Protein kinase C alpha associates with phospholipase D1 and enhances basal phospholipase D activity in a protein phosphorylation-independent manner in human melanoma cells

It is well known that phospholipase D plays a crucial part in the signal transduction of many types of cells, and is activated by protein kinase C alpha when cells are stimulated. To elucidate the role of phospholipase D in melanoma, the expression of phospholipase D1 and protein kinase C alpha in primary and metastatic lesions of acral lentiginous melanoma and superficial spreading melanoma was investigated using immunohistologic techniques. In addition, the mechanism of regulation of phospholipase D1 by protein kinase C alpha was examined in a human melanoma cell line HM3KO using an adenovirus-mediated gene transfer technique. Both phospholipase D1 and protein kinase C alpha were strongly expressed in primary and metastatic lesions of superficial spreading melanoma. Conversely, in acral lentiginous melanoma lesions, the expression of these two proteins increased dramatically with tumor progression; the expression of both phospholipase D1 and protein kinase C alpha was almost negative in the radial growth phase of primary acral lentiginous melanoma lesions, and increased synchronously in a progression-related manner in advanced acral lentiginous melanoma lesions, including vertical growth phase and metastatic lesions. Immunoprecipitation study showed that phospholipase D1 and protein kinase C alpha are associated physiologically in resting melanoma cells. Further immunoprecipitation study using HM3KO cells after adenovirus-mediated simultaneous overexpression of phospholipase D1 and protein kinase C alpha, or phospholipase D1 and the kinase-negative mutant of protein kinase C alpha revealed that both protein kinase C alpha and the kinase-negative mutant of protein kinase C alpha are associated with phospholipase D1 in melanoma cells in the absence of an external signal. Overexpression of protein kinase C alpha or the kinase-negative mutant of protein kinase C alpha in melanoma cells by the adenovirus vectors resulted in the enhancement of basal phospholipase D activity in a viral concentration-dependent manner. Furthermore, enhanced basal phospholipase D activity increased the in vitro invasive potential of HM3KO cells. These results suggest that upregulation of phospholipase D1 and protein kinase C alpha plays a part in the progression of acral lentiginous melanoma from the radial growth phase to the vertical growth phase. The present results also suggest that protein kinase C alpha associates with phospholipase D1 and enhances basal phospholipase D activity in a protein phosphorylation-independent manner in melanoma cells, which contributes to the cell's high invasive potential.     

Protein kinase C-betaII represses hepatocyte growth factor-induced invasion by preventing the association of adapter protein Gab1 and phosphatidylinositol 3-kinase in melanoma cells

The hepatocyte growth factor (HGF) signaling pathway was examined in human normal melanocytes and three malignant melanoma cell lines. HGF-induced activation of c-Met, its receptor-tyrosine kinase, was observed in both melanocytes and melanoma cells, whereas phosphatidylinositol 3-kinase (PI3K), a downstream target of c-Met, was not activated in the melanocytes but enhanced in the melanoma cell lines. The electrophoretic mobility of Gab1, the scaffolding adapter protein that couples activated c-Met and PI3K, was slower in the melanocytes than that in the melanoma cells, and the mobility shifted to that of the melanoma cells after treatment with alkaline phosphatase, indicating that Gab1 is highly phosphorylated on serine and threonine in the melanocytes. Introduction of protein kinase C (PKC)-betaII into the melanoma cells, which is expressed in melanocytes but absent in melanoma cells, resulted in serine and threonine phosphorylation of Gab1 and also prevented tyrosine phosphorylation of Gab1 and its association with PI3K. Furthermore, the introduction of PKC-betaII suppressed HGF-induced activation of PI3K, and attenuated the in vitro invasion activity of the melanoma cells. These results indicate that the HGF signaling process from Gab1 to PI3K is negatively regulated by PKC-betaII, and its loss is critical for melanoma cells to gain invasive potential.     

