Expression of soluble adenylyl cyclase in lentigo maligna: use of immunohistochemistry with anti-soluble adenylyl cyclase antibody (R21) in diagnosis of lentigo maligna and assessment of margins

Biochemical pharmacology of adenylyl cyclases in cancer

Globally, despite extensive research and pharmacological advancement, cancer remains one of the most common causes of mortality. Understanding the signaling pathways involved in cancer progression is essential for the discovery of new drug targets. The adenylyl cyclase (AC) superfamily comprises glycoproteins that regulate intracellular signaling and convert ATP into cyclic AMP, an important second messenger. The present review highlights the involvement of ACs in cancer progression and suppression, broken down for each specific mammalian AC isoform. The precise mechanisms by which ACs contribute to cancer cell proliferation and invasion are not well understood and are variable among cancer types; however, AC overactivation, along with that of downstream regulators, presents a potential target for novel anticancer therapies. The expression patterns of ACs in numerous cancers are discussed. In addition, we highlight inhibitors of AC-related signaling that are currently under investigation, with a focus on possible anti-cancer strategies. Recent discoveries with small molecules regarding more direct modulation AC activity are also discussed in detail. A more comprehensive understanding of different components in AC-related signaling could potentially lead to the development of novel therapeutic strategies for personalized oncology and might enhance the efficacy of chemoimmunotherapy in the treatment of various cancers.

Diagnosis and Management of Lentigo Maligna: Clinical Presentation and Comprehensive Review

Lentigo maligna (LM), also known as Hutchinson's melanotic freckle, is a form of in situ melanoma characterized by the proliferation of atypical melanocytes along the basal epidermis in sun-damaged skin. If left untreated, LM will progress to lentigo maligna melanoma (LMM), a form of invasive melanoma with the same prognosis as other forms of invasive melanoma. LM is more common in the elderly, with a peak occurrence between the ages of 65 and 80 years. LM, however, is rarely present on the trunk and extremities. The diagnosis of LM, confirmed by histopathological and biopsy examination, is based on clinical and dermoscopic features. It typically begins as a tan-brown macule or patch, but it can progress to a variegated pigmentation with dark black color or even amelanotic characteristics. The risk factors involved in the LM development include a history of sunburns, lighter skin types, advanced age, history of nonmelanoma skin cancers, and tendency to form solar lentigines. This article explains the clinical presentation of LM, also reviews the available information on the diagnosis and management of LM, and discusses the potential of such information in facilitating the future prospective.

Molecular and biochemical characterization of the bicarbonate-sensing soluble adenylyl cyclase from a bony fish, the rainbow trout Oncorhynchus mykiss

Soluble adenylyl cyclase (sAC) is a HC O 3   - -stimulated enzyme that produces the ubiquitous signalling molecule cAMP, and deemed an evolutionarily conserved acid-base sensor. However, its presence is not yet confirmed in bony fishes, the most abundant and diverse of vertebrates. Here, we identified sAC genes in various cartilaginous, ray-finned and lobe-finned fish species. Next, we focused on rainbow trout sAC (rtsAC) and identified 20 potential alternative spliced mRNAs coding for protein isoforms ranging in size from 28 to 186 kDa. Biochemical and kinetic analyses on purified recombinant rtsAC protein determined stimulation by HC O 3   - at physiologically relevant levels for fish internal fluids (EC₅₀ ∼ 7 mM). rtsAC activity was sensitive to KH7, LRE1, and DIDS (established inhibitors of sAC from other organisms), and insensitive to forskolin and 2,5-dideoxyadenosine (modulators of transmembrane adenylyl cyclases). Western blot and immunocytochemistry revealed high rtsAC expression in gill ion-transporting cells, hepatocytes, red blood cells, myocytes and cardiomyocytes. Analyses in the cell line RTgill-W1 suggested that some of the longer rtsAC isoforms may be preferentially localized in the nucleus, the Golgi apparatus and podosomes. These results indicate that sAC is poised to mediate multiple acid-base homeostatic responses in bony fishes, and provide cues about potential novel functions in mammals.

Cyclic adenosine monophosphate (cAMP) signaling in melanocyte pigmentation and melanomagenesis

The second messenger cyclic adenosine monophosphate (cAMP) regulates numerous functions in both benign melanocytes and melanoma cells. cAMP is generated from two distinct sources, transmembrane and soluble adenylyl cyclases (tmAC and sAC, respectively), and is degraded by a family of proteins called phosphodiesterases (PDEs). cAMP signaling can be regulated in many different ways and can lead to varied effects in melanocytes. It was recently revealed that distinct cAMP signaling pathways regulate pigmentation by either altering pigment gene expression or the pH of melanosomes. In the context of melanoma, many studies report seemingly contradictory roles for cAMP in tumorigenesis. For example, cAMP signaling has been implicated in both cancer promotion and suppression, as well as both therapy resistance and sensitization. This conundrum in the field may be explained by the fact that cAMP signals in discrete microdomains and each microdomain can mediate differential cellular functions. Here, we review the role of cAMP signaling microdomains in benign melanocyte biology, focusing on pigmentation, and in melanomagenesis.

