Analysis of the protein glycosylation defect of a temperature-sensitive cell cycle mutant by the use of mutant cells overexpressing the human epidermal growth factor receptor after transfection of the gene.
A temperature-sensitive mutant with a defect in glycoprotein synthesis and a cell cycle (G1)-specific arrest at the nonpermissive temperature (Tenner et al., J. Cell. Physiol., 90:145-160, 1977; Tenner and Scheffler, J. Cell. Physiol., 98:251-266, 1979) was investigated further after a human epidermal growth factor (EGF) receptor gene had been transfected and amplified in these cells. While a temperature shift-up lead to an immediate arrest in the biosynthesis of mature EGF receptor and its appearance on the plasma membrane, the observed turnover of the preexisting receptor was too slow to account for the arrest of DNA synthesis in these mutant cells. Tunicamycin could in fact mimic the effect of a temperature shift on the biosynthesis of EGF receptor, but it did not have the same rapid effect on DNA synthesis and cell cycle progression. These mutants have also been shown to induce a set of stress proteins or glucose-regulated proteins, GRPs (Lee et al., J. Cell. Physiol., 129:277-282, 1986). The question is addressed whether the defect in glycoprotein synthesis is the primary defect and a possible cause of the induction of the GRPs, or whether a more basic defect at the level of the endoplasmic reticulum (ER) is responsible for the complex phenotype of the mutant. Our results argue in favor of a primary defect which indirectly affects N-linked glycosylation of proteins, as well as several other functions associated with the ER. We hypothesize that the defect affects the calcium distribution between ER and cytosol, since the calcium ionophore A23187 has an effect similar to that of a temperature shift.