Demonstration that LSTRA cells have an elevated level of proteins phosphorylated on tyrosine residues.

The LSTRA cell line has been shown to have an exceptionally high level of a tyrosine protein kinase (pp56lck). We now report that LSTRA cells also have a much higher level of proteins phosphorylated on tyrosine residues in comparison to several other cell lines with normal levels of pp56lck. The level of phosphotyrosine-containing proteins in LSTRA cells was comparable to that seen in K562 cells, a cell line known to have a constitutively active tyrosine protein kinase. These results provide evidence that LSTRA cells have an elevated level of in vivo tyrosine protein kinase activity, probably due to the overexpression and activation of pp56lck.