Glutaraldehyde fixation increases retention of low molecular weight proteins (growth factors) transferred to nylon membranes for western blot analysis

Basic fibroblast growth factor accumulates in the nuclei of various bFGF-producing cell types

The intracellular localization of basic fibroblast growth factor (bFGF) was studied in BHK-21 cells transfected with an expression vector containing the complementary DNA (cDNA) of the human bFGF gene (pbFGF). The intracellular location of bFGF was determined using indirect immunofluorescence. The antibodies used were polyclonal antibodies directed against either recombinant human bFGF or recombinant Xenopus bFGF. The nuclei of transfected cells that produce bFGF, but not the nuclei of untransfected cells, were labeled strongly by the antibodies. The nuclear staining was totally abolished when anti-bFGF antibodies preadsorbed with bFGF were used. Several types of endothelial cells known to produce bFGF were also stained in their nuclei by the antibodies. Nuclear extracts prepared from transfected cells were found to contain bFGF as determined using heparin-sepharose affinity chromatography, followed by Western blot analysis of fractions, which stimulated the proliferation BHK-21 cells. The mitogenic activity associated with the nuclei was not destroyed when isolated cell nuclei were digested by trypsin. It is therefore likely that the nucleus associated bFGF is intranuclear. These findings suggest that some biological activities of bFGF may be mediated by nuclear bFGF binding proteins or by the direct binding of bFGF to DNA.

The sensitivity of dot immunoassay for the peptides helodermin, histidine-isoleucinamide (PHI) and histidine-methioninamide (PHM) increases after peptide cross-linking to proteins prefixed on nitrocellulose

Two out of three rabbit anti-helodermin antisera previously shown to be useful for radioimmunoassay failed to detect up 100 ng of the peptide helodermin spotted directly on a nitrocellulose membrane. A lesser shortcoming of dot immunoassay was encountered with porcine PHI (peptide histidine-isoleucinamide), a member of the same peptide family, and an anti-PHI antiserum. To improve antigen-antibody interactions in the solid phase, we compared five methods of prior peptide immobilization. The best result was obtained when the nitrocellulose membrane was pretreated for 1 min in 4% ovalbumin, followed by 10 min activation with 2.5% glutaraldehyde, before peptide spotting. After cross-linking, the peptide was immunodetected with a F(ab')2 fragment of an anti-rabbit IgG coupled to alkaline phosphatase. The peptide cross-linking method was capable of increasing the sensitivity of ensuing immunodetection by more than 1000-fold, i.e., made feasible the detection of 0.1 ng peptide/dot in cases when the direct spotting method was inefficient. The sensitivity of this new, reliable and simple dot immunoassay for peptides was comparable to the conventional dot assay of directly immobilized large proteins.