Corticotropin releasing hormone and related peptides can act as bioregulatory factors in human keratinocytes

The expression of corticotropin-releasing hormone family peptides in premalignant and malignant vulvar lesions

OBJECTIVES

To examine the relation of corticotropin-releasing hormone (CRH) family peptides with inflammatory processes and oncogenesis, emphasizing in vulvar inflammatory, premalignant and malignant lesions, as well as to investigate the possibility of lesion cells immunoescaping, utilizing FAS/FAS-L complex.

METHODS

Immunohistochemical expression of CRH, urocortin (UCN), FasL and their receptors CRHR1, CRHR2 and Fas was studied in vulvar tissue sections obtained from patients with histologically confirmed diagnosis of lichen, vulvar intraepithelial neoplasia (VIN) and vulvar squamous cell carcinoma (VSCC). The patient cohort was selected from a tertiary teaching Hospital in Greece, between 2005 and 2015. For each of the disease categories, immunohistochemical staining was evaluated and the results were statistically compared.

RESULTS

A progressive increase of the cytoplasmic immunohistochemical expression of CRH and UCN, from precancerous lesions to VSCC was observed. A similar increase was detected for Fas and FasL expression. Nuclear localization of UCN was demonstrated in both premalignant and VSCC lesions, with staining being significantly intensified in carcinomas, particularly in the less differentiated tumor areas or in the areas at invasive tumor front.

CONCLUSIONS

Stress response system and CRH family peptides seem to have a role in inflammation maintenance and progression of vulvar premalignant lesions to malignancy. It seems that stress peptides may locally modulate the stroma through Fas/FasL upregulation, possibly contributing to vulvar cancer development.

Possible Correlation between Urocortin 1 (Ucn1) and Immune Parameters in Patients with Endometriosis

The etiology of endometriosis (EMS) has not been clearly elucidated yet, and that is probably the reason why its diagnostic process is frequently long-lasting and inefficient. Nowadays, the non-invasive diagnostic methods of EMS are still being sought. Our study aimed to assess the serum and peritoneal fluid levels of urocortin 1 (Ucn1) in patients with EMS and healthy women. Moreover, considering the immune background of the disease, the association between Ucn1 and several immune parameters was studied in both groups. We found that the serum Ucn1 level was significantly upregulated in women with EMS compared to healthy patients. Moreover, higher serum Ucn1 levels tended to correspond with more advanced stages of the disease (p = 0.031). Receiver operating characteristic (ROC) analysis revealed that based on serum Ucn1 levels, it is possible to distinguish deep infiltrating endometriosis (DIE) from among other EMS types. Together, these results indicate Ucn1 as a possible promising biomarker of EMS: however, not in isolation, but rather to enhance the effectiveness of other diagnostic methods.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

The significance of CYP11A1 expression in skin physiology and pathology

CYP11A1, a member of the cytochrome P450 family, plays several key roles in the human body. It catalyzes the first and rate-limiting step in steroidogenesis, converting cholesterol to pregnenolone. Aside from the classical steroidogenic tissues such as the adrenals, gonads and placenta, CYP11A1 has also been found in the brain, gastrointestinal tract, immune systems, and finally the skin. CYP11A1 activity in the skin is regulated predominately by StAR protein and hence cholesterol levels in the mitochondria. However, UVB, UVC, CRH, ACTH, cAMP, and cytokines IL-1, IL-6 and TNFα can also regulate its expression and activity. Indeed, CYP11A1 plays several critical roles in the skin through its initiation of local steroidogenesis and specific metabolism of vitamin D, lumisterol, and 7-dehydrocholesterol. Products of these pathways regulate the protective barrier and skin immune functions in a context-dependent fashion through interactions with a number of receptors. Disturbances in CYP11A1 activity can lead to skin pathology.

New effects of caffeine on corticotropin-releasing hormone (CRH)-induced stress along the intrafollicular classical hypothalamic-pituitary-adrenal (HPA) axis (CRH-R1/2, IP3 -R, ACTH, MC-R2) and the neurogenic non-HPA axis (substance P, p75NTR and TrkA) in ex vivo human male androgenetic scalp hair follicles

BACKGROUND

Human hair is highly responsive to stress, and human scalp hair follicles (HFs) contain a peripheral neuroendocrine equivalent of the systemic hypothalamic-pituitary-adrenal (HPA) stress axis. Androgenetic alopecia (AGA) is supposed to be aggravated by stress. We used corticotropin-releasing hormone (CRH), which triggers the HPA axis, to induce a stress response in human ex vivo male AGA HFs. Caffeine is known to reverse testosterone-mediated hair growth inhibition in the same hair organ culture model.

OBJECTIVES

To investigate whether caffeine would antagonize CRH-mediated stress in these HFs.

METHODS

HFs from balding vertex area scalp biopsies of men affected by AGA were incubated with CRH (10-7 mol L-1 ) with or without caffeine (0·001% or 0·005%).

RESULTS

Compared to controls, CRH significantly enhanced the expression of catagen-inducing transforming growth factor-β2 (TGF-β2) (P < 0·001), CRH receptors 1 and 2 (CRH-R1/2) (P < 0·01), adrenocorticotropic hormone (ACTH) (P < 0·001) and melanocortin receptor 2 (MC-R2) (P < 0·001), and additional stress-associated parameters, substance P and p75 neurotrophin receptor (p75NTR ). CRH inhibited matrix keratinocyte proliferation and expression of anagen-promoting insulin-like growth factor-1 (IGF-1) and the pro-proliferative nerve growth factor receptor NGF-tyrosine kinase receptor A (TrkA). Caffeine significantly counteracted all described stress effects and additionally enhanced inositol trisphosphate receptor (IP3 -R), for the first time detected in human HFs.