Interleukin (IL)-6 modulates transforming growth factor-β expression in skin and dermal fibroblasts from IL-6-deficient mice

Background Interleukin (IL‐6) and transforming growth factor (TGF)‐β have been shown to play a role in skin development and maintenance. Objectives A link between these two cytokines has yet to be identified and therefore in this study we investigated the modulation of TGF‐β1 and TGF‐β type 2 receptor (TGF‐βR2) by IL‐6 in skin. Methods An IL‐6 knockout (IL‐6KO) fibroblast‐populated lattice model and intradermal injections of IL‐6 into unwounded IL‐6KO mice were used to investigate the direct effects of IL‐6 treatment on TGF‐β and TGF‐βR2 expression and to determine the signalling mechanism. In addition, IL‐6KO and C57BL/6 control mice were wounded by a 4‐mm punch biopsy to monitor expression of TGF‐β1 and TGF‐βR2 within a wound over time. The expression of TGF‐β1 and TGF‐βR2 was assessed by real‐time quantitative polymerase chain reaction, enzyme‐linked immunosorbent assay and immunohistology. Results Recombinant IL‐6 treatment of IL‐6KO lattices and intradermal injections of IL‐6 showed a significant induction of TGF‐β1 mRNA and protein, with TGF‐β1 expression localized in the dermis, while TGF‐βR2 expression was primarily in the epidermis in IL‐6KO mice. During healing, the expression of TGF‐β1 and TGF‐βR2 mRNA was significantly greater in unwounded and 7‐day‐old wounds from wild‐type mice; however, protein expression did not differ. Treatment with signal transduction inhibitors indicated that IL‐6 modulates TGF‐β through a mitogen‐activated protein kinase/extracellular signal‐regulated kinase (Mapk/Erk)‐dependent mechanism. Conclusion These studies indicate that IL‐6 has the ability to modulate the expression of TGF‐β and TGF‐βR2 to varying degrees in the skin, which may provide a possible mechanism for defining the role of IL‐6 in skin maintenance and a new association of IL‐6 with TGF‐β in pathologies associated with fibrosis.     

Accelerated proliferation of epidermal keratinocytes by the transgenic expression of the platelet-activating factor receptor

Abstract Transgenic mice overexpressing platelet-activating factor receptor (PAFR) have abnormal pigmentation of the ear and the tail, which can progress to melanocytic tumors as the mice age. Histologically, epidermal hyperproliferation and increases in dermal melanocytes are evident. Examination of these transgenic mice at various ages revealed hyperproliferation of the epidermis even 2 weeks after birth which developed as the mice aged. Dermal melanocytes also increased in number with growth. Expression of the PAFR transgene was found in keratinocytes and not in melanocytes, thereby suggesting that PAF does not play a direct role in proliferation of melanocytes. Topical application of a cream containing WEB2086, a specific PAFR antagonist, to the ear and the dorsal skin significantly suppressed the number of BrdU-positive cells in PAFR transgenic mice. These results suggest that PAF plays a modulatory role in the growth of epidermal keratinocytes. PAFR transgenic mice would be a useful model for investigations of skin diseases related to altered proliferation of epidermal keratinocytes including psoriasis. Received: 26 April 1999 / Received after revision: 5 July 1999 / Accepted: 9 July 1999     

Plexin C1, a receptor for semaphorin 7a, inactivates cofilin and is a potential tumor suppressor for melanoma progression

Melanocytes are progenitor cells for melanoma, which arises through step-wise progression from dysplastic to invasive, to metastatic tumor. Our previous data showed that semaphorin 7A (Sema7A), a protein involved in axon guidance, stimulates melanocyte adhesion and dendricity through opposing actions of beta1-integrin and Plexin C1 receptors. We now show that Plexin C1 is diminished or absent in human melanoma cell lines; analysis of tissue microarrays of nevi, melanoma, and metastatic melanoma showed a decrease in Plexin C1 expression in metastatic melanoma, and an inverse correlation of Plexin C1 expression with depth of invasion. We examined the signaling intermediates of Sema7A and downstream targets of Plexin C1 in human melanocytes. Sema7A activated mitogen-activated protein kinase and inactivated cofilin, an actin-binding protein involved in cell migration. When Plexin C1 expression was silenced, Sema7A failed to phosphorylate cofilin, indicating that cofilin is downstream of Plexin C1. Further, Lim kinase II, a protein that phosphorylates cofilin, is upregulated by Sema7A in a Plexin C1-dependent manner. These data identify Plexin C1 as a potential tumor suppressor protein in melanoma progression, and suggest that loss of Plexin C1 expression may promote melanoma invasion and metastasis through loss of inhibitory signaling on cofilin activation.     

