Attachment and chemotaxis of melanocytes after ultraviolet irradiation in vitro

The effects of UVB irradiance on aberrant epidermal proliferation: Novel insights on how to improve currently available sunscreens

AIMS

Sunscreen use, which prolonged the time required to develop sunburn by reducing the irradiance (mW/cm²) of the UVB radiation, is thought to protect the skin from developing cancers. Recently, in addition to fluence (mJ/cm²), irradiance of the UVB radiation was demonstrated to play an important role leading to photocarcinogenesis of the skin. After equivalent fluence of UVB exposure, enhanced aberrant keratinocyte proliferation contributes significantly to the photocarcinogenic capacity of low irradiance (LI) UVB as compared to its high irradiance (HI) UVB counterpart. However, the mechanism involved remains unclear.

MAIN METHODS

Relevant cell and animal models were employed to investigate the effects of equivalent UVB fluence administered at HI or LI on keratinocyte proliferation. Additionally, the mechanisms involved were also explored.

KEY FINDINGS

We found that at equivalent fluence, LIUVB induces significantly higher reactive oxidative species (ROS) production, cell proliferation, as well as phosphorylated AKT (pAKT) expression in both cell and animal models as compare to its HIUVB counterpart. Pretreating cultured keratinocytes with antioxidant or AKT inhibitor significantly reduced the UVB-induced ROS, cell proliferation, and pAKT expression. Additionally, these pretreatments abrogate the difference between the LI and HIUVB treated keratinocytes. Similar findings were noted using animal model treated with AKT inhibitor.

SIGNIFICANCE

In summary, at equivalent fluence, LIUVB induces significantly more aberrant epidermal proliferation via enhanced ROS and pAKT signaling. Reducing UVB-induced AKT phosphorylation presents a novel strategy to improve the protective capacity of the currently available sunscreens.

Screening of integrins localized on the surface of human epidermal melanocytes

In vivo, melanocytes occupy three-dimensional (3D) space. Nevertheless, most experiments involving melanocytes are performed in a two-dimensional microenvironment, resulting in difficulty obtaining accurate results. Therefore, it is necessary to construct an artificial in vivo-like 3D microenvironment. Here, as a step towards engineering a precisely defined acellular 3D microenvironment supporting the maintenance of human epidermal melanocytes (HEMs), we examined the types of integrin heterodimers that are expressed transcriptionally, translationally, and functionally in HEMs. Real-time PCR and fluorescent immunoassay analyses were used to elucidate the expression of integrin α and β subunit genes at the transcriptional and translational levels, respectively. The functionality of the presumed integrin heterodimers was confirmed using attachment and antibody-inhibition assays. Among the genes encoding 12 integrin subunits (α₁, α₂, α₃, α₄, α₅, α₆, α₇, α_V, β₁, β₃, β₅, and β₈) showing significantly higher transcription levels, proteins translated from the integrin α₂, α₄, α₅, β₁, β₃, and β₅ subunit genes were detected on the surface of HEMs. These HEMs showed significantly increased adhesion to collagen I, fibronectin, laminin, and vitronectin, and functional blockade of the integrin α₂ subunits significantly inhibited adhesion to collagen I, fibronectin, and laminin. In addition, there was no significant inhibition of the adhesion to fibronectin or vitronectin in HEMs with functional blockade of the integrin α₄, α₅, or α_V subunits. These results indicate that the active integrin α₂β₁ heterodimer and the inactive integrin α₄, α₅, α_V, β₃, and β₅ subunits are all localized on the surface of HEMs.

The impact of irradiance on UVB-induced cutaneous immunosuppression: Implications on administering most efficient phototherapy

BACKGROUND

Ultraviolet B (UVB) is commonly used for treating dermatologic conditions. Recently, high irradiance UVB (HIUVB) has been suggested to be more effective for treating skin conditions as compared to its low irradiance (LI) counterpart. The biological impact of UVB radiation emitted at different irradiance on cutaneous immunity remains obscure.

OBJECTIVE

This study aimed to explore the impacts of UVB radiation administered at equivalent fluence (mJ/cm²) but different irradiance (mW/cm²) on cutaneous immune response.

METHODS

Cultured bone marrow derived dendritic cell (BMDC) were treated with equivalent fluence of UVB radiation with HIUVB or LIUVB. The phenotypic and functional alterations of BMDCs were documented. Animal models were used to validate the in vitro results in vivo and explore the mechanisms involved.

