Genomic analysis identifies new drivers and progression pathways in skin basal cell carcinoma

Hedgehog Pathway Inhibitors against Tumor Microenvironment

Targeting the hedgehog (HH) pathway to treat aggressive cancers of the brain, breast, pancreas, and prostate has been ongoing for decades. Gli gene amplifications have been long discovered within malignant glioma patients, and since then, inhibitors against HH pathway-associated molecules have successfully reached the clinical stage where several of them have been approved by the FDA. Albeit this success rate implies suitable progress, clinically used HH pathway inhibitors fail to treat patients with metastatic or recurrent disease. This is mainly due to heterogeneous tumor cells that have acquired resistance to the inhibitors along with the obstacle of effectively targeting the tumor microenvironment (TME). Severe side effects such as hyponatremia, diarrhea, fatigue, amenorrhea, nausea, hair loss, abnormal taste, and weight loss have also been reported. Furthermore, HH signaling is known to be involved in the regulation of immune cell maturation, angiogenesis, inflammation, and polarization of macrophages and myeloid-derived suppressor cells. It is critical to determine key mechanisms that can be targeted at different levels of tumor development and progression to address various clinical issues. Hence current research focus encompasses understanding how HH controls TME to develop TME altering and combinatorial targeting strategies. In this review, we aim to discuss the pros and cons of targeting HH signaling molecules, understand the mechanism involved in treatment resistance, reveal the role of the HH pathway in anti-tumor immune response, and explore the development of potential combination treatment of immune checkpoint inhibitors with HH pathway inhibitors to target HH-driven cancers.

Targeting RAS phosphorylation in cancer therapy: Mechanisms and modulators

RAS, a member of the small GTPase family, functions as a binary switch by shifting between inactive GDP-loaded and active GTP-loaded state. RAS gain-of-function mutations are one of the leading causes in human oncogenesis, accounting for ∼19% of the global cancer burden. As a well-recognized target in malignancy, RAS has been intensively studied in the past decades. Despite the sustained efforts, many failures occurred in the earlier exploration and resulted in an ‘undruggable’ feature of RAS proteins. Phosphorylation at several residues has been recently determined as regulators for wild-type and mutated RAS proteins. Therefore, the development of RAS inhibitors directly targeting the RAS mutants or towards upstream regulatory kinases supplies a novel direction for tackling the anti-RAS difficulties. A better understanding of RAS phosphorylation can contribute to future therapeutic strategies. In this review, we comprehensively summarized the current advances in RAS phosphorylation and provided mechanistic insights into the signaling transduction of associated pathways. Importantly, the preclinical and clinical success in developing anti-RAS drugs targeting the upstream kinases and potential directions of harnessing allostery to target RAS phosphorylation sites were also discussed.

Morphologic, Immunohistochemical, and Genetic Differences Between High-grade and Low-grade Fetal Adenocarcinomas of the Lung

Fetal adenocarcinoma of the lung (FLAC) is a rare lung tumor classified into low-grade fetal adenocarcinoma of the lung (LG-FLAC) and high-grade fetal adenocarcinoma of the lung (HG-FLAC). It remains debatable whether HG-FLAC is a subset of FLAC or a distinct subtype of the conventional lung adenocarcinoma (CLA). In this study, samples of 4 LG-FLAC and 2 HG-FLAC cases were examined, and the clinicopathologic, immunohistochemical (IHC), and mutational differences between the 2 subtypes were analyzed using literature review. Morphologically, LG-FLACs had a pure pattern with complex glandular architecture composed of cells with subnuclear and supranuclear vacuoles, mimicking a developing fetal lung. In contrast, HG-FLACs contained both fetal lung-like (FLL) and CLA components. With regard to IHC markers, β-catenin exhibited a nuclear/cytoplasmic staining pattern in LG-FLACs but a membranous staining pattern in HG-FLACs. Furthermore, p53 was expressed diffusely and strongly in HG-FLACs, whereas in LG-FLACs, p53 staining was completely absent. Using next-generation sequencing targeting a 1021-gene panel, mutations of CTNNB1 and DICER1 were detected in all 4 LG-FLAC samples, and a novel mutation, MYCN P44L, was discovered in 2 LG-FLAC samples. DNA samples of the FLL and CLA components of HG-FLACs were separately extracted and sequenced. The FLL component harbored no CTNNB1, DICER1, or MYCN mutations; moreover, the FLL genetic profile largely overlapped with that of the CLA component. The morphologic, IHC, and genetic features of HG-FLAC indicate that it is a variant of CLA rather than a subset of FLAC. Thus, HG-FLAC should be treated differently from LG-FLAC.

c-FOS drives reversible basal to squamous cell carcinoma transition

While squamous transdifferentiation within subpopulations of adenocarcinomas represents an important drug resistance problem, its underlying mechanism remains poorly understood. Here, using surface markers of resistant basal cell carcinomas (BCCs) and patient single-cell and bulk transcriptomic data, we uncover the dynamic roadmap of basal to squamous cell carcinoma transition (BST). Experimentally induced BST identifies activator protein 1 (AP-1) family members in regulating tumor plasticity, and we show that c-FOS plays a central role in BST by regulating the accessibility of distinct AP-1 regulatory elements. Remarkably, despite prominent changes in cell morphology and BST marker expression, we show using inducible model systems that c-FOS-mediated BST demonstrates reversibility. Blocking EGFR pathway activation after c-FOS induction partially reverts BST in vitro and prevents BST features in both mouse models and human tumors. Thus, by identifying the molecular basis of BST, our work reveals a therapeutic opportunity targeting plasticity as a mechanism of tumor resistance.

Subtype-Specific Analyses Reveal Infiltrative Basal Cell Carcinomas Are Highly Interactive with their Environment

Little is known regarding the molecular differences between basal cell carcinoma (BCC) subtypes, despite clearly distinct phenotypes and clinical outcomes. In particular, infiltrative BCCs have poorer clinical outcomes in terms of response to therapy and propensity for dissemination. In this project, we aimed to use exome sequencing and RNA sequencing to identify somatic mutations and molecular pathways leading to infiltrative BCCs. Using whole-exome sequencing of 36 BCC samples (eight infiltrative) combined with previously reported exome data (58 samples), we determine that infiltrative BCCs do not contain a distinct somatic variant profile and carry classical UV-induced mutational signatures. RNA sequencing on both datasets revealed key differentially expressed genes, such as POSTN and WISP1, suggesting increased integrin and Wnt signaling. Immunostaining for periostin and WISP1 clearly distinguished infiltrative BCCs, and nuclear β-catenin staining patterns further validated the resulting increase in Wnt signaling in infiltrative BCCs. Of significant interest, in BCCs with mixed morphology, infiltrative areas expressed WISP1, whereas nodular areas did not, supporting a continuum between subtypes. In conclusion, infiltrative BCCs do not differ in their genomic alteration in terms of initiating mutations. They display a specific type of interaction with the extracellular matrix environment regulating Wnt signaling.