CONCLUSIONS

These findings provide the first evidence in ex vivo human AGA HFs that the stress mediator CRH induces not only a complex intrafollicular HPA response, but also a non-HPA-related stress response. Moreover, we show that these effects can be effectively antagonized by caffeine. Thus, these data strongly support the hypothesis that stress can impair human hair physiology and induce hair loss, and that caffeine may effectively counteract stress-induced hair damage and possibly prevent stress-induced hair loss.

Extra-adrenal glucocorticoid biosynthesis: implications for autoimmune and inflammatory disorders

Glucocorticoid synthesis is a complex, multistep process that starts with cholesterol being delivered to the inner membrane of mitochondria by StAR and StAR-related proteins. Here its side chain is cleaved by CYP11A1 producing pregnenolone. Pregnenolone is converted to cortisol by the enzymes 3-βHSD, CYP17A1, CYP21A2 and CYP11B1. Glucocorticoids play a critical role in the regulation of the immune system and exert their action through the glucocorticoid receptor (GR). Although corticosteroids are primarily produced in the adrenal gland, they can also be produced in a number of extra-adrenal tissue including the immune system, skin, brain, and intestine. Glucocorticoid production is regulated by ACTH, CRH, and cytokines such as IL-1, IL-6 and TNFα. The bioavailability of cortisol is also dependent on its interconversion to cortisone which is inactive, by 11βHSD1/2. Local and systemic glucocorticoid biosynthesis can be stimulated by ultraviolet B, explaining its immunosuppressive activity. In this review, we want to emphasize that dysregulation of extra-adrenal glucocorticoid production can play a key role in a variety of autoimmune diseases including multiple sclerosis (MS), lupus erythematosus (LE), rheumatoid arthritis (RA), and skin inflammatory disorders such as psoriasis and atopic dermatitis (AD). Further research on local glucocorticoid production and its bioavailability may open doors into new therapies for autoimmune diseases.

Neuroendocrinology and neurobiology of sebaceous glands

The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro-regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α-melanocyte-stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro-autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin-mediated or facial paresis-associated reduction of human sebum secretion suggests that cutaneous nerve-derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin.

Neuroendocrinology of the skin

The skin is considered the mirror of the soul and is affected by neurohormonal triggers, especially stress. Hair follicles, keratinocytes, mast cells, melanocytes, and sebocytes all express sex and stress hormones implicating them in a local "hypothalamic-pituitary-adrenal axis." In particular, the peptides corticotropin-releasing hormone (CRH) and neurotensin (NT) have synergistic action stimulating mast cells and are uniquely elevated in the serum of patients with skin diseases exacerbated by stress. Addressing the neurohormonal regulation of skin function could lead to new targets for effective treatment of inflammatory skin diseases.

Differentiation of Keratinocytes Modulates Skin HPA Analog

It is well established, that epidermal keratinocytes express functional equivalent of hypothalamus-pituitary-adrenal axis (HPA) in order to respond to changing environment and maintain internal homeostasis. We are presenting data indicating that differentiation of primary neonatal human keratinocytes (HPEKp), induced by prolonged incubation or calcium is accompanied by significant changes in the expression of the elements of skin analog of HPA (sHPA). Expression of CRF, UCN1-3, POMC, ACTH, CRFR1, CRFR2, MC1R, MC2R, and GR (coded by NR3C1 gene) were observed on gene/protein levels along differentiation of keratinocytes in culture with similar pattern seen by immunohistochemistry on full thickness skin biopsies. Expression of CRF was more pronounced in less differentiated keratinocytes, which corresponded to the detection of CRF immunoreactivity preferentially in the stratum basale. POMC expression was enhanced in more differentiated keratinocytes, which corresponded to detection of ACTH immunoreactivity, predominantly in the stratum spinosum and stratum granulosum. Expression of urocortins was also affected by induction of HPEKp differentiation. Immunohistochemical studies showed high prevalence of CRFR1 in well differentiated keratinocytes, while smaller keratinocytes showed predominantly CRFR2 immunoreactivity. MC2R mRNA levels were elevated from days 4 to 8 of in vitro incubation, while MC2R immunoreactivity was the highest in the upper layers of epidermis. Similar changes in mRNA/protein levels of sHPA elements were observed in HPEKp keratinocytes treated with calcium. Summarizing, preferential expression of CRF and POMC (ACTH) by populations of keratinocytes on different stage of differentiation resembles organization of central HPA axis suggesting their distinct role in physiology and pathology of the epidermis. J. Cell. Physiol. 232: 154-166, 2017. © 2016 Wiley Periodicals, Inc.

Key role of CRF in the skin stress response system

The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.

The association of PASI scores with CRH-R1 expression in patients with psoriasis

Stress is a well-known triggering factor along with genetic predisposition on the onset and during the course of psoriasis by altering the cellular constituents of the immune system. In the skin, there is a local hypothalamic-pituitary-adrenal (HPA) axis which is the equivalent of the central HPA axis. Corticotropin-releasing hormone (CRH) is a major regulator of the HPA axis in response to stress. This study was planned to show the role of CRH receptor type 1 (CRH-R1) in pathogenesis of psoriasis, the relation with the severity of psoriasis, and interpersonal variance in skin biopsy specimens of the psoriasis patient. Study involved 46 patients with psoriasis and 20 healthy control subjects who were older than 18 years. The clinical sign and PASI scores of psoriasis patients were recorded. Immunohistochemically, expression of CRH-R1 was investigated in psoriatic lesions and control group skin. A statistically significant increase of the expression of CRH-R1 was found in the skin biopsies of psoriasis patients compared with the control group patients. In patients with psoriasis, there was a positive correlation between the expressions of CRH-R1 and PASI scores (p = 0.001, r = +0.572). In addition, a statistically significant increase of PASI scores was found in the intense-stained CRH-R1 group compared with the weakly stained CRH-R1 patient group. The present study has demonstrated that CRH-R1 could have a role in pathogenesis of the psoriasis and stress may increase the intensity of psoriasis.

Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by ultraviolet radiation

The hypothalamic-pituitary-adrenal (HPA) axis maintains basal and stress-related homeostasis in vertebrates. Skin expresses all elements of the HPA axis including corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), ACTH, β-endorphin (β-END) with corresponding receptors, the glucocorticoidogenic pathway, and the glucocorticoid receptor (GR). To test the hypothesis that cutaneous responses to environmental stressors follow the organizational structure of the central response to stress, the activity of the "cutaneous HPA" axis homolog was investigated after exposure to ultraviolet radiation (UVR) wavelengths of UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm) in human skin organ culture and in co-cultured keratinocytes/melanocytes. The level of stimulation of CRH, POMC, MC1R, MC2R, CYP11A1, and CYP11B1 genes was dependent on UV wavelengths and doses, with the highest effects observed for highly energetic UVC and UVB. ELISA and Western assays showed significant production of CRH, POMC, ACTH, and CYP11A1 proteins and of cortisol, with a decrease in GR expression only after UVB and UVC. However, β-END expression was also stimulated by UVA. Immunocytochemistry localized the deposition of the aforesaid antigens predominantly to the epidermis with additional accumulation of CRH, β-END, and ACTH in the dermis. UVR-stimulated CYP11A1 expression was seen in the basal layer of the epidermis and cells of adjacent dermis. Thus, the capacity to activate or change the spatial distribution of the cutaneous HPA axis elements is dependent on highly energetic wavelengths (UVC and UVB), implying a dependence of a local stress response on their noxious activity with overlapping or alternative mechanisms activated by UVA.

The impact of stress on tumor growth: peripheral CRF mediates tumor-promoting effects of stress

Introduction

Stress has been shown to be a tumor promoting factor. Both clinical and laboratory studies have shown that chronic stress is associated with tumor growth in several types of cancer. Corticotropin Releasing Factor (CRF) is the major hypothalamic mediator of stress, but is also expressed in peripheral tissues. Earlier studies have shown that peripheral CRF affects breast cancer cell proliferation and motility. The aim of the present study was to assess the significance of peripheral CRF on tumor growth as a mediator of the response to stress in vivo.

Methods

For this purpose we used the 4T1 breast cancer cell line in cell culture and in vivo. Cells were treated with CRF in culture and gene specific arrays were performed to identify genes directly affected by CRF and involved in breast cancer cell growth. To assess the impact of peripheral CRF as a stress mediator in tumor growth, Balb/c mice were orthotopically injected with 4T1 cells in the mammary fat pad to induce breast tumors. Mice were subjected to repetitive immobilization stress as a model of chronic stress. To inhibit the action of CRF, the CRF antagonist antalarmin was injected intraperitoneally. Breast tissue samples were histologically analyzed and assessed for neoangiogenesis.

Results

Array analysis revealed among other genes that CRF induced the expression of SMAD2 and β-catenin, genes involved in breast cancer cell proliferation and cytoskeletal changes associated with metastasis. Cell transfection and luciferase assays confirmed the role of CRF in WNT- β-catenin signaling. CRF induced 4T1 cell proliferation and augmented the TGF-β action on proliferation confirming its impact on TGFβ/SMAD2 signaling. In addition, CRF promoted actin reorganization and cell migration, suggesting a direct tumor-promoting action. Chronic stress augmented tumor growth in 4T1 breast tumor bearing mice and peripheral administration of the CRF antagonist antalarmin suppressed this effect. Moreover, antalarmin suppressed neoangiogenesis in 4T1 tumors in vivo.

Conclusion

This is the first report demonstrating that peripheral CRF, at least in part, mediates the tumor-promoting effects of stress and implicates CRF in SMAD2 and β-catenin expression.

Corticotropin-releasing hormone attenuates vascular endothelial growth factor release from human HaCaT keratinocytes

OBJECTIVES

Corticotropin-releasing hormone (CRH) is a central component of the local hypothalamic-pituitary-adrenal (HPA) axis, which has a functional equivalent in the skin. To determine whether CRH and its receptor, CRH-R1, modulate the expression of vascular endothelial growth factor (VEGF), which is overexpressed in psoriatic epidermis and plays a causal role in the pathogenesis of psoriasis, we investigated the effect of CRH on the expression of VEGF in a human keratinocyte cell line (HaCaT) and whether this effect is via the mitogen-activated protein kinase (MAPK) signal transduction pathways.

METHODS

Real-time RT-PCR, ELISA assay and western blot were used in the present study to investigate the expression of VEGF in CRH-treated HaCaT cells.

RESULTS

The mRNA and protein levels of VEGF in CRH-treated HaCaT cells were significantly attenuated. However, this downregulation was abrogated by pretreatment with antalarmin, SB203580 and SP600125; pretreatment with PD98059 did not attenuate the effects of CRH on the expression of VEGF. In addition, CRH treatment induced rapid phosphorylation of p38 MAPK and JNK1/2, and antalarmin, SB203580 and SP600125 inhibited CRH-induced phosphorylation of p38 MAPK and JNK1/2.

CONCLUSIONS

CRH might downregulate the expression of VEGF through the CRH-R1 and MAPK (p38 MAPK and JNK1/2) signaling pathways in human HaCaT cells.

Corticotropin Releasing Factor promotes breast cancer cell motility and invasiveness

INTRODUCTION

Cancer cells secrete bioactive peptides that act in an autocrine or paracrine fashion affecting tumor growth and metastasis. Corticotropin-releasing factor (CRF), a hypothalamic neuropeptide that controls the response to stress, has been detected in breast cancer tissues and cell lines. CRF can affect breast cancer cells in an autocrine or paracrine manner via its production from innervating sympathetic neurons or immune cells.