RESULTS

After equivalent fluence of UVB radiation, the HIUVB treated BMDC showed significantly lower MHCII and CD86 expressions, reduced capacity to stimulate T cell proliferation, and enhanced activation of aryl hydrocarbon receptor (AhR)-activated genes as compared to control while their LIUVB treated counterpart showed no significant change. Using animal model, the HIUVB induced significantly higher immune suppressive effect in mice as compared to their LIUVB counterpart after equivalent fluence of UVB treatment. The superior immune suppressive effect of HIUVB over LIUVB radiation was not observed when similar experiments were performed using AhR-deficient mice.

CONCLUSION

We propose irradiance played an important role modulating UVB-induced cutaneous immune suppression. Future works on UVB phototherapy, both clinical and research, should incorporate this important parameter into consideration.

Malignant Melanocytic Matricoma: A Report of 2 Cases and Review of the Literature

BACKGROUND

To describe 2 cases of melanocytic matricoma with malignant histological features and systematically review previously reported cases of malignant melanocytic matricoma.

METHODS

Two cases of malignant melanocytic matricoma were identified from the practice of the authors. Additional 3 cases were identified in the literature. The clinical and pathological features of these 5 cases are described.

RESULTS

Malignant melanocytic matricoma occurs predominantly in sun-damaged skin of elderly individuals. The tumor is composed of atypical epithelial cells with brisk mitotic activity showing evidence of matrical keratinization and widespread positivity with beta-catenin. There is an admixed cytologically bland dendritic melanocytic component. To date, local recurrence has occurred in one case, but no cases of disseminated disease or death have been reported.

CONCLUSIONS

Recognition of this rare tumor and separation from a range of diagnostic mimics is important to ensure adequate treatment by local excision and to allow further cases to be identified to better define the biological potential of this lesion.

Influence of stress on extracellular matrix and integrin biology

Dynamic interactions between cells and extracellular matrix (ECM) through integrins influence most cellular functions. Normal cells, but even more, tumor cells are subjected to different forms of stress, including ischemia, radical oxygen species production, starvation, mechanical stress or genotoxic insults due to anti-cancer drugs or irradiation. In these situations, an adaptative cellular response occurs, integrating a complex network of intracellular signaling modules, which, depending on stress intensity, may result to either damage repair followed by complete restitution of cellular functions, or programmed cell death. Because of its implication in oncogenesis and anti-cancer therapy, cellular stress response has been thoroughly investigated. However, most of these studies have been performed in the context of isolated cells without taking into consideration that most cells are part of the tissue within which they interact with ECM through integrin. Few studies have described the influence of stress on cell-to-ECM interaction. However, one can speculate that, in these conditions, cells could functionally interact with protein microenvironment either to create positive interactions to survive (for example by facilitating protective pathways) or negative interaction to die (for example by facilitating detachment). In this review, we summarize the knowledge relative to the influence of different stress modalities on ECM remodeling, integrin expression and/or function modifications, and possible functional consequences, independently from the cellular model as these findings came from a large variety of cells (mesenchymal, endothelial, muscular, epithelial and glandular) and fields of application (cancer, vascular biology and tissue engineering). Most studies support the general notion that non-lethal stress favors ECM stiffness, integrin activation and enhanced survival. This field opens large perspectives not only in tumor biology but also in anti-cancer therapy by targeting one or several steps of the integrin-mediated signaling pathway, including integrin ligation, or activation of integrin-linked enzymes or integrin adaptors.

Low-energy helium-neon laser induces melanocyte proliferation via interaction with type IV collagen: visible light as a therapeutic option for vitiligo

BACKGROUND

The treatment of vitiligo remains a challenge for clinical dermatologists. We have previously shown that the helium-neon laser (He-Ne laser, 632.8 nm) is a therapeutic option for treatment of this depigmentary disorder.

OBJECTIVES

Addressing the intricate interactions between melanocytes, the most important cellular component in the repigmentation scheme of vitiligo, and their innate extracellular matrix collagen type IV, the current study aimed to elucidate the effects of the He-Ne laser on melanocytes.

METHODS

Cultured melanocytes were irradiated with the He-Ne laser. Relevant biological parameters including cell attachment, locomotion and growth were evaluated. In addition, the potentially involved molecular pathways were also determined.

