Altered endosomal-lysosomal biogenesis in melanoma

Abstract

Cutaneous melanoma is the deadliest form of skin neoplasm and its high mortality rates could be averted by early accurate detection. While the detection of melanoma is currently reliant upon melanin visualisation, research into melanosome biogenesis, as a key driver of pathogenesis, has not yielded technology that can reliably distinguish between atypical benign, amelanotic and melanotic lesions. The endosomal-lysosomal system has important regulatory roles in cancer cell biology, including a specific functional role in melanosome biogenesis. Herein, the involvement of the endosomal-lysosomal system in melanoma was examined by pooled secondary analysis of existing gene expression datasets. A set of differentially expressed endosomal-lysosomal genes was identified in melanoma, which were interconnected by biological function. To illustrate the protein expression of the dysregulated genes, immunohistochemistry was performed on samples from patients with cutaneous melanoma to reveal candidate markers. This study demonstrated the dysregulation of Syntenin-1, Sortilin and Rab25 may provide a differentiating feature between cutaneous melanoma and squamous cell carcinoma, while IGF2R may indicate malignant propensity in these skin cancers.

Keywords: Endosomal-lysosomal biogenesis; IGF2R; Melanoma pathogenesis; Rab25; Sortilin; Syntenin-1.

Fig. 1

Immunohistochemical assessment of differentially expressed endosomal-lysosomal associated genes. Representative sections of normal and cancer FFPE tissue were labelled by immunohistochemistry. Positive immunolabelling is indicated by a brown insoluble precipitate. Nuclei were counterstained blue with Haematoxylin. For each protein, representative micrographs were captured from a normal biopsy and two melanoma samples.

Fig. 2

Expression of Syntenin-1, Sortilin, IGF2R and Rab25 in melanoma versus adjacent normal skin tissue. Sections were immunolabelled with Syntenin-1 (A), Sortilin (B), IGF2R (C) or Rab25 (D). Positive immunolabelling is depicted by a brown immunoprecipitate. Nuclei were counterstained blue with Haematoxylin. Melanocytes in adjacent normal skin tissue are indicated with black arrows. IHC labelling of the markers was semi-quantified in 14 paired melanoma and adjacent normal samples using a H-score system. Data is illustrated as mean ± SEM. Significant differences (p < 0.01, Wilcoxon matched-pairs signed rank test) between adjacent normal and melanoma are indicated by a (***).

Fig. 3

Detection of Syntenin-1, Sortilin, IGF2R and Rab25 at different stages of melanoma. Representative micrographs of tissue sections from patients with melanoma at different stages that were stained with routine H&E or labelled with Syntenin-1, Sortilin, IGF2R or Rab25. Immunolabelling with Syntenin-1, Sortilin, IGF2R and Rab25 is depicted by a brown immunoprecipitate. (P), pagetoid spreading; (N), nests.

Fig. 4

Expression of Syntenin-1, Sortilin, IGF2R and Rab25 in squamous cell carcinoma. Tissue sections were labelled with Syntenin-1 (A), Sortilin (B), IGF2R (C) or Rab25 (D). Positive immunolabelling is depicted by a brown immunoprecipitate. IHC labelling of examined markers was semi-quantified in six paired SCC and adjacent normal samples using a H-score system. Keratin pearl is indicated with a black arrow. Data is illustrated as mean ± SEM. Significant differences (p < 0.05, Wilcoxon matched-pairs signed rank test) between adjacent normal and SCC are indicated by a (*), while no significant differences are indicated by (ns).