Oncogenic BRAF and the tumor suppressor IGFBP7 in the genesis of atypical spitzoid nevomelanocytic proliferations

Depletion of Igfbp7 alleviates zebrafish NAFLD progression through inhibiting hepatic ferroptosis

AIMS

The global increased expression of Insulin-like growth factor binding protein 7 (IGFBP7) has been detected in non-alcoholic fatty liver disease (NAFLD) patients, however, its roles in NAFLD and the mechanism remain largely unclear. The goal of this study is to investigate the effect and mechanism of Igfbp7 using a zebrafish NAFLD model.

MAIN METHODS

The igfbp7-/- null zebrafish mutant and the Igfbp7 liver overexpressed (LOE) transgenic zebrafish based on Gal4/UAS system were generated by CRISPR/Cas9 and Tol2 transgenic technique, respectively. The zebrafish NAFLD models in wildtypes, igfbp7-/- mutants and Igfbp7 LOE fishes have been established by high-fat diet feeding. The Igfbp7 dynamic expression and its effects on NAFLD progression have been detected and analyzed in both human NAFLD patients and zebrafish models. And the potential mechanism has been investigated through transcriptome analysis and subsequent detection and verification.

KEY FINDINGS

High Igfbp7 levels in NASH and fibrosis stages have been detected in liver tissues of both human NAFLD patients and zebrafish models. Depletion of Igfbp7 significantly alleviated liver steatosis, inflammation, and fibrosis, whereas liver specific Igfbp7 overexpression dramatically exacerbated liver fibrosis in zebrafish NAFLD model. The hepatic iron deposition, lipid peroxidation products, and ferroptosis-related index were also significantly reduced at the NASH stage in the absence of Igfbp7. Igfbp7 promotes NAFLD progression through regulating ferroptosis, and Ncoa4-mediated ferritinophagy may be the pathway of Igfbp7-regulated ferroptosis.

SIGNIFICANCE

Igfbp7 is confirmed as an important regulator in NAFLD progression. Depleting Igfbp7 effectively alleviates zebrafish NAFLD progression by inhibiting hepatic ferroptosis, suggesting a novel potential target for NAFLD treatment.

Combined utility of p16 and BRAF V600E in the evaluation of spitzoid tumors: Superiority to PRAME and correlation with FISH

BACKGROUND

Spitzoid melanocytic neoplasms are diagnostically challenging; criteria for malignancy continue to evolve. The ability to predict chromosomal abnormalities with immunohistochemistry (IHC) could help select cases requiring chromosomal evaluation.

METHODS

Fluorescence in situ hybridization (FISH)-tested spitzoid neoplasms at our institution (2013-2021) were reviewed. p16, BRAF V600E, and preferentially expressed antigen in melanoma (PRAME) IHC results were correlated with FISH.

RESULTS

A total of 174 cases (1.9F:1M, median age 28 years; range, 5 months-74 years) were included; final diagnoses: Spitz nevus (11%), atypical Spitz tumor (47%), spitzoid dysplastic nevus (9%), and spitzoid melanoma (32%). Sixty (34%) were FISH positive, most commonly with absolute 6p25 gain (RREB1 > 2). Dermal mitotic count was the only clinicopathologic predictor of FISH. Among IHC-stained cases, p16 was lost in 55 of 134 cases (41%); loss correlated with FISH positive (p < 0.001, Fisher exact test). BRAF V600E (14/88, 16%) and PRAME (15/56, 27%) expression did not correlate with FISH alone (p = 0.242 and p = 0.359, respectively, Fisher exact test). When examined together, however, p16-retained/BRAF V600E-negative lesions had low FISH-positive rates (5/37, 14%; 4/37, 11% not counting isolated MYB loss); all other marker combinations had high rates (56%-75% of cases; p < 0.001).

CONCLUSIONS

p16/BRAF V600E IHC predicts FISH results. "Low-risk" lesions (p16⁺ /BRAF V600E^- ) uncommonly have meaningful FISH abnormalities (11%). PRAME may have limited utility in this setting.