Melanoma therapy: Check the checkpoints

Recent mutational and translational studies have revealed that the Ras/Raf/mitogen‐activated protein kinase kinase (MEK)/extracellular signal‐regulated kinase (ERK) pathway plays a key role in melanomagenesis. Mutations in NRAS and BRAF are found in the majority of melanomas resulting in the formation of constitutively active NRAS and BRAF molecules, which leads to the proliferation and survival of melanoma cells through the activation of MEK/ERK signals. Inhibitors of BRAF or MEK significantly extend the progression‐free survival and overall survival of melanoma patients compared with conventional chemotherapies. Combining BRAF and MEK inhibitors further enhances the clinical effectiveness. Cytotoxic T‐lymphocyte‐associated antigen 4 (CTLA‐4) is an immune checkpoint molecule that downregulates T‐cell activation by binding to B7 (CD80/CD86) molecules on antigen‐presenting cells. Programmed death receptor ligand 1 on melanoma cells negatively regulates T‐cell function by binding to the programmed death‐1 (PD‐1) receptor on T cells. Antibodies against CTLA‐4 and PD‐1 also enhance the survival of melanoma patients. In this review, we summarize the clinical effectiveness and adverse events of the BRAF inhibitors, MEK inhibitors and anti‐immune checkpoint antibodies in melanoma treatment.     

Role of zyxin in differential cell spreading and proliferation of melanoma cells and melanocytes

Cell spreading, proliferation, and survival are modulated by focal adhesions linking extracellular matrix proteins, integrins, and the cytoskeleton. Zyxin is a focal-adhesion-associated phosphoprotein with one domain involved in the control of actin assembly and three protein-protein adapter domains implicated in the regulation of cell growth and differentiation. We characterized zyxin expression in normal human melanocytes and six melanoma cell lines in relation to cell spreading, growth, and differentiation using Western immunoblotting techniques, image analysis, flow cytometry, and confocal microscopy. We found that zyxin, focal adhesion kinase, and paxillin were significantly upregulated in melanoma cells compared to melanocytes. Zyxin expression directly related to cell spreading and proliferation and inversely related to differentiation, whereas focal adhesion kinase correlated only to cell spreading and paxillin did not significantly correlate with any of the parameters. Treatment of melanoma cells with 12-O-tetradecanoylphorbol-13-acetate downregulated zyxin expression, inhibited cell spreading and proliferation, and promoted differentiation. In contrast, 12-O-tetradecanoylphorbol-13-acetate, a mitogen for melanocytes, induced upregulation of zyxin expression in melanocytes. These findings are consistent with a role of zyxin in modulation of cell spreading, proliferation, and differentiation. Therapies directed at the downregulation of this focal adhesion phosphoprotein in melanoma cells implicate a new approach for controlling melanoma cell growth.     

Leukotriene B4-induced human melanocyte pigmentation and leukotriene C4-induced human melanocyte growth are inhibited by different isoquinolinesulfonamides.

Leukotriene C4 (LTC4) is known to be a potent mitogen for cultured human neonatal melanocytes. We now demonstrate that leukotriene B4 (LTB4) can induce pigmentation in cultured human neonatal melanocytes in a dose-dependent fashion. The LTC4-induced mitogenesis is blocked by the cyclic nucleotide-dependent kinase inhibitor N-[2-(methyl-amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H8). The LTB4-induced pigmentation is blocked by the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7). We propose that LTB4-induced pigmentation and LTC4-induced mitogenesis are important in vivo signals. Their different effects in our culture system are blocked by different protein kinase inhibitors.     

Blocking glutamate‐mediated signalling inhibits human melanoma growth and migration

Glutamate is an excitatory neurotransmitter that has been shown to regulate the proliferation, migration and survival of neuronal progenitors in the central nervous system through its action on metabotropic and ionotropic glutamate receptors (GluRs). Antagonists of ionotropic GluRs have been shown to cause a rapid and reversible change in melanocyte dendritic morphology, which is associated with the disorganization of actin and tubulin microfilaments in the cytoskeleton. Intracellular expression of microtubule‐associated protein (MAP) 2a affects the assembly, stabilization and bundling of microtubules in melanoma cells; stimulates the development of dendrites; and suppresses melanoma cell migration and invasion. In this study, we investigated the relationship between glutamate‐mediated signalling and microtubules, cell dendritic morphology and melanoma cell motility. We found that metabotropic GluR1 and N‐methyl‐d ‐aspartate receptor antagonists increased dendritic branching and inhibited the motility, migration and proliferation of melanoma cells. We also demonstrated that the invasion and motility of melanoma cells are significantly inhibited by the combination of increased expression of MAP2a and either metabotropic GluR1 or N‐methyl‐d ‐aspartate receptor antagonists. Moreover, the blockade of glutamate receptors inhibited melanoma growth in vivo. Collectively, these results demonstrate the importance of glutamate signalling in human melanoma and suggest that the blockade of glutamate receptors is a promising novel therapy for treating melanoma.     

