Synthetic epidermal pentapeptide and related growth regulatory peptides inhibit proliferation and enhance differentiation in primary and regenerating cultures of human epidermal keratinocytes

Peptide screening to knockdown Bcl-2's anti-apoptotic activity: implications in cancer treatment

Bcl-2 (B cell lymphoma-2) is an anti-apoptotic member of Bcl-2 family and its overexpression causes development of several types of cancer. The BH3 domain of pro-apoptotic and BH3-only proteins is capable of binding to Bcl-2 protein to induce apoptosis. This binding is the basis for the development of novel anticancer drug which would likely antagonize Bcl-2 overexpression. In this study we have identified BH3 domain of Bax (Bax BH3) as potentially the best Bcl-2 antagonist by performing docking of BH3 peptides (peptides representing BH3 domain of pro-apoptotic and BH3-only proteins) into the Bcl-2 hydrophobic groove formed by BH3, BH1 and BH2 domains (also referred as BH3 cleft). To predict the best small antagonist for Bcl-2, three groups of small peptides (pentapeptide, tetrapeptide and tripeptide) were designed and screened against Bcl-2 which revealed the structural importance of a set of residues playing a vital role in interaction with Bcl-2. The docking and scoring function identified KRIG and KRI as specific peptides among the screened small peptides responsible for Bcl-2 neutralization and would induce apoptosis. The applied pharmacokinetic and pharmacological filters to all small peptides signify that only IGD has drug-like properties and displayed good oral bioavailability. However, the obtained binding affinity of IGD to Bcl-2 was diminutive. Hence deprotonation, amidation, acetylation, benzoylation, benzylation, and addition of phenyl, deoxyglucose and glucose fragments were performed to increase the binding affinity and to prevent its rapid degradation. Benzoylated IGD tripeptide (IGD(bzo)) was observed to have increased binding affinity than IGD with acceptable pharmacokinetic filters. In addition, stability of Bcl-2/IGD(bzo) complex was validated by Molecular Dynamics (MD) simulations revealing improved binding energy, salt bridges and strong interaction energies. This study suggests a new molecule that inhibits Bcl-2 associated cancer/tumor regression.

Directing stem cells into the keratinocyte lineage in vitro

A major area of research in regenerative medicine is the potential application of stem cells in skin grafting and tissue engineering. This would require well defined and efficient protocols for directing the commitment and differentiation of stem cells into the keratinocyte lineage, together with their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying skin tissue biology, as well as facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for skin-related biomaterials and drugs could also utilize protocols developed for the commitment and differentiation of stem cells into the keratinocyte lineage. Hence, this review critically examines the various strategies that could be employed to direct the commitment and differentiation of stem cells into the keratinocyte lineage in vitro.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Synthesis and characterization of tetramethylrhodaminethiocarbamoyl-(Glu(1))-epidermal mitosis-inhibiting pentapeptide

A fluorescent analog of epidermal mitosis-inhibiting pentapeptide (pGlu-Glu-Asp-Ser-Gly) was synthesized by reacting tetramethylrhodamine isothiocyanate with ring-opened epidermal mitosis-inhibiting pentapeptide. The ring-opening reaction of the pyrrolidone moiety was performed with mild acidic hydrolysis and the product purified by reversed-phase high-performance liquid chromatography. Tetramethylrhodaminethiocarbamoyl-(Glu(1))-epidermal mitosis-inhibiting pentapeptide was purified by chromatography on Sephadex G-25 and reversed-phase high-performance liquid chromatography. After characterization by amino acid analysis, the analog was incubated in presence of A431 cell line to visualize the cellular localization of the epidermal mitosis-inhibiting pentapeptide. The data gave negative results.

Antiproliferative effect of the tripeptide pyroGlu-Phe-GlyNH2 on murine melanocytes: transitory delay of cell growth in vitro and the cell cycle specificity

Cell growth and differentiation in melanocyte cell populations are regulated by a wide range of bioactive substances. Recently, the tripeptide pyroGlu-Phe-GlyNH2 which inhibits melanocyte growth in vitro was identified in both murine nontransformed melanocytes and malignant melanoma cells. The present study was undertaken to investigate the cell cycle specificity as well as the growth inhibitory profile of the tripeptide after a single or repeated administration to melanocyte cultures. Dose-related effects of the peptide were studied using three different bioassay systems: estimation of cell number, DNA synthesis, and cell flux into mitosis. Growth of melanocyte cultures as well as melanocyte mitotic activity were found to be reduced significantly by the tripeptide at two separate dose levels (10(-11) and 10(-14)-10(-15) M). Growth inhibition of melanocyte population did not last long: less than 36 h after the first and less than 24 h after the second peptide addition to the cultures. The level of DNA synthesis in melanocytes remained unchanged after a single peptide administration. The findings indicate that the tripeptide pyroGlu-Phe-GlyNH2 causes transitory delay of cell growth in cultured melanocyte population resulting from a reversible inhibition of melanocyte transition from the G2-phase of the cell cycle into mitosis.