METHODS

In the present study we report our findings regarding the impact of CRF on breast cancer cell motility and invasiveness. For this purpose we used the MCF7 breast cancer cell line and evaluated the effect of CRF on motility and invasiveness using the wound-healing and boyden-chamber assays. In addition, we measured the effect of CRF on molecules that mediate motility by western blot, immunofluorescence, ELISA and RT-PCR.

RESULTS

Our findings show that: 1. CRF transiently inhibited the apoptosis of MCF7 cells. 2. CRF enhanced MCF7 cell motility in a wound healing assay and their invasiveness through extracellular matrix. 3. CRF increased actin polymerization, phosphorylation of Focal Adhesion Kinase (FAK), providing a potential mechanism for the observed induction of MCF7 motility. 4. CRF induced the expression of Cox-1 but not Cox-2 in MCF7 cells as well as the production of prostaglandins, factors known to promote invasiveness and metastasis.

CONCLUSION

Overall, our data suggest that CRF stimulates cell motility and invasiveness of MCF7 cells most probably via induction of FAK phosphorylation and actin filament reorganization and production of prostaglandins via Cox1. Based on these findings we postulate that the stress neuropeptide CRF present in the vicinity of tumors (either produced locally by the tumor cells themselves or by nearby normal cells or secreted from the innervations of surrounding tissues) may play an important role on breast tumor growth and metastatic capacity, providing a potential link between stress and tumor progression.

The involvement of altered corticotropin releasing factor receptor 2 expression in prostate cancer due to alteration of anti-angiogenic signaling pathways

BACKGROUND

Expression of urocortin (Ucn) in the human benign prostate and prostate cancer has been reported recently. Ucn binds and activates corticotropin releasing factor (CRF) receptor 1 (CRFR1) and 2 (CRFR2). Activation of CRFR2 has been shown to inhibit tumor growth by regulation of proliferation and apoptosis as well as suppression of vascularization. However, there is no report demonstrating expression profile of CRFR2 in normal prostate versus prostate cancer.

METHODS

CRFR2 mRNA expression was assessed in human normal prostate and prostate cancer by reverse transcriptase PCR. CRFR2 expression on protein level has been performed using double staining immunofluorescence (IF) of tissue microarrays of 32 cases of prostatic adenocarcioma with corresponding normal tissues. Confocal microscopy was carried out to visualize the immunostaining.

RESULTS

PCR of normal prostate lysates exhibited specific signals for CRFR2 mRNA. However PCR of lysates of prostate cancer exhibited no signal for CRFR2 mRNA. IF study exhibited that smooth muscle components of the stroma and endothelial cells of blood vessels express an extensive staining for CRFR2. In a lesser extend vascular smooth muscle cells expressed CRFR2. The tumoral neovascular system and stroma exhibited no immunopositivity for CRFR2.

CONCLUSIONS

The present study demonstrates for the first time that human benign prostate tissue and prostate cancer specimen differentially express CRFR2. While Ucn expression in prostate cancer has been shown to be identical to non-malignant prostate tissues, we hypothesize that expression loss of CRFR2 in prostate cancer and its neovascularization contributes to prostate tumorigenesis, progression, and neoangiogenesis.

A human folliculoid microsphere assay for exploring epithelial- mesenchymal interactions in the human hair follicle

The search for more effective drugs for the management of common hair growth disorders remains a top priority, both for clinical dermatology and industry. In this pilot study, we report a pragmatic organotypic assay for basic and applied hair research. The patented technique produces microdroplets, which generate human folliculoid microspheres (HFMs), consisting of human dermal papilla fibroblasts and outer root sheath keratinocytes within an extracellular matrix that simulates elements of the hair follicle mesenchyme. Studying a number of different markers (for example, proliferation, apoptosis, cytokeratin-6, versican), we show that these HFMs, cultured under well-defined conditions, retain several essential epithelial-mesenchymal interactions characteristic for human scalp hair follicle. Selected, recognized hair growth-modulatory agents modulate these parameters in a manner that suggests that HFMs allow the standardized preclinical assessment of test agents on relevant human hair growth markers under substantially simplified in vitro conditions that approximate the in vivo situation. Furthermore, we show by immunohistochemistry, reverse transcriptase-PCR, and DNA microarray techniques that HFMs also offer a useful discovery tool for the identification of target genes and their products for candidate hair drugs. HFM thus represent an instructive modern experimental and screening tool for basic and applied hair research in the human system.

Urocortin's inhibition of tumor growth and angiogenesis in hepatocellular carcinoma via corticotrophin-releasing factor receptor 2

Urocortin (UCN) functions via corticotrophin-releasing factor receptors (CRFRs), CRFR1 & 2. CRFR2 is reported to be a tonic suppressor of vascularization, implying its role in tumor angiogenesis. Here, it was found that UCN inhibited the growth of hepatocellular carcinoma (HCC) and reduced tumor microvessel density in nude mice. Hepatoma cells didn't express CRFRs whereas vessels expressed CRFRs, mainly CRFR2. In vitro three-dimensional culture assay showed UCN inhibited angiogenesis, this effect was abolished by CRFR2 antagonist, anti-sauvagine-30, demonstrating involvement of CRFR2. Furthermore, UCN inhibited the proliferation and promoted the apoptosis of endothelial cells and down-regulated VEGF expression in vivo via CRFR2.

