Daniel K. Haapala

Normal dba/2 mouse cells synthesize a glycoprotein which interferes with mcf virus infection.

The mechanism of resistance to Friend leukemia virus-induced [mink cell focus-inducing, (MCF)-mediated] leukemogenesis in DBA/2 mice was investigated in cell culture systems. DBA/2 fibroblasts were found to be resistant to infection with MCF viruses but not to ecotropic or amphotropic murine leukemia viruses (MuLVs). Since this resistance has been correlated with the presence of an MCF virus-related gp70 constitutively present on the surface of DBA/2 cells, it seemed possible that the mechanism of resistance in this system involved the saturation of MCF-specific cell surface receptors with the gp70 in analogy to viral interference. Two inhibitors of glycoprotein synthesis, 2-deoxy-d-glucose and tunicamycin, which have been shown to reduce retrovirus-induced interference in productively infected cells, significantly decreased the resistance of DBA/2 cells to productive infection with MCF viruses. This decrease in resistance to MCF virus infection could be correlated with a decrease in the expression of MCF-related gp70 at the cell surface. Cells from several other mouse strains showed neither resistance to MCF virus infection nor enhancement of MCF infectivity following drug treatment. These data indicate that DBA/2 cells are resistant to MCF infection in vitro and, by implication, to MCF-mediated leukemogenesis in vivo by a process analogous to viral interference. Ecotropic pseudotypes of MCF virus were able to productively infect untreated DBA/2 cells, indicating that the cell surface interference-like process described here is the only restriction mechanism responsible for resistance to MCF infection in DBA/2 cells. The results are consistent with the idea that Friend leukemia virus actually causes disease via MCF intermediates.

Reversion of Murine Sarcoma Virus Transformed Mouse Cells: Variants without a Rescuable Sarcoma Virus

Murine sarcoma virus transformed mouse 3T3 cells, which are negative for murine leukemia virus and which yield sarcoma virus after superinfection with murine leukenmia virus, spotaneously give rise to flat variants front which murine sarcoma virus can no longer be rescued. The revertants support leukemia viruis growth and show an enhanced sensitivity to murine sarcoma superinfection and, like normal cells, do not release RNA-dependent DNA polymerase activity. Because revertants could be obtained with high frequency from progeny of single transformed cells, each cell that containts the sarconma virus genome seems to have the capacity to suppress or eliminate an RNA tumor virus native to its species of origin.

Isolation of a continuous epithelioid cell line, HBT-3, from a human breast carcinoma.

Summary A continuous line of human breast carcinoma cells, HBT-3, was established in culture following collagenase treatment of a mucus producing adenocarcinoma. The cells are epithelioid in appearance, multiply rapidly, have a cloning efficiency of approximately 70%, and exhibit an abnormal karyotype with a mode of 66-69 chromosomes/cell and 3 markers. Tumor material and pathological diagnosis were provided through the courtesy of Dr. J. D. Mashburn, Director of Laboratories, Washington Sanitarium and Hospital, Takoma Park, MD. Dr. C. S. Stulberg, Senior Research Associate, The Child Research Center of Michigan, Detroit, kindly performed the immunofluorescence cell typing tests. A portion of these studies was carried out at Bionetics Research Laboratories, Inc., Bethesda, MD, under contract 69-2160 from the Special Virus Cancer Program of the National Cancer Institute. Technical assistance of Cathy K. Smith, Nancy Tuttle Fuller, and Diane Robertson is gratefully acknowledged. The authors thank Drs. Peter J. Fischinger and Tadao Aoki of the National Cancer Institute for their advice and many helpful discussions.

Cells transformed by certain strains of moloney sarcoma virus contain murine p60

It was previously demonstrated that the 60,000 dalton (p60) precursor-like polyprotein containing murine p30 was a constituent of the feline leukemia virus pseudotype of Moloney sarcoma virus [m1MSV(FeLV)]. It is now shown that p60 is detected in cells of five mammalian species transformed by m1MSV, indicating that p60 is specified by this genome. Moreover, little or no murine p30 is detected in the m1MSV-transformed cells, suggesting that the murine group p30 antigenic reactivity of S + L- cells is ude to p60. Pulse-chase studies in cells producing m1MSV(FeLV) show that p60 is the largest polypeptide detectable during the pulse, and that intracellular p60 is not cleaved into smaller (for example, p30) polypeptides during chase periods of up to 10 hr. The lack of cleavage of p60 is in contrast to the properties of p30 precursors detected in cells containing replicating avian or mammalian RNA tumor viruses. The inefficient cleavage of intracellular p60 and the kinetics of appearance of murine p30 in extracellular m1MSV(FeLV) suggest that p60 cleavage to p30 occurs in cells shortly before virus release. While only p60 was detected in the m1MSV-transformed cells, p60 and p70 were detected in m3MSV-transformed cells, and no immunoprecipitable polypeptides were detected in HT-1 MSV-transformed cells. The observed differences in the intracellular polypeptide expression by each of the strains of MSV suggests differences in genetic content.

A p60 polypeptide in the feline leukemia virus pseudotype of Moloney sarcoma virus with murine leukemia virus p30 antigenic determinants.

A 60,000-dalton polypeptide (p60) has been identified in the feline leukemia virus (FeLV) pseudotype of Moloney sarcoma virus [MSV(FeLV)]. This polypeptide is present in the purified virus complex in concentrations greater than either the murine p30 or the feline p27. Purified p60 crossreacts immunologically with murine p30 group antiserum and contains several interspecies determinants, whereas the group specific determinant of FeLV p27 is not detected. Comparison of peptide fingerprints of p60 and murine p30 show many peptides in common. Limited digestion of p60 with either trypsin or chymotrypsin produced p30-35 and p20 peptides which retain the MuLV p30 group and interspecies antigenic activities. The p30 produced by both enzymes comigrates in polyacrylamide gels with the murine p30 of MSV(FeLV), thus suggesting that p60 may be an uncleaved precursor to p30.