Isolation and characterization of BK virus-transformed hamster cells

BK virus and human cancer: innocent until proven guilty

BK virus (BKV) is a polyomavirus that ubiquitously infects the human population. Following a typically subclinical primary infection, BKV establishes a life-long persistent infection in the kidney and urinary tract. BKV is known to reactivate and cause severe disease in immunosuppressed patients, particularly renal and bone marrow transplant patients. Infection of BKV in rodent animal models or cells in culture often results in tumor formation or transformation, respectively. When co-expressed with activated oncogenes, BKV large tumor antigen drives the transformation of primary human cells. An etiological role of BKV in human cancer, however, remains controversial. Multiple reports have demonstrated conflicting results in regards to the presence of BKV sequences and/or proteins in various tumor types. This review compiles the most recent findings of BKV detection in a number of human cancers. Due to the lack of conclusive causality data from these studies, there does not appear to be a definitive association between BKV and human cancers.

Correlation between tumour antigens and malignancy in BKV-transformed hamster cells

Hamster kidney cells transformed by BK virus (HKBK cells) were studied in order to correlate the membrane tumour antigens to the metastatic capability. The presence of the tumour associated surface antigen (TASA) on the surface of HKBK cells was detected by the immunofluorescence test on live cell suspensions. The metastatic ability was investigated by inoculating HKBK cells subcutaneously (s.c.) into newborn hamsters, s.c., intraperitoneally (i.p.) and in the foot pads into adult hamsters, and s.c. into adult hamsters previously immunized with surface antigens extracted from HKBK cells. The results indicate that there is a correlation between the appearance of tumour antigens on the cell surface and the metastatic ability: HKBK cells at low passage (about 30 subcultures after transformation) showed the capping of TASA in the cell membrane and low metastatic ability, whereas HKBK cells at high passage (about 130 subcultures after transformation) exhibited a diffuse appearance of TASA in the cell surface and were highly metastatic.

Biochemical characterization of human carcinoma surface antigen associated with protein kinase activity

MAb 50H.19 immunoprecipitates two proteins from lysates of human carcinoma cell lines, and embryonic fibroblasts intrinsically labelled with 3H-leucine, 35S-methionine, or a 3H-amino acid mixture; a major component of Mr = 22,000 (22 kd component) and a minor component of Mr = 24,000 (24 kd component). Oligomeric forms of the proteins are not observed under reducing or non-reducing conditions. Both proteins are expressed on the plasma membrane, and are glycoproteins. We investigated the relationship between the proteins in terms of their glycosylation and derivation from precursors. The 22 kd component is O-glycosylated as demonstrated by 3H-galactose incorporation, insensitivity to tunicamycin (TM), and its stepwise generation from a 20.5 kd precursor. The 24 kd protein is N-glycosylated, as shown by 3H-mannose incorporation, and by the total inhibition of its synthesis in the presence of TM. Further evidence for its N-glycosylation is provided by the appearance of a 23 kd precursor in lysates from the osteogenic sarcoma cell line SKOSC pulse-labelled for 5 min, a time preceding O-glycosylation of the 20.5 kd protein. Furthermore, mild alkali treatment of the immune complex leads to a loss of approximately 1,000 daltons in each glycoprotein confirming the O-glycosylated nature of the 22 kd component, and suggesting that the 24 kd component is additionally O-glycosylated. Both glycoproteins undergo an apparent increase of molecular weight of about 500 daltons when run in the non-reduced form on SDS polyacrylamide gels under standard electrophoretic conditions, suggesting they contain a similar degree of intra-chain disulphide bonding. Confirmatory evidence that the two components share a common polypeptide backbone is provided by the appearance of only the 20.5 kd component in lysates from SKOSC cells pulse-labelled for 5 min in the presence of TM.