Urocortin2 inhibits tumor growth via effects on vascularization and cell proliferation

The corticotropin-releasing factor (CRF) receptor CRFR2 is expressed widely in peripheral tissues and in the vasculature, although its functional roles in those tissues have only recently begun to be elucidated. Previously we found that genetic deletion of CRFR2 resulted in profound postnatal hypervascularization in mice, characterized by both an increase in total vessel number and a dramatic increase in vessel diameter. These data strongly suggested that ligands for CRFR2 act to limit tissue vascularity, perhaps as a counterbalance to factors that promote neovascularization. Urocortin 2 (Ucn2) is a specific ligand for the CRFR2. We hypothesized that activation of CRFR2 by Ucn2 might thus suppress tumor vascularization and consequently limit tumor growth. Here, we show that viral-mediated expression of Ucn2 strikingly inhibits the growth and vascularization of Lewis Lung Carcinoma Cell (LLCC) tumors in vivo. Further, we found that this effect on tumor growth inhibition was independent of whether exposure to Ucn2 occurred before or after establishment of measurable tumors. In vitro, Ucn2 directly inhibited the proliferation of LLCC, suggesting that the tumor-suppressing effects of CRFR2 activation involve a dual mechanism of both a direct inhibition of tumor cell cycling and the suppression of tumor vascularization. These results establish that Ucn2 inhibits tumor growth, suggesting a potential therapeutic role for CRFR2 ligands in clinical malignancies.

Corticotropin-releasing factor family and its receptors: tumor therapeutic targets?

Urocortin (UCN) and corticotropin-releasing factor (CRF) are members of CRF family. Though CRF is mainly distributed in central nervous system (CNS), UCN has been reported to play biologically diverse roles in several systems such as cardiovascular, respiratory, digestive, reproductive, stress, immunologic system, etc. UCN and CRF bind to two known receptors, CRFR1 and CRFR2, to function. Both CRF receptors are distributed in CNS and periphery tissues, and their expression in cancer tissues has been reported. Now there are many documents indicating UCN/CRF play an important role in the regulation of carcinogenesis. There is also evidence indicating UCN/CRF have anticancer effects via CRFRs. This paper will review the effects of CRF family in cancers.

Differential expression of HPA axis homolog in the skin

Human skin expresses elements of the hypothalamo-pituitary-adrenal (HPA) axis including pro-opiomelanocortin (POMC), corticotropin releasing hormone (CRH), the CRH receptor-1 (CRH-R1), key enzymes of corticosteroid synthesis and synthesizes glucocorticoids. Expression of these elements is organized in functional, cell type-specific regulatory loops, which imitate the signaling hierarchy of the HPA axis. In melanocytes and fibroblasts CRH-induced CRH-R1 stimulation upregulates POMC expression and production of ACTH through activation of cAMP dependent pathway(s). Melanocytes respond with enhanced production of cortisol and corticosterone, which is dependent on POMC activity. Fibroblasts respond to CRH and ACTH with enhanced production of corticosterone, but not cortisol, which is produced constitutively. Organ-cultured human scalp hair follicles also show a fully functional HPA axis equivalent, including cortisol synthesis and secretion and negative feedback regulation by cortisol on CRH expression. Thus, differential, CRH-driven responses of defined cutaneous cell populations reproduce key features of the central HPA axis at the tissue/single cell levels.

Corticotropin releasing hormone and the skin

Cotricotropin-releasing hormone (CRH) and related peptides are produced in skin that is dependent on species and anatomical location. Local peptide production is regulated by ultraviolet radiation (UVR), glucocorticoids and phase of the hair cycle. The skin also expresses the corresponding receptors (CRH-R1 and CRH-R2), with CRH-R1 being the major receptor in humans. CRH-R1 is expressed in epidermal and dermal compartments, and CRH-R2 predominantly in dermal structures. The gene coding for CRH-R1 generates multiple isoforms through a process modulated by UVR, cyclic adenosine monophosphate (cAMP) and phorbol 12-myristate 13-acetate. The phenotypic effects of CRH in human skin cells are largely mediated by CRH-R1alpha through increases in concentrations of cAMP, inositol triphosphate (IP3), or Ca2+ with subsequent activation of protein kinases A (PKA) and C (PKC) dependent pathways. CRH also modulates the activity of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kappaB), activator protein 1 (AP-1) and cAMP responsive element binding protein (CREB). The cellular functions affected by CRH depend on cell type and nutritional status and include modulation of differentiation program(s), proliferation, viability and immune activity. The accumulated evidence indicates that cutaneous CRH is also a component of a local structure organized similarly to the hypothalamo-pituitary-adrenal axis.

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

Modulation of the human hair follicle pigmentary unit by corticotropin-releasing hormone and urocortin peptides

Human skin is a local source of corticotropin-releasing hormone (CRH) and expresses CRH and CRH receptors (CRH-R) at mRNA and protein levels. Epidermal melanocytes respond to CRH by induction of cAMP with up-regulation of pro-opiomelanocortin gene expression and subsequent production of adrenocorticotropin hormone. However, the role of CRH/CRH-R in melanocyte biology is complicated by the significant heterogeneity of cutaneous melanocyte subpopulations, from continuously active and UV-responsive melanocytes in epidermis to UV nonresponsive, hair growth cycle-coupled melanogenesis in hair follicles. In the present study we report that normal human scalp hair follicle melanocytes express CRH at the mRNA level. Furthermore, CRH, urocortin and CRH-R 1 and 2 were differentially expressed in follicular melanocytes, fibroblasts, and keratinocytes depending on anatomic location and differentiation status in situ and in vitro. Stimulation of follicular melanocytes with CRH and CRH peptides, modified for selectivity for CRH-R1 and/or CRH-R2, variably induced cell melanogenesis, dendricity, and proliferation. CRH-peptides also stimulated the expression and activity of Tyrosinase, and expression of Tyrosinase-related protein-1 and-2. However, a modified urocortin peptide highly selective for CRH-R2 down-regulated melanocyte differentiation phenotype. This study indicates that CRH peptides can differentially influence hair follicle melanocyte behavior not only via CRH-R1 signaling but also by complex cross-talk between CRH-R1 and CRH-R2.