Genomic Landscape of Spitzoid Neoplasms Impacting Patient Management

Spitzoid neoplasms are a distinct group of melanocytic proliferations characterized by epithelioid and/ or spindle shaped melanocytes. Intermediate forms that share features of both benign Spitz nevi (SN) and Spitz melanoma, i.e., malignant Spitz tumor (MST) represent a diagnostically and clinically challenging group of melanocytic lesions. A multitude of descriptive diagnostic terms exist for these ambiguous lesions with atypical Spitz tumor (AST) or Spitz tumor of uncertain malignant potential (STUMP) just naming two of them. This diagnostic gray zone creates confusion and high insecurity in clinicians and in patients. Biological behavior and clinical course of this intermediate group still remains largely unknown, often leading to difficulties with uncertainties in clinical management and prognosis. Consequently, a better stratification of Spitzoid neoplasms in benign and malignant forms is required thereby keeping the diagnostic group of AST/STUMP as small as possible. Ancillary diagnostic techniques such as immunohistochemistry, comparative genomic hybridization, fluorescence in situ hybridization, next generation sequencing, micro RNA and mRNA analysis as well as mass spectrometry imaging offer new opportunities for the distinct diagnosis, thereby allowing the best clinical management of Spitzoid neoplasms. This review gives an overview on these additional diagnostic techniques and the recent developments in the field of molecular genetic alterations in Spitzoid neoplasms. We also discuss how the recent findings might facilitate the diagnosis and stratification of atypical Spitzoid neoplasms and how these findings will impact the diagnostic work up as well as patient management. We suggest a stepwise implementation of ancillary diagnostic techniques thereby integrating immunohistochemistry and molecular pathology findings in the diagnosis of challenging ambiguous Spitzoid neoplasms. Finally, we will give an outlook on pending future research objectives in the field of Spitzoid melanocytic lesions.

Genetics of melanocytic nevi

Melanocytic nevi are a benign clonal proliferation of cells expressing the melanocytic phenotype, with heterogeneous clinical and molecular characteristics. In this review, we discuss the genetics of nevi by salient nevi subtypes: congenital melanocytic nevi, acquired melanocytic nevi, blue nevi, and Spitz nevi. While the molecular etiology of nevi has been less thoroughly studied than melanoma, it is clear that nevi and melanoma share common driver mutations. Acquired melanocytic nevi harbor oncogenic mutations in BRAF, which is the predominant oncogene associated with melanoma. Congenital melanocytic nevi and blue nevi frequently harbor NRAS mutations and GNAQ mutations, respectively, while Spitz and atypical Spitz tumors often exhibit HRAS and kinase rearrangements. These initial 'driver' mutations are thought to trigger the establishment of benign nevi. After this initial phase of the cell proliferation, a senescence program is executed, causing termination of nevi growth. Only upon the emergence of additional tumorigenic alterations, which may provide an escape from oncogene-induced senescence, can malignant progression occur. Here, we review the current literature on the pathobiology and genetics of nevi in the hope that additional studies of nevi promise to inform our understanding of the transition from benign neoplasm to malignancy.

Cutaneous malignant melanoma: update on diagnostic and prognostic biomarkers

The incidence of cutaneous malignant melanoma has rapidly increased in recent years in all parts of the world, and melanoma is a leading cause of cancer death. As even relatively small melanomas may have metastatic potential, accurate assessment of progression is critical. Although diagnosis of cutaneous malignant melanoma is usually based on histopathologic criteria, these criteria may at times be inadequate in differentiating melanoma from certain types of benign nevi. As for prognosis, tumor (Breslow) thickness, mitotic rate, and ulceration have been considered the most important prognostic indicators among histopathologic criteria. However, there are cases of thin primary melanomas that have ultimately developed metastases despite complete excision. Given this, an accurate assessment of melanoma progression is critical, and development of molecular biomarkers that identify high-risk melanoma in its early phase is urgently needed. Large-scale genomic profiling has identified considerable heterogeneity in melanoma and suggests subgrouping of tumors by patterns of gene expression and mutation will ultimately be essential to accurate staging. This subgrouping in turn may allow for more targeted therapy. In this review, we aim to provide an update on the most promising new biomarkers that may help in the identification and prognostication of melanoma.

