| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 96 === Podosomes are actin-enriched structures, which represent convolutions and extensions of the ventral surface plasma membrane. The function of podosomes is to decompose extracellular matrix. Following the discovery of podosomes in v-Src-transformed cells, similar structures were identified in osteoclasts, macrophages, and certain invasive human cancer cells. Podosomes in v-Src-transformed fibroblasts are often found to assemble into prominent, ring-shaped structures called podosome rings. Focal adhesion kinase (FAK), a cellular tyrosine kinase mainly localized in focal adhesions, is known to interact with Src. In this study, we found that v-Src induced podosome rings formation in mouse embryo fibroblasts, but failed to do so in their FAK-null counterparts. The reconstituted three-dimensional images revealed that podosome rings are actin-enriched hollow-tube structures approximately 15 μm in diameter with 7 μm lumen and 18 μm in height. To further examine the role of FAK in the formation of podosome rings, an inducible FAK expression system was established in v-Src-transformed FAK-null cells. Without FAK induction, v-Src was not sufficient to form podosome rings. Conversely, the assembly of podosome rings was triggered upon FAK induction, closely associated with the expression level of FAK. In addition, the assembly of podosome rings did not rely on de novo gene expression. FAK and Src were found to co-localize with the F-actin at podosome rings. Using time-lapse video microscopy, the life span of podosome rings was estimated to be 10-30 min. Furthermore, the FAK autophosphorylation site Y397 and FAK activity are essential for podosome ring formation. Taken together, our results not only depict the formation of v-Src-induced podosome rings in more detail but also suggest an essential role for FAK in this process.
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