Rescue of BKV from BKV-transformed hamster, rat, and mouse cells: correlation with levels of nonintegrated viral DNA

Infectious BKV was rescued from 39 of 40 lines of virus-free, BKV-transformed hamster, rat, and mouse cells, which had been either maintained continuously in culture or reestablished in culture after one or more passage in the appropriate host, by Sendai virus-catalyzed fusion with permissive cells. Striking differences were observed among the 39 lines with respect to the efficiency of virus rescue. Fourteen of the lines were examined for the presence of nonintegrated viral DNA by dot-blot hybridization. The values obtained, which ranged from less than 1 to 2880 viral genome equivalents/cell, reveal a strong correlation between the efficiencies with which BKV can be rescued from these lines and the amounts of free viral DNA that they contain.

Characterization of a hamster brain cell line persistently infected with measles virus

A persistent infection of measles virus in hamster brain cell cultures was established. Hamster brain cells were transformed with a human papovavirus strain BK and infected with a wild-type measles virus in order to get the cell line persistently infected with measles virus. About 75 per cent of these M-HB/MVB-cells were measles virus-infected. The cells released only small amount of infectious virus and produced low levels of interferon-like activity into the growth medium. During the first 50 passages no large syncytia typical of a lytic measles virus infection were seen. The products of measles virus infection in the cells and in cell culture fluids were followed at two temperatures. Another cell line persistently infected with measles virus (Lu-carrier-cells, 28) was investigated in parallel. In both cell lines measles antigens were cytoplasmic, but during the observation period large amounts of measles nucleocapsid accumulated in the nuclei of the M-HB/MVB-cells. The virus-specific protein synthesis in M-HB/MVB-cells was weak and the intracellular amount of immunoreactive measles nucleocapsid was only 50 per cent (600 ng/10(5) infected cells) of the (1200 ng/10(5) cells) found in Lu-carrier-cells. Also the release of nucleocapsid was minimal in hamster brain cells. The decreased temperature had no clear-cut effect on virus-specific protein synthesis or on the release of the virus-specific products.

Change of DNA near the origin of replication enhances the transforming capacity of human papovavirus BK

A turbid-plaque-forming mutant (pm522) of human papovavirus BK, which has a small deletion at about 0.7 map unit and grows somewhat more slowly in human cells than does wild-type BK virus, transformed hamster and rat cells in culture much more efficiently than did wild-type virus. Another plaque morphology mutant, pm525, forming turbid plaques larger than those of pm522 also had a high transforming capacity. The similar difference in transforming capability between wild-type and plaque morphology viruses was observed with DNAs extracted from virions. Recombinant viruses were constructed from the wild-type DNA fragment lacking HindIII-C (0.62 to 0.73 map unit) and pm522 HindIII-C (including the origin of replication) by the molecular cloning method. Characterization of the recombinants showed that the change near the origin of DNA replication was responsible both for the altered plaque morphology and for the enhanced transforming capacity of the BK virus mutant.

The measles virus-specific protein synthesis of persistently and lytically infected cells studied in vivo and in vitro

The virus-specific protein synthesis of the hamster brain cells persistently infected with a wild-type measles virus (M-MB/MVB) was investigated in vivo and in vitro and compared to the protein synthesis of the Vero-cells lytically infected with the wild-type measles virus and the SSPE-measles virus strain LEC. The virus-specific protein synthesis in the M-HB/MVB-cells in vivo was weak. Only two virus-specific polypeptides, corresponding to polypeptide G and nucleocapsid polypeptide NP, were detected. On the other hand, the in vitro translation products, coded by the RNA extracted from the actinomycin D-treated M-HB/MVB-cells, were similar compared to those products coded by the RNAs from the lytically infected Vero-cells. The polypeptides with MWs of 75 000, 61 000, 40 000, 37 000 and 18 000 were coded with all three RNA-extracts. So the similar mRNAs were induced in the actinomycin D-treated M-HB/MVB-cells, but their translation in vivo was limited. In addition to those polypeptides mentioned above the polypeptide with a MW of 42 000 was detected among the in vitro translation products of the M-HB/MVB-cells.

