Ras and Raf pathways in epidermis development and carcinogenesis

Spatial multi-omics of human skin reveals KRAS and inflammatory responses to spaceflight

Spaceflight can change metabolic, immunological, and biological homeostasis and cause skin rashes and irritation, yet the molecular basis remains unclear. To investigate the impact of short-duration spaceflight on the skin, we conducted skin biopsies on the Inspiration4 crew members before (L-44) and after (R + 1) flight. Leveraging multi-omics assays including GeoMx™ Digital Spatial Profiler, single-cell RNA/ATAC-seq, and metagenomics/metatranscriptomics, we assessed spatial gene expressions and associated microbial and immune changes across 95 skin regions in four compartments: outer epidermis, inner epidermis, outer dermis, and vasculature. Post-flight samples showed significant up-regulation of genes related to inflammation and KRAS signaling across all skin regions. These spaceflight-associated changes mapped to specific cellular responses, including altered interferon responses, DNA damage, epithelial barrier disruptions, T-cell migration, and hindered regeneration were located primarily in outer tissue compartments. We also linked epithelial disruption to microbial shifts in skin swab and immune cell activity to PBMC single-cell data from the same crew and timepoints. Our findings present the inaugural collection and examination of astronaut skin, offering insights for future space missions and response countermeasures.

Integrative Analysis of Angiogenesis-Related Long Non-Coding RNA and Identification of a Six-DEARlncRNA Signature Associated with Prognosis and Therapeutic Response in Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is a lethal gastrointestinal malignancy worldwide. We aimed to identify an angiogenesis-related lncRNAs (ARlncRNAs) signature that could predict the prognosis in ESCC. The GSE53624 and GSE53622 datasets were derived from the GEO database. The differently expressed ARlncRNAs (DEARlncRNAs) were retrieved by the weighted gene co-expression network analysis (WGCNA), differential expression analysis, and correlation analysis. Optimal lncRNA biomarkers were screened from the training set and the six-DEARlncRNA signature comprising AP000696.2, LINC01711, RP11-70C1.3, AP000487.5, AC011997.1, and RP11-225N10.1 could separate patients into high- and low-risk groups with markedly different survival. The validation of the reliability of the risk model was performed by the Kaplan-Meier test, ROC curves, and risk curves in the test set and validation set. Predictive independence analysis indicated that risk score is an independent prognostic biomarker for predicting the prognosis of ESCC patients. Subsequently, a ceRNA regulatory network and functional enrichment analysis were performed. The IC50 test revealed that patients in the high-risk group were resistant to Gefitinib and Lapatinib. Finally, the six DEARlncRNAs were detected by qRT-PCR. In conclusion, we demonstrated a novel ARlncRNA signature as an independent prognostic factor to distinguish the risk of ESCC patients and benefit the personalized clinical applications.

Cutis verticis gyrata and Noonan syndrome: report of two cases with pathogenetic variant in SOS1 gene

Background

Noonan and Noonan-like syndromes are multisystem genetic disorders, mainly with autosomal dominant trasmission, caused by mutations in several genes. Missense pathogenetic variants of SOS1 gene are the second most common cause of Noonan syndrome (NS) and account approximately for 13% to 17% of cases. Subjects carrying a pathogenetic variant in SOS1 gene tend to exhibit a distinctive phenotype that is characterized by ectodermal abnormalities. Cutis verticis gyrata (CVG) is a rare disease, congenital or acquired, characterized by the redundancy of skin on scalp, forming thick skin folds and grooves of similar aspect to cerebral cortex gyri. Several references in the literature have reported association between nonessential primary form of CVG and NS.

Case presentation

we report two cases of newborns with CVG and phenotype suggestive for NS who have been diagnosed to harbour the same pathogenetic variant in SOS1 gene.

Conclusions

previously described patients with NS presenting CVG had received only clinical diagnosis. Therefore we report the first patients with CVG in which the clinical suspicion of NS is confirmed by molecolar analysis.

Depletion of RIPK4 parallels higher malignancy potential in cutaneous squamous cell carcinoma

BACKGROUND

The RIPK4 (receptor-interacting protein kinase 4), a member of the RIPK family, acts as an important regulator of epidermal differentiation, cutaneous inflammation, and cutaneous wound repair. However, Until now, the role of RIPK4 in tumorigenesis remains elusive. There have been no studies exploring the effects of RIPK4 on the signaling pathway in cutaneous squamous cell carcinoma (SCC). It remains unknown whether RIPK4 expression, which can affect the degree of epidermal differentiation can also influence the radiosensitivity of skin SCC. It is urgent to fully elucidate the biological mechanism by which RIPK4 promotes carcinogenesis in skin SCC and determine whether RIPK4 expression levels predicts the sensitivity to radiotherapy in skin SCC.

METHODS

Human skin SCC cell line, A431, was transfected with either small interfering RNAs (siRNAs) targeting RIPK4 (siR-RIPK4) or negative control siRNA (siR-NC). Western blotting was used to detect the expression of RIPK4 and Raf/MEK/ERK pathway-related proteins. The cells were irradiated using an X-ray irradiator at 6 MV with different radiation doses (0, 2, 6, and 10 Gy). Cell proliferation analysis, colony formation assay, transwell cell migration and invasion assay, cell cycle and apoptosis analysis were conducted to investigate the effect of RIPK4 silencing on skin SCC malignancy and radiosensitivity.

RESULTS

RIPK4 protein expression was significantly decreased in the A431 cells transfected with siR-RIPK4, compared with the A431 cells transfected with siR-NC. RIPK4 silencing facilitated the proliferation, colony formation, migration, and invasion ability of A431 cell line, while cell cycle progression or cell apoptosis were not significantly influenced. In contrast with the previous literature, Raf/MEK/ERK pathway was not effected by RIPK4 knockdown in skin SCC. RIPK4 knockdown could not reverse the radiation resistance of A431 cells to irradiation in vitro.

CONCLUSIONS

In general, although depletion of RIPK4 cannot reverse the radiation resistance of A431 cells in vitro, it parallels higher malignancy potential in cutaneous SCC. To our knowledge, this is the first report of the effects of RIPK4 expression on the Raf/MEK/ERK signaling pathway and radiosensitivity in cutaneous SCC. The better understanding of the molecular mechanism of RIPK4 in cutaneous SCC may provide a promising biomarker for skin SCC prognosis and treatment.