Identification of a melanocyte growth-inhibiting tripeptide and determination of its structure

The function and proliferation of melanocyte cell populations are influenced by a wide range of hormones and growth factors. Local cell renewal after sudden melanocyte loss appears to be regulated according to a negative feedback principle, however. In accordance with this assumption, we have examined growth-inhibitory activity in water extracts of cultured non-transformed melanocytes and melanoma cells (B16 cells). The extracts were fractionated by gel filtration on Sephadex G-25 and Fractogel MG 2000, by ion-exchange chromatography on DEAE-cellulose and Dowex 50 and by reverse-phase high-performance liquid chromatography on Bondesil and Partisil columns. Two peptides were isolated with the structures pyroGlu-Phe-GlyNH2 and pyroGlu-Cys-GlyNH2 as revealed by mass spectrometry, peptide sequencing and amino acid analysis. The two peptides were synthesized and tested for the ability to inhibit the growth of melanocyte cultures. Only pyroGlu-Phe-GlyNH2 was inhibitory. The dose-response curve was bell-shaped with maximum inhibition around 10(-15) M. The melanocyte tripeptide thus appears to be a new member of a group of N-substituted growth-regulating oligopeptides found in other tissues.

Regeneration of rat corneal epithelium is delayed by the inhibitory epidermal pentapeptide (EPP)

The effect of the inhibitory epidermal pentapeptide (EPP) on regeneration of rat corneal epithelium was studied over a 24-h period after removal of the central part of the corneal epithelium by means of n-heptanol and scraping. Both unphosphorylated and phosphorylated EPP inhibited the mitotic rate and the formation of new cells to the same extent. Thus, the mitosis inhibitor that originally was isolated from mouse epidermis, acts even on the ectodermally derived corneal epithelial cells.

Purification and characterisation of swine serum proteinase which hydrolyses epidermal inhibitory pentapeptide

In this paper we describe the purification to molecular homogeneity of the enzyme that cleaves the synthetic epidermal mitosis-inhibiting pentapeptide (pyroGlu-Glu-Asp-Ser-Gly; EPP) from swine serum. Biochemical characterisation of the enzyme shows a glycoprotein with apparent molecular mass of 200 kDa. The Km and Kcat values for EPP hydrolysis are 0.624 mM and 694 s-1, respectively. Use of proteinase inhibitors shows the enzyme's metalloendopeptidase character. Moreover, captopril and lisinopril prevent the cleavage of EPP. The N-terminal amino-acid sequence of the purified protein corresponds to the N-terminal amino-acid sequence of swine kidney angiotensin-converting enzyme, a dipeptidyl carboxypeptidase (EC 3.4.15.1).

Feedback inhibitors in normal and tumor tissues

Negative feedback represents the principal mechanism for regulating growth in biological systems. Over the past 20 years, our understanding of the role played by inhibitory factors governing this process has advanced considerably. This is particularly well illustrated in the field of experimental hematology with the recognition of hemopoietic progenitor cell proliferation inhibitors, an expanding group of unrelated peptides that act to limit proliferation in hemopoietic precursor cells. The characterization and subsequent production of these molecules by chemical synthesis or recombinant DNA technology has enabled investigators to explore their role in normal hemopoiesis and define a potential role in clinical medicine. A number of inhibitory factors, including macrophage inflammatory protein-1 alpha (MIP-1 alpha) and the tetrapeptide AcSDKP appear to share a relative specificity to hemopoietic progenitor cell subsets. Others, such as interferon and tumor necrosis factor, have a more complex action and their hemopoietic effects are likely to be indirect and nonspecific. In addition to the role of inhibitors in normal steady state, it has become increasingly evident that loss of sensitivity to the normal feedback inhibitory signals may be of central importance in carcinogenesis and tumor promotion. This presumably represents a developmental strategy that allows the neoplastic cell to maintain a growth advantage over its normal cell counterpart. The underlying mechanisms that terminate in inhibitor-resistance are yet to be elucidated, but in some instances they may be associated with aberrant tumor suppressor gene function.

