KLK7 (MSVA-707M)

Kallikrein-related peptidase 7 (KLK7) is a 27,5 kDa chymotrypsin-like serine protease which is coded by the KLK7 gene located on chromosome 19q13. KLK7 plays a pivotal role in maintaining skin homeostasis. It is secreted into the stratum granulosum layer of the epidermis as an inactive enzyme requiring proteolytic cleavage of the N-terminal for becoming activated. Activated KLK7 triggers the proteolysis of corneodesmosomes. This enables the desquamation of corneocytes from the outer layer of the epidermis. Dysregulation of KLK7 has been associated with several skin disorders characterized by excessively dry, scaly and inflamed skin such as atopic dermatitis, psoriasis, and the Netherton syndrome. In cancer, over expression of KLK7 has been suggested to represent a possible route for metastasis due to excessive cleavage of cell junction proteins.

KLK7 staining pattern in Normal Tissues with antibody MSVA-707M (images are shown in our “Normal Tissue Gallery”)

The findings described above are this consistent with the RNA data described in the Human Protein Atlas (Tissue expression KLK7) 

Positive control = Skin: A strong KLK7 staining should be seen in the stratum granulosum and possibly also in the keratinizing cell layers.

Negative control = Colon: KLK7 immunostaining should be absent in all cells of the colon mucosa.

Normal tissue gallery

A positive KLK7 immunostaining has been reported in squamous cell carcinomas of various organs of origin, ovarian cancer and in other tumor entities as well. In several tumor entities, overexpression of KLK7 protein has been found to be linked with metastasis and unfavorable prognosis.

The TCGA findings on KLK7 RNA expression in different tumor categories have been summarized in the Human Protein Atlas.

Cancer tissue gallery

No data available at the moment

IHC users have different preferences on how the stains should look like. Some prefer high staining intensity of the target stain and even accept some background. Others favor absolute specificity and lighter target stains. Factors that invariably lead to more intense staining include higher concentration of the antibody and visualization tools, longer incubation time, higher temperature during incubation, higher temperature and longer duration of the heat induced epitope retrieval (slide pretreatment). The impact of the pH during slide pretreatment has variable effects and depends on the antibody and the target protein.

All images and data shown here and in our image galleries are obtained by the manual protocol described below. Other protocols resulting in equivalent staining are described as well.

-Manual protocol

Freshly cut sections should be used (less than 10 days between cutting and staining). Heat-induced antigen retrieval for 5 minutes in an autoclave at 121°C in pH 7,8 Target Retrieval Solution buffer. Apply MSVA-707M at a dilution of 1:150 at 37°C for 60 minutes. Visualization of bound antibody by the EnVision Kit (Dako, Agilent) according to the manufacturer’s directions.

• Immunohistochemical studies on KLK7 expression have been limited so far. The prognostic and diagnostic role of KLK7 expression analysis needs to be further evaluated.

There are two ways how the specificity of antibodies can be documented for immunohistochemistry on formalin fixed tissues. These are: 1. Comparison with a second independent method for target expression measurement across a large number of different tissue types (orthogonal strategy), and 2. Comparison with one or several independent antibodies for the same target and showing that all positive staining results are also seen with other antibodies for the same target (independent antibody strategy). 

Orthogonal validation: For the antibody MSVA-707M specificity is suggested by the strong concordance of the immunostaining data with data from three independent RNA screening studies, including the Human Protein Atlas (HPA) RNA-seq tissue dataset, the FANTOM5 project, and the Genotype-Tissue Expression (GTEx) project, which are all summarized in the Human Protein Atlas (Tissue expression KLK7). RNA expression predominates in organs covered by squamous epithelium (esophagus, vagina, cervix, skin) where a significant staining is observed by MSVA-707M. In addition, low level RNA expression in salivary glands, kidney, and fallopian tube is – in principle – consistent with focal MSVA-707M immunostaining observed in these organs. Low level RNA expression in the gallbladder and the breast is, however, not necessarily explicable by MSVA-707M staining data as these organs were completely negative by IHC. Given the limitation of KLK7 positivity to only few cells in salivary glands, it is possible that few KLK7 expressing cells in gallbladder glands and breast glands were not identified due to a sampling error. 

Comparison of antibodies: True expression of KLK7 in squamous epithelium and in salivary glands is further corroborated by comparison with a commercially available independent second antibody (termed “validation antibody”). Because the validation antibody did not confirm MSVA-707M findings in kidney and fallopian tube, these focal findings are considered possible cross-reactivities (tolerable) of MSVA-707M  in spite of positive RNA findings in these organs. Independence of the two antibodies used for validation is documented by cytoplasmic smooth muscle staining and nuclear staining in several organs (often predominating on nuclear membranes) which was only seen by the validation antibody but not by MSVA-707M.

Antibody Comparison: MSVA-707M vs another commercially available KLK7 antibody called “Validation Antibody”

Normal tissue gallery