Related Experiment Videos
Expression and ultrastructural localization of HMB-45 antigen
A Kikuchi1, H Shimizu, T Nishikawa
1Department of Dermatology, Keio University School of Medicine, Tokyo, Japan.
Abstract:
HMB-45 is a monoclonal antibody specific for melanoma cells and premature developing melanocytes. We examined the expression and specific subcellular binding sites of HMB-45 in various types of melanocytes including epidermal melanocytes from fetuses and infants with or without tyrosinase-negative oculocutaneous albinism (type IA), melanin-producing and non-producing melanoma cell lines (G361 and MeWo), and in vivo melanoma cells (melanotic and amelanotic malignant melanoma). Subcellular HMB-45 binding was examined by using post-embedding immunogold electron microscopy with rapid freezing and freeze substitution fixation methods without the use of chemical fixatives to preserve the intracytoplasmic delicate antigen property of HMB-45. HMB-45 antigen was detected not only in in vivo melanoma cells and normal fetal melanocytes, but also in melanocytes in the other conditions. Post-embedding immunogold electron microscopy revealed that HMB-45 antigen was exclusively localized to stages I and II melanosomes in the cytoplasm of neoplastic melanocytes, but was detected mainly on stages II and III melanosomes in the melanocytes from fetuses and infants. In tyrosinase-negative oculocutaneous albinism, only stages I and II melanosomes were detected in the cytoplasm, but both stages of melanosomes were HMB-45 positive. We conclude that HMB-45 appears mainly on the immature melanosomes during melanogenesis in both neoplastic and non-neoplastic melanocytes regardless of their tyrosinase activity, but the intracytoplasmic localization of HMB-45 antigen is different by each condition of melanocytes.
Insights
The HMB-45 antibody targets immature melanosomes in both melanoma cells and normal melanocytes during melanogenesis. Its specific location within melanosomes varies depending on the melanocyte type and condition.
Area of Science:
- Cell Biology
- Immunohistochemistry
- Melanoma Research
Background:
- HMB-45 is a monoclonal antibody used to identify melanoma cells and developing melanocytes.
- Understanding HMB-45 binding sites is crucial for melanoma diagnosis and understanding melanogenesis.
- Melanogenesis involves the formation and maturation of melanosomes, the organelles responsible for melanin production.
Purpose of the Study:
- To investigate the expression and subcellular localization of the HMB-45 antigen in various melanocyte types.
- To determine if HMB-45 binding differs between neoplastic and non-neoplastic melanocytes.
- To examine HMB-45 localization in melanocytes from normal fetuses, infants with oculocutaneous albinism, and melanoma cell lines.
Main Methods:
- Utilized post-embedding immunogold electron microscopy for high-resolution subcellular analysis.
- Employed rapid freezing and freeze substitution fixation to preserve delicate antigen properties without chemical fixatives.
- Examined HMB-45 expression in epidermal melanocytes, melanoma cell lines (G361, MeWo), and in vivo melanoma samples.
Main Results:
- HMB-45 antigen was detected in neoplastic melanocytes, normal fetal melanocytes, and melanocytes from infants.
- In neoplastic melanocytes, HMB-45 localized to stages I and II melanosomes.
- In normal fetal and infant melanocytes, HMB-45 was mainly on stages II and III melanosomes; in tyrosinase-negative oculocutaneous albinism, it was on stages I and II.
Conclusions:
- HMB-45 primarily binds to immature melanosomes (stages I and II) during melanogenesis in both neoplastic and non-neoplastic cells.
- The intracytoplasmic localization of HMB-45 within melanosomes differs based on the melanocyte's condition.
- HMB-45's binding to immature melanosomes is independent of tyrosinase activity.