Targeted Sequencing Revealed Distinct Mutational Profiles of Ocular and Extraocular Sebaceous Carcinomas

The biological behavior of sebaceous carcinoma (SeC) is relatively indolent; however, local invasion or distant metastasis is sometimes reported. Nevertheless, a lack of understanding of the genetic background of SeC makes it difficult to apply effective systemic therapy. This study was designed to investigate major genetic alterations in SeCs in Korean patients. A total of 29 samples, including 20 ocular SeCs (SeC-Os) and 9 extraocular SeCs (SeC-EOs), were examined. Targeted next-generation sequencing tests including 171 cancer-related genes were performed. TP53 and PIK3CA genes were frequently mutated in both SeC-Os and SeC-EOs with slight predominance in SeC-Os, whereas the NOTCH1 gene was more commonly mutated in SeC-EOs. In clinical correlation, mutations in RUNX1 and ATM were associated with development of distant metastases, and alterations in MSH6 and BRCA1 were associated with inferior progression-free survival (all p < 0.05). In conclusion, our study revealed distinct genetic alterations between SeC-Os and SeC-EOs and some important prognostic molecular markers. Mutations in potentially actionable genes, including EGFR, ERBB2, and mismatch repair genes, were noted, suggesting consideration of a clinical trial in intractable cases.

FBW7 couples structural integrity with functional output of primary cilia

Structural defects in primary cilia have robust effects in diverse tissues and systems. However, how disorders of ciliary length lead to functional outcomes are unknown. We examined the functional role of a ciliary length control mechanism of FBW7-mediated destruction of NDE1, in mesenchymal stem cell (MSC) differentiation. We show that FBW7 functions as a master regulator of both negative (NDE1) and positive (TALPID3) regulators of ciliogenesis, with an overall positive net effect on primary cilia formation, MSC differentiation to osteoblasts, and bone architecture. Deletion of Fbxw7 suppresses ciliation, Hedgehog activity, and differentiation, which are partially rescued in Fbxw7/Nde1-null cells. We also show that NDE1, despite suppressing ciliogenesis, promotes MSC differentiation by increasing the activity of the Hedgehog pathway by direct binding and enhancing GLI2 activity in a cilia-independent manner. We propose that FBW7 controls a protein-protein interaction network coupling ciliary structure and function, which is essential for stem cell differentiation.

Petsouki et al. dissect the importance of FBW7-mediated regulation of NDE1 and TALPID3 in mesenchymal stem cells (MSCs). They find that by modulating the abundance of negative (NDE1) and positive (TALPID3) cilia regulators, FBW7 contributes to both the assembly and signaling functions of primary cilia that are necessary for osteoblast differentiation.

Casein Kinase 1D Encodes a Novel Drug Target in Hedgehog-GLI-Driven Cancers and Tumor-Initiating Cells Resistant to SMO Inhibition

Simple Summary

Uncontrolled activation of hedgehog (HH)—GLI signaling contributes to the development of several human malignancies. Targeted inhibition of the HH—GLI signaling cascade with small-molecule inhibitors can reduce cancer growth, but patient relapse is very common due to the development of drug resistance. Therefore, a high unmet medical need exists for new drug targets and inhibitors to achieve efficient and durable responses. In the current study, we identified CSNK1D as a novel drug target in the HH—GLI signaling pathway. Genetic and pharmacological inhibition of CSNK1D activity leads to suppression of oncogenic HH—GLI signaling, even in cancer cells in which already approved HH inhibitors are no longer effective due to resistance mechanisms. Inhibition of CSNK1D function reduces the malignant properties of so-called tumor-initiating cells, thereby limiting cancer growth and presumably metastasis. The results of this study form the basis for the development of efficient CSNK1D inhibitors for the therapy of HH—GLI-associated cancers.

Abstract

(1) Background: Aberrant activation of the hedgehog (HH)—GLI pathway in stem-like tumor-initiating cells (TIC) is a frequent oncogenic driver signal in various human malignancies. Remarkable efficacy of anti-HH therapeutics led to the approval of HH inhibitors targeting the key pathway effector smoothened (SMO) in basal cell carcinoma and acute myeloid leukemia. However, frequent development of drug resistance and severe adverse effects of SMO inhibitors pose major challenges that require alternative treatment strategies targeting HH—GLI in TIC downstream of SMO. We therefore investigated members of the casein kinase 1 (CSNK1) family as novel drug targets in HH—GLI-driven malignancies. (2) Methods: We genetically and pharmacologically inhibited CSNK1D in HH-dependent cancer cells displaying either sensitivity or resistance to SMO inhibitors. To address the role of CSNK1D in oncogenic HH signaling and tumor growth and initiation, we quantitatively analyzed HH target gene expression, performed genetic and chemical perturbations of CSNK1D activity, and monitored the oncogenic transformation of TIC in vitro and in vivo using 3D clonogenic tumor spheroid assays and xenograft models. (3) Results: We show that CSNK1D plays a critical role in controlling oncogenic GLI activity downstream of SMO. We provide evidence that inhibition of CSNK1D interferes with oncogenic HH signaling in both SMO inhibitor-sensitive and -resistant tumor settings. Furthermore, genetic and pharmacologic perturbation of CSNK1D decreases the clonogenic growth of GLI-dependent TIC in vitro and in vivo. (4) Conclusions: Pharmacologic targeting of CSNK1D represents a novel therapeutic approach for the treatment of both SMO inhibitor-sensitive and -resistant tumors.

The Role of Circular RNAs in Keratinocyte Carcinomas

Keratinocyte carcinomas (KC) include basal cell carcinomas (BCC) and cutaneous squamous cell carcinomas (cSCC) and represents the most common cancer in Europe and North America. Both entities are characterized by a very high mutational burden, mainly UV signature mutations. Predominately mutated genes in BCC belong to the sonic hedgehog pathway, whereas, in cSCC, TP53, CDKN2A, NOTCH1/2 and others are most frequently mutated. In addition, the dysregulation of factors associated with epithelial to mesenchymal transition (EMT) was shown in invasive cSCC. The expression of factors associated with tumorigenesis can be controlled in several ways and include non-coding RNA molecules, such as micro RNAs (miRNA) long noncoding RNAs (lncRNA) and circular RNAs (circRNA). To update findings on circRNA in KC, we reviewed 13 papers published since 2016, identified in a PubMed search. In both BCC and cSCC, numerous circRNAs were identified that were differently expressed compared to healthy skin. Some of them were shown to target miRNAs that are also dysregulated in KC. Moreover, some studies confirmed the biological functions of individual circRNAs involved in cancer development. Thus, circRNAs may be used as biomarkers of disease and disease progression and represent potential targets of new therapeutic approaches for KC.

Known and new facts on basal cell carcinoma

Basal cell carcinoma (BCC) is the most common malignant tumor in light‐skinned people and amounts to about 75 % of all cases of skin cancer. Increasing incidence rates have been reported for decades all over the world. The main risk factors include UV radiation, male sex, light skin type, advanced age, long‐term immunosuppression, a positive individual or family history, and certain genodermatoses. BCC metastasizes only rarely, and its mortality is low, but it is associated with significant morbidity. Genetic mutations especially in the hedgehog pathway play an important role in BCC pathogenesis. Non‐invasive procedures such as optical coherence tomography or confocal laser scan microscopy are increasingly utilized for diagnostics in addition to visual inspection and dermatoscopy, but only in exceptional cases can histological confirmation of the diagnosis be dispensed with. Various clinical and histological subtypes have been defined. Differentiating between BCC with high and low risk of recurrence has a significant influence on the choice of treatment. Most BCC can be treated effectively and safely with standard surgery, or in selected cases with topical treatment. Locally advanced and metastasized BCC must be treated with radiation or systemic therapy. Radiation is also an option for older patients with contraindications for surgery. The hedgehog inhibitors vismodegib and sonidegib are currently approved for systemic therapy of BCC in Europe. Approval for the PD1 inhibitor cemiplimab as second‐line therapy is expected in the near future.

