This review article will re-report the findings from 30 years ago concerning the implications of the acid cystein proteinase inhibitor (ACPI) to the field of cancer research. The original article, published in 1980, has erroneously been omitted from electronic article databases. The findings reported in the original article suggest that some anaplastic lung cancers should be classified as epidermal. In this article we also consider the yet unknown physiological function of ACPI. Furthermore, we will address the simplification of the nomenclature of ACPI and related molecules.

Scientists at the beginning of their careers often rely on the information obtained from review articles. Furthermore, the review articles are commonly used by sponsors in making their funding decisions of scientific projects. Thus it is very important to give a balanced view of the past as well as the present of the field discussed in those papers. In the present letter I wish to complement a review article previously published in Frontiers in Bioscience.

Background: Acid cysteine protease inhibitor ( ACPI) is an intracellular protein, often linked to neoplastic changes in epithelium and thought to have an inhibitory role in malignant transformation.Aim: To analyse the expression and prognostic role of ACPI in non-small-cell lung cancer (NSCLC). Method: Histological samples from 199 patients with resected NSCLC were stained immunohistochemically for the expression of ACPI in normal and preneoplastic bronchial epithelium, and in various types of lung carcinomas.Results: A normal bronchial epithelium showed positive staining for ACPI in the basal cells, whereas the upper two-thirds of the dysplastic epithelium was ACPI positive. High staining for ACPI was found in 74% (91/123) of squamous-cell carcinomas, whereas 16% (8/49) of adenocarcinomas and 30% of (8/27) large-cell carcinomas showed the high expression of ACPI (p < 0.001). Among squamous-cell carcinomas, low expression of ACPI was correlated with poor tumour differentiation (p = 0.032). In the whole tissue, reduced expression of ACPI was associated with tumour recurrence (p = 0.024). In overall survival (OS) and disease-free survival (DFS) analyses, the histological type of the tumour (both p < 0.001) and stage of the tumour (p = 0.001, p = 0.013, respectively) were related to patient outcome. Low expression of ACPI in tumour cells was associated with poor OS and DFS (p < 0.041, p = 0.004, respectively). In multivariate analysis, ACPI did not retain its prognostic value, whereas the traditional factors were the most important prognostic factors.Conclusions: ACPI expression is linked with the malignant transformation of the bronchial epithelium and predicts a risk of tumour recurrence as well as poor rate of survival for the patients. However, ACPI does not have any independent prognostic value in NSCLC.

Prostatic adenocarcinoma is the most common malignancy among men in the western world but the diagnostic and prognostic criteria for it are still not clearly defined. Additional means for its diagnosis and prognosis are clearly needed. Previously it has been shown that cystatin A is expressed in the basal cells of normal prostate and the expression disappears in prostatic carcinoma.

Kininogens are multifunctional proteins found so far mainly in mammals. They carry vasoactive kinins as well as participate in defense, blood coagulation and the acute phase response. In this study, novel kininogens were isolated from Atlantic cod (Gadus morhua L.) and spotted wolffish(Anarhichas minor) by papain-affinity chromatography. The molecular mass of cod kininogen determined by MALDI-TOF mass spectrometry to be 51.0 kDa and it had pI values of 3.6, 3.9 and 4.4. The molecular mass of wolffish kininogen was 45.8 kDa and it had pI values of 4.1, 4.3, 4.35 and 4.4. Partial amino-acid sequences determined from both kininogens showed clear homology with previously determined kininogen sequences. Both kininogens were found to inhibit cysteine proteinases like papain and ficin but they had no effect on trypsin, a serine proteinase. Wolffish kininogen carried alpha2,3-sialylated biantennary and triantennary N-glycans with extensive sialic acid O-acetylation. Cod kininogen carried similar glycan structures but about 1/3 of its glycans carried sulfate at their N-acetylglucosamine units.

