Requirement of Stat3 but not Stat1 activation for epidermal growth factor receptor- mediated cell growth In vitro

Stimulation of epidermal growth factor receptor (EGFR) by ligand(s) leads to activation of signaling molecules including Stat1 and Stat3, two members of the signal transducers and activators of transcription (STAT) protein family. Activation of Stat1 and Stat3 was constitutive in transformed squamous epithelial cells, which produce elevated levels of TGF-alpha, and was enhanced by the addition of exogenous TGF-alpha. Targeting of Stat3 using antisense oligonucleotides directed against the translation initiation site, resulted in significant growth inhibition. In addition, cells stably transfected with dominant negative mutant Stat3 constructs failed to proliferate in vitro. In contrast, targeting of Stat1 using either antisense or dominant-negative strategies had no effect on cell growth. Thus, TGF-alpha/EGFR-mediated autocrine growth of transformed epithelial cells is dependent on activation of Stat3 but not Stat1.

Lipid A mutant Salmonella with suppressed virulence and TNFalpha induction retain tumor-targeting in vivo

Systemically administered tumor-targeted Salmonella has been developed as an anticancer agent, although its use could be limited by the potential induction of tumor necrosis factor alpha (TNFalpha)-mediated septic shock stimulated by lipid A. Genetic modifications of tumor-targeting Salmonella that alter lipid A and increase safety must, however, retain the useful properties of this bacteria. We report here that disruption of the Salmonella msbB gene reduces TNFalpha induction and increases the LD50 of this pathogenic bacteria by 10,000-fold. Notwithstanding this enormous difference, Salmonella retains its tumor-targeting properties, exhibiting tumor accumulation ratios in excess of 1000:1 compared with normal tissues. Administration of this bacteria to mice bearing melanoma results in tumors that are less than 6% the size of tumors in untreated controls at day 18. Thus, the antitumor activity previously demonstrated using tumor-targeting Salmonella with normal lipid A is retained. Lipid modification of tumor-specific bacterial vectors provides a means for reducing septic shock and further suggests that the antitumor activity of these bacteria may be independent of TNFalpha.

Strategy for qualitative and quantitative analysis in proteomics based on signature peptides

This paper describes a new analytical strategy for identifying proteins in concentration flux based on isotopic labeling peptides in tryptic digests. Primary amino groups in peptides from control and experimental samples were derivatized with acetate and trideuteroacetate, respectively. After mixing samples thus labeled from these two sources, the relative concentration of peptides was determined by isotope ratio analysis with MALDI and ESI mass spectrometry. More than a 100-fold difference in relative concentration could be detected. Simplification of complex tryptic digests prior to mass spectral analysis was achieved by selection of histidine-containing peptides with immobilized metal affinity sorbents or of glycopeptides by lectin columns. Because most of these peptides have sequences that are unique to a single protein, they are a signature of the protein from which they were derived; providing a facile route to protein analysis.

Proopiomelanocortin, corticotropin releasing hormone and corticotropin releasing hormone receptor genes are expressed in human skin

Evidence is provided that human skin, the largest body organ exposed to multiple stressors, expresses proopiomelanocortin (POMC), corticotropin releasing hormone (CRH) and CRH-receptor (CRHR) genes in vivo. In vitro studies show that POMC and CRHR mRNAs are transcribed in melanocytes, cells derived from the neural crest, and in keratinocytes, cells derived from the ectoderm. CRH mRNA is transcribed in cultured melanocytes but not in keratinocytes. It is proposed that an equivalent of the 'hypothalamus-pituitary axis' composed of the CRH-CRHR-POMC loop is conserved in mammalian skin.

Melanogenesis during the anagen-catagen-telogen transformation of the murine hair cycle