Spitz nevi and other Spitzoid lesions part I. Background and diagnoses

Spitz nevi are melanocytic proliferations that are characterized by spindled and/or epithelioid nevomelanocytes. First interpreted as juvenile melanoma, these lesions were later characterized as benign and were observed to affect all age groups. Today, contrasting opinions persist regarding the fundamental benignancy versus malignancy within the spectrum of Spitz tumors. Beyond clinical outcome, this controversy has also been fueled by complex and sometimes convoluted classification schemes based on pathologic characteristics. More recently, immunophenotypic and molecular analyses have begun to clarify the etiologic nature of these tumors. Recent evidence suggests that histopathologic features that suggest more aggressiveness in Spitz tumors relate to mitoses and inflammation.

IGFBP7, a novel immunohistochemical marker in differentiating dermatofibroma from dermatofibrosarcoma protuberans

BACKGROUND

Loss of insulin-like growth factor-binding protein 7 (IGFBP7) has been found to be a critical step in the development of melanoma and colon cancer. To our knowledge, immunostaining of IGFBP7 in various dermatofibrosarcoma protuberans (DFSP) and dermatofibroma (DF) has not been studied before.

OBJECTIVES

To assess the immunostaining of IGFBP7 in DFSPs and DFs and to ascertain whether IGFBP7 is superior to antibodies traditionally used in differentiating DFs from DFSPs.

METHODS

Immunohistochemical staining was performed on 28 cases of DFSP and 30 cases of DF, using antibodies to IGFBP7, CD34, factor XIIIa (FXIIIa), CD10 and stromelysin-3 (ST-3).

RESULTS

Six of 28 (21.4%) DFSP samples were positive for IGFBP7, whereas 28 of 30 (93.3%) DF samples were positive. CD34 was positive in 26 of 28 (92.9%) cases of DFSP and 4 of 30 (13.3%) cases of DF. FXIIIa staining was positive in 4 of 28 (14.3%) cases of DFSP and 28 of 30 (93.3%) cases of DF. CD10 staining was positive in 12 of 28 (42.9%) cases of DFSP and ST-3 staining was positive in 7 of 28 (25.0%) cases of DFSP. The preferential IGFP7 staining of DFSPs in comparison with DFs was statistically significant (P < 0.01).

CONCLUSIONS

We confirmed that IGFBP7 is a negative immunohistochemical marker for DFSPs and the combination with CD34, FXIIIa and ST-3 immunostaining could make the distinction more reliable.

Molecular nevogenesis

Despite recent advances, the biology underlying nevogenesis remains unclear. Activating mutations in NRAS, HRAS, BRAF, and GNAQ have been identified in benign nevi. Their presence roughly correlates with congenital, Spitz, acquired, and blue nevi, respectively. These mutations are likely to play a critical role in driving nevogenesis. While each mutation is able to activate the MAP kinase pathway, they also interact with a host of different proteins in other pathways. The different melanocytic developmental pathways activated by each mutation cause the cells to migrate, proliferate, and differentiate to different extents within the skin. This causes each mutation to give rise to a characteristic growth pattern. The exact location and differentiation state of the cell of origin for benign moles remains to be discovered. Further research is necessary to fully understand nevus development given that most of the same developmental pathways are also present in melanoma.

Absence of BRAF and HRAS mutations in eruptive Spitz naevi

BACKGROUND

Eruptive Spitz naevi have been reported rarely in the literature. In solitary Spitz naevi, BRAF and HRAS mutations, as well as increased copy numbers of chromosome 11p have been identified.

OBJECTIVES

To investigate the genetic changes underlying eruptive Spitz naevi.

METHODS

We report on a 16-year-old boy who developed multiple disseminated eruptive Spitz naevi within a few months. We analysed BRAF, HRAS, KRAS and NRAS genes in 39 naevi from this patient for hotspot mutations. Furthermore, comparative genomic hybridization analysis was performed in three lesions.

RESULTS

None of the Spitz naevi displayed a mutation in the analysed genes, and no chromosomal imbalances were observed. Conclusions  Our results indicate that the typical genetic alterations described in solitary Spitz naevi appear to be absent in eruptive Spitz naevi. Yet unknown alternative genetic alterations must account for this rare syndrome.