Mammalian pigmentation is regulated by a distinct cAMP-dependent mechanism that controls melanosome pH

The production of melanin increases skin pigmentation and reduces the risk of skin cancer. Melanin production depends on the pH of melanosomes, which are more acidic in lighter-skinned than in darker-skinned people. We showed that inhibition of soluble adenylyl cyclase (sAC) controlled pigmentation by increasing the pH of melanosomes both in cells and in vivo. Distinct from the canonical melanocortin 1 receptor (MC1R)-dependent cAMP pathway that controls pigmentation by altering gene expression, we found that inhibition of sAC increased pigmentation by increasing the activity of tyrosinase, the rate-limiting enzyme in melanin synthesis, which is more active at basic pH. We demonstrated that the effect of sAC activity on pH and melanin production in human melanocytes depended on the skin color of the donor. Last, we identified sAC inhibitors as a new class of drugs that increase melanosome pH and pigmentation in vivo, suggesting that pharmacologic inhibition of this pathway may affect skin cancer risk or pigmentation conditions.

Melanocytic soluble adenylyl cyclase protein expression around lentigo maligna and in contralateral control skin

Recurrence rates of both lentigo maligna (LM) and lentigo maligna melanoma (LMM) following conventional surgery are usually relatively high. We aimed to assess the frequencies of melanocytes in tumour-free margins around LM/LMM using soluble adenylyl cyclase (sAC) immunohistochemistry, and to compare these with those of matched healthy contralateral skin. Using the primary mouse-anti-human sAC antibody R21, we evaluated pan-nuclear melanocytic R21 immunostaining, and found that it was significantly (P < 0.001) higher in peritumoural melanocytes (median 20%; range 0-100%) than in contralateral healthy skin (mean 0%; range 0-20%). Accordingly, there was no correlation between peritumoural and contralateral R21 immunoreactivity (r = 0.12; P = 0.18). In conclusion, melanocytic R21 immunoreactivity in melanocytes is higher in tumour-free margins around LM/LMM than in site-matched contralateral skin. This observation may indicate that the biology of 'healthy'-appearing melanocytes around LM/LMM might be different from that of truly benign melanocytes.

Evaluation of MITF, SOX10, MART-1, and R21 Immunostaining for the Diagnosis of Residual Melanoma In Situ on Chronically Sun-Damaged Skin

BACKGROUND

Melanocytic immunostains can assist in margin evaluation of melanoma in situ (MIS) excisions; however, their accuracy and reliability relative to hematoxylin & eosin (H&E) is yet to be determined.

OBJECTIVE

The objective of this study was to evaluate the sensitivity, specificity, and concordance of 4 melanocyte-specific immunostains for diagnosing MIS occurring on chronically sun-damaged skin.

MATERIALS AND METHODS

Serial permanent sections from representative areas of negative margin and residual tumor were stained using H&E, MITF, MART-1, SOX10, and R21 and examined in a blinded fashion. The study set included 100 digital microscopy images from 10 cases of MIS excisions from the face. Two board-certified dermatopathologists, 4 fellowship-trained Mohs surgeons, 2 Mohs fellows, and 2 dermatology residents independently reviewed the 100 images.

RESULTS

The average melanocyte density was 11 versus 28 melanocytes per 0.5 mm for chronically sun-damaged skin versus residual MIS on H&E, respectively. Statistically significantly higher melanocyte densities were observed using MITF, MART-1, and SOX10 on negative margins. The sensitivity and interobserver concordance was highest using MITF and SOX10. The intraobserver agreement on 4 duplicate images was 85%.

CONCLUSION

In conclusion, the nuclear immunostains (MITF and SOX10) show the most promise for improving the diagnosis of MIS in chronically sun-damaged skin.

Functional Significance of the Adcy10-Dependent Intracellular cAMP Compartments

Mounting evidence confirms the compartmentalized structure of evolutionarily conserved 3'⁻5'-cyclic adenosine monophosphate (cAMP) signaling, which allows for simultaneous participation in a wide variety of physiological functions and ensures specificity, selectivity and signal strength. One important player in cAMP signaling is soluble adenylyl cyclase (sAC). The intracellular localization of sAC allows for the formation of unique intracellular cAMP microdomains that control various physiological and pathological processes. This review is focused on the functional role of sAC-produced cAMP. In particular, we examine the role of sAC-cAMP in different cellular compartments, such as cytosol, nucleus and mitochondria.

