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Tumor-associated M_r 34,000 and M_r 32,000 Membrane Glycoproteins That Are Serine Phosphorylated Specifically in Bovine Leukemia Virus-induced Lymphosarcoma Cells¹

Laboratory of Gene Technology and Safety [Y. A., H. A.] and Laboratory of Molecular Oncology [M. O.], Tsukuba Life Science Center, The Institute of Physical and Chemical Research (RIKEN), 3-1-1, Koyadai, Tsukuba, Ibaraki 305, and Department of Veterinary Pathology, Faculty of Agriculture, Iwate University, Morioka 020 [K. O.], Japan

² To whom requests for reprints should be addressed.

Tumor-associated antigens that are expressed in tumor cells of cattle with enzootic bovine leukosis (EBL) were analyzed previously by use of 13 monoclonal antibodies. We biochemically identified one of the tumor-associated antigens, which is recognized by the cl43 monoclonal antibody, as two glycoproteins, each having an apparent molecular weight of 32,000 or 34,000. These glycoproteins were found in the plasma membrane of peripheral blood lymphocytes of both bovine leukemia virus (BLV)-free normal and BLV-infected cattle. With the progression of EBL, the proportion and the absolute number of cells positive for the tumor-associated antigen increased. Moreover, the level of the M_r 34,000 component, which was susceptible to cell-surface labeling, increased over the level of the M_r 32,000 component. Partial proteolytic peptide mapping with V8 protease and deglycosylation analysis revealed that the two glycoproteins most likely have an identical M_r 30,000 polypeptide portion but have different N-linked oligosaccharide portions. Both glycoproteins were found to be phosphorylated at serine residue(s) in EBL-derived B-lymphoid cell lines and in tumor cells and peripheral blood lymphocytes from cattle with EBL, but not in peripheral blood lymphocytes from BLV-free normal cattle and BLV-infected cattle without any evidence of tumor, suggesting that the phosphorylation of these glycoproteins is related to the transformed state of the BLV-infected B-lymphoid cells.

¹ Supported by grants from the Ministry of Education, Science, and Culture of Japan and by a Special Grant for Promotion of Research from RIKEN.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 4/27/92. Accepted 9/23/92.

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