The Different Impact of ERK Inhibition on Neuroblastoma, Astrocytoma, and Rhabdomyosarcoma Cell Differentiation

Aberrant ERK activity can lead to uncontrolled cell proliferation, immortalization, and impaired cell differentiation. Impairment of normal cell differentiation is one of the critical stages in malignant cell transformation. In this study, we investigated a relationship between ERK tyrosine kinase activity and the main differentiation features (changes in cell morphology and expression of genes encoding differentiation markers and growth factor receptors) in SH-SY5Y neuroblastoma, U-251 astrocytoma, and TE-671 rhabdomyosarcoma cells. ERK activity was assessed using a reporter system that enabled live measurements of ERK activity in single cells. We demonstrated that suppression of ERK activity by selective ERK inhibitors, in contrast to a commonly used differentiation inducer, retinoic acid, leads to significant changes in TE-671 cell morphology and expression of the myogenic differentiation marker genes PROM1, MYOG, and PAX7. There was a relationship between ERK activity and morphological changes at an individual cell level. In this case, SH-SY5Y cell differentiation induced by retinoic acid was ERK-independent. We showed that ERK inhibition increases the sensitivity of TE-671 cells to the EGF, IGF-1, and NGF growth factors, presumably by reducing basal ERK activity, and to the BDNF growth factor, by increasing expression of the TrkB receptor.

SOS2 Comes to the Fore: Differential Functionalities in Physiology and Pathology

The SOS family of Ras-GEFs encompasses two highly homologous and widely expressed members, SOS1 and SOS2. Despite their similar structures and expression patterns, early studies of constitutive KO mice showing that SOS1-KO mutants were embryonic lethal while SOS2-KO mice were viable led to initially viewing SOS1 as the main Ras-GEF linking external stimuli to downstream RAS signaling, while obviating the functional significance of SOS2. Subsequently, different genetic and/or pharmacological ablation tools defined more precisely the functional specificity/redundancy of the SOS1/2 GEFs. Interestingly, the defective phenotypes observed in concomitantly ablated SOS1/2-DKO contexts are frequently much stronger than in single SOS1-KO scenarios and undetectable in single SOS2-KO cells, demonstrating functional redundancy between them and suggesting an ancillary role of SOS2 in the absence of SOS1. Preferential SOS1 role was also demonstrated in different RASopathies and tumors. Conversely, specific SOS2 functions, including a critical role in regulation of the RAS-PI3K/AKT signaling axis in keratinocytes and KRAS-driven tumor lines or in control of epidermal stem cell homeostasis, were also reported. Specific SOS2 mutations were also identified in some RASopathies and cancer forms. The relevance/specificity of the newly uncovered functional roles suggests that SOS2 should join SOS1 for consideration as a relevant biomarker/therapy target.

Functional Specificity of the Members of the Sos Family of Ras-GEF Activators: Novel Role of Sos2 in Control of Epidermal Stem Cell Homeostasis

Simple Summary

The Sos Ras-GEFs are known to participate in a wide range of skin-related diseases including cutaneous cancers, cardio-facio-cutaneous syndromes, or hirsutism. However, the specific functional roles played by the Sos1 and/or Sos2 family members in specific skin compartments remain largely unknown. This report aimed at precisely characterizing the specific functions played by Sos1 and/or Sos2 in keratinocytes, an essential cellular component of the skin. Our data show that Sos1 and Sos2 make overlapping contributions to both keratinocyte proliferation and survival. However, Sos1 seems to have a preferential involvement in regulating the ERK axis, whereas Sos2 seems to control the signaling output from the PI3K axis. We also uncovered an essential role of Sos2 in the control of the population of epidermal stem cells.

Abstract

Prior reports showed the critical requirement of Sos1 for epithelial carcinogenesis, but the specific functionalities of the homologous Sos1 and Sos2 GEFs in skin homeostasis and tumorigenesis remain unclear. Here, we characterize specific mechanistic roles played by Sos1 or Sos2 in primary mouse keratinocytes (a prevalent skin cell lineage) under different experimental conditions. Functional analyses of actively growing primary keratinocytes of relevant genotypes—WT, Sos1-KO, Sos2-KO, and Sos1/2-DKO—revealed a prevalent role of Sos1 regarding transcriptional regulation and control of RAS activation and mechanistic overlapping of Sos1 and Sos2 regarding cell proliferation and survival, with dominant contribution of Sos1 to the RAS-ERK axis and Sos2 to the RAS-PI3K/AKT axis. Sos1/2-DKO keratinocytes could not grow under 3D culture conditions, but single Sos1-KO and Sos2-KO keratinocytes were able to form pseudoepidermis structures that showed disorganized layer structure, reduced proliferation, and increased apoptosis in comparison with WT 3D cultures. Remarkably, analysis of the skin of both newborn and adult Sos2-KO mice uncovered a significant reduction of the population of stem cells located in hair follicles. These data confirm that Sos1 and Sos2 play specific, cell-autonomous functions in primary keratinocytes and reveal a novel, essential role of Sos2 in control of epidermal stem cell homeostasis.

Photobiomodulation reduces oxidative stress in diabetic wounded fibroblast cells by inhibiting the FOXO1 signaling pathway

This study aimed to elucidate the underlying molecular mechanism of photobiomodulation (PBM) in attenuating oxidative stress in diabetic wounded fibroblast cells. Cell models were exposed to PBM at a wavelength of 660 nm (fluence of 5 J/cm², and power density of 11.2 mW/cm²) or 830 nm (fluence of 5 J/cm², and power density of 10.3 mW/cm²). Non-irradiated cell models were used as controls. Cellular migration was determined at regular time intervals (0, 12, 24 and 48 h) using inverted light microscopy. Cell viability was determined by the Trypan blue exclusion assay. The levels of enzymic antioxidants superoxide dismutase (SOD), catalase (CAT), and heme oxygenase (HMOX1) were determined by the enzyme linked immunosorbent assay (ELISA). The alteration in the levels of AKT and FOXO1 was determined by immunofluorescence and western blotting. Upon PBM treatment, elevated oxidative stress was reversed in diabetic and diabetic wounded fibroblast cells. The reduced oxidative stress was represented by decreased FOXO1 levels and increased levels of SOD, CAT and HMOX1. This might be due to the activation of the AKT signaling pathway. This study concluded that treatment with PBM progressed diabetic wound healing by attenuating oxidative stress through inhibition of the FOXO1 signaling pathway.