FGF-2 blocks TGF-beta1-mediated suppression of Bcl-2 in normal melanocytes

Normal melanocytes require growth support provided by the adjacent basement membrane. In contrast, nevus cells and melanoma cells survive in the dermis, and in vitro on a soft collagen gel. Transforming growth factor-beta1 (TGF-beta1) produced by melanocytes themselves induces apoptosis in normal melanocytes cultured on collagen gel, an effect that can be counteracted by fibroblast growth factor-2 (FGF-2). The purpose of this study was to investigate the mechanisms by which FGF-2 counteracts the apoptotic signals from TGF-beta1 in melanocytes cultured on collagen gel. We report that FGF-2 did not interfere with the signal transduction from the TGF-beta1 receptors to SMAD2/3 proteins. Instead, TGF-beta1 decreased the level of Bcl-2 in normal melanocytes cultured on collagen gel, and FGF-2 reversed the TGF-beta1-mediated reduction in the level of Bcl-2. In nevus and melanoma cells, TGF-beta1 was unable to induce a decrease in the level of Bcl-2, and treatment with FGF-2 did not cause an increase in the level of Bcl-2 in nevus or melanoma cells. In conclusion, our results suggest that a reduction in the level of the anti-apoptotic Bcl-2 is involved in the execution of apoptosis induced by TGF-beta1 in normal melanocytes cultured on collagen gel and that FGF-2 can prevent TGF-beta1 from causing this reduction.     

Oncogenic BRAF signalling increases Mcl‐1 expression in cutaneous metastatic melanoma

The Bcl‐2 family member Mcl‐1 is essential for melanoma survival; however, the influence of oncogenic BRAF signalling remains elusive. In this study, Mcl‐1 splice variant expression was determined in a panel of melanoma cell lines in relation to BRAF mutational status. Mcl‐1L mRNA expression was increased in melanoma cells compared with primary melanocytes with significantly increased mRNA and protein expression observed in BRAF^V600E mutant melanoma cells. Although no change in Mcl‐1S mRNA was observed, Mcl‐1S protein expression also increased in BRAF mutant melanoma cells. Additionally, while over‐expression of mutant BRAF^V600E increased both Mcl‐1L and Mcl‐1S expression, inhibition of hyperactive BRAF signalling resulted in decreased Mcl‐1L expression. These studies suggest that the regulation of Mcl‐1 expression by BRAF signalling is increased by oncogenic activation of BRAF, revealing a mechanism of apoptotic resistance which may be overcome by the use of more specifically targeted Mcl‐1 inhibitors.     

黑素瘤细胞及表皮黑素细胞中酪氨酸激酶c-abl,c-kit和PDGFRα/β的表达

目的观察酪氨酸激酶在多株黑素瘤细胞系及原代表皮黑素细胞中的表达,探讨酪氨酸激酶在黑素瘤发生发展过程中的作用。方法分离并培养人原代表皮黑素细胞,培养浅表垂直生长期黑素瘤细胞株WM793B,转移性黑素瘤细胞株A2058,WM-266-4,Hs294T,SK-MEL-5和SK-MEL-1,用RT-PCR法分别检测7株细胞中酪氨酸激酶c-abl,c-kit和PDGFRα/βmRNA的表达;Western-blot法检测7组细胞中非受体性酪氨酸激酶c-abl蛋白水平的表达。结果与表皮黑素细胞和WM793B细胞相比,5株转移性黑素瘤细胞中的c-ablmRNA及其蛋白水平的表达偏高;而PDGFRα/βmRNA表达明显偏低、c-kitmR-NA在表皮黑素细胞,A2058,WM-266-4和Hs294T中mRNA表达较高,而在WM793B,SK-MEL-5和SK-MEL-1中偏弱。结论酪氨酸激酶c-abl对黑素瘤的发生发展可能有促进作用,而PDGFRα/βmRNA的低表达可能与黑素瘤的转移有关。     

FGF expression allows nevus cells to survive in three-dimensional collagen gel under conditions that induce apoptosis in normal human melanocytes.