Teneurin C-terminal associated peptides: an enigmatic family of neuropeptides with structural similarity to the corticotropin-releasing factor and calcitonin families of peptides

The proliferation of genomic sequence data in recent years has led to the identification of numerous orthologous and paralogous genes in a variety of divergent taxa. Phylogenetic comparisons of this sequence information have led not only to the construction of improved evolutionary relationships among genes and species, but also led to greater understanding of how genes and their proteins evolve differently throughout the Metazoa. Our recent characterization of a biologically active corticotropin-releasing factor (CRF)-like sequence at the C-terminal region of the teneurin transmembrane proteins has led to a number of questions of how peptide genes evolve and develop new functions in the Metazoa. The teneurin C-terminal associated peptides show structural similarity to the calcitonin family of peptides as well as the CRF family, and like both peptide families, plays a role in the regulation of stress and anxiety.

CRH functions as a growth factor/cytokine in the skin

We tested the effect of CRH and related peptides in a large panel of human skin cells for growth factor/cytokine activities. In skin cells CRH action is mediated by CRH-R1, a subject to posttranslational modification with expression of alternatively spliced isoforms. Activation of CRH-R1 induced generation of both cAMP and IP3 in the majority of epidermal and dermal cells (except for normal keratinocytes and one melanoma line), indicating cell type-dependent coupling to signal transduction pathways. Phenotypic effects on cell proliferation were however dependent on both cell type and nutrition conditions. Specifically, CRH stimulated dermal fibroblasts proliferation, by increasing transition from G1/0 to the S phase, while in keratinocytes CRH inhibited cell proliferation. In normal and immortalized melanocytes CRH effect showed dichotomy and thus, it inhibited melanocyte proliferation in serum-containing medium CRH through G2 arrest, while serum free media led instead to CRH enhanced DNA synthesis (through increased transition from G1/G0 to S phase and decreased subG1 signal, indicating DNA degradation). CRH also induced inhibition of early and late apoptosis in the same cells, demonstrated by analysis with the annexin V stains. Thus, CRH acts on epidermal melanocytes as a survival factor under the stress of starvation (anti-apoptotic) as well as inhibitor of growth factors induced cell proliferation. In conclusion, CRH and related peptides can couple CRH-R1 to any of diverse signal transduction pathways; they also regulate cell viability and proliferation in cell type and growth condition-dependent manners.

Corticotropin-releasing hormone receptor-1 and histidine decarboxylase expression in chronic urticaria

Certain skin disorders, such as contact dermatitis and chronic urticaria, are characterized by inflammation involving mast cells and worsen by stress. The underlying mechanism of this effect, however, is not known. The skin appears to have the equivalent of a hypothalamic-pituitary-adrenal (HPA) axis, including local expression of corticotropin-releasing hormone (CRH) and its receptors (CRH-R). We have reported that acute stress and intradermal administration of CRH stimulate skin mast cells and increase vascular permeability through CRH-R1 activation. In this study, we investigated the expression of CRH-R1, the main CRH-R subtype in human skin, and the mast cell related gene histidine decarboxylase (HDC), which regulates the production of histamine, in normal and pathological skin biopsies. Quantitative real time PCR revealed that chronic urticaria expresses high levels of CRH-R1 and HDC as compared to normal foreskin, breast skin and cultured human keratinocytes. The lichen simplex samples had high expression of CRH-R1, but low HDC. These results implicate CRH-R in chronic urticaria, which is often exacerbated by stress.

Human mast cells express corticotropin-releasing hormone (CRH) receptors and CRH leads to selective secretion of vascular endothelial growth factor

Mast cells are critical for allergic reactions, but also for innate or acquired immunity and inflammatory conditions that worsen by stress. Corticotropin-releasing hormone (CRH), which activates the hypothalamic-pituitary-adrenal axis under stress, also has proinflammatory peripheral effects possibly through mast cells. We investigated the expression of CRH receptors and the effects of CRH in the human leukemic mast cell (HMC-1) line and human umbilical cord blood-derived mast cells. We detected mRNA for CRH-R1alpha, 1beta, 1c, 1e, 1f isoforms, as well as CRH-R1 protein in both cell types. CRH-R2alpha (but not R2beta or R2gamma) mRNA and protein were present only in human cord blood-derived mast cells. CRH increased cAMP and induced secretion of vascular endothelial growth factor (VEGF) without tryptase, histamine, IL-6, IL-8, or TNF-alpha release. The effects were blocked by the CRH-R1 antagonist antalarmin, but not the CRH-R2 antagonist astressin 2B. CRH-stimulated VEGF production was mediated through activation of adenylate cyclase and increased cAMP, as evidenced by the fact that the effect of CRH was mimicked by the direct adenylate cyclase activator forskolin and the cell-permeable cAMP analog 8-bromo-cAMP, whereas it was abolished by the adenylate cyclase inhibitor SQ22536. This is the first evidence that mast cells express functional CRH receptors and that CRH can induce VEGF secretion selectively. CRH-induced mast cell-derived VEGF could, therefore, be involved in chronic inflammatory conditions associated with increased VEGF, such as arthritis or psoriasis, both of which worsen by stress.

Corticotropin-releasing hormone triggers differentiation in HaCaT keratinocytes

BACKGROUND

Corticotropin-releasing hormone (CRH) is proposed to be involved in the regulation of the proliferative capacity of keratinocytes, based on its significant actions in the skin. These are mediated by CRH-R1alpha and represented by adenylate cyclase activation, Ca2+ influx, inhibition of cell proliferation and modifications in intracellular signal transduction by NF-kappaB.

OBJECTIVES

To define CRH action in the cell cycle we investigated its effects on the differentiation programme using the HaCaT keratinocytes model.