A systematic summary of survival and death signalling during the life of hair follicle stem cells

Hair follicle stem cells (HFSCs) are among the most widely available resources and most frequently approved model systems used for studying adult stem cells. HFSCs are particularly useful because of their self-renewal and differentiation properties. Additionally, the cyclic growth of hair follicles is driven by HFSCs. There are high expectations for the use of HFSCs as favourable systems for studying the molecular mechanisms that contribute to HFSC identification and can be applied to hair loss therapy, such as the activation or regeneration of hair follicles, and to the generation of hair using a tissue-engineering strategy. A variety of molecules are involved in the networks that critically regulate the fate of HFSCs, such as factors in hair follicle growth and development (in the Wnt pathway, Sonic hedgehog pathway, Notch pathway, and BMP pathway), and that suppress apoptotic cues (the apoptosis pathway). Here, we review the life cycle, biomarkers and functions of HFSCs, concluding with a summary of the signalling pathways involved in HFSC fate for promoting better understanding of the pathophysiological changes in the HFSC niche. Importantly, we highlight the potential mechanisms underlying the therapeutic targets involved in pathways associated with the treatment of hair loss and other disorders of skin and hair, including alopecia, skin cancer, skin inflammation, and skin wound healing.

The combined effect of CO2 laser, topical diclofenac 3%, and imiquimod 5% in treating high-risk basal cell carcinoma

BACKGROUND

Some basal cell carcinoma (BCC) patients are considered as a high risk regarding the site, size, histopathological variant, or recurrence. High-risk BCC is a challenging therapeutic problem due to the trial to balance between complete surgical excision from one side and tissue preservation from the other side.

AIM

To evaluate the efficacy of combining ablative CO₂  laser, imiquimod 5%, and diclofenac 3% as a therapeutic regimen in high-risk and inoperable BCC.

PATIENTS/METHODS

The study was conducted on 14 patients that were assessed clinically and pathologically then categorized regarding the site, size, histopathology, and fitness for surgery as high-risk inoperable BCC. They received an ablative session of CO₂  laser, followed by application of diclofenac sodium 3% gel once daily for 5 days and imiquimod 5% cream for another 2 days.

RESULTS

The study included 11 males and 3 females. Nine lesions were located on the scalp, 4 on the face, and one lesion on the trunk. All lesions were of large size >5 cm in diameter. Histopathology showed 4 patterns: nodular type in 8 patients, infiltrating type in 3 patients, metatypical type in 2 patients, and micronodular type in one patient. At the end of the treatment period, 9 patients showed significant (moderate to marked) improvement while 5 patients showed weak (poor to mild) response. Significant improvement was more observed in nodular type. Relapse was more observed during the 5^th to 6th months with 2 patients showed no relapse.

CONCLUSION

This combined regimen is a good alternative therapeutic modality in high-risk inoperable BCC especially the nodular pathologic pattern.

Review of the Molecular Genetics of Basal Cell Carcinoma; Inherited Susceptibility, Somatic Mutations, and Targeted Therapeutics

Simple Summary

Basal cell carcinoma is the most common human cancer worldwide. The molecular basis of BCC involves an interplay of inherited genetic susceptibility and somatic mutations, commonly induced by exposure to UV radiation. In this review, we outline the currently known germline and somatic mutations implicated in the pathogenesis of BCC with particular attention paid toward affected molecular pathways. We also discuss polymorphisms and associated phenotypic traits in addition to active areas of BCC research. We finally provide a brief overview of existing non-surgical treatments and emerging targeted therapeutics for BCC such as Hedgehog pathway inhibitors, immune modulators, and histone deacetylase inhibitors.

Abstract

Basal cell carcinoma (BCC) is a significant public health concern, with more than 3 million cases occurring each year in the United States, and with an increasing incidence. The molecular basis of BCC is complex, involving an interplay of inherited genetic susceptibility, including single nucleotide polymorphisms and genetic syndromes, and sporadic somatic mutations, often induced by carcinogenic exposure to UV radiation. This review outlines the currently known germline and somatic mutations implicated in the pathogenesis of BCC, including the key molecular pathways affected by these mutations, which drive oncogenesis. With advances in next generation sequencing and our understanding of the molecular genetics of BCC, established and emerging targeted therapeutics are offering new avenues for the non-surgical treatment of BCC. These agents, including Hedgehog pathway inhibitors, immune modulators, and histone deacetylase inhibitors, will also be discussed.

Molecular profiling of basal cell carcinomas in young patients

BACKGROUND

Basal cell carcinoma (BCC) represents by far the most common non-melanoma skin cancer (NMSC) in the world with an increasing incidence of 3% to 10% per year, especially in patients under the age of 40. While variants in the sonic Hedgehog and cell cycle regulation pathways account for the majority of BCC cases in adults, the molecular etiology of BCC in young patients is unelucidated yet. This study aims to investigate the molecular profile of BCC in the young population.

METHODS

28 tumors belonging to 25 Lebanese patients under the age of 40, presenting different stages of BCC and diagnosed at Hôtel Dieu de France-Saint Joseph University Medical Center were included in this study. A selected panel of 150 genes involved in cancer was analyzed by Next Generation Sequencing (NGS) in the 28 included tumors.

RESULTS

Genetic variants detected in more than 5% of the reads, with a sequencing depth ≥ 50x, were selected. Two hundred and two genetic variants in 48 different genes were detected, with an overall average sequencing depth of 1069x. Among the 28 studied tumors, 18 (64.3%) show variations in the PTCH1 gene, 6 (21.4%) in TP53 and 3 (10.7%) in SMO.

CONCLUSIONS

This is the first study reporting NGS-based analysis of BCC in a cohort of young patients. Our results highlight the involvement of the hedgehog and cell cycle regulation pathways in the genesis of BCC in the general population. The inclusion of a larger cohort of young patients is needed to confirm our findings.

Hippo Signaling Pathway as a New Potential Target in Non-Melanoma Skin Cancers: A Narrative Review

Non-melanoma skin cancers (NMSCs), including basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), are the most frequently diagnosed cancers in humans, however, their exact pathogenesis is not fully understood. In recent years, it has been hypothesized that the recently discovered Hippo pathway could play a detrimental role in cutaneous carcinogenesis, but no direct connections have been made. The Hippo pathway and its effector, YAP, are responsible for tissue growth by accelerating cell proliferation, however, YAP upregulation and overexpression have also been reported in numerous types of tumors. There is also evidence that disrupted YAP/Hippo signaling is responsible for cancer growth, invasion, and metastasis. In this short review, we will explore whether the Hippo pathway is an important regulator of skin carcinogenesis and if it could be a promising target for future therapies.