Melanocytes, the pigment forming cells of the skin, form an almost nonproliferating cell population located to the lowermost part of the epidermis. Normally melanocytes are not found higher in the epidermis or in the dermis. Nevi consist of melanocytes with altered growth characteristics and localization. The common pigmented nevus, a benign skin lesion, develops when melanocytes proliferate in the dermo-epidermal junction or in the dermis. Here we report growth characteristics of in vitro cultured normal human melanocytes and dermal nevus-derived melanocytes. As previously reported, nevus cells have a moderate to high FGF-2 expression level. Here we demonstrate that dermal nevus cells are able to survive in three-dimensional type 1 collagen culture, while normal human melanocytes rapidly undergo apoptosis. Melanocytes also, however, survive in collagen cultures in the presence of exogenous FGF-2. The survival of nevus cells in collagen is suppressed by protamine, an inhibitor of FGF-mediated cell stimulation. The in vivo growth environment of dermal nevus cells consists largely of type I and type III collagens. The results suggest that FGF-2 expression by nevus cells allows them to adapt to grow in the dermis. FGF-2 obviously has importance as a melanocyte survival factor and probably also in the development of malignant melanoma.     

Vemurafenib‐induced interface dermatitis manifesting as radiation‐recall and a keratosis pilaris‐like eruption

Vemurafenib is a specific inhibitor of the V600E mutated BRAF protein kinase used for the treatment of unresectable or metastatic melanoma harboring this mutation. Multiple predictable side effects have been described with use of this targeted therapy, and implicate BRAF and mitogen activated protein kinase (MAPK) signaling pathways in their pathogenesis. Herein, we report the novel finding of an interface dermatitis in radiation recall and a keratosis pilaris‐like clinical reaction in a patient treated with vemurafenib.     

Congenital nevi versus metastatic melanoma in a newborn to a mother with malignant melanoma – diagnosis supported by sex chromosome analysis and Imaging Mass Spectrometry

A 37‐year‐old pregnant woman presented with a 2‐cm irregular reddish nodule on her left upper arm during pregnancy. A biopsy from the lesion showed a 2.2‐mm thick malignant melanoma with intravascular invasion, 25 mitosis/mm² and no ulceration. Following induction of labor, the patient underwent re‐excision with sentinel lymph node biopsy. This showed no residual melanoma and no lymph node metastasis. The newborn boy had multiple pigmented lesions on the trunk, some of which were large and irregular. Two were biopsied and histologic examination showed dense dermal proliferation of medium sized melanocytes with multiple mitotic figures and no maturation with their descent into the dermis, raising suspicion of transplacental metastases. Examination of the placenta failed to show metastatic lesions. Multiplex polymerase chain reaction (PCR)‐based genotyping, including testing for amelogenin locus for sex chromosome determination, demonstrated the presence of Y chromosome material in the melanocytes of the newborn's lesions excluding maternal origin. A diagnosis of congenital nevi was rendered. Subsequently, Imaging Mass Spectrometric analysis of the mother's lesion showed proteomic signature expression indicative of malignant melanoma, whereas the two lesions in the newborn showed changes indicative of nevi. This case demonstrates the utility of genotyping and Mass Spectrometry analysis in this challenging clinical scenario     

Small‐animal PET imaging analysis with [18F]FHBG in a mouse model of HSV1‐tk gene expression in melanoma

The purpose of this study was to establish a small‐animal model for molecular imaging and to acquire basic data on assessing the efficacy of candidate melanoma drugs using small‐animal PET imaging analysis with [¹⁸F]FHBG for herpes simplex virus 1‐thymidine kinase (HSV1‐tk) gene expression in a melanoma mouse model. The B16 melanoma cell line was transduced with a recombinant lentiviral vector containing the HSV1‐tk gene and inoculated into the back skin of C57BL/6J mice. [¹⁸F]FHBG PET imaging showed better contrast for HSV1‐tk(+) melanomas compared to brain, heart, gall bladder, intestine and kidney than did [¹⁸F]FDG PET imaging.