RESULTS

Our results show that in addition to suppressing mobility but increasing attachment to type IV collagen, the He-Ne laser stimulates melanocyte proliferation through enhanced alpha2beta1 integrin expression. The expression of phosphorylated cyclic-AMP response element binding protein (CREB), an important regulator of melanocyte growth, was also upregulated by He-Ne laser treatment. Using a specific mitochondrial uncoupling agent [carbonyl cyanide m-chlorophenyl-hydrazone (CCCP)], the proliferative effect of the He-Ne laser on melanocytes was abolished and suppression of melanocyte growth was noted.

CONCLUSIONS

In summary, we have demonstrated that the He-Ne laser imparts a growth stimulatory effect on functional melanocytes via mitochondria-related pathways and proposed that other minor pathways including DNA damage may also be inflicted by laser treatment on irradiated cells. More importantly, we have completed the repigmentation scheme of vitiligo brought about by He-Ne laser light in vitro and provided a solid theoretical basis regarding how the He-Ne laser induces recovery of vitiligo in vivo.

Semaphorin 7a promotes spreading and dendricity in human melanocytes through beta1-integrins

Described as secreted and membrane-bound proteins important for neural pathfinding, the class of proteins called Semaphorins are expressed in multiple tissue types and are involved in diverse biologic processes. In this study, we describe the function of Semaphorin 7a, a membrane-bound Semaphorin known to stimulate neurite outgrowth, on human melanocytes. We show that Semaphorin 7a is expressed by human keratinocytes and fibroblasts in vitro and in vivo and that melanocytes express Plexin C1, a receptor for Semaphorin 7a. Upregulation of Semaphorin 7a was observed in fibroblasts treated with UV irradiation, a potent stimulus for melanocyte dendricity. Because of the importance of melanocyte dendrites in cutaneous photoprotection, we performed functional studies examining the effect of Semaphorin 7a in melanocyte dendrite formation. We also examined the contribution of beta1-integrin and Plexin C1 receptor signaling in mediating effects of Semaphorin 7a in melanocytes. We show that Semaphorin 7a induces significant melanocyte spreading and dendricity in human melanocytes. Furthermore, we show that beta1-integrins and Plexin C1 receptors are ligands for Semaphorin 7a, and that signaling by these receptors has opposing effects on Semaphorin 7a-induced dendrite formation.

Low-energy helium-neon laser induces locomotion of the immature melanoblasts and promotes melanogenesis of the more differentiated melanoblasts: recapitulation of vitiligo repigmentation in vitro

Helium-neon laser (He-Ne Laser, 632.8 nm) is a low-energy laser that has therapeutic efficacy on various clinical conditions. Our previous study has demonstrated efficacy of He-Ne laser on vitiligo, a disease characterized by skin depigmentation. To regain skin tone on vitiligo lesions, the process began by the migration of the immature melanoblasts (MBs) to the epidermis, which was followed by their functional development to produce melanin. In this study, we investigated the physiologic effects of He-Ne laser irradiation on two MB cell lines: the immature NCCmelb4 and the more differentiated NCCmelan5. The intricate interactions between MBs with their innate extracelluar matrix, fibronectin, were also addressed. Our results showed that He-Ne laser irradiation enhanced NCCmelb4 mobility via enhanced phosphorylated focal adhesion kinase expression and promoted melanogenesis in NCCmelan5. In addition, He-Ne laser decreased the affinity between NCCmelb4 and fibronectin, whereas the attachment of NCCmelan5 to fibronectin increased. The alpha5beta1 integrin expression on NCCmelb4 cells was enhanced by He-Ne laser. In conclusion, we have demonstrated that He-Ne laser induced different physiologic changes on MBs at different maturation stages and recapitulated the early events during vitiligo repigmentation process brought upon by He-Ne laser in vitro.

[Factors influencing the microscopic appearance of melanocytic nevi]

Both clinicians and dermatopathologists must be aware of the various factors which can influence the histopathologic appearance of melanocytic nevi in order to avoid mistaken diagnoses.

Ultraviolet A exposure alters adhesive properties of mouse melanoma cells

BACKGROUND

We have examined whether ultraviolet A (UVA) irradiation could alter adhesive properties of melanoma cells. As an experimental in vitro model, we have used C57BL/6 mouse-derived B16- F1 and B16-F10 melanoma cell lines and the syngeneic MS-1 endothelial cell line.