Constitutive GLI1 expression in chondrosarcoma is regulated by major vault protein via mTOR/S6K1 signaling cascade

Hedgehog signaling plays a pivotal role in embryonic pattern formation and diverse aspects of the postnatal biological process. Perturbation of the hedgehog pathway and overexpression of GLI1, a downstream transcription factor in the hedgehog pathway, are highly relevant to several malignancies including chondrosarcoma (CS). We previously found that knocking down expression of GLI1 attenuates the disrupted Indian hedgehog (IHH) signal pathway and suppresses cell survival in human CS cells. However, the underlying mechanisms regulating the expression of GLI1 are still unknown. Here, we demonstrated the implication of GLI1 in SMO-independent pathways in CS cells. A GLI1 binding protein, major vault protein (MVP), was identified using the affinity purification method. MVP promoted the nuclear transport and stabilization of GLI1 by compromising the binding affinity of GLI1 with suppressor of fused homolog (SUFU) and increased GLI1 expression via mTOR/S6K1 signaling cascade. Functionally, knockdown of MVP suppressed cell growth and induced apoptosis. Simultaneous inhibition of MVP and GLI1 strongly inhibits the growth of CS in vitro and in vivo. Moreover, IHC results showed that MVP, GLI1, and P-p70S6K1 were highly expressed and positively correlated with each other in 71 human CS tissues. Overall, our findings revealed a novel regulating mechanism for HH-independent GLI1 expression and provide a rationale for combination therapy in patients with advanced CS.

Ppp6c deficiency accelerates K-rasG12D -induced tongue carcinogenesis

BACKGROUND

Effective treatments for cancer harboring mutant RAS are lacking. In Drosophila, it was reported that PP6 suppresses tumorigenicity of mutant RAS. However, the information how PP6 regulates oncogenic RAS in mammals is limited.

METHODS

We examined the effects of PP6 gene (Ppp6c) deficiency on tongue tumor development in K (K-rasG12D)- and KP (K-rasG12D + Trp53-deficient)-inducible mice.

RESULTS

Mice of K and KP genotypes developed squamous cell carcinoma in situ in the tongue approximately 2 weeks after the induction of Ppp6c deficiency and was euthanized due to 20% loss of body weight. Transcriptome analysis revealed significantly different gene expressions between tissues of Ppp6c-deficient tongues and those of Ppp6c wild type, while Trp53 deficiency had a relatively smaller effect. We then analyzed genes commonly altered by Ppp6c deficiency, with or without Trp53 deficiency, and identified a group concentrated in KEGG database pathways defined as 'Pathways in Cancer' and 'Cytokine-cytokine receptor interaction'. We then evaluated signals downstream of oncogenic RAS and those regulated by PP6 substrates and found that in the presence of K-rasG12D, Ppp6c deletion enhanced the activation of the ERK-ELK1-FOS, AKT-4EBP1, and AKT-FOXO-CyclinD1 axes. Ppp6c deletion combined with K-rasG12D also enhanced DNA double-strand break (DSB) accumulation and activated NFκB signaling, upregulating IL-1β, COX2, and TNF.

PI3K Promotes Basal Cell Carcinoma Growth Through Kinase-Induced p21 Degradation

Basal cell carcinoma (BCC) is a locally invasive epithelial cancer that is primarily driven by the Hedgehog (HH) pathway. Advanced BCCs are a critical subset of BCCs that frequently acquire resistance to Smoothened (SMO) inhibitors and identifying pathways that bypass SMO could provide alternative treatments for patients with advanced or metastatic BCC. Here, we use a combination of RNA-sequencing analysis of advanced human BCC tumor-normal pairs and immunostaining of human and mouse BCC samples to identify a PI3K pathway expression signature in BCC. Pharmacological inhibition of PI3K activity in BCC cells significantly reduces cell proliferation and HH signaling. However, treatment of Ptch1^fl/fl; Gli1-Cre^ERT2 mouse BCCs with the PI3K inhibitor BKM120 results in a reduction of tumor cell growth with no significant effect on HH signaling. Downstream PI3K components aPKC and Akt1 showed a reduction in active protein, whereas their substrate, cyclin-dependent kinase inhibitor p21, showed a concomitant increase in protein stability. Our results suggest that PI3K promotes BCC tumor growth by kinase-induced p21 degradation without altering HH signaling.

Molecular alterations in basal cell carcinoma subtypes

A number of genes have been implicated in the pathogenesis of BCC in addition to the Hedgehog pathway, which is known to drive the initiation of this tumour. We performed in-depth analysis of 13 BCC-related genes (CSMD1, CSMD2, DPH3 promoter, PTCH1, SMO, GLI1, NOTCH1, NOTCH2, TP53, ITIH2, DPP10, STEAP4, TERT promoter) in 57 BCC lesions (26 superficial and 31 nodular) from 55 patients and their corresponding blood samples. PTCH1 and TP53 mutations were found in 71.9% and 45.6% of BCCs, respectively. A high mutation rate was also detected in CSMD1 (63.2%), NOTCH1 (43.8%) and DPP10 (35.1%), and frequent non-coding mutations were identified in TERT (57.9%) and DPH3 promoter (49.1%). CSMD1 mutations significantly co-occurred with TP53 changes (p = 0.002). A significant association was observed between the superficial type of BCC and PTCH1 (p = 0.018) and NOTCH1 (p = 0.020) mutations. In addition, PTCH1 mutations were significantly associated with intermittent sun exposure (p = 0.046) and the occurrence of single lesions (p = 0.021), while NOTCH1 mutations were more frequent in BCCs located on the trunk compared to the head/neck and extremities (p = 0.001). In conclusion, we provide further insights into the molecular alterations underlying the tumorigenic mechanism of superficial and nodular BCCs with a view towards novel rationale-based therapeutic strategies.

Merkel Cell Carcinoma from Molecular Pathology to Novel Therapies

Merkel cell carcinoma (MCC) is an uncommon and highly aggressive skin cancer. It develops mostly within chronically sun-exposed areas of the skin. MCPyV is detected in 60-80% of MCC cases as integrated within the genome and is considered a major risk factor for MCC. Viral negative MCCs have a high mutation burden with a UV damage signature. Aberrations occur in RB1, TP53, and NOTCH genes as well as in the PI3K-AKT-mTOR pathway. MCC is highly immunogenic, but MCC cells are known to evade the host's immune response. Despite the characteristic immunohistological profile of MCC, the diagnosis is challenging, and it should be confirmed by an experienced pathologist. Sentinel lymph node biopsy is considered the most reliable staging tool to identify subclinical nodal disease. Subclinical node metastases are present in about 30-50% of patients with primary MCC. The basis of MCC treatment is surgical excision. MCC is highly radiosensitive. It becomes chemoresistant within a few months. MCC is prone to recurrence. The outcomes in patients with metastatic disease are poor, with a historical 5-year survival of 13.5%. The median progression-free survival is 3-5 months, and the median overall survival is ten months. Currently, immunotherapy has become a standard of care first-line therapy for advanced MCC.

Aberrant Expression of PTPN-14 and Wilms’ Tumor 1 as Putative Biomarker for Locoregional Recurrence in Oral Squamous Cell Carcinoma

Objective Locoregional recurrence in oral squamous cell carcinoma (OSCC) is a major concern that leads to metastasis. Its detection at earliest stage is very important to increase the overall survival of the patient. There is no any biomarker for locoregional recurrence in oral squamous cell carcinoma (OSCC). The aim of this study was to find a biomarker for locoregional recurrence in tissue and serum at gene and protein level.

