

Effect of prolactin-induced protein on human skin: new insight into the digestive action of this aspartic peptidase on the stratum corneum and its induction of keratinocyte proliferation

Human prolactin-induced protein (PIP) is a major protein found in exocrine fluids such as saliva and sweat. Intriguingly, PIP possesses residues (human PIP (hPIP): PIP (29-63)) that display similarity to the aspartic peptidase candidapepsin. Here, we aimed to determine the effect of PIP as a protease on normal skin structure. Using an adhesive tape-stripping technique, we applied hPIP peptide on the corneocytes of normal-appearing facial skin from infants with eczema and healthy infants and then analyzed the morphological structure of corneocytes with Nile Red fluorescence. We also repeatedly applied the hPIP peptide onto the surface of a three-dimensional (3-D) human skin model and then analyzed any changes to the stratum corneum and epidermis using light microscopy and scanning electron microscopy. In both infant groups, a decrease in hydrophobic lipids from the cornified envelope was observed after treatment with hPIP. The peptide hPIP appeared to digest the fine structure of the stratum corneum and induce a proliferation of epidermal keratinocytes within the 3-D human skin model. Our results suggest that aspartic peptidase of PIP found in sweat or saliva deteriorates the skin barrier in a de novo manner, which potentially leads directly to the proliferation of epidermal keratinocytes without any external antigenic factors.

Immunosuppressive effect of prolactin-induced protein: a new insight into its local and systemic role in chronic allergic contact dermatitis

BACKGROUND

Prolactin-induced protein (PIP) has been shown to bind to CD4 and is speculated to block CD4-HLA-DR interaction. However, the immunomodulatory effect of PIP on chronic allergic contact dermatitis (ACD) remains to be elucidated.

OBJECTIVES

To define the role of PIP during the immunoresponse.

METHODS

Using a low-dose oxazolone-induced mouse chronic ACD model, expression of PIP was examined immunohistologically. Furthermore, effects of continued exposure to a peptide mimicking the major binding site of PIP (amino acids 106-132) for CD4 was examined in a mouse chronic ACD model.

RESULTS

We clarified that keratinocytes, dermal infiltrating cells and spleen infiltrating mononuclear cells are positively stained with anti-PIP antibody. The PIP peptide significantly downregulated oxazolone-induced mouse ACD compared with controls. We also found that inflammation of the control ear, to which the PIP peptide had not been applied, was also suppressed in a synchronized manner in the late phase of ACD.

CONCLUSIONS

These findings suggest that PIP might have a local and systemic immunosuppressive effect in mouse chronic ACD.

A functional and regulatory network associated with PIP expression in human breast cancer

BACKGROUND

The PIP (prolactin-inducible protein) gene has been shown to be expressed in breast cancers, with contradictory results concerning its implication. As both the physiological role and the molecular pathways in which PIP is involved are poorly understood, we conducted combined gene expression profiling and network analysis studies on selected breast cancer cell lines presenting distinct PIP expression levels and hormonal receptor status, to explore the functional and regulatory network of PIP co-modulated genes.

PRINCIPAL FINDINGS

Microarray analysis allowed identification of genes co-modulated with PIP independently of modulations resulting from hormonal treatment or cell line heterogeneity. Relevant clusters of genes that can discriminate between [PIP+] and [PIP-] cells were identified. Functional and regulatory network analyses based on a knowledge database revealed a master network of PIP co-modulated genes, including many interconnecting oncogenes and tumor suppressor genes, half of which were detected as differentially expressed through high-precision measurements. The network identified appears associated with an inhibition of proliferation coupled with an increase of apoptosis and an enhancement of cell adhesion in breast cancer cell lines, and contains many genes with a STAT5 regulatory motif in their promoters.

CONCLUSIONS

Our global exploratory approach identified biological pathways modulated along with PIP expression, providing further support for its good prognostic value of disease-free survival in breast cancer. Moreover, our data pointed to the importance of a regulatory subnetwork associated with PIP expression in which STAT5 appears as a potential transcriptional regulator.

Crystal structure of the novel complex formed between zinc alpha2-glycoprotein (ZAG) and prolactin-inducible protein (PIP) from human seminal plasma

This is the first report on the formation of a complex between zinc alpha2-glycoprotein (ZAG) and prolactin-inducible protein (PIP). The complex was purified from human seminal plasma and crystallized using 20% polyethylene glycol 9000 and 5% hexaethylene glycol. The structure of the complex has been determined using X-ray crystallographic method and refined to an R(cryst) of 0.199 (R(free)=0.239). The structure of ZAG is broadly similar to the structure of serum ZAG. The scaffolding of PIP consists of seven beta-strands that are organized in the form of two antiparallel beta-pleated sheets, resulting in the formation of a sandwiched beta-sheet. The amino acid sequence of PIP contains one potential N-glycosylation site at Asn77, and the same is found glycosylated with four sugar residues. The structure of the complex shows that the beta-structure of PIP is ideally aligned with the beta-structure of domain alpha3 of ZAG to form a long interface between two proteins. The proximal beta-strands at the long interface are arranged in an antiparallel manner. There are 12 hydrogen bonds and three salt bridges between ZAG and PIP. At the two ends of vertical interface, two salt bridges are formed between pairs of Lys41-Asp233 and Lys68-Glu229. On the perpendicular interface involving alpha1-alpha2 domains of ZAG and a loop of PIP, another salt bridge is formed. The internal space at the corner of the L-shaped structure is filled with solvent molecules including a carbonate ion. The overall buried area in the complex is approximately 914 A(2), which is considerably higher than the 660 A(2) reported for the class I major histocompatibility complex structures.