METHOD/RESULT

The melanoma cells were exposed to different doses of UVA irradiation. We have determined that a single dose of UVA at 8 and 12 J/cm(2) causes an 88% (P<0.001) and a 32% (P<0.05) increase in B16-F1 melanoma cell adhesiveness to the non-irradiated endothelial monolayer, respectively. The peak of the response was 24 h after the irradiation. The UVA dose of 8 J/cm(2) delivered in four doses separated by 1 h intervals (4 x 2 J/cm(2)) had led to a caused 149% (P<0.001) increase of B16-F1 melanoma adhesiveness already at 1 h after the last dose of UVA. Besides the induction of increase in the melanoma-endothelial cell adhesion, UVA exposure has induced a rapid decline (1 h after exposure) in homotypic melanoma-melanoma cell adhesion (clustering). The clustering decline of B16-F1 cells with a single dose of UVA at 8 J/cm(2) was by 61% (P<0.05) and by 35% (P<0.05) with 4 x 2 J/cm(2). Pilot experiments have shown that the changes of the adhesive properties of melanoma cells were accompanied by an increase in N-cadherin expression and a decline in E-cadherin expression. Such a change in cadherin expression profile has been shown to be an indicator of the increased metastatic potential.

CONCLUSION

Our results suggest that UVA radiation appears to alter the adhesive properties of melanoma cells in vitro, by diminishing the melanoma-melanoma adhesion and by increasing melanoma adhesion to the endothelium. This suggests that UVA exposure might increase the metastatic capability of the melanoma cells.

Pigmentation in basal cell carcinoma involves enhanced endothelin-1 expression

Basal cell carcinoma (BCC) is the most prevalent malignant skin tumor. In Asian patients, marked pigmentation in BCC lesions is often observed. Recently, endothelins (ETs) have been implicated to participate in the pigmentation process of BCC. Therefore, we set out to investigate the involvement of ET in the pigmentation process of BCC and the potential regulators in the pigmentation pathway. We explored the effects of an established BCC cell line on melanocytes. The growth factor profiles of BCC culture supernatant and effects of supernatant on melanocytes were documented. Potential regulators involved in the pigmentation pathway were also studied. The immunohistochemical staining of pigmented and non-pigmented BCC specimens was performed to confirm our in vitro findings. Our results showed that BCC supernatant contained significant amount of ET-1, basic fibroblast growth factor, and nerve growth factor. Furthermore, BCC supernatant stimulated melanin formation of cultured melanocytes. Addition of ET-receptor antagonist abrogated the melanogenic effect of BCC supernatant on melanocytes. Introduction of UVB irradiation decreased the ET-1 secretion by BCC cells. Immunohistochemical staining of the pigmented facial BCC specimens showed prominent expression of ET-1 on pigmented BCC, while the non-pigmented facial BCC specimens showed little ET-1 reactivity. Tumor necrosis factor-alpha (TNF-alpha) staining showed little expression on BCC specimens, regardless of pigmentation status. In summary, our results indicate that enhanced ET-1 expression in pigmented BCC plays an important role in the hyperpigmentation of this tumor. Moreover, this enhanced ET-1 cascade showed little correlation with UV irradiation and TNF-alpha expression in our study.

Selective down-regulation of the alpha6-integrin subunit in melanocytes by UVB light

In vivo, melanocytes bind to laminin (LM) molecules of the basement membrane (BM) via the integrins alpha3beta1 and alpha6beta1, and they adhere to neighbouring keratinocytes via E-cadherin. Only few studies have addressed the impact of ultraviolet (UV) light on the interaction of melanocytes with their microenvironment. In this report, we examined the influence of UVB irradiation on the expression of the most important melanocyte-adhesion molecules (E-, N-cadherin, alpha2-, alpha3-, alpha5-, alpha6-, alphaV-, beta1-, beta3-integrins and ICAM-1) in vitro by flow cytometry. We were able to demonstrate that the alpha6-integrin subunit is selectively and reversibly down-regulated by UVB in a dwzm 150ose-dependent manner. In comparison, keratinocytes lacked UVB-inducible alterations in the expression of alpha6-integrin. In the presence of LM-1, the UVB-induced down-regulation of alpha6-integrin in melanocytes was significantly reduced. Moreover, LM-1 increased the resistance of melanocytes to UVB-induced cell death, as measured by annexinV-binding analysis. This effect was reversed by preincubation with an alpha6-integrin-blocking antibody. By immunofluorescence, we could demonstrate that UVB leads to a dose-dependent internalization of alpha6-integrin, providing an obvious explanation for the down-regulation on the outer cell surface observed by flow cytometry. We suggest that adhesion to LM-1 through alpha6-integrin represents a protective mechanism for melanocytes to withstand UVB damage. Through alpha6-integrin internalization, sunburns might alter the interaction between melanocytes and the BM, resulting in apoptosis induced by loss of anchorage (anoikis). Repeated sunburns may then lead to the selection of a population of melanocytes which are capable of anchorage-independent survival, culminating in solar nevogenesis and melanoma development.

