MECHANISM OF TRANSFORMATION BY TYROSINE KINASES

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Our ultimate goal remains to determine the mechanism of meoplastic transformation by tyrosine-specific protein kinases. We propose here to further test our hypothesis that altered tyrosine phosphorylation by cellular tyrosyl kinases functions in the anchorage independent growth property of transformed cells. We have observed that a membrane-enveloped virus, vesicular stomatitis virus (VSV), selectively acquires specific tyrosyl kinase species from anchorage independent cells. We will therefore purify and prepare immunological reagents to the VSV-associated tyrosyl kinase to be used to investigate location and amount of this enzyme in anchorage independent cells. To test the hypothesis that the tyrosyl kinase acquired by VSV functions in anchorage independence, it will be determined whether the VSV-acquired enzyme is the same as the tyrosyl kinase which has previously been shown to cause anchorage independence in some transformed cells. To determine how tyrosine-phosphorylation of specific substrate proteins may be regulated, we will test whether cellular tyrosyl kinase species are amplified in activity or relocalized in achorage independent cells. This will be by HPLC gel filtration of individual species of tyrosyl kinases and quantitations of their activities and subcellular locations. Our preliminary data suggests that another mechanism for regulation is by dephosphorylation of phosphotyrosine by prostatic acid phosphatase. This mode of regulation will be tested in human prostate carcinoma cells where prostatic acid phosphatase activity can be regulated by androgens. To begin to understand how tyrosine phosphorylation of proteins may cause malignant growth of cells, we will investigate a new class of tyrosyl kinase substrates identified by us in the extracellular fraction of human prostate carcinoma cells. We will determine whether these are secreted proteins and prepare immunological reagents to be used in their further characterization.