Melanin synthesis of follicular melanocytes is strictly coupled to the growth stage of the hair cycle (anagen), ceases during follicle regression (catagen), and is absent throughout the resting stage (telogen). Having previously characterized the expression and activity of melanogenesis-related proteins during the telogen-anagen transition of the murine hair cycle (JID 96:172, 1991), we here report a biophysical and biochemical analysis of follicular melanogenesis during the anagen-catagen-telogen transformation of the C57 BL-6 mouse hair cycle. Tyrosinase activity and concentration as well as dopachrome tautomerase activity were compared with melanin synthesis, as measured by electron paramagnetic resonance spectroscopy (EPR). The visible changes in skin color and the histologically appreciable switch-off of melanin formation during the anagen-catagen transformation were accompanied by a steep decline in 1) the melanin-associated EPR signal of full-thickness mouse skin, 2) tyrosinase and dopachrome tautomerase activities, and 3) the skin concentration of 80-85-kD melanogenesis related protein and 66-68-kD tyrosinase protein. Telogen skin displayed a minimum of the EPR amplitude as well as of tyrosinase and dopachrome tautomerase activity detected. By EPR, only eumelanin was identified during all hair cycle stages. The gradual switch-off of melanogenesis during anagen VI started with an unexpectedly early decline of the EPR melanin signal, followed by dopachrome tautomerase activity and the concentration of 80-85-kD melanogenesis related protein. The initiation of catagen was characterized by a significant and rapid decrease in activity and concentration of tyrosinase, and was accompanied by a second drop in dopachrome tautomerase activity. Together, these biochemical and biophysical parameters of follicular melanogenesis serve as novel and differential markers for the imminent termination of anagen and the development of catagen. They also show that the switch-off of melanogenesis during the anagen-catagen-telogen transition is a stochastic process commencing already in mid anagen VI.

Melanoma x macrophage hybrids with enhanced metastatic potential

Studies were conducted on the hypothesis that melanoma metastasis might be initiated through the generation of hybrids comprised of cells of the primary tumor and tumor-infiltrating leukocytes. Fusion hybrids were generated in vitro between weakly metastatic Cloudman S91 mouse melanoma cells and normal mouse or human macrophages. Hybrids were implanted s.c. in the tail and mice were monitored for metastases. Controls included parental S91 cells, autologous S91 x S91 hybrids, and B16F10 melanoma cells. Of 35 hybrids tested, most were more aggressive than the parental melanoma cells, producing metastases sooner and in more mice. A striking characteristic was heterogeneity amongst hybrids, with some lines producing no metastases and others producing metastases in up to 80% of mice. With few exceptions, hybrids with the highest metastatic potential also had the highest basal melanin content whereas those with the lowest metastatic potential were basally amelanotic, as were the parental melanoma cells. A spontaneous in vivo supermelanotic hybrid between an S91 tumor cell and DBA/2J host cell was one of the most metastatic lines. Hybrids with the highest metastatic potential also exhibited markedly higher chemotaxis to fibroblast-conditioned media. Histologically, the metastatic hybrids demonstrated vascular invasion and spread to distant organs similar to that of metastatic melanomas in mice and humans. Thus previous findings of enhanced metastasis in leukocyte x lymphoma hybrids can now be extended to include leukocyte x melanoma hybrids. Whether such hybridization is a natural cause of metastasis in vivo remains to be determined; however the fusion hybrids with genetically-matched parents described herein so closely resembled naturally-occurring metastatic melanoma cells that they could serve as useful new models for studies of this complex and deadly phenomenon.

Ultraviolet B and melanocyte-stimulating hormone (MSH) stimulate mRNA production for alpha MSH receptors and proopiomelanocortin-derived peptides in mouse melanoma cells and transformed keratinocytes

Cell lines of cutaneous origin, namely melanocytes and keratinocytes, were previously demonstrated to exhibit functional melanocyte-stimulating hormone (MSH) receptors that are up-regulated by ultraviolet (UV) radiation and by MSH itself. In this study, it is demonstrated that UVB irradiation, exposure to MSH, or exposure to N6,O2-dibutyryl cyclic adenosine monophosphate stimulates production of mRNAs for both alpha MSH receptors and proopiomelanocortin in cultured mouse Cloudman S91 melanoma cells, and that UVB stimulates production and release of MSH and adrenocorticotropin peptides in both melanoma cells and transformed PAM 212 mouse keratinocytes. The results add support to the hypothesis that the effects of UVB on cutaneous melanogenesis are mediated through a series of coordinated events in which MSH receptors and proopiomelanocortin-derived peptides play a central role.

