A novel gelatinolytic enzyme secreted by amelanotic cells isolated from B16 melanoma cell line

Nanoscale imaging and quantification of local proteolytic activity

Proteolytic cleavage of extracellular matrix (ECM) is a critical feature of tumor cell invasion, and affects cancer cell growth, differentiation, apoptosis, and migration. Malignant cells secrete most proteases as inactive proenzymes that undergo proteolytic cleavage for activation, and proteolytic activity is elevated in close proximity to these cells. Therefore, local activity rather than protease concentration determines ECM proteolysis. Precise quantification of local proteolytic activity, functional investigation, and high resolution imaging of morphological ECM alterations have proven difficult. In this study, we present a novel approach for measuring proteolytic activity in the microenvironment of cells by using atomic force microscopy (AFM). Amelanotic melanoma cells (A7-clone) were seeded on fluorescent gelatin or collagen-IV coatings. Proteolysis reduced fluorescence of these coatings. Fluorescence microscopy (FM) in combination with AFM was used to maneuver the AFM-tip to tumor cell induced proteolytic spots. AFM enabled nanoscale volume measurement, three-dimensional reconstruction of single proteins and demonstrated that ECM cleavage is restricted to the proteolytic microenvironment of cancer cells. This method detected significant decreases in molecular weight of protein clusters (-76.6%), matrix volume (-46.6%), and height (-38.1%) between intact and proteolyzed gelatin. Similar parameter changes were demonstrated without FM, by AFM-scanning gelatin in close proximity to invasive cells. Furthermore, AFM depicted significantly stronger local degradation of gelatin than collagen-IV by A7-cells. Taken together, AFM allows specific quantification and imaging of local proteolytic processes at a nanometer level, thus providing a unique method for the functional evaluation of invasiveness and metastatic potential of tumor cells in small scale samples.

Secretion of different types of gelatinases from cultured human keratinocytes

We investigated gelatinolytic enzymes derived from cultured human keratinocytes. Using a zymograph, we detected 92 kDa and 72 kDa gelatinases as major components and 83 kDa as a minor component from a conditioned cultured medium (BSL-K110, Kyokutoseiyaku Co.) of keratinocytes. After several passages, the 72 kDa band disappeared, and the 83 kDa band became dominant in another conditioned culture medium (K-GM, Kurashikibouseki Co.); these keratinocytes had a relatively differentiated appearance. These results suggest that some mechanism may regulate the secretion of selected types of gelatinase from keratinocytes under different conditions.