Bob Nowinski called today to tell me of your kind offer to collaborate with us in studies of base sequence homologies between
nucleic acids from human breast tumors and from Mu MTV. As Bob probably told you, we have been measuring rather precisely
the amount of MuMTV-specific RNA in a variety of mouse tissues, in an effort to describe the degree of transcriptional regulation
of the large amount of MuMTV DNA found in both GR and C57Bl strains (see enclosed preprint). The mouse studies indicated
that we could anneal all of a single stranded DNA probe made by MuMTV polymerase to RNA from mammary tumors, virus-producing
mammary glands, and lactating mammary glands from C57 mice. Annealing was demonstrated by assay with a single-strand-specific
DNA nuclease and in CsSO4 gradients. Incomplete annealing was obtained with spleen RNA. About .5% of RNA in the virus-producing
tissues is MuMTV-specific, about .01% in the C57LMG is MuMTV-specific, and less than .001% in the spleens in viral-specific.
In view of the high sensitivity and stringency of our hybridization and assay procedures, we decided to try to confirm Spiegelman's
results with human breast tissue. To our frank surprise, the first breast tumor sent to us by Nurul Sarker contained 0.01%
MuMTV-like RNA. We have been able to anneal 100% of our single-stranded DNA probe from MuMTV to this RNA as tested with both
nuclease and CsSO4 assays. In addition, we have studied the melting properties of this hybrid and find that it melts sharply
with a Tm 4 degrees celsius below the Tm for the presumably completely specific hybrid formed between the same probe and RNA
from a virus-producing mouse tumor. This suggests the differences in base sequence between the probe and the RNA it is detecting
are about 6%.
We have tested several other breast specimens; all normal breasts and benign tumors have been negative, but the 4 tumors we
have subsequently tested have also been negative or questionable. The problem at this point is principally that the amount
of tumor tissue in these specimens tends to be small; consequently we get little RNA (which may be contaminated by RNA from
adjacent normal cells) and cannot push the level of detection to the limits the assay itself can bear. Therefore we asked
Bob to approach you about supplying us with tumors (metastatic or primary). The suggestion that we examine your established
human breast tumor lines is a very appealing one.
I will call you next week to discuss the specifics of the amounts of tissues or cells we would need. I am enclosing some recent
papers from this lab to give you some details about the techniques involved. (I should mention that we are about to examine
human tissues for MuMTV-like DNA and would want to do the same with any tissues you might provide us). In addition, I will
be in New York the second week in August and perhaps could get together with you at that time.