Two-dimensional gel electrophoretic analysis of the changes after immortalization of human cells: decrease of...

Area of Science:

• Biochemistry
• Cell Biology
• Cancer Research

Background:

• Cellular immortalization is a critical early event in cancer development.
• Understanding protein alterations during immortalization is key to cancer research.
• Alpha-2-macroglobulin (a-2M) is a large multifunctional protease inhibitor found in plasma.

Purpose of the Study:

• To investigate changes in cellular proteins during human fibroblast immortalization.
• To identify specific protein alterations associated with cancer development.
• To explore the role of alpha-2-macroglobulin in cellular transformation.

Main Methods:

• Comparative analysis of cellular proteins from normal and immortalized human fibroblasts using two-dimensional gel electrophoresis.
• Identification of protein fragments via N-terminal amino acid sequencing.
• Investigation of protein labeling using [35S]methionine.

Main Results:

• A specific 20 kDa protein spot (pI 6.0) significantly decreased in immortalized cells compared to normal cells.
• This 20 kDa spot was rarely detected in human liver cancer cell lines.
• N-terminal sequencing identified the spot as a fragment of alpha-2-macroglobulin, likely originating from the culture medium.
• The fragment, despite containing methionine, was not labeled with [35S]methionine, supporting its exogenous origin.

Conclusions:

• Intracellular metabolism of alpha-2-macroglobulin (a-2M) is altered following human cell transformation.
• Changes in a-2M processing may be indicative of cellular immortalization and cancer development.
• The findings suggest a potential role for extracellular protein metabolism in cancer progression.