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Laminin-binding integrin alpha 7 beta 1: functional characterization and expression in normal and malignant
R H Kramer1, M P Vu, Y F Cheng
1Department of Stomatology, University of California, San Francisco 94143.
Insights
A novel alpha 7 beta 1 integrin binds laminin's E8 region on melanoma cells. This integrin is absent in normal melanocytes, suggesting a role in cancer development.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Integrins are crucial cell surface receptors mediating cell-matrix and cell-cell adhesion.
- Laminin is a key component of the extracellular matrix involved in cell differentiation, migration, and survival.
- Melanoma, a type of skin cancer, exhibits altered expression of adhesion molecules.
Purpose of the Study:
- To identify and characterize novel integrins involved in melanoma cell adhesion.
- To investigate the binding specificity of the identified integrin to laminin.
- To determine the potential role of this integrin in melanoma pathogenesis.
Main Methods:
- Laminin-affinity chromatography was used to purify the integrin complex from melanoma cells.
- Gel electrophoresis and N-terminal amino acid sequencing were employed to identify the integrin subunits.
- Binding assays using specific laminin fragments (E8 and P1) were performed to determine the binding site.
Main Results:
- A novel integrin, alpha 7 beta 1, was identified and purified from human and murine melanoma cells.
- N-terminal sequencing confirmed alpha 7 beta 1 as a distinct integrin, similar to alpha 6.
- The alpha 7 beta 1 integrin selectively binds to the E8 region of laminin, not the P1 fragment.
- Alpha 7 beta 1 was commonly expressed in melanoma cells but not detected in normal melanocytes.
Conclusions:
- The alpha 7 beta 1 integrin represents a novel receptor that binds to the E8 domain of laminin.
- This integrin mediates melanoma cell adhesion to laminin.
- Its selective expression in melanoma suggests a potential association with malignant transformation.
Abstract:
A novel integrin, alpha 7 beta 1, that specifically binds with high affinity to laminin has been identified on melanoma cells. This complex was purified from both human and murine melanoma cells by laminin-affinity chromatography, and the alpha 7 subunit was recovered after gel electrophoresis. N-terminal amino acid sequence analysis of the alpha 7 subunit from both human and mouse cells verifies that this integrin is distinct from other alpha chains in the beta 1 family, although strikingly similar to the alpha 6 subunit. By using specific proteolytically derived fragments of laminin, it was determined that the alpha 7 beta 1 complex binds selectively to the E8 region, which represents part of the long arm of laminin. In contrast, the receptor failed to bind to the P1 fragment, which contains the intersection of the short arms of laminin. Although the alpha 7 beta 1 complex was commonly expressed in melanoma cells, this integrin was not detected in normal melanocytes, suggesting that alpha 7 expression may be associated with malignant transformation. These results establish the existence of a novel integrin that binds to the E8 domain of laminin and appears to mediate cell adhesion to this ligand.