Co-purification of proteases with basic fibroblast growth factor (FGF)

Evidence of serine-protease activity closely associated with Drosophila alcohol dehydrogenase

With the use of monoclonal antibodies against alcohol dehydrogenase (ADH) we detected ADH proteolysis in different Drosophila melanogaster tissues during development [Visa, N., Fiblas, J., Santa-Crus, M. C. & Gonzàlez-Duarte R. (1992) J. Histochem. Cytochem. 40, 39-49]. We now report the analysis of this proteolytic activity in crude homogenates and in purified ADH preparations of several Drosophila species. Our results indicate that in non-denaturing IEF gels the proteolytic activity comigrates with native ADH electromorphs of all the species analyzed. In addition, we show that it copurifies with ADH and is responsible for the instability of apparently homogeneous ADH preparations in the presence of SDS. When purified ADH preparations were analyzed, the endogenous proteolytic activity yielded the same banding pattern as that obtained with crude homogenates. Even after rechromatography on Sephacryl S-200, the usual last step in our standard purification protocol, the proteolytic activity remained associated with the ADH fractions. Among the various agents which could explain the ADH-linked proteolytic effect, a pre-existing nicked state of the enzyme or chemical proteolysis have been ruled out. The kinetics observed on pure ADH preparations, the effect of specific protease inhibitors and substrate specificity have led us to ascribe this activity to the subtilase serine-protease family. Given that proteolysis is evident even in rechromatographed Sephacryl S-200 fractions, if incubated in SDS for enough time, we propose two alternative hypotheses to explain this phenomenon. First, the proteolytic activity may come from a protease which is inseparable from the ADH active forms and second, the ADH itself may behave as a subtilase when it adopts a particular conformation. Moreover, the previously reported differential banding pattern during development suggests a role for this activity in vivo, in which fatty acids could produce the inducer effect attributed to SDS in vitro.

Cyclic AMP potentiates bFGF-induced neurite outgrowth in PC12 cells

We report here that basic fibroblast growth factor (bFGF)-elicited neurite outgrowth in PC12 cells is potentiated by dibutyryl cyclic adenosine monophosphate (dbcAMP) or forskolin. This property was also described for nerve growth factor (NGF), suggesting that both NGF and bFGF may share common intracellular events leading to neurite outgrowth and synergism with dbcAMP and forskolin. The synergistic effect of dbcAMP and forskolin is specific, since treatment of PC12 cells with bFGF and dibutyryl cyclic guanosine monophosphate (dbcGMP) or phorbol ester did not change the neurite outgrowth response of cells treated with bFGF alone. Furthermore, neurite outgrowth depends on cellular adhesion. Increasing adhesion by plate treatment with poly-d-lysine increases the neurite outgrowth elicited by bFGF alone or bFGF plus dbcAMP. On the other hand, decreasing cellular adhesiveness by plating PC12 cells in semi-solid agarose renders the cells unable to develop neuritic processes. In addition, 3H-methylthymidine incorporation studies showed that bFGF-treated PC12 cells cease growth only when they become fully differentiated after 3-5 days of treatment. In contrast, dbcAMP, which is a poor differentiation factor, is able to block cellular growth after 24 hour treatment. These results suggest that when PC12 cells become differentiated, they stop growing. However, growth inhibition does not necessarily lead to differentiation.

Biologically active basic fibroblast growth factor migrates at 27 kD in "non-denaturing" SDS-polyacrylamide gel electrophoresis

Using mild conditions of SDS-PAGE, i.e. no heating of the sample, and the PhastSystem (Pharmacia), we found that bFGF, either natural bovine or recombinant human migrated at a 27 kD position in addition to the classical 18 kD one. By the cell-blot technique, we found that the biological activity toward rat astroblasts and 3T3 mouse fibroblasts was always restricted to the 27 kD band. Partial heat denaturation experiments revealed a close correlation between the remaining biological activity of bFGF in solution and the ratio of the 27 kD band versus the 18 kD band seen on SDS gels. These observations suggest that the bFGF which is biologically active in solution migrates at an apparent Mr of 27 kD in our conditions of electrophoresis, keeping its biological activity after electrophoresis, and the molecules which are inactive (denatured) in solution migrate at 18 kD and remain inactive. These experimental conditions, in which the biological activity appears to be preserved, could be referred to as "non-denaturing SDS-polyacrylamide gel electrophoresis" and could be useful, associated to cell-blot, for the search and characterization of new growth factors active on cells in culture.

Calcium protects pituitary basic fibroblast growth factors from limited proteolysis by co-purifying proteases

Extracts from bovine pituitaries and other tissues contained basic fibroblast growth factor-like peptides of 22-26 kda, co-fractionating with smaller, 16-20 kda bFGFs. Heparin-bound, 22-26 kda bFGFs were converted to smaller, heparin-binding forms by tryptic proteolysis. In solution, 22-26 kda bFGFs were converted to smaller, heparin-binding forms by an activity present in pituitary extracts. Calcium protected higher molecular weight pituitary bFGFs from truncation by the endogenous activity, which was not acid-activated, co-purified with bFGF during heparin-sepharose chromatography, remained operant at high salt concentrations and was inhibited by phenylmethan-sulfonyl fluoride.