METHODS

HaCaT keratinocytes were incubated with CRH in Dulbecco's modified Eagles's medium (containing 1.8 mmol L(-1) calcium) or EpiLife (containing 0.06 mmol L(-1) calcium) medium. Cell proliferation was assessed with the MTT assay. Flow cytometry was used for the measurement of DNA content, cell size and granularity and the expression of cytokeratin 14, cytokeratin 1 and involucrin. The electrophoretic mobility shift assay was used to determine DNA binding activity by AP-1 transcription factor. Expression of cytokeratin 1 was also assessed with immunofluorescence microscopy.

RESULTS

CRH did produce inhibition of proliferation, which was dose-dependent; the shape of the inhibition curve was determined by the media calcium concentration. CRH action was pinpointed at inhibition of the G0/1 to the S phase transition of the cell cycle. CRH also increased AP-1 binding activity, cell granularity, cytokeratin 1 and involucrin expression, and inhibited cytokeratin 14 expression.

CONCLUSIONS

These results are consistent with CRH induction of the keratinocyte differentiation programme. Thus, the overall CRH cutaneous actions connote protective functions for the epidermis, that appear to include the triggering or acceleration of the differentiation programme.

Corticotropin-releasing hormone induces keratinocyte differentiation in the adult human epidermis

Previously we documented that human epidermis exclusively expresses corticotropin releasing hormone receptor 1 (CRH-R1). To define the role of CRH in the epidermis, we investigated its effects on differentiation of normal human adult epidermal keratinocytes. Thus, CRH inhibited proliferation in a dose dependent fashion and significantly decreased Ki-67 antigen expression. This effect was independent of either the presence or the absence of growth factors in the medium. Flow cytometry analysis demonstrated that CRH inhibited the transition from G0/1 to S phase of the cell cycle, which was accompanied by an increased expression of cdk inhibitor p16 (Ink4a) protein. The antiproliferative effect was attenuated by protein kinase C inhibitor (GF109203X) but not by H89 (protein kinase A inhibitor), PD98059, or SB203580 (MAP kinase inhibitors). The cell cycle withdrawal was associated with the induction of keratinocyte differentiation. Thus, CRH stimulated the expression of cytokeratin 1 and involucrin, and inhibited cytokeratin 14 on both mRNA and protein levels. It also increased cell granularity and cell size. Furthermore, CRH induced signal transduction cascade that included stimulation of inositol 1,4,5-triphosphate, which was time and dose dependent. CRH also increased activator protein-1 DNA binding activity with JunD identified as the most important element. Thus, activation of CRH-R1 induces a non-random and sequential signal transduction cascade governing both keratinocyte differentiation and the inhibition of cell proliferation through G0/1 arrest. We propose that this program, triggered by CRH interaction with CRH-R1, includes induction of a transduction pathway involving the sequential activation of phospholipase C, protein kinase C, activator protein-1 (including Jun D), and p16.

Corticotropin-Releasing Hormone (CRH) Downregulates Interleukin-18 Expression in Human HaCaT Keratinocytes by Activation of p38 Mitogen-Activated Protein Kinase (MAPK) Pathway

It is generally accepted that corticotropin-releasing hormone (CRH) acts as the main coordinator of the central response to stress. Stress or an abnormal response to stressors has been found to modify the evolution of skin disorders, including psoriasis and atopic dermatitis. Nevertheless, the specific pathogenic role of stress remains unknown in skin diseases. Interleukin (IL)-18, a member of the IL-1 family, is a key mediator of peripheral inflammation and host defense responses, and is secreted by human keratinocytes. Here, we investigated the regulatory effect of CRH on expression of IL-18 in skin keratinocytes. Exposure of HaCaT cells to CRH resulted in a reduction of IL-18 mRNA transcripts and its production was in a concentration-dependent manner. In order to investigate whether the mitogen-activated protein kinase (MAPK) signaling pathway is involved in the downregulation of IL-18 production, cells were pre-treated with SB203580, an inhibitor of p38 MAPK, prior to the addition of CRH. This pre-treatment blocked the decrease in IL-18 production. In addition, CRH treatment induced rapid phosphorylation of p38 MAPK. SB203580 were able to inhibit CRH-induced p38 MAPK phosphorylation. CRH also inhibited production of IL-18 in human primary keratinocytes. These results suggest that CRH regulates IL-18 production through the MAPK signaling pathway in human keratinocytes.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

Differential expression of a cutaneous corticotropin-releasing hormone system

We completed the mapping of a cutaneous CRH signaling system in two species with widely different determinants of skin functions, humans and mice. In human skin, the CRH receptor (CRH-R) 1 was expressed in all major cellular populations of epidermis, dermis, and subcutis with CRH-R1alpha being the most prevalent isoform. The CRH-R2 gene was expressed solely in hair follicle keratinocytes and papilla fibroblasts, whereas CRH-R2 antigen was localized predominantly in hair follicles, sebaceous and eccrine glands, muscle and blood vessels. In mouse skin, the CRH-R2 gene and protein were widely expressed in all cutaneous compartments and in cultured normal and malignant melanocytes. CRH-binding protein mRNA was present in dermal fibroblasts, melanoma cells, and sc fat of human skin and undetectable in mouse skin. The urocortin II gene was expressed equally in mouse and human skin. Taken together with our previous investigations, the present studies document the preferential expression of CRH-R1 in human skin, which mirrors CRH-R2 expression patterns in human and mouse skin. They are likely reflecting different functional activities of human and mouse skin. The adnexal location of CRH-R2 suggests a role for the receptor in hair growth. The differential interspecies CRH signaling expression pattern probably reflects adaptation to species-specific skin function determinants.

