Lysosomal enzymes, cathepsins in brain tumour invasion

The expression patterns of different classes of peptidases in central nervous system (CNS) tumours have been most extensively studied in astrocytomas and meningiomas. Although the two types of tumours are very different in most respects, both may invade locally into normal brain. This process of invasion includes increased synthesis and secretion of lysosomal proteolytic enzymes - cathepsins. Aspartic endopeptidase cathepsin (Cat) D levels were found to be elevated in high-grade astrocytoma and partial inhibition of glioblastoma cell invasion by anti-Cat D antibody suggests that the enzyme activity is involved in the invasion process. Several studies on cysteine endopeptidase (CP) Cat B in gliomas agreed that transcript abundance, protein level and activity of Cat B increased in high-grade astrocytoma cultures compared with low-grade astrocytoma cultures and normal brain. Moreover, in glioma biopsies Cat B levels correlated with evidence of clinical invasion and it has been demonstrated that Cat B both in tumour cells and in endothelial cells can serve as a new biological marker for prognosis in glioblastoma patients. A high level of Cat B protein was also a diagnostic marker for invasive types of meningioma, distinguishing between histomorphologically benign, but invasive meningiomas and noninvasive, so-called clear-benign meningiomas. Cat L was also significantly increased in high-grade astrocytoma compared with low-grade astrocytoma and normal brain. Specific Cat L antibodies and antisense Cat L RNA transfection significantly lowered glioblastoma cell invasion. In meningioma, Cat L was a less-significant marker of invasion than Cat B. In contrast to cathepsins, the activities of endogenous cysteine peptidase inhibitors (CPIs), including stefins, cystatins and kininogens, were significantly higher in benign and atypical meningioma cell extracts than in malignant meningioma, and low-grade compared to high-grade astrocytoma. However, very low levels of stefins A and B were found in meningioma and glioblastoma tissues. Further studies on the expression levels and balance between cysteine endopeptidases (CPs) and CPIs would improve the clinical application of cathepsins in prognosis, which would lead to more-informed therapeutic strategies.