The metabolic/pH sensor soluble adenylyl cyclase is a tumor suppressor protein

cAMP signaling pathways can both stimulate and inhibit the development of cancer; however, the sources of cAMP important for tumorigenesis remain poorly understood. Soluble adenylyl cyclase (sAC) is a non-canonical, evolutionarily conserved, nutrient- and pH-sensing source of cAMP. sAC has been implicated in the metastatic potential of certain cancers, and it is differentially localized in human cancers as compared to benign tissues. We now show that sAC expression is reduced in many human cancers. Loss of sAC increases cellular transformation in vitro and malignant progression in vivo. These data identify the metabolic/pH sensor soluble adenylyl cyclase as a previously unappreciated tumor suppressor protein.

Elevated cyclic AMP levels promote BRAFCA/Pten-/- mouse melanoma growth but pCREB is negatively correlated with human melanoma progression

Melanocyte development and differentiation are regulated by cAMP, which is produced by the adenylate cyclase (AC) enzyme upon activation of the melanocortin-1-receptor (MC1R). Individuals carrying single amino acid substitution variants of MC1R have impaired cAMP signaling and higher risk of melanoma. However, the contribution of AC to this risk is not clear. Downstream of AC, the phosphorylated transcription factor, cyclic AMP Responsive Element Binding Protein (pCREB), which is activated by protein kinase A, regulates the expression of several genes including the melanocyte master regulator MITF. The roles of AC and CREB in melanoma development and growth are not well understood. Here, we investigated the effect of topical application of AC inhibitor on Braf^CA/Pten^-/- mouse melanoma development. We show that AC inhibitor delays melanoma growth independent of MAPK pathway activity and melanin content. Next, employing a primary melanoma tissue microarray and quantitative immunohistochemistry, we show that pCREB levels are positively correlated with the proliferative status of melanoma, but low pCREB expression is associated with tumor aggressiveness and metastatic recurrence. These data suggest that low cAMP signaling inhibits tumor growth but is a predictor of melanoma aggressiveness.

Reviewing Challenges in the Diagnosis and Treatment of Lentigo Maligna and Lentigo-Maligna Melanoma

Lentigo maligna (LM) and lentigo-maligna melanoma (LMM) are pigmented skin lesions that may exist on a continuous clinical and pathological spectrum of melanocytic skin cancer. LM is often described as a "benign" lesion and is accepted as a melanoma in situ; LM can undergo malignant transformation to particularly aggressive melanoma. LMM is an invasive melanoma that shares properties of LM, as well as exhibiting the metastatic potential of malignant melanoma. Unfortunately, LM/LMM diagnosis based on dermoscopy is rather ambiguous, and these lesions are often mistaken for junctional dysplastic nevi over sun-damaged skin, pigmented actinic keratosis, solar lentigo, or seborrheic keratosis. Diagnosis must be made on biopsy using distinct dermatopathologic features. These include a pagetoid appearance of melanocytes, melanocyte atypia, non-uniform pigmentation/distribution of melanocytes, and increased melanocyte density in a background of extensive photodamage. Advancements in immunohistochemical staining techniques, including soluble adenylyl cyclase (antibody R21), makes diagnosis easier and allows the definition of borders down to a single cell. After a pathologic diagnosis, there are a variety of treatment options, both surgical and non-surgical. Although surgical removal with a wide excision border is the preferred treatment due to decreased recurrence rates, experimental combination therapies are gaining popularity. However, no matter the treatment, LM/LMM carries a high recurrence rate, and patients must be monitored rigorously for recurrence as well as the appearance of additional skin lesions/cancers.

Diagnosis and management of lentigo maligna: a review

Lentigo maligna is a melanocytic neoplasm occurring on sun-exposed skin, usually on the head and neck, of middle-aged and elderly patients. It is thought to represent the in situ phase of lentigo maligna melanoma. The ill-defined nature and potentially large size of lesions can pose significant diagnostic and treatment challenges. The goal of therapy is to cure the lesions in order to prevent development of invasive disease, and surgical excision is the treatment of choice to achieve clear histological margins. Nonsurgical treatment modalities have been reported; however, evidence is lacking to support their use. Age, general health, and comorbidities need to be taken into account when deciding the right treatment modality for each individual patient.

