Human cancer and animal viral oncology

A PCR primer system for detecting oncoretroviruses based on conserved DNA sequence motifs of animal retroviruses and its application to human leukaemias and lymphomas

Many C- and D-type retroviruses are known to cause a broad spectrum of malignant diseases in animals. Certain genome regions of these animal retroviruses are highly conserved between different animal species. It should be possible to detect new members of the retrovirus family with consensus PCR primers derived from these conserved sequence motifs. The consensus PCR primers developed in this study are generic enough to detect nearly all known oncogenic mammalian and avian exogenous C- and D-type retroviruses but do not amplify human endogenous retroviral sequences. In contrast to previous investigations, the present study involved highly stringent PCR conditions and truly generic PCR primers. Forty-four samples from patients with various immunophenotyped malignant diseases (acute and chronic T-/B-cell lymphocytic leukaemias, acute myeloid leukaemias, T-/B-cell lymphomas, chronic myeloproliferative disorders) and three cell lines (Hodgkin's lymphoma, Burkitt's lymphoma) have thus far been investigated using these PCR primers. The fact that no retroviruses have been found argues against an involvement of known animal oncoretroviruses or related hitherto undetected human retroviruses in the aetiopathogenesis of these diseases. The retrovirus detection system developed here may be used to confirm suspected retroviral involvement in other (malignant or nonmalignant) human diseases as well as to identify new animal retroviruses.

The mechanism of interferon effect on cell transformation by murine sarcoma virus

Mouse interferon (IFN) was found to inhibit murine sarcoma virus (MSV)-induced neoplastic transformation of normal rat kidney (NRK) cells. This effect was observed upon examining the formation of foci of morphologically altered cells and colonies of anchorage-independent cells. IFN had no cytotoxic effect on MSV-transformed NRK cells, nor on their focus or colony-forming ability. It was therefore apparent that its inhibitory effect was directed against the viral role in cell transformation. In attempts to define the mechanism of this effect, we found that IFN delayed the initiation of the cytoplasmic viral DNA synthesis. However, the amount of this DNA eventually formed in IFN-treated cells was the same as in the control cells. Furthermore, the transport of this DNA to the nucleus was slower in IFN-treated cells, although all of it was finally transferred. However, while most of the viral DNA integrated into the genome of the control cells, very little integration occurred in IFN-treated cells. The unintegrated viral DNA of these cells was slowly degraded. Therefore, if the cells recovered from the antiviral effect of IFN when intact viral DNA molecules still existed in their nucleus, they could resume viral DNA integration and cell transformation. IFN was found to block viral DNA supercoiling. Since supercoiled viral DNA is considered to be a precursor to integrated provirus, it seems that the inhibition of both integration and cell transformation is due to this impaired coiling.

Effect of mouse interferon on cell transformation and virus production in rat cells exogenously infected with moloney murine sarcoma and leukemia viruses

Foci of transformed cells, produced by MSV(124), appeared to result only from the primary infection, since this virus stock yielded a virus-nonproducing infection. On the other hand, the majority of foci scored in MSV/MLV-infected cultures, were generated by multiple secondary infections with the progenies of the primary infection. Mouse interferon (IF) was highly inhibitory for cell transformation by both virus stocks. However, this inhibition was apparent in MSV(124) infected cultures only if IF was added at least 12 h before infection, whereas in MSV/MLV-infected cultures IF was highly effective even if added 24 h after infection. The inhibition of focus formation by MSV(124) was irreversible after removal of IF, suggesting that IF inhibited an early step before provirus integration into the host genome. By contrast, in MSV/MLV-infected cultures focus formation was almost completely restored after recovery from the IF effect. Nevertheless, examination of virus production after IF removal proved that in MSV/MLV infection, too IF exerted and inhibitory effect before provirus integration.

The role of viruses in the development of ocular tumors

The role of viruses as a cause of human cancer has been investigated by a variety of techniques in recent years. While no definitive answer exists at present, several lines of evidence indicating a viral role in human tumors and reviewed. These include the well-documented role of viruses in causing animal tumors; evidence for an association of certain viruses with human tumors; and virally induced animal models of human tumors, melanoma, retinoblastoma, and ocular malignant melanoma.

Evidence for type-C retrovirus production by Burkitt's lymphoma-derived cell line

Burkitt's lymphoma cell line, P3HR-I, was found to secrete virions with properties of known type-C RNA tumor viruses. The viral particles had a buoyant density of 1.16 g/ml in sucrose gradients and contained a high-molecular-weight RNA and an RNA-instructed DNA polymerase. The viral polymerase was active in an endogenous reaction requiring the presence of the four deoxyriboside triphosphates and manganese ions, and was sensitive to RNase. The DNA product of the endogenous reaction specifically hybridized to P3HR-I viral 60 to 70S RNA. Electron microscopic examination of ultrathin sections of P3HR-I cells revealed immature, mature and budding virions typical of type-C retroviridae. Nucleic acid hybridization assays showed no sequence homoblastosis virus, murine oncornaviruses, simian sarcoma virus or RD114 virus.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: IV. The viruses

Speculations are developed for a mechanism by which oncogenic viruses can induce alterations in cells allowing them to express embryonic genes. It is suggested that if viral deoxyribonucleic acid, directly or via ribonucleic acid directed deoxyribonucleic acid polymerase activity becomes inserted at particular euchromatin - heterochromatin junctions of quasidifferentiated stem-like cells, then deheterochromatization may result, causing in turn derepression of genes for acidic protein phosphokinases. This sets into motion a series of events including altered acid protein repressors of embryonic genes which are repressed by uniquely weak type repressors. This explains how viruses can act as specific embryonic gene-inducing agents similar to chemical inducing agents such as the hepatocarcinogen ethinine.

Immunology, tumor markers, and breast cancer

Although our knowledge of immunologic processes in breast cancer is still inadequate, many preliminary studies described here may yield valuable information after long-term patient follow-up. At present, there is no specific tumor marker diagnostic of breast cancer, but markers such as CEA, ferritin, immune complexes, and specially estrogen receptors have strong potential as prognostic indicators. As a group, breast cancer patients, as do those with other malignancies, demonstrate reduced immunologic capacity, therefore assays of nonspecific immune function may not be relevant. Assays of "specific" reactivity to breast tumor antigens, however, warrant further investigation as clinical tools. Application of immunotherapy to breast cancer is relatively recent and few trials have more than preliminary data. Determination of estrogen receptors should be included in future clinical immunotherapy protocols so that true evaluation of immunologic responses may benefit, hopefully, from our awareness of the endocrine milieu.