Failure to detect papovavirus-associated T antigens in human brain tumor cells by anticomplement immunofluorescence

To probe the possible presence of papovavirus-related T antigen(s) in human brain tumors, the imprinted or cultured cells at various passage levels were examined by anticomplement immunofluorescence using antisera to T antigen of each BK virus, JC virus, and simian virus 40. No T antigen was demonstrated in any tests with cells derived from 69 patients with various brain tumors. Twenty-two tumor cell strains cultured in the presence of a tumor promoter, phorbol ester, also failed to show the T antigen.

Tumorigenicity and karyotype of rat embryo cell lines transformed by BK virus

A rat embryo cell line transformed by BK virus was used to induce tumors in rats. Cell lines were established from these tumors. Other sublines were obtained by in vitro cloning of the parental line. Growth characteristics and karyotypes were compared to the tumorigenicity of these cell lines. The in vitro cloned sublines had a low tumorigenicity. Tumorigenicity of the tumor cell lines varied from high to undetectable. The tumor cell line with the highest tumorigenicity also had the highest saturation density in vitro, but otherwise there was little correlation between tumorigenicity and the in vitro characteristics of the cells. Karyotype analysis was done for two cell lines with high or low tumorigenicity which both had a near-diploid complement of chromosomes. The findings were in agreement with the expression-supression model of Rabinowitz and Sachs (1970). The suppression chromosomes seemed to be confined in group A, the expression chromosomes in group B.

Two polypeptide changes associated with butyric acid resistance and the neoplastic state of Syrian hamster cells

Seven differences in the polypeptide species of parental Syrian hamster embryo cells and cells of the highly tumorigenic derivative cell line BP6T were identified previously by employing the technique of two-dimensional polyacrylamide gel electrophoresis (Leavitt, J. and Moyzis, R. (1978) J. Biol. Chem. 253, 2497-2500). To determine which of these polypeptide changes are correlated with expression of the neoplastic state this work was extended to the comparative examination of nine established neoplastic cell lines which resulted from independent transformation events catalyzed by chemical carcinogen treatment, virus infection, or an unknown spontaneous event. Although no perfect correlation with a specific polypeptide change was found, two polypeptide changes, occurring independently or simultaneously, appear to be consistently associated with expression of neoplasticity. One polypeptide species, designated tau, having an isoelectric point of 4.6 and a molecular weight of 60 000 was lost or physically altered in all but one of these transformed cell lines; a second polypeptide species designated nu having an isoelectric point 5.5 and a molecular weight of 42 000 appeared in highly tumorigenic chemically transformed cell lines and in two virally transformed cell lines. A butyric acid supplement, used as a selective agent for butyric acid resistant cells, was employed to identify and isolate in a single step nascent neoplastic clonal lines transformed by ethylmethanesulfonate. These cell lines exhibited alterations either in tau or nu. The changes observed in tau are consistent with those expected to result from a somatic mutation event in the structural gene coding for tau; however, the alterations in tau could also be governed by a post-translational process. These findings suggest that alterations in expression of at least two major polypeptide species, tau and nu, are closely associated with primary steps in the neoplastic transformation process of Syrian hamster cells irrespective of the nature of the transforming agent.

BK virus: II. Serologic studies in children with congenital disease and patients with malignant tumors and immunodeficiencies

Sera of 451 children with congenital diseases and 185 tumor patients were tested for BK virus-specific antibodies by hemagglutination inhibition and IgM-immunofluorescence tests. Compared to age-matched control groups, higher percentages and significantly elevated geometric mean titers of HI antibodies were found in all patient groups tested. Of children under six months of age with congenital diseases such as dysplasia, cerebral defects, and hyperbilirubinemia and hepatosplenomegaly, 4.2% (17/402) had BK virus-specific IgM antibodies. No positive sera were found in 68 control sera. Of tumor patients 5--15 years of age, 8.6% (16/185) had IgM antibodies to BK virus. In the control group, 30% (3/99) had them. Serial serum samples from 76 tumor patients treated with cytostatic drugs showed seroconversion in three cases. No relationship between certain clinical features and BK virus infection was noted. Isolation of BK virus was successful from urines of two infants with connatal defects, six patients suffering from malignant tumors, and four patients with inherited immunodeficiencies.