Lentigo maligna and lentigo maligna melanoma: contemporary issues in diagnosis and management

Lentigo maligna and lentigo maligna melanomas present diagnostic and treatment dilemmas due to their frequent presence within a background of sun-damaged skin, and their location on cosmetically and functionally sensitive areas. As the incidence of this entity is increasing, diagnostic and management controversies have developed. While surgery remains the gold standard of treatment, nonsurgical treatment options are also emerging for both adjunctive and primary therapy.

Established and potential physiological roles of bicarbonate-sensing soluble adenylyl cyclase (sAC) in aquatic animals

Soluble adenylyl cyclase (sAC) is a recently recognized source of the signaling molecule cyclic AMP (cAMP) that is genetically and biochemically distinct from the classic G-protein-regulated transmembrane adenylyl cyclases (tmACs). Mammalian sAC is distributed throughout the cytoplasm and it may be present in the nucleus and inside mitochondria. sAC activity is directly stimulated by HCO3(-), and sAC has been confirmed to be a HCO3(-) sensor in a variety of mammalian cell types. In addition, sAC can functionally associate with carbonic anhydrases to act as a de facto sensor of pH and CO2. The two catalytic domains of sAC are related to HCO3(-)-regulated adenylyl cyclases from cyanobacteria, suggesting the cAMP pathway is an evolutionarily conserved mechanism for sensing CO2 levels and/or acid/base conditions. Reports of sAC in aquatic animals are still limited but are rapidly accumulating. In shark gills, sAC senses blood alkalosis and triggers compensatory H(+) absorption. In the intestine of bony fishes, sAC modulates NaCl and water absorption. And in sea urchin sperm, sAC may participate in the initiation of flagellar movement and in the acrosome reaction. Bioinformatics and RT-PCR results reveal that sAC orthologs are present in most animal phyla. This review summarizes the current knowledge on the physiological roles of sAC in aquatic animals and suggests additional functions in which sAC may be involved.

Investigation of cAMP microdomains as a path to novel cancer diagnostics

Understanding of cAMP signaling has greatly improved over the past decade. The advent of live cell imaging techniques and more specific pharmacologic modulators has led to an improved understanding of the intricacies by which cAMP is able to modulate such a wide variety of cellular pathways. It is now appreciated that cAMP is able to activate multiple effector proteins at distinct areas in the cell leading to the activation of very different downstream targets. The investigation of signaling proteins in cancer is a common route to the development of diagnostic tools, prognostic tools, and/or therapeutic targets, and in this review we highlight how investigation of cAMP signaling microdomains driven by the soluble adenylyl cyclase in different cancers has led to the development of a novel cancer biomarker. Antibodies directed against the soluble adenylyl cyclase (sAC) are highly specific markers for melanoma especially for lentigo maligna melanoma and are being described as "second generation" cancer diagnostics, which are diagnostics that determine the 'state' of a cell and not just identify the cell type. Due to the wide presence of cAMP signaling pathways in cancer, we predict that further investigation of both sAC and other cAMP microdomains will lead to additional cancer biomarkers. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Cyclic AMP (cAMP) signaling in melanocytes and melanoma

G-protein coupled receptors (GPCRs), which include melanocortin-1 receptor (MC1R), play a crucial role in melanocytes development, proliferation and differentiation. Activation of the MC1R by the α-melanocyte stimulating hormone (α-MSH) leads to the activation of the cAMP signaling pathway that is mainly associated with differentiation and pigment production. Some MC1R polymorphisms produce cAMP signaling impairment and pigmentary phenotypes such as the red head color and fair skin phenotype (RHC) that is usually associated with higher risk for melanoma development. Despite its importance in melanocyte biology, the role of cAMP signaling cutaneous melanoma is not well understood. Melanoma is primarily driven by mutations in the components of mitogen-activated protein kinases (MAPK) pathway. Increasing evidence, however, now suggests that cAMP signaling also plays an important role in melanoma even though genetic alterations in components of this pathway are note commonly found in melanoma. Here we review these new roles for cAMP in melanoma including its contribution to the notorious treatment resistance of melanoma.

The application of monoclonal antibodies in cancer diagnosis

Cancer becomes the second leading cause of death in the world. An effective strategy for early diagnosis of the disease is key to reduce the mortality and morbidity. Development of effective monoclonal antibody (mAb)-based assays or diagnostic imaging techniques for detection of antigens and small molecules that are released from cancerous cells will enhance modern diagnostic medicine of cancer significantly. Although mAb technology is still under development, recent advances in preparation of recombinant antigen and antibody engineering techniques have dramatically enhanced the applications of this technology in cancer diagnosis. Compared with other methods, mAb-based assays may provide spatial, temporal, accurate and quantitative measurement for diagnosis of the disease. This review summarizes the progress of the mAb-based assays in the field of molecular diagnosis of cancer.