Tissue localization of cysteine proteinases (cathepsins) and their inhibitors (salarin, salmon kininogen) was performed in tissues of the Atlantic salmon. In skin, both epidermis and dermis were strongly stained by antisera against salarin and salmon kininogen. In epidermis the intercellular space seemed to be heavily stained (salarin). In kidney, the inhibitors were mainly localized to the interstitial capillaries. Also, some epithelial cells of the tubules (salarin) and some cells of the interstitium were stained. Mostly, the staining had a diffuse cytoplasmic localization. In the liver some hepatocytes were strongly positive for salarin and salmon kininogen. Purified fish cysteine proteinase inhibitors were not found to inhibit the growth of fish pathogenic bacteria and viruses. In the trunk kidney cathepsins B and L were localized in epithelial cells of the tubules (proximal part) and in cells of the interstitium. Mostly, the staining showed a prominent lysosomal localization. In head kidney large macrophage-like cells were positively stained for cathepsin B. The staining was localized to granula/vacuoles in the cytoplasm. In the liver, some hepatocytes were strongly stained and some were less strongly positive for cathepsin B and L. Mostly, the hepatocytes showed lysosomal staining. Cathepsin L was found in some big macrophage-like cells in the spleen. Mucosal epithelial cells of the esophagus and intestine seemed to be strongly stained for cathepsin B and L. The results show that cathepsins and their inhibitors are specifically and widely distributed in the Atlantic salmon skin indicating that they perform some biologically important and specific but so far unknown functions.

To determine the mechanisms of cell death in rhabdovirus-infected cells, we studied the infection of the epithelial papilloma of carp cell line with spring viremia of carp virus, Studies using electron microscopy, confocal microscopy, and agarose gel electrophoresis revealed changes in cell morphology and DNA fragmentation indicative of apoptosis, The virus-induced apoptosis was inhibited in cells treated with a human endogenous acid cysteine proteinase inhibitor.

Renal cell carcinoma contains significantly lower concentrations of the lysosomal cysteine proteases, cathepsins B, C, H, L and S, than does normal kidney, as shown by several methods, such as activity determination, enzyme-linked immunosorbent assay, immunoblotting and immunohistochemistry. The same low levels of enzyme activity and concentration have been determined in renal cell carcinoma metastases in the lung. Our results on the decreased concentration of cysteine peptidases at the protein level would seem to conflict with earlier results on an increased concentration of the cathepsin L mRNA in renal cell carcinoma.

We report a study of the organization of accessory cell populations, in normal mucosal lymphoid tissue from small intestine (8 cases), large intestine (6) and appendix (9) using a panel of monoclonal antibodies and polyclonal antisera in paraffin-embedded tissue. Two populations were identified in dome areas, one positive for acid cysteine proteinase inhibitor and HLA class II (WR18) only and the second positive for S-100 protein, CD68, and WR18 and negative for acid cysteine proteinase inhibitor and factor XIIIa. Superficial colonic mucosal and small intestinal villous tip macrophages stained positively with CD68 and WR18 only, while deeper cryptal and submucosal populations exhibited additional positivity for factor XIIIa, but both populations were negative for acid cysteine proteinase inhibitor and S-100 protein. Germinal centre macrophages were positive for CD68, WR18 and acid cysteine proteinase inhibitor and negative for factor XIIIa, and S-100 protein. T zone dendritic cells included a population which stained positively for S-100 protien, WR18 and were negative for factor XIIIa, CD68 and acid cysteine proteinase inhibitor, an immunophenotype typical of interdigitating dendritic reticulum cells. This distribution of phenotypically identifiable accessory cell subpopulations was apparent at all three sites examined. We suggest that the specialized subpopulations of dendritic cells staining for S-100 protein and for acid cysteine proteinase inhibitor which are restricted to the dome areas, may have a potential role in the transfer of antigen across the epithelium to the germinal centres, while factor XIIIa appears to identify a tissue macrophage population with a potential role in stromal modulation distant from direct antigen challenge.

Lysosomal proteinases (cathepsins) and their endogenous inhibitors (cystatins) have been found to be closely associated with senile plaques, cerebrovascular amyloid deposits, and neurofibrillary tangles in Alzheimer disease (AD). Further, profound changes in the lysosomal system seem to be an early event in “at-risk” neurons of AD brains. There is an ongoing controversy as to whether lysosome-associated proteolytic mechanisms are causally related to the development and/or further progression of the disease. The present article deals with some arguments “pro” and “contra” an involvement of the endosomal/lysosomal pathway in amyloidogenesis as a cardinal process in AD. Other putative targets of acidic proteinases and their natural inhibitors in the pathogenesis of AD (such as formation of neurofibrillary tangles and regulation of apolipoprotein E) are also discussed.