SOS GEFs in health and disease

SOS1 and SOS2 are the most universal and widely expressed family of guanine exchange factors (GEFs) capable or activating RAS or RAC1 proteins in metazoan cells. SOS proteins contain a sequence of modular domains that are responsible for different intramolecular and intermolecular interactions modulating mechanisms of self-inhibition, allosteric activation and intracellular homeostasis. Despite their homology, analyses of SOS1/2-KO mice demonstrate functional prevalence of SOS1 over SOS2 in cellular processes including proliferation, migration, inflammation or maintenance of intracellular redox homeostasis, although some functional redundancy cannot be excluded, particularly at the organismal level. Specific SOS1 gain-of-function mutations have been identified in inherited RASopathies and various sporadic human cancers. SOS1 depletion reduces tumorigenesis mediated by RAS or RAC1 in mouse models and is associated with increased intracellular oxidative stress and mitochondrial dysfunction. Since WT RAS is essential for development of RAS-mutant tumors, the SOS GEFs may be considered as relevant biomarkers or therapy targets in RAS-dependent cancers. Inhibitors blocking SOS expression, intrinsic GEF activity, or productive SOS protein-protein interactions with cellular regulators and/or RAS/RAC targets have been recently developed and shown preclinical and clinical effectiveness blocking aberrant RAS signaling in RAS-driven and RTK-driven tumors.

Insight Into the Function of RIPK4 in Keratinocyte Differentiation and Carcinogenesis

The receptor-interacting protein kinase 4 (RIPK4), a member of the RIPK family, was originally described as an interaction partner of protein kinase C (PKC) β and PKCδ. RIPK4 is identified as a key regulator of keratinocyte differentiation, cutaneous inflammation, and cutaneous wound repair. The mechanism by which RIPK4 integrates upstream signals to initiate specific responses remains elusive. Previous studies have indicated that RIPK4 can regulate several signaling pathways, including the NF-κB, Wnt/β-catenin, and RAF/MEK/ERK pathways. Furthermore, RIPK4-related biological signaling pathways interact with each other to form a complex network. Mounting evidence suggests that RIPK4 is aberrantly expressed in various kinds of cancers. In several types of squamous cell carcinoma (SCC), the mutations that drive aggressive SCC have been found in RIPK4. In addition, the function of RIPK4 in carcinogenesis is probably tissue-specific, since RIPK4 can play a dual role as both a tumor promoter and a tumor suppressor in different tumor types. Therefore, RIPK4 may represent as an independent prognostic factor and a promising novel therapeutic target, which can be used to identify the risks of patients and guide personalized treatments. In future, RIPK4-interacting pathways and precise molecular targets need to be investigated in order to further elucidate the mechanisms underlying epidermal differentiation and carcinogenesis.

Costello syndrome model mice with a HrasG12S/+ mutation are susceptible to develop house dust mite-induced atopic dermatitis

Costello syndrome is an autosomal dominant disorder that is caused by germline HRAS mutations. Patients with Costello syndrome present craniofacial abnormalities, cardiac defects, and cancer predisposition, as well as skin abnormalities, including papillomas, keratosis pilaris, and eczematous dermatitis. However, the mechanisms underlying the dermatological abnormalities remain unclear. Here, we demonstrated that knock-in mice expressing an Hras G12S mutation (Hras^G12S/+ mice) are susceptible to develop atopic dermatitis (AD)-like skin lesions, including eczema, pruritus, elevated serum IgE levels, acanthosis, and the infiltration of mast cells, basophils, and type-2 innate lymphoid cells in the dermis, after stimulation with house dust mite allergens (Dermatophagoides farinae, Dfb). Reduced skin barrier function, increased proliferation of phosphorylated ERK (p-ERK)-positive epidermal cells, and increased Th2-type cytokines as well as epithelial cell-derived cytokines, including IL-33, were observed in the skin tissue of Hras^G12S/+ mice compared with Hras^+/+ mice. Cultured Hras^G12S/+ keratinocytes exhibited increased IL-33 expression after Dfb stimulation. PD0325901, an MEK inhibitor, ameliorated AD-like symptoms in Hras^G12S/+ mice, showing decreased proliferation of p-ERK-positive epidermal cells and decreased expression of IL-33. Our findings indicate that the epidermis of Hras^G12S/+ mice stimulated by Dfb strongly induced IL-33 expression and type-2 innate lymphoid cells, resulting in AD-like skin lesions. These results suggest that the epidermis of Hras^G12S/+ mice are prone to development of eczematous dermatitis stimulated with house dust mite allergens.

Deciphering the Molecular Landscape of Cutaneous Squamous Cell Carcinoma for Better Diagnosis and Treatment

Cutaneous squamous cell carcinoma (cSCC) is a common type of neoplasia, representing a terrible burden on patients' life and clinical management. Although it seldom metastasizes, and most cases can be effectively treated with surgical intervention, once metastatic cSCC displays considerable aggressiveness leading to the death of affected individuals. No consensus has been reached as to which features better characterize the aggressive behavior of cSCC, an achievement hindered by the high mutational burden caused by chronic ultraviolet light exposure. Even though some subtypes have been recognized as high risk variants, depending on certain tumor features, cSCC that are normally thought of as low risk could pose an increased danger to the patients. In light of this, specific genetic and epigenetic markers for cutaneous SCC, which could serve as reliable diagnostic markers and possible targets for novel treatment development, have been searched for. This review aims to give an overview of the mutational landscape of cSCC, pointing out established biomarkers, as well as novel candidates, and future possible molecular therapies for cSCC.

Acral Lentiginous Melanomas Harbour Intratumor Heterogeneity in BRAF Exon 15, With Mutations Distinct From V600E/V600K

The choice of appropriate therapeutic strategies may be influenced by intratumor heterogeneity and makes cancer treatment considerably more challenging. We aimed to evaluate the heterogeneity of BRAF exon 15 mutations in different areas of acral lentiginous melanoma (ALM). The entire exon 15 was sequenced in 4 different areas of paraffin-embedded samples from 26 patients with ALM. A total of 26 of 49 cases of ≥1 mm in depth of ALM identified by clinical, anatomical, and pathological data fulfilled the inclusion and exclusion criteria for this study. Tumors had a mean Breslow depth of 7.2 mm and an average mitotic index of 3 mitosis/mm. Mutations distinct from the common V600E and V600K were detected in 31%, and intratumor heterogeneity was observed in 31% of samples. Interestingly, 63.5% of all mutations had been previously associated with cancer. Most (62.5%) of the missense BRAF exon 15 mutations found in the ALM samples examined here were deemed "detrimental" for protein function according to at least 2 functional prediction programs, and 3 mutations (37.5%) were predicted to be "neutral," with no effect on protein function. BRAF exon 15 mutations were detected frequently in ALM and displayed heterogeneity, a finding to be further investigated.