Inhibition of epidermal growth factor receptor gene expression and function decreases proliferation of head and neck squamous carcinoma but not normal mucosal epithelial cells

Previous reports have shown that fresh tissues and cell lines from patients with squamous cell carcinoma of the head and neck (SCCHN) overexpress transforming growth factor alpha (TGF-alpha) and its receptor, the epidermal growth factor receptor (EGFR) at both the mRNA and protein levels. Protein localization studies confirm that TGF-alpha and EGFR are produced by the same epithelial cells in tissues from head and neck cancer patients further supporting an autocrine growth pathway. Using three strategies, we examined the hypothesis that downmodulation of EGFR would reduce the proliferation of SCCHN cells. We targeted EGFR mRNA using antisense oligonucleotides and the mature EGFR protein at two sites, the ligand-binding domain and the kinase domain, and determined the effects of this targeting on SCCHN proliferation. Treatment of several SCCHN cell lines with a pair of antisense oligodeoxynucleotides directed against the translation start site and first intron-exon splice junction of the human EGFR gene resulted in decreased EGFR protein production and inhibited growth by 86% compared to a 13% reduction in cells treated with sense oligonucleotides (P=0.03). Growth inhibition was specific for carcinoma cells since the same EGFR antisense oligonucleotides had no effect on the proliferation of normal mucosa cells harvested from non-cancer patients. Two monoclonal antibodies which block ligand binding to EGFR (MAbs 425 and 528) inhibited the growth of several SCCHN cell lines by up to 97% which suggests that EGFR is participating in an autocrine pathway in SCCHN that is, at least in part, external. An EGFR-specific tyrosine kinase inhibitor (PD 153035) was found to inhibit EGFR phosphorylation in SCCHN cell lines and to reduce growth by 68% although it had no effect on the growth rate of normal mucosal epithelial cells. These experiments indicate that EGFR gene expression and function is critical for SCCHN cell growth but not for growth of normal mucosa cells and therefore may serve as a tumor-specific target for preventive and therapeutic strategies in head and neck cancer.

Deformable boundary finding in medical images by integrating gradient and region information

Accurately segmenting and quantifying structures is a key issue in biomedical image analysis. The two conventional methods of image segmentation, region-based segmentation, and boundary finding, often suffer from a variety of limitations. Here the authors propose a method which endeavors to integrate the two approaches in an effort to form a unified approach that is robust to noise and poor initialization. The authors' approach uses Green's theorem to derive the boundary of a homogeneous region-classified area in the image and integrates this with a gray level gradient-based boundary finder. This combines the perceptual notions of edge/shape information with gray level homogeneity. A number of experiments were performed both on synthetic and real medical images of the brain and heart to evaluate the new approach, and it is shown that the integrated method typically performs better when compared to conventional gradient-based deformable boundary finding. Further, this method yields these improvements with little increase in computational overhead, an advantage derived from the application of the Green's theorem.

The eukaryotic initiation factor 2-associated 67-kDa polypeptide (p67) plays a critical role in regulation of protein synthesis initiation in animal cells

The eukaryotic initiation factor 2 (eIF-2)-associated 67-kDa polypeptide (p67) isolated from reticulocyte lysate protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation and promotes protein synthesis in the presence of active eIF-2 kinases. We have now studied the roles of p67 and eIF-2 kinases in regulation of protein synthesis using several animal cell lysates and an animal cell line (KRC-7) in culture under various growth conditions. The results are as follows. (i) Both p67 and eIF-2 kinase(s) are present in active forms in all animal cells under normal growth conditions and p67 protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation, thus promoting protein synthesis in the presence of active eIF-2 kinases. (ii) In heme-deficient reticulocyte lysates and in serum-starved KRC-7 cells in culture, p67 is deglycosylated and subsequently degraded. This leads to eIF-2 kinase-catalyzed eIF-2 alpha-subunit phosphorylation and thus to protein synthesis inhibition. (iii) Addition of a mitogen (namely, phorbol 12-myristate 13-acetate) to serum-starved KRC-7 cells in culture induces an increase of p67 and thus increases protein synthesis. These results suggest the following conclusions. (i) Protein synthesis inhibition in a heme-deficient reticulocyte lysate is not due to the activation of an eIF-2 kinase (heme-regulated inhibitor), as is generally believed, but is due to degradation of p67. The heme-regulated inhibitor is present in an active form and possibly in equal amounts in both heme-deficient and heme-supplemented reticulocyte lysates but cannot phosphorylate eIF-2 alpha subunit because of the presence of p67. (ii) p67 is essential for protein synthesis as it protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation and promotes protein synthesis in the presence of one or more active eIF-2 kinases present in all animal cells. (iii) p67 is both degradable and inducible. Only the p67 level correlates directly with the protein synthesis activity of the cell, indicating that p67 is a critical factor in protein synthesis regulation in animal cells.

