We have recently discovered that the oncogene products p68v-ros of avian sarcoma virus UR2 and p150fps of UR1 sarcoma virus are associated with a phosphatidyl inositol (PtdIns) kinase activity in vitro, and that UR2-transformed cells show enhanced polyphosphoinoistide turnover. It is possible that PtdIns phosphorylation might result in malignant transformation of susceptible cells by generating abnormally high levels of 1,2-diacylglycerol, which appears to be the endogenous activator of the phorbol ester receptor (kinase C). This hypothesis will be tested by answering the following questions: (1) Is the structure of the in vitro product of PtdIns phosphorylation the same as that produced by 'authentic' PtdIns kinases? (2) Is endogenous PtdIns phosphorylation enhanced in membranes from UR2, UR1 or Fujinami sarcoma-virus-transformed cells? (3) Is phosphoinositide turnover and kinase C activity increased in a temperature-sensitive manner in cells transformed by ASV-ts mutants? (4) Do tyrosine kinase and PtdIns kinase activities from red blood cell membranes co-purify? (5) Do purified PtdIns kinases show functional and structural homologies with oncogene kinases? This work should provide new insights into the mechanisms of viral tumorigenesis, and might eventually be exploited in the search for novel therapeutic measures for cancer.
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