Quantitative ultrastructural study of acrylamide induced cytoplasmic desmosome-like structures in cultured rat...

Although present in many tumours, the mechanism of formation and the significance of the so-called 'cytoplasmic desmosome' (CD) remain speculative. Recently, we reported an in vitro model for the induction of CD in rat keratinocytes following acrylamide treatment. In the present study and based on quantitative and qualitative evidence, CD could be divided into two categories. The first comprised individually scattered desmosomes always located in the cortical cytoplasm and associated with tonofilament bundles. Their sizes were comparable with those of intercellular desmosomes (ID) in control cells. The second category comprised clusters of homogeneously small-size desmosomes that may be located deep in the cytoplasm and were not always associated with tonofilament bundles. Whilst the latter group may be formed de novo in the cytoplasm as a result of the acrylamide-induced inhibition of protein kinases, the first group may be the result of internalization of surface desmosomes by certain tonofilaments under tension. In order to assess this possibility, we examined tonofilament organization following wounding of the epithelial sheet. Injured cells exhibited spiral-form tonofilaments extending close to the cell membrane. This retraction could be justified ultrastructurally by direct association between tonofilaments and microfilaments.