Mathematical modeling of circadian cortisol concentrations using indirect response models: comparison of several methods

Six mathematical functions to describe the chronobiology of cortisol concentrations were assessed. Mean data from a dose-proportionality study of inhaled fluticasone propionate were fitted with an indirect response model using various biorhythmic functions (single cosine, dual ramps, dual zero-order, dual cosines, and Fourier series with 2 and n-harmonics) for production rate. Data with known parameters and random variation were also generated and fitted using the ADAPT II program. Fitted parameters, model estimation criteria, and runs tests were compared. Models with preassigned functions: the dual ramps, the dual zero-order and the dual cosines provide maximum and minimum times for cortisol release rate, were suitable for describing asymmetric circadian patterns and yielding IC50 values. Fourier analysis differs from the other methods in that it uses the placebo data to recover equations for cortisol secretion rate rather than by postulation. Nonlinear regression for Fourier analysis, instead of the L2-norm method, was useful to characterize the baseline cortisol data but was restricted to a maximum of two harmonics. Apart from the single cosine function, which predicts symmetrical cortisol concentrations, all methods were satisfactory in describing the baseline and suppressed cortisol concentrations. On the other hand, Fourier series with L2-norm produced the best unbiased estimate for baseline patterns. The Fourier method is flexible, accurate, and can be extended to other drug-induced changes in normal periodic rhythms.

The blood brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people worldwide. One of the prominent causative factors of AD pathogenesis is cerebral vascular dysfunction, which results in diminished cerebral perfusion. Moreover, due to the loss of the protective function of the blood-brain barrier (BBB), impaired clearance of excess neurotoxic amyloid beta (Aβ) occurs, causing vascular perturbation and diminished cognitive functioning. The relationship between the prevalence of AD and vascular risk factors is complex and not fully understood. In this review we illustrate the vascular risk factors, their effects on BBB function and their contributions to the onset of AD. Additionally, we discuss the underlying factors that may lead to altered neurovascular function and/or cerebral hypoperfusion in AD.

Ultraviolet B stimulates production of corticotropin releasing factor (CRF) by human melanocytes

Here we show that human melanocytes express the corticotropin releasing factor (CRF) gene and produce CRF peptide. The CRF production and secretion is markedly stimulated by ultraviolet B (UVB) radiation. This is the first demonstration that cutaneous melanocytes respond to environmental stress (UVB) through the production of CRF.

Stat3 and G-CSF-induced myeloid differentiation

Granulocyte colony-stimulating factor (G-CSF) is the cytokine critical for directing neutrophilic granulocyte differentiation. Early G-CSF signaling events in myeloid cells involves activation of STATs, proteins that serve the dual function of signal transduction and activation of transcription, especially the activation of Stat3. A dominant-negative mutant construct of Stat3 inhibited G-CSF-mediated neutrophilic differentiation indicating that Stat3 is a essential component for driving the G-CSF-mediated differentiation program in myeloid cells. Three isoforms of Stat3 have been identified, alpha(p92), beta(p83) and gamma(p72) each derived from a single gene. Stat3alpha is the predominant isoform expressed in most cells. Stat3beta is derived from Stat3alpha by alternative RNA splicing. Stat3gamma is derived from Stat3alpha by limited proteolysis. Mapping of Stat3alpha and Stat3beta activation in M1 murine myeloid leukemia cells revealed that their optimal activation required G-CSFR constructs containing both Y704 and Y744. These amino acid residues has previously been demonstrated to be essential for G-CSF-induced differentiation in this cells. Phosphopeptide affinity and phosphopeptide inhibition studies indicate that Stat3alpha and Stat3beta are recruited to the G-CSF receptor complex through their interaction with the receptor at phosphotyrosines Y704 and Y744. Y744 is followed at the +3 position by Cys (C). This sequence YXXC, represents a novel motif implicated in the recruitment and activation of Stat3alpha, Stat3beta and Stat3gamma by the hG-CSFR. Structurally, Stat3alpha, Stat3beta and Stat3gamma differ from each other in their C-terminal transactivation domain. In the beta isoform, the Stat3alpha transactivation domain is replaced by 7 amino acid residues which enable Stat3beta to interact with c-Jun. In the gamma isoform, the Stat3alpha transactivation domain is removed by limited proteolysis creating a dominant negative isoform. In immature human myeloid cells capable of differentiating into neutrophils in response to G-CSF, G-CSF did not activate Stat3alpha; rather. it activated predominantly Stat3beta. These findings combined with recent reports linking Stat3alpha with proliferation and transformation suggest that the beta isoform of Stat3 may be more critical for G-CSF-mediated differentiation. Activation of Stat3gamma occurred predominantly in terminally differentiated neutrophils suggesting that it may be part of a controlled proteolytic mechanism modulating pro-proliferative protein(s) in mature myeloid cells.