Methods This work studied the expression of protein tyrosine phosphatase nonreceptor type 14 (PTPN-14) and Wilms’ tumor 1 (WT-1) in patients and correlated their expression with locoregional recurrence and survival. Tissue expression was observed in formalin fixed tissue biopsies of 96 OSCC and 32 healthy controls by immunohistochemistry using antibody against PTPN-14 and WT-1 and serum level was estimated by enzyme-linked immunosorbent assay in pre- and post-chemoradiotherapy samples. mRNA expression was determined by using real-time polymerase chain reaction. Patients were followed for 3 years for locoregional recurrence.

Results Expression of PTPN-14 and WT-1 in OSCC was upregulated (aberrant) in tissue and sera in both gene and protein level as compared with healthy controls. Locoregional recurrence was observed in 10 (23.80%) patients and significantly associated with PTPN-14 (p < 0.047) and WT-1 expression (p < 0.031).

Conclusion PTPN-14 and WT-1 may be used as biomarker to identify patients for higher risk of locoregional recurrence. This study drove molecular aspect and phenotypic level to derive new emergent strategies in future for recurrent OSCC.

Hippo signaling pathway in companion animal diseases, an under investigated signaling cascade

The Hippo pathway is a highly conserved kinase cascade in mammals with the proteins YAP and TAZ as its most important downstream effectors that shuttle between cytoplasma and nucleus. It has a crucial role in processes such as embryogenesis, organ size control, homeostasis and tissue regeneration, where mechanosensing and/or cell-cell interactions are involved. As the pathway is associated with many essential functions in the body, its dysregulation is related to many diseases. In contrast to human pathology, a PubMed-search on Hippo, YAP/TAZ and companion animals (horse, equine, dog, canine, cat, feline) retrieved few publications. Because of its high level of functional conservation, it is anticipated that also in veterinary sciences aberrant Hippo YAP/TAZ signaling would be implicated in animal pathologies. Publications on Hippo YAP/TAZ in companion animals are mainly in cats and dogs and related to oncology. Here, we emphasize the important role of YAP/TAZ in liver diseases. First the liver has a remarkable regeneration capacity and a strict size control and the liver has a moderate liver cell renewal (homeostasis). The last years numerous papers show the importance of YAP/TAZ in hepatocellular carcinoma (HCC), hepatocyte differentiation and bile duct epithelial (BEC) cell survival. YAP/TAZ signaling is involved in activation of hepatic stellate cells crucial in fibrogenesis. The availability of drugs (e.g. verteporfin) targeting the YAP/TAZ pathway are described as is their potential usage in veterinary medicine. The aim of this overview is to stimulate researchers' and clinicians' interest in the potential role of Hippo YAP/TAZ signaling in veterinary medicine.

PTCH1 mutation promotes antitumor immunity and the response to immune checkpoint inhibitors in colorectal cancer patients

Immunotherapy has emerged as an effective therapeutic strategy for various cancers, including colorectal cancer (CRC), but only a subset of MSI-H patients can benefit from such therapy. Patched1 (PTCH1) is a frequently altered gene in CRCs and its mutations contribute to unregulated Hedgehog (Hh) signaling. In the study, we evaluated the association of PTCH1 mutations with CRC immunity based on our single-center cohort and multiple cancer genomic datasets. Among 21 enrolled patients, six (28.6%) harbored a PTCH1 mutation based on WES analyses. In CRC patients, the PTCH1 mutation subgroup experienced a higher durable clinical benefit rate than the PTCH1 wild-type subgroup (100% vs. 40%, P = 0.017). In addition, patients with the PTCH1 mutation experienced greater progression-free survival (PFS, P = 0.037; HR, 0.208) and overall survival (OS, P = 0.045; HR, 0.185). A validation cohort from the MSKCC also confirmed the correlation between PTCH1 mutation and better prognosis (P = 0.022; HR, 0.290). Mechanically, diverse antitumor immune signatures were more highly enriched in PTCH1-mutated tumors than in PTCH1 wild-type tumors. Furthermore, PTCH1-mutated tumors had higher proportions of CD8 + T cells, activated NK cells, and M1 type macrophage infiltration, as well as elevated gene signatures of several steps in the cancer-immunity cycle. Notably, the PTCH1 mutation was correlated with tumor mutational burden (TMB), loss of heterozygosity score, and copy number variation burden. Our results show that the mutation of PTCH1 is a potential biomarker for predicting the response of CRC patients to immunotherapy.

Generation and Characterization of a CRISPR/Cas9-Mediated SNAP29 Knockout in Human Fibroblasts

Loss-of-function mutations in the synaptosomal-associated protein 29 (SNAP29) lead to the rare autosomal recessive neurocutaneous cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma (CEDNIK) syndrome. SNAP29 is a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein. So far, it has been shown to be involved in membrane fusion, epidermal differentiation, formation of primary cilia, and autophagy. Recently, we reported the successful generation of two mouse models for the human CEDNIK syndrome. The aim of this investigation was the generation of a CRISPR/Cas9-mediated SNAP29 knockout (KO) in an immortalized human cell line to further investigate the role of SNAP29 in cellular homeostasis and signaling in humans independently of animal models. Comparison of different methods of delivery for CRISPR/Cas9 plasmids into the cell revealed that lentiviral transduction is more efficient than transfection methods. Here, we reported to the best of our knowledge the first successful generation of a CRISPR/Cas9-mediated SNAP29 KO in immortalized human MRC5Vi fibroblasts (c.169_196delinsTTCGT) via lentiviral transduction.

The transcriptional landscape analysis of basal cell carcinomas reveals novel signalling pathways and actionable targets

Basal cell carcinoma (BCC) is the most common skin cancer and human malignancy. By analyzing BCC RNA sequencing data according to clinically important features, we identified novel differentially regulated genes and new targetable pathways. Several biomarkers were validated in patient-derived BCC samples.

Basal cell carcinoma (BCC) is the most common skin cancer and human malignancy. Although most BCCs are easily managed, some are aggressive locally, require Mohs micrographic surgery, or can even metastasize. In the latter, resistance to Sonic Hedgehog inhibitors may occur. Despite their frequent occurrence in clinical practice, their transcriptional landscape remains poorly understood. By analyzing BCC RNA sequencing data according to clinically important features (all BCCs versus normal skin, high-risk versus low-risk BCCs based solely on histopathological subtypes with aggressive features, advanced versus non-advanced BCCs, and vismodegib-resistant versus vismodegib-sensitive tumors), we have identified novel differentially regulated genes and new targetable pathways implicated in BCC tumorigenesis. Pathways as diverse as IL-17, TLR, Akt/PI3K, cadherins, integrins, PDGF, and Wnt/β-catenin are promising therapeutic avenues for local and systemic agents in managing this common malignancy, including through drug re-purposing of existing medications. We experimentally validated several of these targets as biomarkers in our patient-derived cohort of primary BCC tumors.

