Biological, immunological, and molecular properties of revertants of cat cells transformed by murine sarcoma virus
Fischinger, P.J.; Blevins, C.S.; Frankel, A.E.; Tuttle-Fuller, N.; Haapala, D.K.; Nomura, S.; Robey, W.G.
Cancer Research 41(3): 958-965
1981
ISSN/ISBN: 0008-5472 PMID: 6257388 Document Number: 177334
Cloned cat cells (CCC) transformed by the m1 isolate of Moloney murine sarcoma virus (MSV) have the properties of sarcoma-positive, leukemia-negative (S+L-) cells. Over the past 5 yr, partially flat as well as very contact-inhibited variant clones were isolated from S+L- cat cells. Partially flat subclones still contained the MSV genome and could serve as useful cell systems for quantal assays for replicating retroviruses. The frequency of isolation of rescue-negative, very flat subclones diminished with sequential cloning cycles of S+L- cells. The rescue-negative revertant cells grew to low density in liquid media, were more similar to normal cells in soft-agar colony formation and were intermediate in concanavalin A agglutinability when compared to normal or S+L- cells. Revertants could be retransformed by pseudotypes of MSV other than MSV coated with feline endogenous xenotropic virus. Feline endogenous xenotropic virus was readily induced from S+L- cells but was not inducible from some revertants by halogenated pyrimidines. Rescue-negative revertants could support the growth of helper viruses. Chromosomes of parental CCC normal cells, MSV producer cells, S+L- cells or revertants were significantly hypodiploid. No stable pathognomonic changes were observed relative to type and chromosome number among the above. The MSV-coded precursor polyprotein with a MW of 60,000 was detected in producer and S+L- cells but not in revertants. Producer and S+L- cells had multiple MSV src copies in their DNA; revertants did not contain residual src DNA. The number of feline endogenous xenotropic virus or feline leukemia virus-like DNA copies was not different among producer, S+L- or revertant cells. All rescue-negative cat cell revertants tested have lost multiple copies of MSV proviral DNA.