Mounting evidence supports the role of truncated
vinculin in the intracellular actin-based motility of Shigella flexneri.
Vinculin's role was recently questioned by Goldberg [1997: Cell Motil Cytoskeleton 37:44-53] who observed Shigella motility in mouse
embryonal carcinoma 5.51 cells, a genetically modified cell line that reputedly lacked
vinculin. That challenge implicitly relied on the assumption that 5.51 cells had no detectable
vinculin polypeptide and lacked full-length
vinculin mRNA. Despite the appearance of being an unambiguous test of
vinculin's role in Shigella motility, 5.51 cells were shown to contain adequate amounts of truncated
vinculin (as well as the corresponding
mRNA transcript) to support bacterial locomotion. We also examined Shigella locomotion in gamma229 cells, a related embryonal carcinoma cell line containing approximately one-half the
vinculin content found in 5.51 cells. We observed that there was a commensurate twofold decrease in the Shigella motility rate, as compared to 5.51 cells; this finding raises the possibility that
vinculin can become a rate-limiting factor under some circumstances. Immunofluorescence microscopy using vin 11-5
monoclonal antibody directed against the
vinculin head domain showed intense staining of Shigella rocket tails in both gamma229 and 5.51 cells. Our findings clearly demonstrate that motility in 5.51 cells cannot be regarded as a valid criterion for evaluating the role of truncated
vinculin in Shigella motility.