Abnormal activation of the hedgehog-signaling pathway is the pivotal abnormality driving the growth of basal cell carcinomas (BCCs), the most common type of human cancer. Antagonists of this pathway such as cyclopamine may therefore be useful for treatment of basal cell carcinomas and other hedgehog-driven tumors. We report here that chronic oral administration of cyclopamine dramatically reduces (ϳ66%) UVBinduced basal cell carcinoma formation in Ptch1 ؉/؊ mice. Fas expression is low in human and murine basal cell carcinomas but is up-regulated in the presence of the smoothened (SMO) antagonist, cyclopamine, both in vitro in the mouse basal cell carcinoma cell line ASZ001 and in vivo after acute treatment of mice with basal cell carcinomas. This parallels an elevated rate of apoptosis. Conversely, expression of activated SMO in C3H10T1/2 cells inhibits Fas expression. Fas/Fas ligand interactions are necessary for cyclopamine-mediated apoptosis in these cells, a process involving caspase-8 activation. Our data provide strong evidence that cyclopamine and perhaps other SMO antagonists are potent in vivo inhibitors of UVB-induced basal cell carcinomas in Ptch1 ؉/؊ mice and likely in humans because the majority of human basal cell carcinomas manifest mutations in PTCH1 and that a major mechanism of their inhibitory effect is through up-regulation of Fas, which augments apoptosis.

Background: The hedgehog pathway plays a critical role in the development of prostate. However, the role of the hedgehog pathway in prostate cancer is not clear. Prostate cancer is the second most prevalent cause of cancer death in American men. Therefore, identification of novel therapeutic targets for prostate cancer has significant clinical implications.

The hedgehog (Hh) pathway plays a critical role during development of embryos and cancer. Although the molecular basis by which protein kinase A (PKA) regulates the stability of hedgehog downstream transcription factor cubitus interruptus, the Drosophila homologue of vertebrate Gli molecules, is well documented, the mechanism by which PKA inhibits the functions of Gli molecules in vertebrates remains elusive. Here, we report that activation of PKA retains Gli1 in the cytoplasm. Conversely, inhibition of PKA activity promotes nuclear accumulation of Gli1. Mutation analysis identifies Thr 374 as a major PKA site determining Gli1 protein localization. In the three-dimensional structure, Thr 374 resides adjacent to the basic residue cluster of the nuclear localization signal (NLS). Phosphorylation of this Thr residue is predicted to alter the local charge and consequently the NLS function. Indeed, mutation of this residue to Asp (Gli1/T374D) results in more cytoplasmic Gli1 whereas a mutation to Lys (Gli1/T374K) leads to more nuclear Gli1. Disruption of the NLS causes Gli1/T374K to be more cytoplasmic. We find that the change of Gli1 localization is correlated with the change of its transcriptional activity. These data provide evidence to support a model that PKA regulates Gli1 localization and its transcriptional activity, in part, through modulating the NLS function.

An increasing progress on the role of Hedgehog (Hh) signaling for carcinogenesis has been achieved since the link of Hh pathway to human cancer was firstly established. In particular, the critical role of Hh signaling in the development of Basal cell carcinoma (BCC) has been convincingly demonstrated by genetic mutation analyses, mouse models of BCCs, and successful clinical trials of BCCs using Hh signaling inhibitors. In addition, the Hh pathway activity is also reported to be involved in the pathogenesis of Squamous Cell Carcinoma (SCC), melanoma and Merkel Cell Carcinoma. These findings have significant new paradigm on Hh signaling transduction, its mechanisms in skin cancer and even therapeutic approaches for BCC. In this review, we will summarize the major advances in the understanding of Hh signaling transduction, the roles of Hh signaling in skin cancer development, and the current implications of “mechanism-based” therapeutic strategies.