Loss of BubR1 acetylation provokes replication stress and leads to complex chromosomal rearrangements

Accurate chromosomal segregation during mitosis is regulated by the spindle assembly checkpoint (SAC). SAC failure results in aneuploidy, a hallmark of cancer. However, many studies have suggested that aneuploidy alone is not oncogenic. We have reported that BubR1 acetylation deficiency in mice (K243R/+) caused spontaneous tumorigenesis via weakened SAC signaling and unstable chromosome-spindle attachment, resulting in massive chromosomal mis-segregation. In addition to aneuploidy, cells derived from K243R/+ mice exhibited moderate genetic instability and chromosomal translocation. Here, we investigated how the loss of BubR1 acetylation led to genetic instability and chromosomal rearrangement. To rescue all chromosomal abnormalities generated by the loss of BubR1 acetylation during development, K243R/+ mice were crossed with p53-deficient mice. Genome-wide sequencing and spectral karyotyping of tumors derived from these double-mutant mice revealed that BubR1 acetylation deficiency was associated with complex chromosomal rearrangements, including Robertsonian-like whole-arm translocations. By analyzing the telomeres and centromeres in metaphase chromosome spreads, we found that BubR1 acetylation deficiency increased the collapse of stalled replication forks, commonly referred to as replication stress, and led to DNA damage and chromosomal rearrangements. BubR1 mutations that are critical in interacting with PCAF acetyltransferase and acetylating K250, L249F and A251P, were found from human cancers. Furthermore, a subset of human cancer cells exhibiting whole-arm translocation also displayed defects in BubR1 acetylation, supporting that defects in BubR1 acetylation in mitosis contributes to tumorigenesis. Collectively, loss of BubR1 acetylation provokes replication stress, particularly at the telomeres, leading to genetic instability and chromosomal rearrangement.

Involvement of transcribed lncRNA uc.291 and SWI/SNF complex in cutaneous squamous cell carcinoma

While non-melanoma skin cancers (NMSCs) are the most common tumours in humans, only the sub-type cutaneous squamous cell carcinoma (cSCC), might become metastatic with high lethality. We have recently identified a regulatory pathway involving the lncRNA transcript uc.291 in controlling the expression of epidermal differentiation complex genes via the interaction with ACTL6A, a component of the chromatin remodelling complex SWI/SNF. Since transcribed ultra-conserved regions (T-UCRs) are expressed in normal tissues and are deregulated in tumorigenesis, here we hypothesize a potential role for dysregulation of this axis in cSCC, accounting for the de-differentiation process observed in aggressive poorly differentiated cutaneous carcinomas. We therefore analysed their expression patterns in human tumour biopsies at mRNA and protein levels. The results suggest that by altering chromatin accessibility of the epidermal differentiation complex genes, down-regulation of uc.291 and BRG1 expression contribute to the de-differentiation process seen in keratinocyte malignancy. This provides future direction for the identification of clinical biomarkers in cutaneous SCC. Analysis of publicly available data sets indicates that the above may also be a general feature for SCCs of different origins.

Targeting epigenetic mechanisms to overcome venetoclax resistance

The BH-3 mimetic venetoclax overcomes apoptosis and therapy resistance caused by high expression of BCL2 or loss of BH3-only protein function. Although a promising therapy for hematologic malignancies, increased expression of anti-apoptotic MCL-1 or BCL-XL, as well as other resistance mechanisms prevent a durable response to venetoclax. Recent studies demonstrate that agents targeting epigenetic mechanisms such as DNA methyltransferase inhibitors, histone deacetylase (HDAC) inhibitors, histone methyltransferase EZH2 inhibitors, or bromodomain reader protein inhibitors may disable oncogenic gene expression signatures responsible for venetoclax resistance. Combination therapies including venetoclax and epigenetic therapies are effective in preclinical models and the subject of many current clinical trials. Here we review epigenetic strategies to overcome venetoclax resistance mechanisms in hematologic malignancies.

The Role of Notch, Hedgehog, and Wnt Signaling Pathways in the Resistance of Tumors to Anticancer Therapies

Resistance to therapy is the major hurdle in the current cancer management. Cancer cells often rewire their cellular process to alternate mechanisms to resist the deleterious effect mounted by different therapeutic approaches. The major signaling pathways involved in the developmental process, such as Notch, Hedgehog, and Wnt, play a vital role in development, tumorigenesis, and also in the resistance to the various anticancer therapies. Understanding how cancer utilizes these developmental pathways in acquiring the resistance to the multi-therapeutic approach cancer can give rise to a new insight of the anti-therapy resistance mechanisms, which can be explored for the development of a novel therapeutic approach. We present a brief overview of Notch, Hedgehog, and Wnt signaling pathways in cancer and its role in providing resistance to various cancer treatment modalities such as chemotherapy, radiotherapy, molecular targeted therapy, and immunotherapy. Understanding the importance of these molecular networks will provide a rational basis for novel and safer combined anticancer therapeutic approaches for the improvement of cancer treatment by overcoming drug resistance.

Dnmt3a deficiency in the skin causes focal, canonical DNA hypomethylation and a cellular proliferation phenotype

DNA hypomethylation is a feature of epidermal cells from aged and sun-exposed skin, but the mechanisms responsible for this methylation loss are not known. Dnmt3a is the dominant de novo DNA methyltransferase in the skin; while epidermal Dnmt3a deficiency creates a premalignant state in which keratinocytes are more easily transformed by topical mutagens, the conditions responsible for this increased susceptibility to transformation are not well understood. Using whole genome bisulfite sequencing, we identified a focal, canonical DNA hypomethylation phenotype in the epidermal cells of Dnmt3a-deficient mice. Single-cell transcriptomic analysis revealed an increased proportion of cells with a proliferative gene expression signature, while other populations in the skin were relatively unchanged. Although total DNMT3A deficiency has not been described in human disease states, rare patients with an overgrowth syndrome associated with behavioral abnormalities and an increased risk of cancer often have heterozygous, germline mutations in DNMT3A that reduce its function (Tatton-Brown Rahman syndrome [TBRS]). We evaluated the DNA methylation phenotype of the skin from a TBRS patient with a germline DNMT3A ^R882H mutation, which encodes a dominant-negative protein that reduces its methyltransferase function by ∼80%. We detected a focal, canonical hypomethylation phenotype that revealed considerable overlap with hypomethylated regions found in Dnmt3a-deficient mouse skin. Together, these data suggest that DNMT3A loss creates a premalignant epigenetic state associated with a hyperproliferative phenotype in the skin and further suggest that DNMT3A acts as a tumor suppressor in the skin.

Clonal expansion in non-cancer tissues

Cancer is a clonal disorder derived from a single ancestor cell and its progenies that are positively selected by acquisition of 'driver mutations'. However, the evolution of positively selected clones does not necessarily imply the presence of cancer. On the contrary, it has become clear that expansion of these clones in phenotypically normal or non-cancer tissues is commonly seen in association with ageing and/or in response to environmental insults and chronic inflammation. Recent studies have reported expansion of clones harbouring mutations in cancer driver genes in the blood, skin, oesophagus, bronchus, liver, endometrium and bladder, where the expansion could be so extensive that tissues undergo remodelling of an almost entire tissue. The presence of common cancer driver mutations in normal tissues suggests a strong link to cancer development, providing an opportunity to understand early carcinogenic processes. Nevertheless, some driver mutations are unique to normal tissues or have a mutation frequency that is much higher in normal tissue than in cancer, indicating that the respective clones may not necessarily be destined for evolution to cancer but even negatively selected for carcinogenesis depending on the mutated gene. Moreover, tissues that are remodelled by genetically altered clones might define functionalities of aged tissues or modified inflammatory processes. In this Review, we provide an overview of major findings on clonal expansion in phenotypically normal or non-cancer tissues and discuss their biological significance not only in cancer development but also in ageing and inflammatory diseases.

Cancer type-specific alterations in actin genes: Worth a closer look?

