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Owing to subtle but potentially crucial structural and functional differences between calmodulin (CaM) of different species, the biochemical study of low-affinity CaM-binding proteins from Dictyostelium discoideum likely necessitates the use of CaM from the same organism. In addition, most of the methods used for identification and purification of CaM-binding proteins require native CaM in nonlimiting biochemical quantities. The gene encoding D. discoideum CaM has previously been cloned allowing production of recombinant protein. The present study describes the expression of D. discoideum CaM in Escherichia coli and its straightforward and rapid purification. Furthermore, we describe the optimization of a complete palette of assays to detect as little as nanogram quantities of proteins binding CaM with middle to low affinities. Purified CaM was used to raise high-affinity polyclonal antibodies suitable for immunoblotting, immunofluorescence, and immunoprecipitation experiments. The purified CaM was also used to optimize a specific and sensitive nonradioactive CaM overlay assay as well as to produce a high-capacity CaM affinity chromatography matrix. The effectiveness of this methods is illustrated by the detection of potentially novel D. discoideum CaM-binding proteins and the preparatory purification of one of these proteins, a short tail myosin I., (Copyright 1999 Academic Press.)

Cathepsins B and L play roles in intracellular and extracellular proteolysis in normal and malignant processes. A directed extracellular proteolysis by regulated secretion could facilitate the process of invasion. We have therefore investigated the effect of the physiological signal mediator 12(S)-hydroxy-eicosatetraenoic acid on the release of cathepsins B and L in normal and malignant human lung cells. Quantitative determinations of cathepsin activities were done by flow cytometry and spectrofluorometry using synthetic dipeptidyl substrates coupled to fluorogens. Most interestingly, a difference in the secretion of cathepsins B and L was found: only release of active cathepsin B was detected. The effect was specific for 12(S)-hydroxy-eicosatetraenoic acid, 12(R)-hydroxy-eicosatetraenoic acid, and 5(S)-hydroxy-eicosatetraenoic acid were ineffective. The response was immediate but a substantial amount of nonreleasable activity remained cell bound. Alveolar macrophages, Wi-38 fibroblasts, and tumor cells derived from large cell carcinomas and adenocarcinomas were sensitive to 12(S)-hydroxy-eicosatetraenoic acid, but cells from undifferentiated squamous cell carcinomas were not. Sensitivity did not parallel malignancy but more likely the degree of differentiation of cells. The investigated tumor cell lines showed no detectable endogenous 12-lipoxy-genase activity to synthesize 12(S)-hydroxy-eicosatetraenoic acid from arachidonate; therefore, we assume a paracrine mechanism for 12(S)-hydroxy-eicosatetraenoic acid action. Protein kinase C alpha, a key enzyme involved in 12(S)-hydroxy-eicosatetraenoic acid-elicited responses, was expressed in all sensitive tumor cells, but insignificantly in a sensitive normal cell line and an insensitive tumor cell line. From our experiments we propose two separate intracellular pools of active cathepsin B: an unreleasable, lysosomal fraction and a fraction available for regulated secretion. Different processing and sorting mechanisms may be responsible for the generation of these cathepsin B-fractions in these pools.