Calmodulin in human skin-localizations and interpretations

Cahnodulin, one of the major calcium-binding proteins, is highly conservative, but is still a hot topic in dermatology. I really enjoyed the recent contribution of Drs. Kamamori and Shimizu in this journal [1]. This is the third group of investigators to search to day for the distribution of immunoreactive calmodulin in human skin (see [3-6]). However, this is also the third pattern of distribution described for this ubiquitous protein, which means that the problem of interpretation in back to zero. Which are the majors factors contributing to the distinct findings reported in the literature? First of all, tissue processing has the greatest impact on staining patterns with anti-calmodulins. We used both frozen sections and formalin-fixed routinely processed samples, but found the former to be more useful (see [3, 6, 7]). Second, the antibody is of particular importance. We tested two different antibodies: ACAM (rabbit polyclonal antibody against performic acid-oxidized ram testes calmodulin) and BF8 (a monoclonal mouse IgG2 antibody against plant calmodulin) and experienced quite different staining patterns. In human skin, there was no staining with BFS, although it worked very well in lower vertebrates [6]. What about cross-reactivity with other calcium-binding proteins? Third, the cell type and its degree of differentiation act on the immunoreactivity of calmodutin. It has been assumed that the association of cahnodulin to actin or other components of the cytoskeletal network is responsible [2]. As far as we known, calmodulin immunoreactivity in epithelial cells of skin seems to be related to their role in permeability control [6]. For the dermatologist, it is therefore not too surprising that in psoriasis immunostaining for calmodulin fades away in the lesions where skin barrier function is disturbed [4]. Fourth, the choice of visualizing systems (immunofluorescence, APAAP, or ABC) has some importance for sensitivity. From the data available, the major factor responsible for different staining patterns with anti-catmodulin described by Drs. Kanamori and Shimizu [1] and our group [4, 5] might be the antibody. For us ACAM staining was clearly dependent on tissue processing. This indicates that the antigen was only in part formalin-resistant. The antibody used by the Japanese researches disclosed "basically no difference between paraffin and frozen sections in the distribution and the intensity of calmodulin". How should we interpret calmodulin immunoreactivity? It turns out that calmodulin itself is involved in cell proliferation. On the other hand, immunoreactive calmodulin, which is obviously a minor part of the total protein content, seems more closely related to permeability control, although its involvement in proliferation must be considered as well [4, 6].