Inhibition of collagen synthesis in cultured cells by hypertonic culture medium

Translational efficiency of cytoplasmic nonpolysomal messenger ribonucleic acid from sea urchin embryos

“…The simpliest explanation for this finding is that the RNA moiety of the free RNPs itself is less capable of being translated. Intrinsic differences in the abilities of specific mRNAs to be translated have been reported (Nuss & Koch, 1976;Sonenshein & Brawerman, 1976;Koch et al, 1977;Kozak & Shatkin, 1978;Kaempfer et al, 1978), and this proposal is analogous to that advanced by Lodish (1974) to explain the presence of a-globin mRNA in the free RNPs of reticulocytes. It is attractive to explain the reduced efficiency of the free RNP RNA on the basis of a nonrandom selection, in vivo, of "strong" mRNA into polysomes, thereby leaving behind a higher proportion of less efficient ("weak") mRNAs in free RNPs.…”

Differential effect of hypertonic initiation block on the synthesis of collagen chains by cultured chick embryo cells

“…The mechanism by which HIB inhibits the initiation of protein synthesis is unknown, but its use in many different systems has shown a wide response in the synthesis of individual proteins (Saborio et al, 1974;Nuss & Koch, 1976a,b). It has also been shown that HIB is readily reversible even at NaCl concentrations much higher than those used in this study (Saborio et al, 1974;Koch et al" 1977), indicating that it does not affect cell viability.…”

“…Collagenase digestions of control cells revealed that 15-17.5% of the incorporated label was susceptible to collagenase digestion. The somewhat higher values of proline incorporation for leg cells compared to calvaria, at the same NaCl concentration, are most likely a result of collagen's increased susceptibility to HIB (Koch et al, 1977) and a larger amount of collagen synthesized by calvaria cells.…”

“…These studies, using both intact cells and cell-free protein-synthesizing systems, have led to models pertaining to the regulation of protein synthesis at the translational level (Lodish, 1974). Previous work in this laboratory has shown that type I collagen synthesis, in cultured chick cells, is more sensitive to hypertonic initiation block (HIB)1 *than the majority of cellular proteins (Koch et al, 1977). As there are several reports of the synthesis of a collagen molecule containing three a^I) chains rather than the commonly found «i(I)2a2 (Mayne et al, 1975(Mayne et al, ,1976Benya et al, 1977;Crouch & Bornstein, 1978), I closely examined the chain ratio under conditions of reduced initiation to see if there was a difference in initiation efficiency which might explain the occurrence of [ai(I)]3 molecules.…”