Hsp 78: A prominent heat shock protein of the lepidopteran Choristoneura fumiferana that is immunologically unrelated to members of the major hsp families

Cultured cells of the spruce budworm (Choristoneura fumiferana) respond to heat shock with the new and/or enhanced synthesis of six proteins with Mrs of 84,000, 78,000, 70,000, 68,000, 21,000, and 14,000, as measured by one- and two-dimensional PAGE. The most prominent hsp of these cells is a 78,000 Da protein which is maximally induced at 39 degrees C and which consists of three isoforms with different pl. Hsp 78 is found in the detergent-soluble cytosolic fraction of cell lysates. In vitro translation of RNA extracted from cultured cells and from larvae shows that the induction of hsp 78 is regulated mainly at the transcriptional level. Hsp 78 does not cross-react with a variety of antibodies made to members of the hsp 70 and hsp 83 families. In particular, antibodies to hsp 70 that do cross-react with a 70 kDa protein of C. fumiferana do not cross-react with hsp 78. Homologous 75-78 kDa hsps are also present in heat-shocked cells from other lepidopterans (Spodoptera frugiperda and Bombyx mori). Cf1 cells exposed to elevated levels of arsenite or cadmium respond with the new and/or enhanced synthesis of only two of their hsps (hsp 84 and hsp 70); hsp 78 is not induced by these treatments. The data suggest that hsp 78 of C. fumiferana represents a new family of hsps unique to lepidopterans.