Large scale isolation, purification, and partial characterization of the intermediate filament-specific, Ca2+-activated proteinase from porcine kidney and Ehrlich ascites tumor cells: a comparative study

Induction of glucose regulated proteins during growth of a murine tumor

Chronic anoxia, glucose starvation, low pH, and numerous other conditions induce the glucose-regulated system of stress proteins (GRPs), whose principal members are observed at 78, 94, and 170 kDa. These stresses may be expected to occur during growth in untreated tumors. To examine the possibility that GRPs are correspondingly induced, we have examined the protein profiles of small (< 0.1 g), intermediate (0.2-0.8 g), and large (> 1.8 g) radiation-induced fibrosarcoma (RIF) tumors grown on C3H mice. One and two-dimensional gel electrophoresis indicate that the principal GRPs at 78 and 94 are coordinately and substantially increased in large tumor masses, relative to the small, and may be partially increased in the intermediate tumors. Necrotic material removed from large tumors exhibited an identical pattern of GRP induction with no visible indication of protein degradation and also contained a significant fraction of viable cells. Western blot analysis using rabbit antisera raised against the 78 and 170 kDa GRPs also demonstrated the enhanced accumulation of these proteins in the large tumors. The antibody against the 170 kDa GRP was also capable of detecting the induction of this stress protein in large tumors by indirect immunofluorescence analysis. Northern blot studies using a probe for the GRP 78 gene also showed an increase in GRP 78 message in large tumors as well as in RIF cells exposed to anoxic stress in vitro. Two-dimensional gel electrophoresis indicated that the major heat shock proteins at 70 and 90 kDa were not increased in the larger tumors, and the amount of the 90 kDa species was reduced. Finally, the quantity of vimentin and its degradation products is significantly diminished in large tumors and in anoxic cells. This study demonstrates that RIF tumor cells undergo a glucose regulated stress response in situ during tumor growth.

Characterization of calpains and calpastatins from hamster skeletal muscle

1. Hamster skeletal muscle contains a wide-specificity calpain which was found to be a calpain II type and which is composed of a single Mr 80,000 polypeptide. 2. The muscle also contains a calpain I type enzyme which is specific for desmin degradation, and this enzyme consists of a single subunit of Mr 67,000. 3. Three calpastatins were detected in the tissue, one of which inhibited both calpains, whereas the other two appeared to be specific for the desmin-specific calpain. These calpastatins possessed the same inhibition properties when assayed with chicken gizzard calpains.

Protein-chemical identification of the major cleavage sites of the Ca2+ proteinase on murine vimentin, the mesenchymal intermediate filament protein

Neutral thiol proteinases (calpains), activated by calcium are involved in the intracellular turnover of intermediate filaments but the precise position of the cleavage points has remained unknown. Here we identify by direct sequence analysis the major cleavage sites found when murine vimentin is digested by limited proteolysis in vitro with calpain purified from porcine kidney. Contrary to some previous suggestions, no absolute sequence specifity could be detected although 10 specific sites have been identified. This result is in line with the cDNA derived amino-acid sequence of a calpain, which pointed to a similarity of the catalytic site with the active sites in papain, cathepsin and actinidin. However, all major cleavage sites are located within regions of the vimentin molecule, which in current models of intermediate filament structure are thought to be non-helical: the amino-terminal headpiece, the carboxy-terminal tailpiece and the spacer separating the two major coiled-coil domains. The sequence information about the cleavage sites was extended to provide the amino-terminal 119 residues of murine vimentin.

Efficient degradation in vitro of all intermediate filament subunit proteins by the Ca2+-activated neutral thiol proteinase from Ehrlich ascites tumor cells and porcine kidney

Vimentin, desmin, glial fibrillary acidic protein, neurofilament triplet proteins, and a mixture of cytokeratins were digested with Ca2+-activated neutral thiol proteinase isolated from Ehrlich ascites tumor (EAT) cells and porcine kidney. All intermediate filament proteins were degraded by the proteinase, although with different rates and Ca2+ optima. These results are in part at variance with our previous statement that the Ca2+-activated proteinase from EAT cells is specific for vimentin and desmin.