Acid cysteine proteinase inhibitor (ACPI or cystatin A) is a protein (12 kDa) which inhibits the action of several cysteine proteinases, e.g. cathepsins B, H, L and S. In this study the cellular location of ACPI has been immunohistochemically investigated in the normal human prostate, in benign prostatic hyperplasia (BPH) and in adenocarcinoma. ACPI was found in the basal epithelial cells of the normal prostate. The secretory epithelial cells did not express ACPI. In the hyperplastic prostate, the expression of ACPI was decreased and it was also expressed more focally in the basal cells. Hyperplastic basal cells also expressed ACPI. In prostatic adenocarcinoma, no ACPI expression was found. The absence of ACPI expression was obvious and if the sections contained both benign and malignant cells, only the benign glandular structures always expressed ACPI. The results suggest that expression of ACPI might be related to prostatic epithelial cell proliferation and differentiation. Possibly the detection of ACPI in tissue sections might be helpful in identifying prostatic adenocarcinoma, especially in cases with small carcinomatous foci.

Acid cysteine proteinase inhibitor (ACPI, cystatin A) is normally present in squamous epithelium and dendritic cells of lymphoid follicles. Its expression is altered both in proliferative and malignant squamous epithelium and in neoplastic lymphoid follicles. The expression of ACPI in the lymphoid infiltrates of cutaneous psuedolymphomas and B-cell lymphomas was studied. Eighteen pseudolymphomas from 15 patients were divided into three groups according to the proportion of B and T lymphocytes. The B-cell-type lesions with well-developed follicles and germinal centers showed a pronounced ACPI expression in dendritic cells. Varying amounts of ACPI-positive cells were present in the mixed B- and T-cell-type and also in the T-cell-type lesions. The labeled cell population was distinct from the factor XIIIa-positive dermal dendrocytes, S-100-positive histiocytes, and HAM 56-positive histiocytes. Malignant lymphomas contained a few haphazardly arranged ACPI-positive cells with short dendrites and granular cytoplasm. It was concluded that follicular dendritic cells can be reliably labeled with ACPI antiserum in cutaneous pseudolymphomas. The structure and distribution of ACPI-containing cells in malignant cutaneous B-cell lymphomas is altered when compared with pseudolymphomas.

It has been shown previously that dendritic reticulum cells (DRC) in human secondary lymphoid follicles possess an immunoreactive acid cysteine-proteinase inhibitor (ACPI). In the present study, lymph nodes from 12 patients with AIDS-related persistent generalized lymphadenopathy (PGL) were investigated in order to detect whether or not any alterations occur in ACPI-immunoreactive DRC in this disorder. In the majority of PGL cases, profound alterations were found, the main characteristics of which were erosion, partial or total disruption of lymphoid follicles. However, similar though much less marked alterations were also found in some control cases. It is concluded that this type of follicular damage is a common and characteristic feature in PGL. It is not specific to PGL, however, but represents rather a special type of reaction in lymphatic tissue. The advantage of ACPI immunohistology for demonstrating the DRC pattern is that it can be performed on routinely fixed and paraffin-embedded tissues.

In autologen Epidermistransplantaten im Bereich der Gingiva von Zahn-Protheseträgern wurde immunhistochemisch die Verteilung der Cysteinproteinaseinhibitoren untersucht. Der saure Cysteinproteinaseinhibitor (ACPI) wurde im Plattenepithel der Epidermis des Transplantats und der Mucosa nachgewiesen. Der neutrale Cysteinproteinaseinhibitor (NCPI) konnte nur im Mucosaepithel lokalisiert werden. Das Epidermistransplantat hat bei guter Adaptation an die neue Umgebung nicht die Eigenschaft des neutralen Cysteinproteinaseinhibitors iibernommen.

Human tissues are known to contain two low molecular weight (MW about 12,000) cysteine proteinase inhibitors, i.e. an acid inhibitor (ACPI) with pI 4.7–5.0 and a neutral inhibitor (NCPI) with pI 6.0–6.5. ACPI is abundant in cornifying epithelial tissues and in the dendritic reticulum cells of germinal centres of the lymph nodes. NCPI is abundant in lymphatic tissue and is known to be synthesized and released by mononuclear phagocytes. In this report NCPI was localized immunohistochemically in the epitheloid cells of most sarcoidotic lymph nodes, in lymph node macrophages after lymphangiography and in alveolar macrophages, while no ACPI could be demonstrated in the same cells by similar methods. These inhibitors were not demonstrable in lymph node sinus histiocytosis. Peripheral blood monocytes did not exhibit any NCPI immunoreactivity. In occasional blood monocytes anti-ACPI serum gave a weak reaction, the specificity of which is questionable. These data suggest that studies on cysteine proteinase inhibitors reveal basic differences in the various histiomonocytic cells and possibly differences in their functional stages.