A.S. Levine

Mesotheliomas are pleural, pericardial, or peritoneal neoplasms frequently associated with asbestos exposure, and it is estimated that over the next twenty years up to 80,000 new cases are expected in the USA alone. We found simian virus 40-like DNA sequences in 29 of 48 mesotheliomas studied (60%) and demonstrated simian virus large-T antigen expression in 13 of 16 specimens. The matching lung samples did not contain simian virus 40-like sequences; however, they contained asbestos. These findings are to our knowledge the first demonstration of a physical link between DNA virus-like sequences and human mesothelioma. We suggest that a simian virus 40-like virus may act independently or as a co-carcinogen with asbestos. Moreover, the selective large T antigen expression by mesothelioma and not by the surrounding pulmonary parenchyma may have both diagnostic and therapeutic implications.

An isopycnic Metrizamide-detergent gradient system was developed in which the newly synthesized precursor (polypeptide P-VII) to the major core protein of adenovirus type 2 (polypeptide VII) was confined to a spectrum of complexes with densities equal to or higher than that of adenovirions. The majority of the newly synthesized P-VII was, at the beginning of the logarithmic period of virus production, present as an entity of protein density. This pool of P-VII was efficiently depleted. P-VII was also associated with high-molecular-weight structures of intermediate density, sharing some properties with empty capsids or incomplete particles. The transfer of P-VII from the intermediate-density region was not quantitative, and only particles of true virion density subsequently contained polypeptide VII. No structures equivalent to the core structure of disrupted virions or identical to incomplete particles were detected in this system. A temperature-dependent transition of radioactivity from polypeptide P-VII into polypeptide VII was also detectable after in vitro incubation of P-VII-containing complexes. Addition of Ad2-infected cell extracts was required for processing of complexes derived from regions of protein density, whereas P-VII was processed spontaneously upon incubation in complexes of virion density.

We have studied the intracellular distribution of the two simian virus 40-specific proteins, with apparent molecular weights of 56,000 and 42,000, detectable in human KB cells infected by a nondefective adenovirus 2-simian virus 40 hybrid, Ad2/sup +/ND/sub 2/. After a 20-min pulse of (/sup 35/S) methionine, about two-thirds of the newly synthesized 56K protein and one-third of the 42K protein were found localized on the plasma membrane. The remainder of each protein was found in the cytoplasm, whereas the nuclear fraction was virtually free of either component. A significant portion of both proteins present in the cytoplasmic fraction was complexed to the 40S ribosomal subunits and was not removed by treatment with 0.5 M KC1. Moreover, the portion that was found free in the cytoplasm could bind preferentially and quantitatively to purified 40S ribosomes in vitro, leading us to propose that these simian virus 40 proteins may act as translational control elements in cells.