De Novo assembly and comparative transcriptome analyses of purple and green morphs of Apostichopus japonicus during body wall pigmentation process

Pigmentation processes provide a traceable and relevant trait for understanding key issues in evolutionary biology such as adaptation, speciation and the maintenance of balanced polymorphisms. The sea cucumber Apostichopus japonicus, which has nutritive and medical properties, is considered the most valuable commercial species in many parts of Asia. Compared with the green morph, the purple morph is rare and has great appeal to consumers. However, little is currently known about the molecular mechanism of body color formation in A. japonicus, even in echinoderm. Here, we employ illumina sequencing to examine expression patterns of the gene network underlying body wall development in purple and green morphs of A. japonicus. Overall, the number of down-regulated genes in the green morph was significantly more than in the purple morph during the pigmentation stage. We observed dynamic expression patterns of a large number of pigment, regulation and growth genes from the "Melanogenesis", "Melanoma", "Wnt signaling pathway", "Notch signaling pathway", "epithelium development", "epidermal growth factor receptor binding","growth factor activity" and "growth", including contrasting expression patterns of these genes in green and purple morph. This study provides comprehensive lists of differentially expressed genes during body wall development in the green and purple morphs, revealing potential candidate genes that may be involved in regulating body color formation and polymorphism. These data will provide valuable information for future genetic studies on sea cucumbers elucidating the molecular mechanisms underlying pigmentation, and may support the culture of desirable color morphs.

Suppression of Wnt/β-catenin signaling by EGF receptor is required for hair follicle development

Mice that lack the epidermal growth factor receptor (EGFR) fail to develop a hair coat, but the mechanism responsible for this deficit is not completely understood. Here, we show that EGFR plays a critical role to attenuate wingless-type MMTV integration site family member (Wnt)/β-catenin signaling during postnatal hair follicle development. Genetic ablation of EGFR in mice resulted in increased mitotic activity in matrix cells, apoptosis in hair follicles, and impaired differentiation of epithelial lineages that form hair. EGFR is activated in wild-type hair follicle stem cells marked with SOX9 or NFATc1 and is essential to restrain proliferation and support stem cell numbers and their quiescence. We observed elevated levels of Wnt4, 6, 7b, 10a, 10b, and 16 transcripts and hyperactivation of the β-catenin pathway in EGFR knockout follicles. Using primary keratinocytes, we linked ligand-induced EGFR activation to suppression of nascent mRNA synthesis of Wnt genes. Overexpression of the Wnt antagonist sFRP1 in mice lacking EGFR demonstrated that elevated Wnts are a major cause for the hair follicle defects. Colocalization of transforming growth factor α and Wnts regulated by EGFR in stem cells and progeny indicates that EGFR autocrine loops control Wnts. Our findings define a novel mechanism that integrates EGFR and Wnt/β-catenin pathways to coordinate the delicate balance between proliferation and differentiation during development.

Differential Role of the RasGEFs Sos1 and Sos2 in Mouse Skin Homeostasis and Carcinogenesis

Using Sos1 knockout (Sos1-KO), Sos2-KO, and Sos1/2 double-knockout (Sos1/2-DKO) mice, we assessed the functional role of Sos1 and Sos2 in skin homeostasis under physiological and/or pathological conditions. Sos1 depletion resulted in significant alterations of skin homeostasis, including reduced keratinocyte proliferation, altered hair follicle and blood vessel integrity in dermis, and reduced adipose tissue in hypodermis. These defects worsened significantly when both Sos1 and Sos2 were absent. Simultaneous Sos1/2 disruption led to severe impairment of the ability to repair skin wounds, as well as to almost complete ablation of the neutrophil-mediated inflammatory response in the injury site. Furthermore, Sos1 disruption delayed the onset of tumor initiation, decreased tumor growth, and prevented malignant progression of papillomas in a DMBA (7,12-dimethylbenz[α]anthracene)/TPA (12-O-tetradecanoylphorbol-13-acetate)-induced skin carcinogenesis model. Finally, Sos1 depletion in preexisting chemically induced papillomas resulted also in decreased tumor growth, probably linked to significantly reduced underlying keratinocyte proliferation. Our data unveil novel, distinctive mechanistic roles of Sos 1 and Sos2 in physiological control of skin homeostasis and wound repair, as well as in pathological development of chemically induced skin tumors. These observations underscore the essential role of Sos proteins in cellular proliferation and migration and support the consideration of these RasGEFs as potential biomarkers/therapy targets in Ras-driven epidermal tumors.

Shared and independent functions of aPKCλ and Par3 in skin tumorigenesis

The polarity proteins Par3 and aPKC are key regulators of processes altered in cancer. Par3/aPKC are thought to dynamically interact with Par6 but increasing evidence suggests that aPKC and Par3 also exert complex-independent functions. Whereas aPKCλ serves as tumor promotor, Par3 can either promote or suppress tumorigenesis. Here we asked whether and how Par3 and aPKCλ genetically interact to control two-stage skin carcinogenesis. Epidermal loss of Par3, aPKCλ, or both, strongly reduced tumor multiplicity and increased latency but inhibited invasion to similar extents, indicating that Par3 and aPKCλ function as a complex to promote tumorigenesis. Molecularly, Par3/aPKCλ cooperate to promote Akt, ERK and NF-κB signaling during tumor initiation to sustain growth, whereas aPKCλ dominates in promoting survival. In the inflammatory tumorigenesis phase Par3/aPKCλ cooperate to drive Stat3 activation and hyperproliferation. Unexpectedly, the reduced inflammatory signaling did not alter carcinogen-induced immune cell numbers but reduced IL-4 Receptor-positive stromal macrophage numbers in all mutant mice, suggesting that epidermal aPKCλ and Par3 promote a tumor-permissive environment. Importantly, aPKCλ also serves a distinct, carcinogen-independent role in controlling skin immune cell homeostasis. Collectively, our data demonstrates that Par3 and aPKCλ cooperate to promote skin tumor initiation and progression, likely through sustaining growth, survival, and inflammatory signaling.