Epidermal dipeptide: a new regulatory factor in proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is the most severe complication of retinal detachment surgery, occurring approximately in one out of ten operated eyes. The proliferation of retinal pigment epithelial (RPE) cells and fibroblasts is a cornerstone in the pathogenesis of PVR. Since inhibitory peptides may take a part in the feedback mechanism underlying this proliferation, we assessed the effect of synthesized epidermal dipeptide, pyroglu-glyOH (EDP), on the proliferation of RPE cells and fibroblasts in vitro. The maximum inhibitory effect of EDP on the RPE cells was reached at concentrations ranging from 1.07*10(-13) to 1.07*10(-15) M. Its inhibitory effect on fibroblasts followed a similar pattern at all concentrations applied, 1.07*10(-6) to 1.07*10(-15) M. These results enhance the possibility that PVR may be due to an imbalance of inhibition/disinhibition mechanism under participation of several regulatory molecules like EDP. EDP might have the potential for reducing the risk of PVR.

Lateral growth and terminal differentiation during repeated epidermal regeneration in vitro

By incubating multilayered primary cultures of human epidermal keratinocytes in a low calcium medium, the suprabasal layers can be stripped off leaving a basal cell monolayer. When this monolayer is refed normal calcium medium a reproducible series of cell kinetic, morphological and biochemical changes take place resulting in the regeneration of a multilayered tissue. The stripping procedure seems to induce the selective proliferation of a cohort of basal cells that is committed to vertical migration and rapid terminal differentiation. In contrast, when the basal cells are allowed to regenerate in the presence of the strong mitogen, cholera toxin, lateral growth and continued proliferation are favoured at the expense of the capacity of the cells to differentiate. Repeated stripping of the same cultures disclosed a considerable heterogeneity in the capacity of the basal cells to regenerate the suprabasal layers. The number of times the basal cells could restore the suprabasal layers after repeated stripping varied from four to nine times. A negative correlation between donor age and regenerative capacity was observed. The experiments with repeated stripping of the same cultures also showed that the capacity to proliferate and to restore the multilayering was fully retained for at least four cycles of stripping-regeneration, whereas the capacity to terminally differentiate was rapidly lost. It is suggested that the present system of regenerating epidermal tissue cultures may serve as an experimental model for the study of epidermal tissue homeostasis and cellular aging.

Morphological differentiation and changes in polypeptide synthesis pattern during regeneration of human epidermal tissue developed in vitro

By incubating multilayered primary cultures of human keratinocytes in low-calcium medium the suprabasal cell layers can be stripped off leaving a basal cell monolayer. When this monolayer is re-fed normal calcium medium a reproducible series of cell kinetic, morphological, and biochemical changes takes place resulting in the reestablishment of a multilayered tissue. Analysis of cell-cycle-specific proteins indicated that, during regeneration, a large cohort of cells became synchronized undergoing DNA replication after 3 days. Examination of culture morphology at the ultrastructural level confirmed the capacity of the basal cell monolayer to gradually reestablish a multilayered, differentiated epithelium. The ultrastructural appearance at 7 days poststripping was similar to that of unstripped cultures and was indicative of a tissue in steady state. Quantitation of cornified envelope formation at different times during regeneration showed that an increasing proportion of the cells were able to undergo terminal differentiation. In general, the pattern of keratin synthesis in the original epidermal explant labelled in vitro was similar to the pattern observed in human epidermis in vivo; however, in contrast to epidermis in vivo the explant also synthesized the hyperproliferative keratins 6 and 16. The in vitro differentiated keratinocytes showed underexpression of several proteins identified as differentiation markers, whereas several basal cell markers were overexpressed compared to the original explant. In addition, the in vitro differentiated keratinocytes synthesized some new proteins, notably keratins 7, 15 and 19. The basal layer remaining after stripping mainly expressed basal cell markers; however, during recovery, some of the differentiation-specific markers (e.g. keratin 10 and 15) were again expressed together with keratin no. 19, which is also expressed during wound healing in vivo. It is suggested that the present system of regenerating epidermal tissue cultures may serve as an experimental model to investigate certain aspects of the regulation of epidermal tissue homeostasis.

Identification and partial characterisation of a serum enzyme which hydrolyses epidermal inhibitory pentapeptide

We have identified an enzyme present in mammalian, avian, and reptilian serum which cleaves epidermal inhibitory pentapeptide (pGlu-Glu-Asp-Ser-GlyOH) to form a relatively stable tripeptide (pGlu-Glu-Asp). The enzyme has an inhibitor profile unlike any readily identifiable serum enzyme, and is stable at 4 degrees C for up to 3 months. As most experiments using the pentapeptide are carried out in the presence of serum this finding may have important implications on future research into the biological function of the pentapeptide.