Prevalence of head and neck cancers in the north east-An institutional study

In India, head and neck cancers (HNCA) account for 30-40% cancers at all sites. In North-eastern India, where this study was conducted, tobacco related oral cancer is very common which may be due to widespread habit of chewing tobacco. The lack of any study in this regard and alarmingly high prevalence of cancers of head and neck in this part of India has prompted us to take up this study. A retrospective study on prevalence of cancer in various head and neck regions like oropharynx, oral cavity, pharynx, larynx, oesophagus and nasal cavity was conducted in Department of Otolaryngology, Silchar Medical College and Hospital from 1993 to 2004.The prevalence is found to be significantly high at 54.48%, affecting males more than females in the age group of 40-69 years. HNCA of oropharynx and oral cavity constituted a major burden of total body cancer.This study hopes to quantify and analyze the spectrum of HNCA and should help as a starting point for a much needed population based study in this region. A comprehensive effort is needed to identify the cause of such high prevalence, generate awareness and treatment options suited to meet this challenge.

Granulocyte colony-stimulating factor activates a 72-kDa isoform of STAT3 in human neutrophils

Granulocyte colony-stimulating factor (G-CSF) signaling involves activation of STATs, proteins that serve the dual function of signal transduction and activation of transcription. We previously demonstrated that G-CSF activated a distinct Stat3-like protein in immature and mature normal myeloid cells, StatG. StatG in normal immature human myeloid cells, i.e. adult CD34+ bone marrow cells, was composed of Stat3beta. This investigation was undertaken to determine the composition of StatG in mature normal human myeloid cells, i.e. polymorphonuclear neutrophilic granulocytes (PMN). These studies revealed that the major protein in extracts of PMN activated by G-CSF to bind the high-affinity serum-inducible element (hSIE) is a 72-kDa protein that cross-reacts with Stat3 monoclonal antibody, which we have designated Stat3gamma. Stat3gamma is derived from Stat3alpha by limited proteolysis and lacks the carboxyl-terminal portion of Stat3alpha. Because this region of Stat3alpha is involved in transcriptional activation, our findings suggest the possibility that Stat3gamma may be transcriptionally inactive and may compete with Stat3alpha for Stat3 binding sites in these terminally differentiated myeloid cells.

MSH receptors in immortalized human epidermal keratinocytes: a potential mechanism for coordinate regulation of the epidermal-melanin unit

Receptors for melanotropin (MSH) were found to be expressed by immortalized primary human epidermal keratinocytes (RHEK-1). Using 125I-beta MSH as a probe, the MSH receptors from mouse melanoma cells and human keratinocytes were found to be remarkably similar. In each cell line, there were high and low affinity receptors, with the high affinity classes showing positive cooperativity. Competition of 125I-beta MSH for binding with non-radioactive MSH revealed similar profiles. Cross-linking studies, followed by gel electrophoresis and autoradiography, showed almost identical gel migration patterns. Both cell types expressed internal as well as plasma membrane binding sites. MSH receptors on both cell types were up-regulated by ultraviolet light and by MSH itself. Although the function of MSH receptors expressed by the immortalized keratinocytes is unknown, the results are consistent with recent reports that proliferation of epidermal keratinocytes is stimulated by MSH and that proopiomelanocortin genes are expressed in the epidermis. These results support a model in which keratinocytes and melanocytes, interacting in an "epidermal-melanin unit," each respond to UV light signals with increased MSH receptor activity.

Coffee consumption protects human lymphocytes against oxidative and 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2) induced DNA-damage: Results of an experimental study with human volunteers