Decoding the full picture of Raf1 function based on its interacting proteins

Raf1 is a member of the Raf kinase family and regulates many fundamental cell processes, including proliferation, differentiation, apoptosis, motility, and metabolism. However, the functions of Raf1 have not been completely elucidated. To better understand Raf1 function, we investigated the proteins that interacted with Raf1. We identified 198 Raf1 interacting proteins and our data suggested that Raf1 may regulate cell processes through these interactions. These interaction partners were involved in all ten hallmarks of cancer, suggesting that Raf1 is involved in different aspects of carcinogenesis. In addition, we showed that Raf1 interacting proteins were enriched in six signaling pathways and many human diseases. The interaction partners identified in this study may represent oncological candidates for future investigations into Raf1 function. Our findings have provided an overview of Raf1 function from a systems biology perspective.

Comprehensive analysis of differential co-expression patterns reveal transcriptional dysregulation mechanism and identify novel prognostic lncRNAs in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide and occurs at a relatively high frequency in People's Republic of China. However, the molecular mechanism underlying ESCC is still unclear. In this study, the mRNA and long non-coding RNA (lncRNA) expression profiles of ESCC were downloaded from the Gene Expression Omnibus database, and then differential co-expression analysis was used to reveal the altered co-expression relationship of gene pairs in ESCC tumors. A total of 3,709 mRNAs and 923 lncRNAs were differentially co-expressed between normal and tumor tissues, and we found that most of the gene pairs lost associations in the tumor tissues. The differential regulatory networking approach deciphered that transcriptional dysregulation was ubiquitous in ESCC, and most of the differentially regulated links were modulated by 37 TFs. Our study also found that two novel lncRNAs (ADAMTS9-AS1 and AP000696.2) might be essential in the development of ectoderm and epithelial cells, which could significantly stratify ESCC patients into high-risk and low-risk groups, and were much better than traditional clinical tumor markers. Further inspection of two risk groups showed that the changes in TF-target regulation in the high-risk patients were significantly higher than those in the low-risk patients. In addition, four signal transduction-related DCmRNAs (ERBB3, ENSA, KCNK7, MFSD5), which were differentially co-expressed with the two lncRNAs, might also have the predictive capacity. Our findings will enhance the understanding of ESCC transcriptional dysregulation from a view of cross-link of lncRNA and mRNA, and the two-lncRNA combination may serve as a novel prognostic biomarker for clinical applications of ESCC.

IBT-based quantitative proteomics identifies potential regulatory proteins involved in pigmentation of purple sea cucumber, Apostichopus japonicus

Sea cucumbers are an important economic species and exhibit high yield value among aquaculture animals. Purple sea cucumbers are very rare and beautiful and have stable hereditary patterns. In this study, isobaric tags (IBT) were first used to reveal the molecular mechanism of pigmentation in the body wall of the purple sea cucumber. We analyzed the proteomes of purple sea cucumber in early pigmentation stage (Pa), mid pigmentation stage (Pb) and late pigmentation stage (Pc), resulting in the identification of 5580 proteins, including 1099 differentially expressed proteins in Pb: Pa and 339 differentially expressed proteins in Pc: Pb. GO and KEGG analyses revealed possible differentially expressed proteins, including"melanogenesis", "melanosome", "melanoma", "pigment-biosynthetic process", "Epidermis development", "Ras-signaling pathway", "Wnt-signaling pathway", "response to UV light", and "tyrosine metabolism", involved in pigment synthesis and regulation in purple sea cucumbers. The large number of differentially expressed proteins identified here should be highly useful in further elucidating the mechanisms underlying pigmentation in sea cucumbers. Furthermore, these results may also provide the base for further identification of proteins involved in resistance mechanisms against melanoma, albinism, UV damage, and other diseases in sea cucumbers.

Phosphorylation of Pkp1 by RIPK4 regulates epidermal differentiation and skin tumorigenesis

Tissue homeostasis of skin is sustained by epidermal progenitor cells localized within the basal layer of the skin epithelium. Post-translational modification of the proteome, such as protein phosphorylation, plays a fundamental role in the regulation of stemness and differentiation of somatic stem cells. However, it remains unclear how phosphoproteomic changes occur and contribute to epidermal differentiation. In this study, we survey the epidermal cell differentiation in a systematic manner by combining quantitative phosphoproteomics with mammalian kinome cDNA library screen. This approach identified a key signaling event, phosphorylation of a desmosome component, PKP1 (plakophilin-1) by RIPK4 (receptor-interacting serine-threonine kinase 4) during epidermal differentiation. With genome-editing and mouse genetics approach, we show that loss of function of either Pkp1 or Ripk4 impairs skin differentiation and enhances epidermal carcinogenesis in vivo Phosphorylation of PKP1's N-terminal domain by RIPK4 is essential for their role in epidermal differentiation. Taken together, our study presents a global view of phosphoproteomic changes that occur during epidermal differentiation, and identifies RIPK-PKP1 signaling as novel axis involved in skin stratification and tumorigenesis.

Epidermal CD147 expression plays a key role in IL-22-induced psoriatic dermatitis

Psoriasis is a chronic inflammatory skin disease characterized by abnormal keratinocyte proliferation and terminal differentiation. Interleukin-22 (IL-22) and the transcription factor Stat3 play pivotal roles in the pathogenesis of psoriasis. CD147 is a transmembrane glycosylation protein that belongs to the immunoglobulin superfamily. Our previous studies have shown that CD147 is a marker of high keratinocyte proliferation and poor keratinocyte differentiation as well as a psoriasis susceptibility gene. The current study demonstrates that CD147 is highly expressed in psoriatic skin lesions. Specific CD147 over-expression in the epidermis of K5-promoter transgenic mice promotes imiquimod (IMQ)-induced psoriasis-like inflammation characterized by acanthosis, granular layer loss and inflammatory cell infiltration. We also found that IL-22 increases CD147 transcription in vitro and in vivo and that Stat3 binds directly to the CD147 promoter between positions -854 and -440, suggesting that CD147 expression is up-regulated in patients with psoriasis through Stat3 activation. In addition, CD147 knockdown dramatically blocks IL-22-mediated Stat3 activation as well as IL-22-induced cytokine, chemokine and antimicrobial factor expression. Together, these findings show that CD147 is a novel and key mediator of IL-22-induced psoriatic alterations in the epidermis and might be a therapeutic target in patients with psoriasis.