Basal cell carcinoma (BCC), the most common form of human cancer, is understood to be associated with activation of the sonic hedgehog pathway, through lossof-function mutations of tumor suppressor PTCH1 or gain-of-function mutations of smoothened. Interferon (IFN)-based therapy is quite effective in BCC treatment, but the molecular basis is not well understood. Here we report a novel mechanism by which IFNa mediates apoptosis in BCCs. In the presence of IFNa, we observed increased apoptosis in a BCC cell line ASZ001, in which PTC is null, and therefore with constitutive activation of the sonic hedgehog pathway. We demonstrate that SMO agonist Ag-1.4 mediates activation of extracellular signalregulated kinase (Erk) phosphorylation, which is abrogated by IFNa in sonic hedgehog responsive C3H10T1/2 cells. In transient transfection experiments, we demonstrate that IFNa inhibits Erk phosphorylation and serum response element activation induced by expression of SMO, Gli1, PDGFRa and activated Raf, but not activated mitogen-activated Erk-regulating kinase (Mek), suggesting that IFNa targets mainly on Mek function. We further show that IFNa induces expression of Fas in BCC cells through interfering with Mek function. The role of the Fas-L/Fas signaling axis in IFNa-mediated apoptosis is demonstrated by the fact that addition of Fas-L neutralizing antibodies, just as caspase-8 inhibitor Z-IETD-FMK, effectively prevents IFNa-mediated apoptosis. Thus, our data indicate that IFNa-based BCC therapy induces Fas expression and apoptosis through interfering with Mek function.

Cancer has been considered to be the result of accumulated gene mutations, which result in uncontrolled cell proliferations for a long time. Cancers are also regarded to be capable of immune evasion. Furthermore, resistance to apoptosis was recognized as an important trait of cancer in the last score of years. However, there are numerous paradoxical issues in this whole set of theory. For example, there is no known set of genes of which mutations are responsible for human cancers. As for the trait of ‘resistance to apoptosis’, the fact is that cancer has increased frequency of apoptosis. The more malignant the tumour is, the more apoptosis shows. In this study, we propose a new theory that apoptosis plays a key role in the malignant progression and metastasis of cancer. The growth of tumour is the difference between tumour cell proliferation and attrition plus the hyperplastic growth of stroma. Increased and unpreventable death caused by innate or environmental factors such as ischaemia and inflammation drives the tumour cells to proliferate relentlessly, move to new lands to establish colonies. In short, increased cell death is the origin of malignancy.

The influence of UV irradiation on pigmentation is well established, but the molecular and cellular mechanisms controlling dendrite formation remain incompletely understood. MicroRNAs (miRNAs) are a class of small RNAs that participate in various cellular processes by suppressing the expression of target mRNAs. In this study, we investigated the expression of miRNAs in response to UVB irradiation using a microarray screen and then identified potential mRNA targets for differentially expressed miRNAs among the genes governing dendrite formation. We subsequently determined the ability of miRNA 340 (miR-340) to suppress the expression of RhoA, which is a predicted miR-340 target gene that regulates dendrite formation. The overexpression of miR-340 promoted dendrite formation and melanosome transport, and the downregulation of miR-340 inhibited UVBinduced dendrite formation and melanosome transport. Moreover, a luciferase reporter assay demonstrated direct targeting of RhoA by miR-340 in the immortalized human melanocyte cell line Pig1. In conclusion, this study has established an miRNA associated with UVB irradiation. The significant downregulation of RhoA protein and mRNA expression after UVB irradiation and the modulation of miR-340 expression suggest a key role for miR-340 in regulating UVB-induced dendrite formation and melanosome transport. Melanocytes originate from neural crest-derived melanoblasts, which migrate and differentiate in the basal layer of the epidermis (1). A hallmark of melanocytes is their ability to form dendrites, which are specialized cell structures that transport melanosomes to their tips for transfer to the surrounding keratinocytes in response to growth factors and UV irradiation. Following skin penetration by UV rays and subsequent DNA damage, thymidine dinucleotide fragments induce melanogenesis and cause the melanocyte to produce melanosomes (2).These melanosomes are then transferred to neighboring keratinocytes through the intricate network of melanocyte dendrites, contributing to skin darkening and thereby providing protection from UV radiation (3, 4). Melanocyte dendrites can vary markedly in length and number in response to different growth factors and, in a manner analogous to the way in which neural cells seek out target neurons, these dendrites form growth cone-like structures that attach to keratinocytes. Melanocyte-keratinocyte adhesion is a prerequisite for the transfer of melanosomes to keratinocytes; therefore, the formation of melanocyte dendrites, particularly of the appropriate length and number, is essential for efficient melanosome transfer. Due to the importance of dendricity for melanocyte activity, cutaneous pigmentation, and photoprotection, it is critical to determine the precise mechanisms involved in the regulation of melanocyte dendrite formation.It is well known that melanocytes are sensitive to UV irradiation, with substantial evidence suggesting that it plays a pivotal role in regulating melanocyte dendricity. Studies have shown that UV irradiation induce...

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