Jennifer Y. Zhang

NF-kappaB blockade and oncogenic Ras trigger invasive human epidermal neoplasia.

The nuclear factor NF-κB and oncogenic Ras can alter proliferation in epidermis, the most common site of human cancer. These proteins are implicated in epidermal squamous cell carcinoma in mice, however, the potential effects of altering their function are uncertain. Whereas inhibition of NF-κB enhances apoptosis in certain tumours, blockade of NF-κB predisposes murine skin to squamous cell carcinoma. Because therapeutics inhibiting Ras and NF-κB pathways are being developed to treat human cancer, it is essential to assess the effects of altering these regulators. The medical relevance of murine studies is limited, however, by differences between mouse and human skin, and by the greater ease of transforming murine cells. Here we show that in normal human epidermal cells both NF-κB and oncogenic Ras trigger cell-cycle arrest. Growth arrest triggered by oncogenic Ras can be bypassed by IκBα-mediated blockade of NF-κB, generating malignant human epidermal tissue resembling squamous cell carcinoma. Human cell tumorigenesis is dependent on laminin 5 and α6β4 integrin. Thus, IκBα circumvents restraints on growth promotion induced by oncogenic Ras and can act with Ras to induce invasive human tissue neoplasia.

Innate Inhibition of Adaptive Immunity: Mycobacterium tuberculosis-Induced IL-6 Inhibits Macrophage Responses to IFN-γ

In humans and in mice, control of the intracellular pathogen, Mycobacterium tuberculosis (Mtb), requires IFN-γ. Although the adaptive immune response results in production of substantial amounts of IFN-γ in response to Mtb, the immune response is unable to eradicate the infection in most cases. We have previously reported evidence that Mtb inhibits macrophage responses to IFN-γ, suggesting that this may limit the ability of IFN-γ to stimulate macrophages to kill Mtb. We have also observed that uninfected macrophages, adjacent to infected macrophages in culture, exhibit decreased responses to IFN-γ. Here we report that IL-6 secreted by Mtb-infected macrophages inhibits the responses of uninfected macrophages to IFN-γ. IL-6 selectively inhibits a subset of IFN-γ-responsive genes at the level of transcriptional activation without inhibiting activation or function of STAT1. Inhibition of macrophage responses to IFN-γ by IL-6 requires new protein synthesis, but this effect is not attributable to suppressor of cytokine signaling 1 or 3. These results reveal a novel function for IL-6 and indicate that IL-6 secreted by Mtb-infected macrophages may contribute to the inability of the cellular immune response to eradicate infection.

CDK4 regulation by TNFR1 and JNK is required for NF-κB–mediated epidermal growth control

Nuclear factor κB (NF-κB) mediates homeostatic growth inhibition in the epidermis, and a loss of NF-κB function promotes proliferation and oncogenesis. To identify mechanisms responsible for these effects, we impaired NF-κB action in the epidermis by three different genetic approaches, including conditional NF-κB blockade. In each case, epidermal hyperplasia was accompanied by an increase in both protein levels and tissue distribution of the G1 cell cycle kinase, CDK4. CDK4 up-regulation required intact TNFR1 and c-Jun NH2-terminal kinase (JNK) function. Cdk4 gene deletion concomitant with conditional NF-κB blockade demonstrated that CDK4 is required for growth deregulation. Therefore, epidermal homeostasis depends on antagonist regulation of CDK4 expression by NF-κB and TNFR1/JNK.

In vivo and ex vivo epi-mode pump-probe imaging of melanin and microvasculature

We performed epi-mode pump-probe imaging of melanin in excised human pigmented lesions and both hemoglobin and melanin in live xenograft mouse melanoma models to depths greater than 100 µm. Eumelanin and pheomelanin images, which have been previously demonstrated to differentiate melanoma from benign lesions, were acquired at the dermal-epidermal junction with cellular resolution and modest optical powers (down to 15 mW). We imaged dermal microvasculature with the same wavelengths, allowing simultaneous acquisition of melanin, hemoglobin and multiphoton autofluorescence images. Molecular pump-probe imaging of melanocytes, skin structure and microvessels allows comprehensive, non-invasive characterization of pigmented lesions.

