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A radiometric assay has been developed for the detection of proteolytic activity capable of releasing transforming growth factor alpha (TGF alpha) from its membrane bound precursor. The assay is dependent upon the separation by thin layer chromatography of hydrolytic products of a nonapeptide substrate containing a radioactive iodinated tyrosine residue as a reporting group N-terminal to an octapeptide which is cognate to the N-terminal cleavage sequence of TGF alpha. We describe the selectivity of the peptidase assay with commercially purified proteases and with cell-associated peptidases, its exquisite sensitivity, and its applicability to defining peptidase activity, which may be responsible for the processing of the membrane-bound prepro TGF alpha. The activity of two different elastases had different profiles which thus may be of use in characterizing them. The characteristics of the intact and extracted HeLa cell assay with respect to time, cell density, and peptidase concentration are defined, as are conditions needed to remove endogenous, confounding, proteolytic activity from the serum used to support cell culture. Intact HeLa cell cultures exhibit both exo- and endo-peptidase activity at approximately equal levels in both sparse and dense monolayer culture without relationship to cell density, and at a level equal to 1-2% of total cell activity of these enzyme classes.

Expression of proliferating cell nuclear antigen (PCNA) has been shown to be of prognostic value in patients with certain types of cancer. The aim of this study was to determine if the abundance of PCNA is inversely correlated with survival of patients with breast cancer. Paraffin blocks were available from 68 patients, all of whom had been followed clinically for at least 5 years. Sections from 20 patients showed no reactivity to PCNA and were excluded from the study because it was not possible to distinguish between true negatives and false negatives (those due to poor fixation of the original specimens). The PCNA index (the number of stained cancer cells as a percentage of the total number of cancer cells present) was calculated for the remaining 48 patients. Results were analysed by Wilcoxon's rank sum test (two tailed) and Pearson's correlation coefficient. There was no statistical difference between the PCNA indices of those patients dead from their disease within 5 years of diagnosis compared with those alive and without signs of breast cancer at 5 years. There was also no correlation between PCNA index and size of the cancer, involvement of axillaly lymph nodes, time to recurrence or time to death. There was, however, a significant correlation between PCNA index and histological grade (P= 0.029). It appears that PCNA staining of stored paraffin sections is of little prognostic value in patients with breast cancer.

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