Actins form a strongly conserved family of proteins that are central to the functioning of the actin cytoskeleton partaking in natural processes such as cell division, adhesion, contraction and migration. These processes, however, also occur during the various phases of cancer progression. Yet, surprisingly, alterations in the six human actin genes in cancer studies have received little attention and the focus was mostly on deregulated expression levels of actins and even more so of actin-binding or regulatory proteins. Starting from the early mutation work in the 1980s, we propose based on reviewing literature and data from patient cancer genomes that alterations in actin genes are different in distinct cancer subtypes, suggesting some specificity. These actin gene alterations include (missense) mutations, gene fusions and copy number alterations (deletions and amplifications) and we illustrate their occurrence for a limited number of examples including actin mutations in lymphoid cancers and nonmelanoma skin cancer and actin gene copy number alterations for breast, prostate and liver cancers. A challenge in the future will be to further sort out the specificity per actin gene, alteration type and cancer subtype. Even more challenging is (experimentally) distinguishing between cause and consequence: which alterations are passengers and which are involved in tumor progression of particular cancer subtypes?

Protein tyrosine phosphatases in cell adhesion

Adhesive structures between cells and with the surrounding matrix are essential for the development of multicellular organisms. In addition to providing mechanical integrity, they are key signalling centres providing feedback on the extracellular environment to the cell interior, and vice versa. During development, mitosis and repair, cell adhesions must undergo extensive remodelling. Post-translational modifications of proteins within these complexes serve as switches for activity. Tyrosine phosphorylation is an important modification in cell adhesion that is dynamically regulated by the protein tyrosine phosphatases (PTPs) and protein tyrosine kinases. Several PTPs are implicated in the assembly and maintenance of cell adhesions, however, their signalling functions remain poorly defined. The PTPs can act by directly dephosphorylating adhesive complex components or function as scaffolds. In this review, we will focus on human PTPs and discuss their individual roles in major adhesion complexes, as well as Hippo signalling. We have collated PTP interactome and cell adhesome datasets, which reveal extensive connections between PTPs and cell adhesions that are relatively unexplored. Finally, we reflect on the dysregulation of PTPs and cell adhesions in disease.

The Tree Shrew as a Model for Cancer Research

Animal disease models are necessary in medical research, and an appropriate animal model is of great importance for studies about the prevention or treatment of cancer. The most important thing in the selection of animal models is to consider the similarity between animals and humans. The tree shrew (Tupaia belangeri) is a squirrel-like mammal which placed in the order Scandentia. Whole-genome sequencing has revealed that tree shrews are extremely similar to primate and humans than to rodents, with many highly conserved genes, which makes the data from studies that use tree shrews as models more convincing and the research outcomes more easily translatable. In tumor research, tree shrews are often used as animal models for hepatic and mammary cancers. As research has progressed, other types of tree shrew tumor models have been developed and exhibit clinical manifestations similar to those of humans. Combining the advantages of both rodents and primates, the tree shrew is expected to be the most powerful animal model for studying tumors.

Basal cell carcinomas of the scalp after radiotherapy for tinea capitis in childhood: A genetic and epigenetic study with comparison with basal cell carcinomas evolving in chronically sun-exposed areas

BACKGROUND

Basal cell carcinoma (BCC) has been mostly associated with sun exposure, but ionizing radiation is also a known risk factor. It is not clear if the pathogenesis of BCC, namely at a genomic and epigenetic level, differs according to the underlying triggering factors.

OBJECTIVE

The present study aims to compare genetic and epigenetic changes in BCCs related to ionizing radiation and chronic sun exposure.

METHODS

Tumor samples from BCCs of the scalp in patients submitted to radiotherapy to treat tinea capitis in childhood and BCCs from sun-exposed areas were analysed through array comparative genomic hybridization (array-CGH) and methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) to detect copy number alterations and methylation status of specific genes.

RESULTS

Genomic characterization of tumor samples revealed several copy number gains and losses in all chromosomes, with the most frequent gains observed at 2p, 6p, 12p, 14q, 15q, 18q, Xp and Yp, and the most frequent losses observed at 3q, 14q, 16p, 17q, 22q, Xp, Yp and Yq. We developed a statistical model, encompassing gains in 3p and 16p and losses in 14q and 20p, with potential to discriminate BCC samples with sporadic aetiology from BCC samples that evolve after radiotherapy in childhood for the treatment of tinea capitis, which presented statistical significance (P = 0.003). Few methylated genes were detected through MS-MLPA, most frequently RARB and CD44.

CONCLUSIONS

Our study represents a step forward in the understanding of the genetic mechanisms underlying the pathogenesis of BCC and suggests potential differences according to the underlying ris k factors.

Hedgehog signaling in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment

The Hedgehog (HH) signaling pathway plays important roles in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment (TME). Aberrant HH signaling activation may accelerate the growth of gastrointestinal tumors and lead to tumor immune tolerance and drug resistance. The interaction between HH signaling and the TME is intimately involved in these processes, for example, tumor growth, tumor immune tolerance, inflammation, and drug resistance. Evidence indicates that inflammatory factors in the TME, such as interleukin 6 (IL-6) and interferon-γ (IFN-γ), macrophages, and T cell-dependent immune responses, play a vital role in tumor growth by affecting the HH signaling pathway. Moreover, inhibition of proliferating cancer-associated fibroblasts (CAFs) and inflammatory factors can normalize the TME by suppressing HH signaling. Furthermore, aberrant HH signaling activation is favorable to both the proliferation of cancer stem cells (CSCs) and the drug resistance of gastrointestinal tumors. This review discusses the current understanding of the role and mechanism of aberrant HH signaling activation in gastrointestinal carcinogenesis, the gastrointestinal TME, tumor immune tolerance and drug resistance and highlights the underlying therapeutic opportunities.

MTOR promotes basal cell carcinoma growth through atypical PKC

Advanced basal cell carcinomas (BCCs) are driven by the Hedgehog (HH) pathway and often possess inherent resistance to SMO inhibitors. Identifying and targeting pathways that bypass SMO could provide alternative treatments for patients with advanced or metastatic BCC. Here, we use a combination of RNA-sequencing analysis of advanced human BCC tumor-normal pairs and immunostaining of human and mouse BCC samples to identify an MTOR expression signature in BCC. Pharmacological inhibition of MTOR activity in BCC cells significantly reduces cell proliferation without affecting HH signalling. Similarly, treatment of the Ptch1 ^fl/fl ; Gli1-Cre^ERT2 mouse BCC tumor model with everolimus reduces tumor growth. aPKC, a downstream target of MTOR, shows reduced activity, suggesting that MTOR promotes tumor growth by activating aPKC and demonstrating that suppressing MTOR could be a promising target for BCC patients.

