Modulation of epidermal growth factor receptor activity and related responses by the 7-deazaguanine derivative, queuine.

Epidermal growth factor (EGF) induces autophosphorylation of its cognate receptor at tyrosine residues. Here we show that queuine (q), a widely distributed modified guanine analogue occurring free or as a tRNA wobble base, modulates this EGF receptor activity in vitro and in intact cells. Autophosphorylation of the immunopurified receptor from human A431 epidermoid carcinoma cells was enhanced three to fourfold in the presence of physiological concentrations of q. Using a membrane fraction of A431 cells, a twofold increase in autophosphorylation activity in the presence of q was observed, however, only when the receptor was activated by the ligand. In intact A431 cells, q enhanced the initial ligand-induced autophosphorylation of the EGF receptor three to fourfold. However, upon longer treatment of the cells with EGF in the presence of q, significantly less autophosphorylated receptor was detectable compared with stimulation of cells in the absence of q. A similar q-dependent modulation of EGF receptor autophosphorylation was observed also in human cervical carcinoma cells HeLa-S3. Treatment of q-deficient HeLa cells with EGF induced the c-fos gene expression, transiently increased the activity of the anoxic stress protein LDH k, and stimulated proliferation. Treatment of HeLa cells with EGF in the presence of q resulted in a delayed c-fos gene expression and an accelerated increase and decrease of LDH k activity. The stimulatory effect of low doses of EGF on HeLa cell proliferation was completely antagonized in the presence of q. The results suggest that the mitogenic signalling initiated by the EGF receptor is modulated by q.