Tumor Necrosis Factor Receptor 1/c-Jun-NH2-Kinase Signaling Promotes Human Neoplasia

The tumor necrosis factor alpha receptor (TNFR1) activates downstream effectors that include the mitogen-activated protein kinase kinase 7 (MKK7)/c-Jun-NH(2)-kinase (JNK)/activator protein 1 (AP1) cascade. Here, we report that JNK is activated in a majority of spontaneous human squamous cell carcinomas (SCC). JNK pathway induction bypassed cell cycle restraints induced by oncogenic Ras and cooperated with Ras to convert normal human epidermis into tumors indistinguishable from SCC, confirming its oncogenic potency in human tissue. Inhibiting MKK7, JNK, and AP1 as well as TNFR1 itself using genetic, pharmacologic, or antibody-mediated approaches abolished invasive human epidermal neoplasia in a tumor cell autonomous fashion. The TNFR1/MKK7/JNK/AP1 cascade thus promotes human neoplasia and represents a potential therapeutic target for human epithelial cancers.

The c-Jun NH2-Terminal Kinase 2 Plays a Dominant Role in Human Epidermal Neoplasia

The c-Jun NH(2)-terminal kinase (JNK) signaling cascade has been implicated in a wide range of diseases, including cancer. It is unclear how different JNK proteins contribute to human cancer. Here, we report that JNK2 is activated in more than 70% of human squamous cell carcinoma (SCC) samples and that inhibition of JNK2 pharmacologically or genetically impairs tumorigenesis of human SCC cells. Most importantly, JNK2, but not JNK1, is sufficient to couple with oncogenic Ras to transform primary human epidermal cells into malignancy with features of SCC. JNK2 prevents Ras-induced cell senescence and growth arrest by reducing the expression levels of the cell cycle inhibitor p16 and the activation of NF-kappaB. On the other hand, JNK, along with phosphoinositide 3-kinase, is essential for Ras-induced glycolysis, an energy-producing process known to benefit cancer growth. These data indicate that JNK2 collaborates with other oncogenes, such as Ras, at multiple molecular levels to promote tumorigenesis and hence represents a promising therapeutic target for cancer.

BCL2 inhibits cell adhesion, spreading, and motility by enhancing actin polymerization.

BCL2 is best known as a multifunctional anti-apoptotic protein. However, little is known about its role in cell-adhesive and motility events. Here, we show that BCL2 may play a role in the regulation of cell adhesion, spreading, and motility. When BCL2 was overexpressed in cultured murine and human cell lines, cell spreading, adhesion, and motility were impaired. Consistent with these results, the loss of Bcl2 resulted in higher motility observed in Bcl2-null mouse embryonic fibroblast (MEF) cells compared to wild type. The mechanism of BCL2 regulation of cell adhesion and motility may involve formation of a complex containing BCL2, actin, and gelsolin, which appears to functionally decrease the severing activity of gelsolin. We have observed that the lysate from MCF-7 and NIH3T3 cells that overexpressed BCL2 enhanced actin polymerization in cell-free in vitro assays. Confocal immunofluorescent localization of BCL2 and F-actin during spreading consistently showed that increased expression of BCL2 resulted in increased F-actin polymerization. Thus, the formation of BCL2 and gelsolin complexes (which possibly contain other proteins) appears to play a critical role in the regulation of cell adhesion and migration. Given the established correlation of cell motility with cancer metastasis, this result may explain why the expression of BCL2 in some tumor cell types reduces the potential for metastasis and is associated with improved patient prognosis.

