20-Hydroxyecdysone control of the synthesis of putative calcium-binding proteins in the epidermis of Tenebrio molitor

The altered pattern of synthesis of putative calcium-binding proteins (pCaBPs) in the mid-instar epidermis following exposure to 20-hydroxyecdysone (20HE) in vitro was followed through the incorporation of [³⁵S]methionine into newly synthesized polypeptides. pCaBPs were separated from other epidermal polypeptides by Ca²⁺-dependent hydrophobic interaction chromatography, followed by polyacrylamide gel electrophoresis and fluorography. The dominant effect of 20HE is to depress pCaBP synthesis. Of the 17 newly-synthesized pCaBPs consistently detected in total cell lysates, the synthesis of ten was depressed strongly and that of the remaining seven was unaltered by exposure to 20HE. Most newly-synthesized pCaBPs identified were found in the cytosolic fraction of the epidermis. One pCaBP was identified as Tenebrio calmodulin based on its altered electrophoretic mobility in the absence of calcium ions, its isoelectric focusing point, its binding to phenyl-Sepharose and phenothiazine and its binding to antibodies against purified mammalian calmodulin. The synthetic rate of this pCaBP was not affected by 20HE. The distribution of another pCaBP (32 kDa) shifted from the cytosolic to the microsomal fraction on adding Ca²⁺ (or reversed by adding EGTA) to the cell extract before fractionation. The synthesis of this protein was depressed by 20HE. These findings suggest that 20HE influences epidermal behaviour, at least in part, through its ability to modulate the synthetic rate of several pCaBPs.