Stellera chamaejasme and its constituents induce cutaneous wound healing and anti-inflammatory activities

Stellera chamaejasme L. (Thymelaeaceae) is a perennial herb that is widely used in traditional Chinese medicine to treat tumours, tuberculosis and psoriasis. S. chamaejasme extract (SCE) possesses anti-inflammatory, analgesic and wound healing activities; however, the effect of S. chamaejasme and its active compounds on cutaneous wound healing has not been investigated. We assessed full-thickness wounds of Sprague-Dawley (SD) rats and topically applied SCE for 2 weeks. In vitro studies were performed using HaCaT keratinocytes, Hs68 dermal fibroblasts and RAW 264.7 macrophages to determine cell viability (MTT assay), cell migration, collagen expression, nitric oxide (NO) production, prostaglandin E₂ (PGE₂) production, inflammatory cytokine expression and β-catenin activation. In vivo, wound size was reduced and epithelisation was improved in SCE-treated SD rats. In vitro, SCE and its active compounds induced keratinocyte migration by regulating the β-catenin, extracellular signal-regulated kinase and Akt signalling pathways. Furthermore, SCE and its active compounds increased mRNA expression of type I and III collagen in Hs68 fibroblasts. SCE and chamechromone inhibited NO and PGE₂ release and mRNA expression of inflammatory mediators in RAW 264.7 macrophages. SCE enhances the motility of HaCaT keratinocytes and improves cutaneous wound healing in SD rats.

Epidermal RAF prevents allergic skin disease

The RAS pathway is central to epidermal homeostasis, and its activation in tumors or in Rasopathies correlates with hyperproliferation. Downstream of RAS, RAF kinases are actionable targets regulating keratinocyte turnover; however, chemical RAF inhibitors paradoxically activate the pathway, promoting epidermal proliferation. We generated mice with compound epidermis-restricted BRAF/RAF1 ablation. In these animals, transient barrier defects and production of chemokines and Th2-type cytokines by keratinocytes cause a disease akin to human atopic dermatitis, characterized by IgE responses and local and systemic inflammation. Mechanistically, BRAF and RAF1 operate independently to balance MAPK signaling: BRAF promotes ERK activation, while RAF1 dims stress kinase activation. In vivo, JNK inhibition prevents disease onset, while MEK/ERK inhibition in mice lacking epidermal RAF1 phenocopies it. These results support a primary role of keratinocytes in the pathogenesis of atopic dermatitis, and the animals lacking BRAF and RAF1 in the epidermis represent a useful model for this disease.

Oncogenic Ras: A double-edged sword for human epidermal stem and transient amplifying cells

The human epidermal clonal evolution, i.e. the transition from stem cells (SCs) to transient amplifying (TA)-cells and post-mitotic cells, is a continuous and tightly regulated process that ensures physiologic tissue homeostasis. The Ras family of small GTPases has a key role in skin homeostasis and tumorigenesis. Indeed, activating mutations in Ras genes have been found in human cutaneous squamous cell carcinomas (cSCCs) and in experimentally-induced murine cSCCs. In mouse models, the Ras signaling might lead to hyperproliferative phenotypes, including the development of cSCCs, depending on the nature of the founding cells. Tumor-initiating cells or Cancer Stem Cells (CSCs) have been demonstrated in murine and human cSCCs even if the mechanism of their development from normal SCs or TA-cells is not completely elucidated. Here, the relation between the Ras expression outcome and the clonogenic potential of the target keratinocyte is discussed.

The role of oncogenic Ras in human skin tumorigenesis depends on the clonogenic potential of the founding keratinocytes

The role of Ras in human skin tumorigenesis induction is still ambiguous. Overexpression of oncogenic Ras causes premature senescence in cultured human cells and hyperplasia in transgenic mice. Here, we investigated whether the oncogenic insult outcome might depend on the nature of the founding keratinocyte. We demonstrate that overexpression of the constitutively active Ras-V12 induces senescence in primary human keratinocyte cultures, but that some cells escape senescence and proliferate indefinitely. Ras overexpression in transient-amplifying- or stem-cell-enriched cultures shows that p16 (encoded by CDKN2A) levels are crucial for the final result. Indeed, transient-amplifying keratinocytes expressing high levels of p16 are sensitive to Ras-V12-induced senescence, whereas cells with high proliferative potential, but that do not display p16, are resistant. The subpopulation that sustains the indefinite culture growth exhibits stem cell features. Bypass of senescence correlates with inhibition of the pRb (also known as RB1) pathway and resumption of telomerase reverse transcriptase (TERT) activity. Immortalization is also sustained by activation of the ERK1 and ERK2 (ERK1/2, also known as MAPK3 and MAPK1) and Akt pathways. Moreover, only transduced cultures originating from cultures bearing stem cells induce tumors in nude mice. Our findings demonstrate that the Ras overexpression outcome depends on the clonogenic potential of the recipient keratinocyte and that only the stem cell compartment is competent to initiate tumorigenesis.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

EGFR-ras-raf signaling in epidermal stem cells: roles in hair follicle development, regeneration, tissue remodeling and epidermal cancers

The mammalian skin is the largest organ of the body and its outermost layer, the epidermis, undergoes dynamic lifetime renewal through the activity of somatic stem cell populations. The EGFR-Ras-Raf pathway has a well-described role in skin development and tumor formation. While research mainly focuses on its role in cutaneous tumor initiation and maintenance, much less is known about Ras signaling in the epidermal stem cells, which are the main targets of skin carcinogenesis. In this review, we briefly discuss the properties of the epidermal stem cells and review the role of EGFR-Ras-Raf signaling in keratinocyte stem cells during homeostatic and pathological conditions.

Gardiquimod inhibits the expression of calcium-induced differentiation markers in HaCaT cells

Toll-like receptor 7 (TLR7) is an important member in pattern recognition receptors families. TLR7 signal pathway is involved in the physiological process in many type cells, but the impact of TRL7 on differentiation in the human keratinocytes is still unknown. In this study, we investigated the expression of TLR7 in keratinocytes, and the effect of TLR7 agonist gardiquimod on the expression of calcium (Ca(2+))-induced keratinocytes differentiation markers in HaCaT cells. Immunohistochemistry and western-blotting analysis showed that TLR7 is expressed in basal keratinocytes of normal skin and in the human keratinocyte cell line HaCaT, but not expressed in the keratinocytes of psoriasis lesions. Pretreatment with gardiquimod could down-regulate Ca(2+)-induced differentiation marker expression and activate Raf-MEK-ERK and PI3K-AKT signal pathways in HaCaT cells. However, specific inhibitors studies showed that the down-regulation of the differentiation markers expression by gardiquimod was not dependent on the activation of these two pathways. TLR7 may play an important role in the pathogenesis of psoriasis through regulating the differentiation of the keratinocytes, and will give a new insight into the psoriasis.