Corticotropin-releasing hormone inhibits nuclear factor-kappaB pathway in human HaCaT keratinocytes

Treatment of human HaCaT keratinocytes with corticotropin-releasing hormone modulates cell proliferation and expression of inflammation markers. In this study we report that corticotropin-releasing hormone also inhibits nuclear factor-kappaB binding and transcriptional activity. Incubating cells in the absence of growth factors increased nuclear factor-kappaB activity; this effect was significantly attenuated by corticotropin-releasing hormone. Specifically, corticotropin-releasing hormone downregulated p50/p50 and p50/p65 dimers of nuclear factor-kappaB, diminished kappaB-driven CAT reporter gene activity and inhibited IkappaB-beta degradation. Moreover, corticotropin-releasing hormone inhibited the trans-cription of the nuclear factor-kappaB responsive genes, interleukin-2 and heat shock protein 90.

Intermittent foot shock stress prolongs the telogen stage in the hair cycle of mice

Stress significantly influences skin diseases and cutaneous functions. Recently, interactions between stress and skin conditions have been studied in animal models using various systemic stressors. Here, we studied the effect of intermittent foot shock stress on the hair cycle of C57BL/6 mice. After a 2-week period of intermittent foot shock stress, we examined the changes in the depilation-synchronized hair cycle macroscopically and histologically and we also measured the plasma levels of corticosterone. We found that foot shock stress prolonged the telogen stage and delayed the subsequent anagen induction in the hair cycle. The distribution patterns of corticotrophin releasing factor or corticotrophin releasing factor receptor positive cells in the skin of stressed or of control mice were identical with those in the ordinal hair cycle. It is noteworthy that corticotrophin releasing factor positive keratinocytes were observed in the telogen follicles of the stressed mice but were negative in the telogen follicles of the non-stressed mice in this study. Plasma corticosterone levels were significantly higher in the stressed group than in the control group. These results suggest that increased levels of plasma corticosterone may be involved in the mechanism underlying the stress-induced delay of the hair cycle.

Alternative splicing of CRH-R1 receptors in human and mouse skin: identification of new variants and their differential expression

We identified four new isoforms of human CRH-R1 (e-h) and three of mouse (mCRH-R1c, e, and f). In all new forms exon 6 was missing. Human CRH-R1e was characterized by the deletion of exons 3 and 4; exon 12 from CRH-R1f; exon 11, 27 base pairs (bp) of exon 10 and 28 bp of exon 12 from CRH-R1g and CRH-R1h by the addition of a cryptic exon. In mouse CRH-R1c exon 3 was spliced out; in mCRH-R1e exons 3 and 4 and in mCRH-R1f exon 11 were spliced from mRNA. CRH-R1 was expressed in all skin specimens in patterns dependent on the cell type, physiological status, and presence of pathology. CRH-R1a, the most prevalent form, was detected in almost all samples. Ultraviolet radiation (UV) changed the splicing pattern and induced or increased expression of CRH-R1a in cultured skin cells. Continuing UV treatment of succeeding generations of cells resulted in a progressive increase in the number of CRH-R1 isoforms, which suggests that receptor heterogeneity might favor cell survival. TPA (phorbol 12-myristate 13-acetate), forskolin, dbcAMP (N6, 2'-O-dibutyryladenosine 3':5'-cyclic monophospate sodium), and IBMX (3-isobutyl-1-methylxanthine) also changed the splicing pattern. We suggest that a polymorphism of CRH-R1 expression is related to anatomic location, skin physiological or pathologic status, specific cell type, and external stress (UV), and that cAMP-dependent pathways and TPA may regulate CRH-R1.

Cutaneous expression of corticotropin-releasing hormone (CRH), urocortin, and CRH receptors

Studies in mammalian skin have shown expression of the genes for corticotropin-releasing hormone (CRH) and the related urocortin peptide, with subsequent production of the respective peptides. Recent molecular and biochemical analyses have further revealed the presence of CRH receptors (CRH-Rs). These CRH-Rs are functional, responding to CRH and urocortin peptides (exogenous or produced locally) through activation of receptor(s)-mediated pathways to modify skin cell phenotype. Thus, when taken together with the previous findings of cutaneous expression of POMC and its receptors, these observations extend the range of regulatory elements of the hypothalamic-pituitary-adrenal axis expressed in mammalian skin. Overall, the cutaneous CRH/POMC expression is highly reactive to common stressors such as immune cytokines, ultraviolet radiation, cutaneous pathology, or even the physiological changes associated with the hair cycle phase. Therefore, similar to its central analog, the local expression and action of CRH/POMC elements appear to be highly organized and entrained, representing general mechanism of cutaneous response to stressful stimuli. In such a CRH/POMC system, the CRH-Rs may be a central element.

Pleiotropic effects of corticotropin releasing hormone on normal human skin keratinocytes

The hypothalamic-pituitary-adrenal (HPA) axis is the major stress response system. Several components of the HPA axis, such as corticotropin-releasing hormone (CRH) and POMC peptides and their receptors are also present in the skin. In earlier studies, we showed that CRH inhibits cellular proliferation of immortalized human keratinocytes. We now examine further the functional activity of the HPA axis in the skin, by characterizing the actions of CRH on normal foreskin keratinocytes. The CRH receptor was detected as CRH-R1 antigen at 47 kDa in the cultured keratinocytes by Western blotting, and immunohistochemistry demonstrated its presence in the epidermal and follicular keratinocytes. CRH is also biologically active in cultured keratinocytes, where it inhibits proliferation and enhances the interferon-gamma-stimulated expression of the hCAM and ICAM-1 adhesion molecules and of the HLA-DR antigen. These effects were concentration-dependent, with maximal activity at CRH 10(-7) M. Thus, in the keratinocyte, the most important cellular component of the epidermis, CRH appears to induce a shift in energy metabolism away from proliferation activity, and toward the enhancement of immunoactivity. Therefore, similar to its central actions, cutaneous CRH may also he involved in the stress response, but at a highly localized level.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.