Altered microfilament structure in cells transformed with a temperature-sensitive transformation mutant of murine sarcoma virus.

The structure and distribution of microfilaments were examined by electron microscopy in uninfected normal rat kidney (NRK) cells, murine sarcoma virus (MSV)-transformed NRK cells, and NRK cells infected with a cold-sensitive transformation mutant of MSV, i.e., NRK (MSV-1b) cells, grown at both permissive (39 degrees) and nonpermissive (33 degrees) temperature. The uninfected cells contained numerous microfilaments which were especially prominent at sites of intercellular adherens junctions. In contrast, the MSV-transformed cells contained few microfilaments and did not form adherens junctions. At 33 degrees, the NRK (MSV-1b) cells appeared normal but formed an altered form of adherens junction with disorganized microfilaments. At 39 degrees, these cells resembled NRK cells transformed by wild-type MSV but still formed a few of the altered type of adherens junctions. Disorganized adherens junction microfilaments were also found in cells newly infected with wild-type MSV. These results suggest that the perturbed assembly of microfilaments at adherens junctions may be an intermediate stage in the loss of adherens junctions during viral transformation.