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Immunohistochemical localization of basic fibroblast growth factor in A431 human epidermoid carcinoma cells
N Yamamoto1, S Matsutani, Y Yoshitake
1Department of Functional Morphology, Kitasato University School of Nursing, Kanagawa, Japan.
Insights
Basic fibroblast growth factor (bFGF) is found in the cytoplasm of quiescent A431 cells. Upon stimulation, bFGF translocates to the nucleolus, indicating signal-dependent intracellular sorting.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Basic fibroblast growth factor (bFGF) is a key regulator of cell growth and differentiation.
- The precise intracellular localization and trafficking of bFGF in response to external stimuli are not fully understood.
- A431 human epidermoid carcinoma cells are a well-established model for studying growth factor signaling.
Purpose of the Study:
- To determine the intracellular localization of endogenous bFGF in A431 cells.
- To investigate the dynamic changes in bFGF location in response to extracellular signals.
- To elucidate the pathway of bFGF intracellular transport.
Main Methods:
- Immunofluorescence microscopy was employed to visualize bFGF distribution.
- Immunoelectron microscopy with a specific monoclonal anti-bFGF antibody was used for high-resolution localization.
- A431 cells were cultured under quiescent conditions and stimulated with Fetal Calf Serum (FCS).
Main Results:
- In quiescent A431 cells, bFGF was primarily detected in the cytoplasm.
- Addition of FCS induced rapid translocation and accumulation of bFGF within the nucleolus.
- bFGF was not found in typical components of the secretory pathway (ER, Golgi, secretory granules).
- Immunogold particles for bFGF were observed near ribosomes.
Conclusions:
- Endogenous bFGF undergoes regulated intracellular sorting in A431 cells.
- Extracellular growth signals trigger the translocation of bFGF to the nucleolus.
- bFGF does not follow the canonical secretory pathway for its intracellular trafficking.
Abstract:
The intracellular location of basic fibroblast growth factor (bFGF) was determined in A431 human epidermoid carcinoma cells both on immunofluorescence and on immunoelectron microscopy using a monoclonal anti-bFGF antibody. The immunofluorescence was located in the cytoplasm in quiescent cells. Following the addition of FCS to the culture medium of quiescent sparse cells the growth factor was translocated to and accumulated in the nucleolus. Immunogold particles were dense near the ribosomes, but were not recognized in the cytoplasmic structures concerned with the usual secretory pathway such as the rough endoplasmic reticulum, the Golgi apparatus, and secretory granules. These results suggest that endogenous bFGF undergoes intracellular sorting and enters the nucleoli in A431 cells according to an extracellular growth signal.