Distinct transcriptomic landscapes of cutaneous basal cell carcinomas and squamous cell carcinomas

The majority of non-melanoma skin cancer (NMSC) is cutaneous basal cell carcinoma (BCC) or squamous cell carcinoma (SCC), which are also called keratinocyte carcinomas, as both of them originate from keratinocytes. The incidence of keratinocyte carcinomas is over 5 million per year in the US, three-fold higher than the total incidence of all other types of cancer combined. While there are several reports on gene expression profiling of BCC and SCC, there are significant variations in the reported gene expression changes in different studies. One reason is that tumor-adjacent normal skin specimens were not included in many studies as matched controls. Furthermore, while numerous studies of skin stem cells in mouse models have been reported, their relevance to human skin cancer remains unknown. In this report, we analyzed gene expression profiles of paired specimens of keratinocyte carcinomas with their matched normal skin tissues as the control. Among several novel findings, we discovered a significant number of zinc finger encoding genes up-regulated in human BCC. In BCC, a novel link was found between hedgehog signaling, Wnt signaling, and the cilium. While the SCC cancer-stem-cell gene signature is shared between human and mouse SCCs, the hair follicle stem-cell signature of mice was not highly represented in human SCC. Differential gene expression (DEG) in human BCC shares gene signature with both bulge and epidermal stem cells. We have also determined that human BCCs and SCCs have distinct gene expression patterns, and some of them are not fully reflected in current mouse models.

Mechanochemical control of epidermal stem cell divisions by B-plexins

The precise spatiotemporal control of cell proliferation is key to the morphogenesis of epithelial tissues. Epithelial cell divisions lead to tissue crowding and local changes in force distribution, which in turn suppress the rate of cell divisions. However, the molecular mechanisms underlying this mechanical feedback are largely unclear. Here, we identify a critical requirement of B-plexin transmembrane receptors in the response to crowding-induced mechanical forces during embryonic skin development. Epidermal stem cells lacking B-plexins fail to sense mechanical compression, resulting in disinhibition of the transcriptional coactivator YAP, hyperproliferation, and tissue overgrowth. Mechanistically, we show that B-plexins mediate mechanoresponses to crowding through stabilization of adhesive cell junctions and lowering of cortical stiffness. Finally, we provide evidence that the B-plexin-dependent mechanochemical feedback is also pathophysiologically relevant to limit tumor growth in basal cell carcinoma, the most common type of skin cancer. Our data define a central role of B-plexins in mechanosensation to couple cell density and cell division in development and disease.

Loss-of-Function Variants in the Tumor-Suppressor Gene PTPN14 Confer Increased Cancer Risk

The success of genome-wide association studies (GWAS) in identifying common, low-penetrance variant-cancer associations for the past decade is undisputed. However, discovering additional high-penetrance cancer mutations in unknown cancer predisposing genes requires detection of variant-cancer association of ultra-rare coding variants. Consequently, large-scale next-generation sequence data with associated phenotype information are needed. Here, we used genotype data on 166,281 Icelanders, of which, 49,708 were whole-genome sequenced and 408,595 individuals from the UK Biobank, of which, 41,147 were whole-exome sequenced, to test for association between loss-of-function burden in autosomal genes and basal cell carcinoma (BCC), the most common cancer in Caucasians. A total of 25,205 BCC cases and 683,058 controls were tested. Rare germline loss-of-function variants in PTPN14 conferred substantial risks of BCC (OR, 8.0; P = 1.9 × 10^-12), with a quarter of carriers getting BCC before age 70 and over half in their lifetime. Furthermore, common variants at the PTPN14 locus were associated with BCC, suggesting PTPN14 as a new, high-impact BCC predisposition gene. A follow-up investigation of 24 cancers and three benign tumor types showed that PTPN14 loss-of-function variants are associated with high risk of cervical cancer (OR, 12.7, P = 1.6 × 10^-4) and low age at diagnosis. Our findings, using power-increasing methods with high-quality rare variant genotypes, highlight future prospects for new discoveries on carcinogenesis. SIGNIFICANCE: This study identifies the tumor-suppressor gene PTPN14 as a high-impact BCC predisposition gene and indicates that inactivation of PTPN14 by germline sequence variants may also lead to increased risk of cervical cancer.

Molecular Mechanisms of MYCN Dysregulation in Cancers

MYCN, a member of MYC proto-oncogene family, encodes a basic helix-loop-helix transcription factor N-MYC. Abnormal expression of N-MYC is correlated with high-risk cancers and poor prognosis. Initially identified as an amplified oncogene in neuroblastoma in 1983, the oncogenic effect of N-MYC is expanded to multiple neuronal and nonneuronal tumors. Direct targeting N-MYC remains challenge due to its "undruggable" features. Therefore, alternative therapeutic approaches for targeting MYCN-driven tumors have been focused on the disruption of transcription, translation, protein stability as well as synthetic lethality of MYCN. In this review, we summarize the latest advances in understanding the molecular mechanisms of MYCN dysregulation in cancers.

Selection of Oncogenic Mutant Clones in Normal Human Skin Varies with Body Site

Skin cancer risk varies substantially across the body, yet how this relates to the mutations found in normal skin is unknown. Here we mapped mutant clones in skin from high- and low-risk sites. The density of mutations varied by location. The prevalence of NOTCH1 and FAT1 mutations in forearm, trunk, and leg skin was similar to that in keratinocyte cancers. Most mutations were caused by ultraviolet light, but mutational signature analysis suggested differences in DNA-repair processes between sites. Eleven mutant genes were under positive selection, with TP53 preferentially selected in the head and FAT1 in the leg. Fine-scale mapping revealed 10% of clones had copy-number alterations. Analysis of hair follicles showed mutations in the upper follicle resembled adjacent skin, but the lower follicle was sparsely mutated. Normal skin is a dense patchwork of mutant clones arising from competitive selection that varies by location. SIGNIFICANCE: Mapping mutant clones across the body reveals normal skin is a dense patchwork of mutant cells. The variation in cancer risk between sites substantially exceeds that in mutant clone density. More generally, mutant genes cannot be assigned as cancer drivers until their prevalence in normal tissue is known.See related commentary by De Dominici and DeGregori, p. 227.This article is highlighted in the In This Issue feature, p. 211.

Genomic profiling of late-onset basal cell carcinomas from two brothers with nevoid basal cell carcinoma syndrome

BACKGROUND

Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant genetic disorder. It is commonly caused by mutations in PTCH1 and chiefly characterized by multiple basal cell carcinomas (BCCs) developing prior to the age of 30 years. In rare cases, NBCCS presents with a late onset of BCC development.

OBJECTIVE

To investigate BCC tumorigenesis in two brothers, who showed characteristic features of NBCCS but developed their first BCCs only after the age of 40 years. Two other siblings did not show signs of NBCCS.

RESULTS

We obtained blood samples from four siblings and nine BCCs from the two brothers with NBCCS. Whole exome sequencing and RNA sequencing revealed loss of heterozygosity (LOH) of PTCH1 in eight out of nine tumours that consistently involved the same haplotype on chromosome 9. This haplotype contained a germinal splice site mutation in PTCH1 (NM_001083605:exon9:c.763-6C>A). Analysis of germline DNA confirmed segregation of this mutation with the disease. All BCCs harboured additional somatic loss-of-function (LoF) mutations in the remaining PTCH1 allele which are not typically seen in other cases of NBCCS. This suggests a hypomorphic nature of the germinal PTCH1 mutation in this family. Furthermore, all BCCs had a similar tumour mutational burden compared to BCCs of unrelated NBCCS patients while harbouring a higher number of damaging PTCH1 mutations.

CONCLUSIONS

Our data suggest that a sequence of three genetic hits leads to the late development of BCCs in two brothers with NBCCS: a hypomorphic germline mutation, followed by somatic LOH and additional mutations that complete PTCH1 inactivation. These genetic events are in line with the late occurrence of the first BCC and with the higher number of damaging PTCH1 mutations compared to usual cases of NBCCS.