Narrow-band ultraviolet-B stimulates proliferation and migration of cultured melanocytes

Narrow-band ultraviolet-B (UVB) radiation is an effective treatment for vitiligo vulgaris. However, the mechanisms of narrow-band UVB in inducing repigmentation of vitiligo lesions are not thoroughly clarified. The purpose of our study was to investigate the effects of narrow-band UVB irradiation on melanocyte proliferation and migration in vitro. Our results showed that the cell counts as well as [3H]thymidine uptake of melanocytes were significantly enhanced by narrow-band UVB-irradiated keratinocyte supernatants. In these supernatants, a significant increase in basic fibroblast growth factor (bFGF) and in endothelin-1 (ET-1) release was observed. bFGF is a natural mitogen for melanocytes, whereas ET-1 can stimulate DNA synthesis in melanocytes. This stimulatory effect of melanocyte proliferation by supernatants derived from narrow-band UVB-irradiated keratinocytes was significantly reduced by a selective endothelin-B (ET-B) receptor antagonist (BQ788), suggesting an essential role of ET-1 on melanocyte proliferation. Our results of time-lapse microphotography revealed a stimulatory effect of narrow-band UVB irradiation on melanocyte migration. Focal adhesion kinase (FAK) plays a pivotal role in cell migration. Phosphorylated FAK (p125(FAK)) expression on melanocyte was enhanced by narrow-band UVB irradiation. In this study, narrow-band UVB irradiation stimulated a significant increase in matrix metalloproteinase-2 (MMP-2) activity in melanocyte supernatants. Narrow-band UVB-irradiation-induced migration of melanocytes was significantly annihilated by the addition of p125(FAK) inhibitor (herbimycin-A) or MMP-2 inhibitor (GM6001). These results suggest that p125(FAK) and MMP-2 activity play important roles in narrow-band UVB-induced migration of melanocytes. Our results provide a theoretical basis for the effectiveness of narrow-band UVB irradiation in treating vitiligo.

Neutrophils influence melanoma adhesion and migration under flow conditions

We have studied human melanoma cell (C8161) adhesion and migration in response to stimulation by soluble collagen IV (CIV) using a modified Boyden chamber. In this modified chamber, shear flow can be introduced over the cell-substrate interface, affecting tumor cell chemotactic migration through a microporous filter. A relatively high level of intercellular adhesion molecule-1 (ICAM-1) was found on C8161 cells. In contrast, levels of beta(2)-integrins (e.g., LFA-1 and Mac-1), the molecules that would be necessary for C8161 stable adhesion to the endothelium substrate, were found to be very low on these melanoma cells. As a result, C8161 transendothelial migration under a flow condition of 4 dyn/cm(2) decreased by 70% as compared to static migration. When human neutrophils (PMNs) were present in the tumor cell suspension, C8161 migration recovered by 85% over C8161 cells alone under the 4 dyn/cm(2) flow condition. Blocking ICAM-1 on C8161 cells or Mac-1 on PMNs significantly inhibited C8161-PMN adhesion and subsequent C8161 migration through the endothelium under flow conditions. In addition, increased interleukin-8 production and Mac-1 expression by PMNs were detected when they were co-cultured with C8161 melanoma cells. These results suggest that transmigration of C8161 cells under flow conditions can be influenced by PMNs, mediated by Mac-1/ICAM-1 adhesive interactions and enhanced by altered cytokine production.

Melanocyte detachment after skin friction in non lesional skin of patients with generalized vitiligo

BACKGROUND

In vitiligo, melanocytes are gradually lost in depigmented macules of the skin. The disappearance of melanocytes has, however, not been clearly observed and consequently the aetiology of the disease (autoimmune, neural, cytotoxic) is still elusive. The starting point of vitiligo macules is frequently determined by local conditions such as wounds and excoriations, but may also follow minor traumas such as pressure or repeated friction. This prominent feature is often neglected.

OBJECTIVES

To clarify the biological consequences of repeated friction on the attachment and survival of melanocytes in non lesional vitiligo skin.