Transient receptor potential vanilloid 4 ion channel functions as a pruriceptor in epidermal keratinocytes to evoke histaminergic itch

TRPV4 ion channels function in epidermal keratinocytes and in innervating sensory neurons; however, the contribution of the channel in either cell to neurosensory function remains to be elucidated. We recently reported TRPV4 as a critical component of the keratinocyte machinery that responds to ultraviolet B (UVB) and functions critically to convert the keratinocyte into a pain-generator cell after excess UVB exposure. One key mechanism in keratinocytes was increased expression and secretion of endothelin-1, which is also a known pruritogen. Here we address the question of whether TRPV4 in skin keratinocytes functions in itch, as a particular form of “forefront” signaling in non-neural cells. Our results support this novel concept based on attenuated scratching behavior in response to histaminergic (histamine, compound 48/80, endothelin-1), not non-histaminergic (chloroquine) pruritogens in Trpv4 keratinocyte-specific and inducible knock-out mice. We demonstrate that keratinocytes rely on TRPV4 for calcium influx in response to histaminergic pruritogens. TRPV4 activation in keratinocytes evokes phosphorylation of mitogen-activated protein kinase, ERK, for histaminergic pruritogens. This finding is relevant because we observed robust anti-pruritic effects with topical applications of selective inhibitors for TRPV4 and also for MEK, the kinase upstream of ERK, suggesting that calcium influx via TRPV4 in keratinocytes leads to ERK-phosphorylation, which in turn rapidly converts the keratinocyte into an organismal itch-generator cell. In support of this concept we found that scratching behavior, evoked by direct intradermal activation of TRPV4, was critically dependent on TRPV4 expression in keratinocytes. Thus, TRPV4 functions as a pruriceptor-TRP in skin keratinocytes in histaminergic itch, a novel basic concept with translational-medical relevance.

c-Jun Promotes whereas JunB Inhibits Epidermal Neoplasia

Deregulation of the activator protein 1 (AP1) family gene regulators has been implicated in a wide range of diseases, including cancer. In this study we report that c-Jun was activated in human squamous cell carcinoma (SCC) and coexpression of c-Jun with oncogenic Ras was sufficient to transform primary human epidermal cells into malignancy in a regenerated human skin grafting model. In contrast, JunB was not induced in a majority of human SCC cells. Moreover, exogenous expression of JunB inhibited tumorigenesis driven by Ras or spontaneous human SCC cells. Conversely, the dominant-negative JunB mutant (DNJunB) promoted tumorigenesis, which is in contrast to the tumor-suppressor function of the corresponding c-Jun mutant. At the cellular level, JunB induced epidermal cell senescence and slowed cell growth in a cell-autonomous manner. Consistently, coexpression of JunB and Ras induced premature epidermal differentiation concomitant with upregulation of p16 and filaggrin and downregulation of cyclin D1 and cyclin-dependent kinase 4 (CDK4). These findings indicate that JunB and c-Jun differentially regulate cell growth and differentiation and induce opposite effects on epidermal neoplasia.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://www.nature.com/jid/journalclub.

CYLD Inhibits Melanoma Growth and Progression through Suppression of the JNK/AP-1 and β1-Integrin Signaling Pathways

The molecular mechanisms mediating CYLD tumor suppressor function appear to be manifold. Here, we demonstrated that, in contrast to the increased levels of pJNK, CYLD was decreased in a majority of melanoma cell lines and tissues examined. Exogenous expression of CYLD but not its catalytically deficient mutant markedly inhibited melanoma cell proliferation and migration in vitro and subcutaneous tumor growth in vivo. In addition, the melanoma cells expressing exogenous CYLD were unable to form pulmonary tumor nodules following tail-vein injection. At the molecular level, CYLD decreased β1-integrin and inhibited pJNK induction by TNFα or cell-attachment to collagen IV. Moreover, CYLD induced an array of other molecular changes associated with modulation of the ‘malignant’ phenotype, including a decreased expression of cyclin D1, N-cadherin and nuclear Bcl3, and an increased expression of p53 and E-cadherin. Most interestingly, co-expression of the constitutively active MKK7 or c-Jun mutants with CYLD prevented the above molecular changes, and fully restored melanoma growth and metastatic potential in vivo. Our findings demonstrate that JNK/AP-1 signaling pathway underlies the melanoma growth and metastasis that is associated with CYLD loss-of-function. Thus, restoration of CYLD and inhibition of JNK and β1-integrin function represent potential therapeutic strategies for treatment of malignant melanoma.