Ras chaperons for cancer therapy and Ras transfer from cell-to-cell

All Ras proteins in their active GTP-bound forms bind to chaperons such as galetin-1, galectin-3 and nucleolin. Interference with Ras-GTP binding to their chaperons by the farnesylated compound Salirasib (FTS) blocks Ras nanoclustering in the cell membrane and tumor growth. Salirasib is a non-toxic drug that passed successfully phase1/2 trials (pancreatic carcinoma) and non-small-lung carcinoma. One possibility of active Ras proteins and of small RNAs to induce oncogenic functions or to regulate immune functions is to transfer from one cell to another. It is not known however whether intact intracellular proteins and small RNAs can indeed transfer from cell-to-cell in a contact-dependent manner to allow the transmission of signals across cell boundaries. We provide evidence for this new concept. By the use of fluorescence-activated cell sorting (FACS) and confocal fluorescence microscopy we showed the functional transfer of H-Ra(G12V) from B to T or NK cells and from melanoma to tumor infiltrating lymphocytes (TILs). Cell-to-cell transfer appears not to be unique for H-Ras protein. By means of an original quantitative proteomics platform termed trans-SILAC, (stable isotope labeling of amino acids in culture) that was designed to identify with high fidelity on-cell-autonomous proteins, we showed that a multitude of proteins (~200), transfer from a B cell line to primary human NK cells. Among them we found, for example, the lipidated proteins H-Ras (confirming our previous results with GFP-tagged Ras), RalA, RalB, Rab11a and Rab10. In related studies we found that such intercellular connections allow also transfer of small RNAs among lymphocytes. We found that upon cell-cell contact synthetic-mimetics and cell-endogenous microRNAs (miRNAs) as well as virally derived miRNAs can transfer from B to T lymphocytes. We also confirmed that such non-cell-autonomous small RNAs could impact expression of target genes in the recipient T cells. Together these recent discoveries of extensive proteome and RNA mixing among lymphocytes challenge the classical model of cell autonomy.