METHODS

Light reproducible skin friction was performed for 4 min on the volar forearm of 18 patients with extensive vitiligo and five controls with normal healthy skin. Biopsies from the test area and control skin were taken at 1, 4, 24 and 48 h following friction. Serial sections were examined with standard light microscopy, transmission electron microscopy, histochemistry and immunohistochemistry (dihydroxyphenylalanine, HMB-45, E-cadherin and an early apoptosis marker, M30 cytoDEATH antibody).

RESULTS

The observation of sections at 1 and 48 h after friction on vitiligo skin and at all time points in controls revealed no changes. In contrast, in vitiligo skin at 4 and 24 h after friction, several melanocytes had undergone detachment and were found in various suprabasal positions, including the stratum spinosum, granular layer, and within and outside the stratum corneum.

CONCLUSIONS

Detachment and transepidermal elimination of melanocytes following minor mechanical trauma in non lesional vitiligo skin is probably the cause of depigmentation occurring in the isomorphic response (Koebner phenomenon). We propose that transepidermal elimination of melanocytes in vitiligo should be regarded as a possible mechanism of chronic loss of pigment cells, perhaps previously damaged by another process.

A tumor with composite pilo-folliculosebaceous differentiation harboring a recently described new entity--melanocytic matricoma

We report on a case of a peculiar tumor of the pilosebaceous unit showing a composite histologic appearance. The case presented as a pigmented crusted lesion on the back of the nose of a 62-year-old woman with markedly sun-damaged skin. Histologically, the superficial portion of the neoplasm was composed of buds and nests of basaloid epithelium with varying degrees of pilar and sebaceous differentiation. Adjacent to this component, lobules of squamous cells with cytoplasmic glycogenation suggesting the mature outer root sheath were seen. In the underlying dermis, there was a well-defined nodular proliferation composed of variably pigmented basaloid matrical cells forming clusters of "shadow" or "ghost cells" admixed with numerous melanized dendritic melanocytes; this last component of the neoplasm was identical to a recently described entity, melanocytic matricoma. The small size, circumscription, and absence of necrosis favored benignity, although the cytologic atypia of matrical cells did not exclude malignancy. The case is interesting not only because it is the third reported case of a peculiar neoplasm imitating the epithelial-melanocytic interaction in the embryonal hair follicle or bulb of the anagen follicle but because the part resembling melanocytic matricoma presented as a component of a complex lesion. We believe that sunlight may have played a role in the development of this peculiar neoplasm.

MMP-2, TIMP-2 and MT1-MMP are differentially expressed in lesional skin of melanocytic nevi and their expression is modulated by UVB-light

BACKGROUND

In malignant melanoma, recent studies have demonstrated an important role of matrix-metalloproteinase 2 (MMP-2), its co-activating enzyme membrane-type matrix-metalloproteinase 1 (MT1-MMP), and the endogenous inhibitor of MMP-2, tissue-inhibitor of matrix metalloproteinase 2 (TIMP-2). Melanocytic nevi are benign neoplasms of the melanocytic lineage, but may exhibit dysplastic features that can be difficult to distinguish from early stage melanoma. As shown in earlier studies, nevi show important morphological and phenotypical changes in response to ultraviolet light (UVB) irradiation.

OBJECTIVE

To clarify the role of MMP-2, TIMP-2 and MT1-MMP in UVB-irradiated vs. non-irradiated melanocytic nevi.

METHODS

Immunohistochemical comparison of the MMP-2, TIMP-2 and MT1-MMP expression pattern.

RESULTS

MMP-2 is expressed by lesional keratinocytes and its expression is up-regulated by UVB-irradiation. MMP-2 expression was not observed in melanocytic cells. TIMP-2, by contrast, is predominantly expressed by melanocytic nevus cells, and its expression is in part down-regulated by UVB-irradiation. MT1-MMP is expressed by basal keratinocytes and to a weaker extent by melanocytic nevus cells.

CONCLUSIONS

MMP-2 expression by keratinocytes in nevi probably represents the result of activation of keratinocyte turnover in lesional epidermis. MMP-2 could play a role in the downward movement of junctional nevus cells into the dermis. The reduction of TIMP-2 expression in melanocytic cells by UV-light together with the enhanced expression of MMP-2 in the adjacent epidermis may promote basement membrane degradation. The expression pattern of MT1-MMP in close proximity to epithelial-mesenchymal interfaces underlines the synergistic role of MT1-MMP in this process.