Ras signaling is essential for skin development

Proliferation in the epidermis is a tightly controlled process. During skin development, epidermis formation and hair follicle morphogenesis crucially depend on the regulated balance between proliferation and differentiation. Here we deleted all three Ras loci (H-Ras, N-Ras and K-Ras) from keratinocytes in vitro as well as specifically from the epidermis in mice using a K5Cre strain. Upon Ras elimination, keratinocytes ceased proliferation and entered into senescence without any signs of apoptosis induction. Constitutive activation of the mitogen-activated protein kinase pathway was able to partially rescue the proliferative defects. In mice, Ras signaling was essential for proper development of the epidermis and hair follicles. Deletion of the three Ras loci during epidermis formation in mouse embryos caused a dramatic decrease in proliferation, resulting in a substantially thinner epidermis and delayed appearance of differentiation markers. We could not detect apoptotic or senescent cells in these embryos suggesting that loss of Ras protein expression only leads to severe hypoproliferation. These observations provide genetic evidence for an essential role of Ras proteins in the control of keratinocyte and epidermal proliferation.

RKIP regulates MAP kinase signaling in cells with defective B-Raf activity

MAP kinase (MAPK) signaling results from activation of Raf kinases in response to external or internal stimuli. Here, we demonstrate that Raf kinase inhibitory protein (RKIP) regulates the activation of MAPK when B-Raf signaling is defective. We used multiple models including mouse embryonic fibroblasts (MEFs) and primary keratinocytes from RKIP- or Raf-deficient mice as well as allografts in mice to investigate the mechanism. Loss of B-Raf protein or activity significantly reduces MAPK activation in these cells. We show that RKIP depletion can rescue the compromised ERK activation and promote proliferation, and this rescue occurs through a Raf-1 dependent mechanism. These results provide formal evidence that RKIP is a bona fide regulator of Raf-1. We propose a new model in which RKIP plays a key role in regulating the ability of cells to signal through Raf-1 to ERK in B-Raf compromised cells.

In Drosophila, RhoGEF2 cooperates with activated Ras in tumorigenesis through a pathway involving Rho1-Rok-Myosin-II and JNK signalling

The Ras oncogene contributes to ≈ 30% of human cancers, but alone is not sufficient for tumorigenesis. In a Drosophila screen for oncogenes that cooperate with an activated allele of Ras (Ras(ACT)) to promote tissue overgrowth and invasion, we identified the GTP exchange factor RhoGEF2, an activator of Rho-family signalling. Here, we show that RhoGEF2 also cooperates with an activated allele of a downstream effector of Ras, Raf (Raf(GOF)). We dissect the downstream pathways through which RhoGEF2 cooperates with Ras(ACT) (and Raf(GOF)), and show that RhoGEF2 requires Rho1, but not Rac, for tumorigenesis. Furthermore, of the Rho1 effectors, we show that RhoGEF2 + Ras (Raf)-mediated tumorigenesis requires the Rho kinase (Rok)-Myosin-II pathway, but not Diaphanous, Lim kinase or protein kinase N. The Rho1-Rok-Myosin-II pathway leads to the activation of Jun kinase (JNK), in cooperation with Ras(ACT). Moreover, we show that activation of Rok or Myosin II, using constitutively active transgenes, is sufficient for cooperative tumorigenesis with Ras(ACT), and together with Ras(ACT) leads to strong activation of JNK. Our results show that Rok-Myosin-II activity is necessary and sufficient for Ras-mediated tumorigenesis. Our observation that activation of Myosin II, which regulates Filamentous actin (F-actin) contractility without affecting F-actin levels, cooperates with Ras(ACT) to promote JNK activation and tumorigenesis, suggests that increased cell contractility is a key factor in tumorigenesis. Furthermore, we show that signalling via the Tumour necrosis factor (TNF; also known as Egr)-ligand-JNK pathway is most likely the predominant pathway that activates JNK upon Rok activation. Overall, our analysis highlights the need for further analysis of the Rok-Myosin-II pathway in cooperation with Ras in human cancers.

The molecular genetics of eyelid tumors: recent advances and future directions

BACKGROUND

Unprecedented recent advances in the molecular genetics of cutaneous malignancies have markedly improved our ability to diagnose, treat, and counsel patients with skin tumors. This review provides an update on molecular genetics of periocular cutaneous basal cell carcinoma, squamous cell carcinoma, sebaceous carcinoma, Merkel cell carcinoma, and malignant melanoma and describes how the knowledge of molecular genetics is translated into clinical practice.

METHODS

A literature search of peer-reviewed and indexed publications from 1965 to 2012 using the PubMed search engine was performed. Key terms included: molecular genetics, eyelid, basal cell carcinoma, squamous cell carcinoma, sebaceous adenoma, sebaceous epithelioma, sebaceoma, sebaceous carcinoma, Merkel cell carcinoma, and melanoma. Seminal articles prior to 1965 were selected from primary sources and reviews from the initial search. Articles were chosen based on pertinence to clinical, genetic, and therapeutic topics reviewed in this manuscript.

RESULTS

We reviewed the literature regarding the advances in molecular genetics of cutaneous basal cell carcinoma, squamous cell carcinoma, sebaceous neoplasia, Merkel cell carcinoma, and malignant melanoma, and possible future directions towards diagnosing and treating cutaneous tumors at the genetic level. Cell culture experiments, animal models, and molecular genetic studies on the patients' tumor tissues helped to elucidate genetic aberrations in these lesions. Cell culture experiments, animal studies and, ultimately, clinical trials provided means to test and develop novel therapeutic strategies, namely targeted therapy directed at specific molecular genetic defects. While remarkable progress has been made in this process, the complexity of the molecular genetics of skin tumors makes complete elucidation of the genetic mechanisms and the search for ideal therapies challenging.

CONCLUSIONS

The recent studies focusing on molecular genetics of cutaneous malignancies show promising results, thereby improving our ability to diagnose, treat and counsel patients with these lesions. Future studies will hopefully help unravel further molecular mechanisms involved in cutaneous neoplasia and provide insights into novel preventative and therapeutic modalities.