Aim of the study was to investigate the impact of coffee on DNA-stability in humans. DNA-damage was monitored in lymphocytes of eight individuals with single cell gel electrophoresis assays before and after consumption of 600 ml coffee (400 ml paper filtered and 200 ml metal filtered/d) for five days. Under standard conditions, no alteration of DNA-migration was seen, but a strong reduction of DNA-migration attributable to endogenous formation of oxidised purines and pyrimidines was detected with restriction enzymes; furthermore DNA-damage caused by reactive oxygen radicals (H2O2 treatment) and by the heterocyclic aromatic amine 3-amino-1-methyl-5H-pyrido[4,3-b]indole-acetate was significantly reduced after coffee consumption by 17% and 35%, respectively. Also in in vitro experiments, inhibition of H2O2 induced DNA-damage was observed with coffee at low concentrations (<or= 25 microl/ml) whereas the diterpenoids cafestol and kahweol caused only marginal effects indicating that the effects of coffee are due to scavenging effects of other constituents. Enzyme measurements showed that additionally induction of antioxidant enzymes may play a role: while the activity of glutathione peroxidase was only marginally increased after coffee consumption, a significant (38%) increase of superoxide dismutase activity was detected. Comparisons with results of earlier studies suggest that coffee consumption may prevent oxidative DNA-damage to a higher extent as diets enriched in fruits and vegetables.

Characterization of Escherichia coli Phylogenetic Groups Associated with Extraintestinal Infections in South Indian Population

Background:

Escherichia coli strains mainly fall into four phylogenetic groups (A, B1, B2, and D) and that virulent extra-intestinal strains mainly belong to groups B2 and D.

Aim:

The aim was to determine the association between phylogenetic groups of E. coli causing extraintestinal infections (ExPEC) regarding the site of infection, expression of virulence factors, antimicrobial resistance patterns, and clinical outcome. This descriptive study was carried out in a multi-specialty Tertiary Care Hospital.

Materials and Methods:

A total of 300 E. coli causing ExPEC were studied. Triplex polymerase chain reaction was used to classify the phylogenetic groups; hemolysin production was assessed on sheep blood agar and biofilm production in a microtiter plate assay. Production of extended spectrum of beta-lactamase (ESBLs) was detected by combination disk method; AmpC was detected by AmpC disk test, Carbapenemase production was detected by modified Hodge test and metallo-β-lactamase by metallo-beta-lactamases (MBL) E-test.

Results:

Of 300 isolates, 61/300 (20%) belonged to phylogroup A, 27/300 (9%) to phylogroup B1, 104/300 (35%) were B2 and 108/300 (36%) belonged to group D, respectively. Phylogroups B2 and D were the most predominant groups in urinary tract infection and sepsis. Prognoses were better in infections with group A and B1 isolates, and relapses and death were common in infections with B2 and D. Expression of biofilm was greatest in B1 and hemolysin in group B2. Group A and B1 showed higher resistance to ciprofloxacin and were most frequent β-lactamase (ESBL, AmpC, Carbapenemase and MBL) producers.

Conclusions:

Phylogenetic group B2 and D were predominant in ExPEC and exhibited least antimicrobial resistance among the groups. Resistance to multiple antibiotics was most prevalent in group A and B1. Regular monitoring of antimicrobial susceptibility in commensal strains is essential as they might transfer the property of antimicrobial resistance to pathogenic strains.

Pharmacological disruption of hair follicle pigmentation by cyclophosphamide as a model for studying the melanocyte response to and recovery from cytotoxic drug damage in situ

Here we show that cyclophosphamide induces disruption of follicular melanogenesis, which is characterized by abnormal transfer of pigment granules to ectopic hair bulb locations, extrafollicular melanin incontinence, disordered formation of melanosomes, and inhibition of melanosome transfer into precortical keratinocytes. This is in contrast to dexamethasone-induced termination of follicle melanogenesis, which activates premature but predominantly normal catagen development. Cyclophosphamide-induced pigmentation disruption was accompanied by significant alterations of biochemical and biophysical markers of melanogenesis, compared to control mice treated either with vehicle or with topical dexamethasone. Electron paramagnetic resonance spectroscopy shows a decline in the melanin signal and predominant eumelanin production. Tyrosine hydroxylase activity of tyrosinase and dihydroxyphenylalanine oxidation drop rapidly, while DOPAchrome tautomerase activity increases and dihydroxyindole carboxylic acid conversion factor activity remains unchanged in cyclophosphamide-treated mice compared to controls. These observations emphasize the key role of tyrosinase as opposed to postdihydroxyphenylalanine oxidase steps in normal and pathological termination of melanogenesis and shows that tyrosinase is the most sensitive target of the melanogenic apparatus for pharmacological regulation. Follicle pigmentation recovers only during the subsequent hair cycle, i.e., after a new anagen hair bulb has been constructed, which points to the existence of a relatively chemoresistant melanoblast-like cell population residing in the noncycling part of the hair follicle.