Synergic antitumoral effect of an IGF-IR inhibitor and trastuzumab on HER2-overexpressing breast cancer cells

BACKGROUND

Receptor tyrosine kinases play an important role in breast cancer. One of them, the type I insulin-like growth factor, has been linked to resistance to trastuzumab (Herceptin), an agent that targets human epidermal growth factor receptor 2. Here, we show that the insulin-like growth factor-I receptor (IGF-IR) antagonist NVP-AEW541 inhibits proliferation of breast cancer cells and synergizes with trastuzumab.

PATIENTS AND METHODS

Patient samples and breast cancer cell lines were evaluated for IGF-IR expression or activation by western blotting. 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) uptake assays and Annexin V staining were used for the analyses of cell proliferation/apoptosis. Biochemical and genomic studies were carried out to gain insights into the mechanism of action of NVP-AEW541.

RESULTS

The IGF-IR was expressed above normal levels in a number of breast cancer samples. Activation of this receptor was inhibited by NVP-AEW541 that also decreased cell proliferation and increased apoptosis. NVP-AEW541 decreased the amount of pAkt and increased the level of p27. Combination studies with several drugs used in the breast cancer clinic showed that NVP-AEW541 synergistically increased the action of trastuzumab.

CONCLUSIONS

Our results show the anti-breast cancer action of NVP-AEW541 and support the clinical development of anti-IGF-IR agents, especially in combination with trastuzumab.

Origin and evolution of gene for prolactin-induced protein

Prolactin-induced protein (PIP) is a small protein secreted into the fluid in several glands. We determined the PIP coding sequences of 5 hominoid species and estimated the numbers of synonymous and nonsynonymous substitutions for each branch of the mammalian PIP gene tree. The branch connecting hominoids and Old World monkeys showed significantly higher nonsynonymous than synonymous substitutions. These changes tended to be accumulated in the fibronectin-binding domain. Many other primate branches also showed higher nonsynonymous than synonymous substitutions, thus suggesting that the PIP genes of primates have experienced some kind of positive selection. We also considered the phylogenetic relationship of the PIP gene with the alpha-2-macroglobulin gene family. The results indicate that the PIP gene arose by partial gene duplication from a member of the alpha-2-macroglobulin gene family after the divergence between amphibians and other tetrapods.

Identification of gp17 glycoprotein and characterization of prostatic acid phosphatase (PAP) and carboxypeptidase E (CPE) fragments in a human seminal plasma fraction interacting with concanavalin A

The decapacitating fraction of human seminal plasma, which strongly interacts with concanavalin A, is constituted by high mannose-type N-linked glycoproteins, most of them of less than 44 kDa. Each component with apparent molecular mass of 30, 18, and 17 kDa respectively, as judged by SDS-PAGE, was submitted to "in gel" digestion with trypsin followed by HPLC separation of the peptides and sequencing. They were characterized at microscale as gp17, an aspartyl protease that possibly contributes to liquefaction of the seminal plasma coagulum, two fragments of human acid phosphatase (17 and 30 kDa, respectively), and a 17-kDa fragment of carboxypeptidase E. Neither the fragments of prostatic acid phosphatase nor that of carboxypeptidase E had been described before in the human seminal fluid. Very weak bands, of apparent molecular masses 44 and 52 kDa, are consistent with presence of small amounts of parent compounds, prostatic acid phosphatase and carboxypeptidase E.

Study of disabling T-cell activation and inhibiting T-cell-mediated immunopathology reveals a possible inverse agonist activity of CD4 peptidomimetics

We designed a new class of aromatically modified exocyclic peptides based on the structure of CD4 by engineering one of the cysteine residues in a peptidomimetic derived from the CDR3 region of the CD4 molecule. All three species mediate inhibition of T-cell proliferation at concentrations ranging from 10 to 100 microM. The mimetics CD4-Cys and CD4-Met bind to sCD4 with affinities ranging from 1 to 2 microM, while CD4-Ser shows poor binding in radioisotope assay. Though these mimetics have similar structures, they exhibit different biochemical and biological functions. Activation of T-cells as measured by thymidine incorporation or IL-2 production revealed that CD4-Cys and CD4-Ser mimetics behave as classical antagonists. On the other hand, the CD4-Met species inhibited T-cell proliferation with an IC(50) of 30 microM but unexpectedly increased IL-2 secretion modestly at a less than 3 microM concentration. In experimental autoimmune encephalitis (EAE), CD4-Ser and CD4-Cys mimetics reduced the severity of EAE symptoms while the CD4-Met mimetic exacerbated the conditions. We propose that CD4-Cys and CD4-Ser are classical antagonists, but CD4-Met may possess properties of an inverse agonist. The structure-activity relationship of mimetics reveals that a minor change in the net hydropathic value is enough to alter the dynamic nature of the receptor-ligand complex.

Survey of the year 2000 commercial optical biosensor literature

We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.

Integration of genome data and protein structures: prediction of protein folds, protein interactions and "molecular phenotypes" of single nucleotide polymorphisms

With the massive amount of sequence and structural data being produced, new avenues emerge for exploiting the information therein for applications in several fields. Fold distributions can be mapped onto entire genomes to learn about the nature of the protein universe and many of the interactions between proteins can now be predicted solely on the basis of the genomic context of their genes. Furthermore, by utilising the new incoming data on single nucleotide polymorphisms by mapping them onto three-dimensional structures of proteins, problems concerning population, medical and evolutionary genetics can be addressed.