The Scribble-Dlg-Lgl polarity module in development and cancer: from flies to man

The Scribble, Par and Crumbs modules were originally identified in the vinegar (fruit) fly, Drosophila melanogaster, as being critical regulators of apico-basal cell polarity. In the present chapter we focus on the Scribble polarity module, composed of Scribble, discs large and lethal giant larvae. Since the discovery of the role of the Scribble polarity module in apico-basal cell polarity, these proteins have also been recognized as having important roles in other forms of polarity, as well as regulation of the actin cytoskeleton, cell signalling and vesicular trafficking. In addition to these physiological roles, an important role for polarity proteins in cancer progression has also been uncovered, with loss of polarity and tissue architecture being strongly correlated with metastatic disease.

Valproic acid induces cutaneous wound healing in vivo and enhances keratinocyte motility

Background

Cutaneous wound healing is a complex process involving several signaling pathways such as the Wnt and extracellular signal-regulated kinase (ERK) signaling pathways. Valproic acid (VPA) is a commonly used antiepileptic drug that acts on these signaling pathways; however, the effect of VPA on cutaneous wound healing is unknown.

Methods and Findings

We created full-thickness wounds on the backs of C3H mice and then applied VPA. After 7 d, we observed marked healing and reduced wound size in VPA-treated mice. In the neo-epidermis of the wounds, β-catenin and markers for keratinocyte terminal differentiation were increased after VPA treatment. In addition, α-smooth muscle actin (α-SMA), collagen I and collagen III in the wounds were significantly increased. VPA induced proliferation and suppressed apoptosis of cells in the wounds, as determined by Ki67 and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining analyses, respectively. In vitro, VPA enhanced the motility of HaCaT keratinocytes by activating Wnt/β-catenin, ERK and phosphatidylinositol 3-kinase (PI3-kinase)/Akt signaling pathways.

Conclusions

VPA enhances cutaneous wound healing in a murine model and induces migration of HaCaT keratinocytes.

Tumor type-dependent function of the par3 polarity protein in skin tumorigenesis

Cell polarization is crucial during development and tissue homeostasis and is regulated by conserved proteins of the Scribble, Crumbs, and Par complexes. In mouse skin tumorigenesis, Par3 deficiency results in reduced papilloma formation and growth. Par3 mediates its tumor-promoting activity through regulation of growth and survival, since Par3 deletion increases apoptosis and reduces growth in vivo and in vitro. In contrast, Par3-deficient mice are predisposed to formation of keratoacanthomas, cutaneous tumors thought to originate from different cellular origin and frequently observed in humans. Par3 expression is reduced in both mouse and human keratoacanthomas, indicating tumor-suppressive properties of Par3. Our results identify a dual function of Par3 in skin cancer, with both pro-oncogenic and tumor-suppressive activity depending on the tumor type.

Essential, non-redundant roles of B-Raf and Raf-1 in Ras-driven skin tumorigenesis

Ras-driven tumorigenesis is assumed to depend on Raf for ERK activation and proliferation; yet, an in vivo requirement for Raf as MEK/ERK activator in this setting has not been demonstrated to date. Here, we show that epidermis-restricted B-Raf ablation restrains the onset and stops the progression of established Ras-driven tumors by limiting MEK/ERK activation and proliferation. Concomitant elimination of B-Raf and Raf-1 enforces the abrupt regression of established tumors owing to the decrease in ERK activation and proliferation caused by B-Raf ablation combined with the ERK-independent increase in Rho-dependent kinase (Rok) signaling and differentiation triggered by Raf-1 inactivation. Thus, B-Raf and Raf-1 have non-redundant functions in Ras-driven tumorigenesis. Of note, Raf kinase inhibitors achieve impressive results in melanomas harboring oncogenic BRAF, but are ineffective against Ras-driven tumors; moreover, therapy-related skin tumors driven by a paradox ERK activation as well as primary and acquired resistance have been reported. Our results suggest that therapies targeting both Raf kinase-dependent and -independent pathways may be effective against a broader range of malignancies and reduce the risks of adverse effects and/or resistance.

Cell polarity proteins and cancer

Cell polarity is essential in many biological processes and required for development as well as maintenance of tissue integrity. Loss of polarity is considered both a hallmark and precondition for human cancer. Three conserved polarity protein complexes regulate different modes of polarity that are conserved throughout numerous cell types and species. These complexes are the Crumbs, Par and Scribble complex. Given the importance of cell polarity for normal tissue homeostasis, aberrant polarity signaling is suggested to contribute to the multistep processes of human cancer. Most human cancers are formed from epithelial cells. Evidence confirming the roles for polarity proteins in different phases of the oncogenic trajectory comes from functional studies using mammalian cells as well as Drosophila and zebrafish models. Furthermore, several reports have revealed aberrant expression and localization of polarity proteins in different human tumors. In this review we will give an overview on the current data available that couple polarity signaling to tumorigenesis, particularly in epithelial cells.

The molecular basis of making spiral ganglion neurons and connecting them to hair cells of the organ of Corti

The bipolar spiral ganglion neurons apparently delaminate from the growing cochlear duct and migrate to Rosenthal's canal. They project radial fibers to innervate the organ of Corti (type I neurons to inner hair cells, type II neurons to outer hair cells) and also project tonotopically to the cochlear nuclei. The early differentiation of these neurons requires transcription factors to regulate migration, pathfinding and survival. Neurog1 null mice lack formation of neurons. Neurod1 null mice show massive neuronal death combined with aberrant central and peripheral projections. Prox1 protein is necessary for proper type II neuron process navigation, which is also affected by the neurotrophins Bdnf and Ntf3. Neurotrophin null mutants show specific patterns of neuronal loss along the cochlea but remaining neurons compensate by expanding their target area. All neurotrophin mutants have reduced radial fiber growth proportional to the degree of loss of neurotrophin alleles. This suggests a simple dose response effect of neurotrophin concentration. Keeping overall concentration constant, but misexpressing one neurotrophin under regulatory control of another one results in exuberant fiber growth not only of vestibular fibers to the cochlea but also of spiral ganglion neurons to outer hair cells suggesting different effectiveness of neurotrophins for spiral ganglion neurite growth. Finally, we report here for the first time that losing all neurons in double null mutants affects extension of the cochlear duct and leads to formation of extra rows of outer hair cells in the apex, possibly by disrupting the interaction of the spiral ganglion with the elongating cochlea.